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Troy Built Trimmer Wont Rev Up
#1
B
BillCT
B
BillCT
I have a TB20CS trimmer that suddenly just stopped the other day. I discovered there was no spark so I installed a new coil, gaped it with a business card and it started right up but it would not rev up at all. It'll idle perfectly but not high enough to trim. So I've done the following:
1. Installed a new Champion Plug
2. Replaced all the fuel lines including the filter
3. Replaced the carburetor with a new one
4. Drained and replaced the fuel.
5. I removed the intake and inspected the Reed Valve. It appears to be OK, has a slight bow like it's supposed to and appears in like new condition. It's stainless steel.
6. Checked the compression and it's slightly over 120 psi.
7. Removed and checked the spark arrestor
8. Ran without muffler to verify it wasn't plugged
It'll run at WOT but it runs like the mixture is not correct, no power and won't rev up, but if the high mixture needle valve is adjusted it'll stall out. It reacts exactly the same with either carb. Idle is fine.
Any ideas?? (Besides throwing it out!!)
1. Installed a new Champion Plug
2. Replaced all the fuel lines including the filter
3. Replaced the carburetor with a new one
4. Drained and replaced the fuel.
5. I removed the intake and inspected the Reed Valve. It appears to be OK, has a slight bow like it's supposed to and appears in like new condition. It's stainless steel.
6. Checked the compression and it's slightly over 120 psi.
7. Removed and checked the spark arrestor
8. Ran without muffler to verify it wasn't plugged
It'll run at WOT but it runs like the mixture is not correct, no power and won't rev up, but if the high mixture needle valve is adjusted it'll stall out. It reacts exactly the same with either carb. Idle is fine.
Any ideas?? (Besides throwing it out!!)
#2
J
Jeff P51
J
Jeff P51
Check ignition timing. I recently worked on trimmer with same symptom and found flywheel key sheared off and slipped enough to throw off ignition timing but still run, but wouldn't accelerate.
#3
Hammermechanicman
Hammermechanicman
OEM or Ebay coil?
#4
B
BillCT
B
BillCT
Ok will do, never thought it could do that. ThanksCheck ignition timing. I recently worked on trimmer with same symptom and found flywheel key sheared off and slipped enough to throw off ignition timing but still run, but wouldn't accelerate.
#5
B
BillCT
B
BillCT
First replacement was an EBay and was marked 173 on the bottom, the second was OEM and came in a bag stating it was OEM for several models and makes and was also stamped 173. I’m thinking it came from MTD somehow.OEM or Ebay coil?
#6
B
BillCT
B
BillCT
I pulled the flywheel, key is in the flywheel as it should and has not moved. Doesn’t look like there’s anything to this flywheel that could go bad, magnets seem pretty strong.Ok will do, never thought it could do that. Thanks
#7
J
Jeff P51
J
Jeff P51
Wow, that's a real head scratcher..seems like u have replaced almost everything. What does plug look like..black, tan ,white..? Crankcase need to be sealed also or it won't get enough fuel. Have u checked crankcase seals? I fabricated some plates to cover intake and exhaust ports, put piston at bdc and applied pressure with a pressure/ vacuum tool..(available at harbor freight) about 8- 10 psi...it should hold pressure..
#8
B
BillCT
thanks for the input.
B
BillCT
Haven’t checked crankcase seals but I can. Has great compression 120 psi. I could spray carb cleaner around carb and crankcase seals when running I guess to see if there’s any change. I put in a new plug the old one looked normal, grey / sandy color. After running it’s slightly black but not really excessive or wet. I can take a picture later and post it.Wow, that's a real head scratcher..seems like u have replaced almost everything. What does plug look like..black, tan ,white..? Crankcase need to be sealed also or it won't get enough fuel. Have u checked crankcase seals? I fabricated some plates to cover intake and exhaust ports, put piston at bdc and applied pressure with a pressure/ vacuum tool..(available at harbor freight) about 8- 10 psi...it should hold pressure..
thanks for the input.
#9
B
bertsmobile1
B
bertsmobile1
You have not answere Hammers question
Where did you get the coil from ?
did it have a brand name cast / stamped into it ?
The ratio of faulty to good ones sold through annonomus vendor platforms like Amazon/ ebay is about 3 to 1
Where did you get the coil from ?
did it have a brand name cast / stamped into it ?
The ratio of faulty to good ones sold through annonomus vendor platforms like Amazon/ ebay is about 3 to 1
#11
StarTech
If it has the dual mixture adjustments then it needs tuning to the engine. They only come tune to a will start condition.
StarTech
Of course it came in a MTD. MTD made the trimmer. And carburetor PN 753-05133 should be a Walbro WT-827.First replacement was an EBay and was marked 173 on the bottom, the second was OEM and came in a bag stating it was OEM for several models and makes and was also stamped 173. I’m thinking it came from MTD somehow.
If it has the dual mixture adjustments then it needs tuning to the engine. They only come tune to a will start condition.
#12
B
BillCT
B
BillCT
Yes, I did adjust the high speed adjustment to see if it would make an improvement in performance, it did not. Actually I took it to the lawmower shop down town because I needed that special wrence and he tried to get it to rev adjusting the screw.Of course it came in a MTD. MTD made the trimmer. And carburetor PN 753-05133 should be a Walbro WT-827.
If it has the dual mixture adjustments then it needs tuning to the engine. They only come tune to a will start condition.
#13
B
BillCT
B
BillCT
OK, I'll check it again to make sure the spark is robust just to make sure.Remove spark plug , ground it to the head..pull starter look for nice blue spark
#14
B
BillCT
B
BillCT
Ebay and Amazon. Amazon came in a bag noting it was genuine OEM part for various trimmers marked on the bag, I don't have the bag any longer. No manufacturers name on the part but was stamped with the number 173.You have not answere Hammers question
Where did you get the coil from ?
did it have a brand name cast / stamped into it ?
The ratio of faulty to good ones sold through annonomus vendor platforms like Amazon/ ebay is about 3 to 1
#16
H
hlw49
H
hlw49
Not a good test, does not simulate firing under compression. Needs to jump 1/4 inch gap.Remove spark plug , ground it to the head..pull starter look for nice blue spark
#17
Hammermechanicman
Hammermechanicman
Original problem: ran fine then just stopped with no spark.
Replaced coil: now starts but won't rev up.
Started chasing problem: no change.
Remove the carb. Spray a half second shot of starting fluid in the intake and try to start. Engine should start and rev up high for a couple seconds. If not either incorrect spark timing, low compression or bad crank seals.
My money is on the coil having wrong timing. Seen it too many times from AM coils.
Replaced coil: now starts but won't rev up.
Started chasing problem: no change.
Remove the carb. Spray a half second shot of starting fluid in the intake and try to start. Engine should start and rev up high for a couple seconds. If not either incorrect spark timing, low compression or bad crank seals.
My money is on the coil having wrong timing. Seen it too many times from AM coils.
#18
B
bertsmobile1
An OEM part in a package with the OEM brand name is an OEM part that passed quality testing .
The 2 are not the same .
The carbs that were sold down here with the makers name ground off were OEM parts .
They just happen to be OEM parts that failed the quality test .
Then there are OEM parts made at the factory who originally had the contract but lost it because their pats were responsible fr too many warranty claims
Again still legally an OEM part , just not current OEM part .
B
bertsmobile1
A partt that was made by the original equipment supplier but rejected by quality control because it was sub standard is still an OEM part .Ebay and Amazon. Amazon came in a bag noting it was genuine OEM part for various trimmers marked on the bag, I don't have the bag any longer. No manufacturers name on the part but was stamped with the number 173.
An OEM part in a package with the OEM brand name is an OEM part that passed quality testing .
The 2 are not the same .
The carbs that were sold down here with the makers name ground off were OEM parts .
They just happen to be OEM parts that failed the quality test .
Then there are OEM parts made at the factory who originally had the contract but lost it because their pats were responsible fr too many warranty claims
Again still legally an OEM part , just not current OEM part .
#19
StarTech
There is a lot of crooks on Amazon and eBay. You got to deal with known good guys. And even some my distributors get burned at times. I know Stens has gotten at least once thenselves as those primers failed to make it through the initial repair job.
StarTech
If it was a true OEM carburetor it would had the manufactures name on it. Either Walbro, Zama, or Ruixing which are the only OEMs that MTD had used to my knowledge. I could stamp 173 on my Chevy's carb but that doesn't mean it now fits the weed eater.Ebay and Amazon. Amazon came in a bag noting it was genuine OEM part for various trimmers marked on the bag, I don't have the bag any longer. No manufacturers name on the part but was stamped with the number 173.
There is a lot of crooks on Amazon and eBay. You got to deal with known good guys. And even some my distributors get burned at times. I know Stens has gotten at least once thenselves as those primers failed to make it through the initial repair job.
#20
J
Jeff P51
J
Jeff P51
Your full of shitNot a good test, does simulate firing under compression. Needs to jump 1/4 inch gap.
#21
B
bertsmobile1
A good spark will jump a 1/4" air gap which is why all of the engine makers try and sell us techs a very expensive 3 point spark tester.
Down side is than on hand helds the spark is very hard to see .
The Stihl Lightning clonee / copies that you see all over evilpay have a poor magneto
It will throw a spark when resting on the head
It won't throw a spark inside the cylinder .
Got caught out which a couple of those as there was a con artist who was buying the kits assembling them then selling them as "Restored Stihl chainsaws "
B
bertsmobile1
No he is quite correctYour full of shit
A good spark will jump a 1/4" air gap which is why all of the engine makers try and sell us techs a very expensive 3 point spark tester.
Down side is than on hand helds the spark is very hard to see .
The Stihl Lightning clonee / copies that you see all over evilpay have a poor magneto
It will throw a spark when resting on the head
It won't throw a spark inside the cylinder .
Got caught out which a couple of those as there was a con artist who was buying the kits assembling them then selling them as "Restored Stihl chainsaws "
#22
J
Jeff P51
J
Jeff P51
So u are telling me that if he grounds plug to head and gets a strong blue spark jumping across the spark plug electrode , that the coil could still be bad enough to prevent engine from starting or revving up? And im guessing this guy that wants to get his trimmer running doesn't have any fancy spark testing tools, and neither do I, and I've been able to determine a bad coil without it. Why do u people have to make things more difficult than they are..
#23
Hammermechanicman
Hammermechanicman
Many 2 stroke engines have a spark advance built into them. I have seen ebay coils in stihl equipment have incorrect timing and no spark advance. I have seen ebay coils cause kickback, popping and spitting back out the carb, starting with no power.
And yes, the definitive test to see if the ignition system has the energy to run the engine is to see if it will jump a 1/4" or 6mm gap in air. This does not check the spark plug or the timing, just that there is enough energy to run the engine.
It is fairly difficult to check spark timing on a string trimmer. If it sparks we assume it is correct. I have 2 hopped up chainsaws with advanced timing. The difference between more power and a mistake is only a couple degrees.
And yes, the definitive test to see if the ignition system has the energy to run the engine is to see if it will jump a 1/4" or 6mm gap in air. This does not check the spark plug or the timing, just that there is enough energy to run the engine.
It is fairly difficult to check spark timing on a string trimmer. If it sparks we assume it is correct. I have 2 hopped up chainsaws with advanced timing. The difference between more power and a mistake is only a couple degrees.
#24
J
Jeff P51
J
Jeff P51
Why dont u use all your knowledge and help this guy get his trimmer working?. Nobody was helping him, so I gave him some ideas and all I got was how my ideas were wrong. Im here to help if I can.
#25
B
bertsmobile1
What appears to ba a good strong spark at atmospheric pressure can fail at combustion cylinder compression ( same for the plug )
There are 3 simple tools for testing the strength of a magneto's spark.
one is the 3 point tester , the next is a clip on spark plug with a 1/4" electrode gap and the last one is a HT lead with an adjustable gap.
All of them are around $ 20, not fancy or expensive & takes the guess work out of diagnosis
Back in the old days we used clear biro tube with a fixed wire in one end and a sliding wire at the other
Add to that hand helds are designed to run 7,000 rpm to 12,000 rpm
Magneto generated sparks tend always to appear poor at cranking speeds because the flywheel is turning so slow.
If the coil is wound to make a big fat blue spark at cranking speed then it will burn out at full revs.
If it had a capacitor discharge ignition or a battery coil ignition like your car then yes a fat blue spark at cranking speed is vital because both of those systems produce a better spark at idle than they do at running speeds because the coil has longer to saturate.
Your initial reply was very good .
It is quite rare for the flywheel keys to shear off , but it does happen I have seen 1 that sheared off in use and one that got mutilated durning assembly, and this is in 11years of roughly 300 invoices a year .
Now back to Bill's original problem.
Cases like this are near impossible to make a diagnosis on because he has just kept on throwing parts at the trimmer of unknown quality
I get at least 5 jobs through the gate every week where the owner has fitted cheap parts that were faulty right out the box.
Usually they insist that their new parts are all good and it has to be some sort of secret adjustments that they are unaware of because most will not accept that they could have made it worse.
So now we have a dubious coil, dubious carb , dubious spark plug . plus a trimmer that just quit during use
This is near impossible to sort out on a web forum as there are way too many variables to work through .
From what Bill has posted , the current problem appears to be a carb that is way out of adjustment and to me it sounds like it is starting & running on the high speed jet alone .
but it still could be the wrong or faulty coil so a badly timed or failing spark is limiting the revs
So if it came into my shop right now I would start by putting all of the old parts back on then seeing if it will start by itself or with carb cleaner down the plug hole .
If not then I remove the kill wires at the coil & try again with a flashing spark tester fitted ( my preferred tool also under $ 20 ) and a brand new spark plug , gapped as per the manual.
On mowers the gap is not all that important but on high reving hand helds accurate gaps are vital .
If it was confirmed that the coil was at fault ( fairly rare ) and not the kill wires or switch shorting ( very common ) then the magneto gets replaced with one from a know supplier of good quality parts and that rules out ebay , amazon , face book market , and even craigs list ( in the USA ) .
If the tool will not run properly when the new coil was fitted then the first suspect would be the new coil.
The coil has a timing chip in it and most of them are different however the mounting centres for coils tend to be fairly standard .
So a lot of wrong coils will bolt up and look right so the starting point would be to put a dab of paint on one of the fins to use as timing mark then a dab of paint on the body some where to correspond to TDC aligned with the dab of paint on the fin and hook up a timing light to see just where the spark is
If you are really into it then you can print out a timing disc for free , glue it to a piece of tim or alloy and actually measure the advance
printable timing disc
My first guess would be you have the wrong magneto , particularly as it has the same symptoms with both carbs, but a new plug correctly gapped is cheap and if not needed becomes a spare for latter on .
B
bertsmobile1
Because we fix these things on a daily basisSo u are telling me that if he grounds plug to head and gets a strong blue spark jumping across the spark plug electrode , that the coil could still be bad enough to prevent engine from starting or revving up? And im guessing this guy that wants to get his trimmer running doesn't have any fancy spark testing tools, and neither do I, and I've been able to determine a bad coil without it. Why do u people have to make things more difficult than they are..
What appears to ba a good strong spark at atmospheric pressure can fail at combustion cylinder compression ( same for the plug )
There are 3 simple tools for testing the strength of a magneto's spark.
one is the 3 point tester , the next is a clip on spark plug with a 1/4" electrode gap and the last one is a HT lead with an adjustable gap.
All of them are around $ 20, not fancy or expensive & takes the guess work out of diagnosis
Back in the old days we used clear biro tube with a fixed wire in one end and a sliding wire at the other
Add to that hand helds are designed to run 7,000 rpm to 12,000 rpm
Magneto generated sparks tend always to appear poor at cranking speeds because the flywheel is turning so slow.
If the coil is wound to make a big fat blue spark at cranking speed then it will burn out at full revs.
If it had a capacitor discharge ignition or a battery coil ignition like your car then yes a fat blue spark at cranking speed is vital because both of those systems produce a better spark at idle than they do at running speeds because the coil has longer to saturate.
Your initial reply was very good .
It is quite rare for the flywheel keys to shear off , but it does happen I have seen 1 that sheared off in use and one that got mutilated durning assembly, and this is in 11years of roughly 300 invoices a year .
Now back to Bill's original problem.
Cases like this are near impossible to make a diagnosis on because he has just kept on throwing parts at the trimmer of unknown quality
I get at least 5 jobs through the gate every week where the owner has fitted cheap parts that were faulty right out the box.
Usually they insist that their new parts are all good and it has to be some sort of secret adjustments that they are unaware of because most will not accept that they could have made it worse.
So now we have a dubious coil, dubious carb , dubious spark plug . plus a trimmer that just quit during use
This is near impossible to sort out on a web forum as there are way too many variables to work through .
From what Bill has posted , the current problem appears to be a carb that is way out of adjustment and to me it sounds like it is starting & running on the high speed jet alone .
but it still could be the wrong or faulty coil so a badly timed or failing spark is limiting the revs
So if it came into my shop right now I would start by putting all of the old parts back on then seeing if it will start by itself or with carb cleaner down the plug hole .
If not then I remove the kill wires at the coil & try again with a flashing spark tester fitted ( my preferred tool also under $ 20 ) and a brand new spark plug , gapped as per the manual.
On mowers the gap is not all that important but on high reving hand helds accurate gaps are vital .
If it was confirmed that the coil was at fault ( fairly rare ) and not the kill wires or switch shorting ( very common ) then the magneto gets replaced with one from a know supplier of good quality parts and that rules out ebay , amazon , face book market , and even craigs list ( in the USA ) .
If the tool will not run properly when the new coil was fitted then the first suspect would be the new coil.
The coil has a timing chip in it and most of them are different however the mounting centres for coils tend to be fairly standard .
So a lot of wrong coils will bolt up and look right so the starting point would be to put a dab of paint on one of the fins to use as timing mark then a dab of paint on the body some where to correspond to TDC aligned with the dab of paint on the fin and hook up a timing light to see just where the spark is
If you are really into it then you can print out a timing disc for free , glue it to a piece of tim or alloy and actually measure the advance
printable timing disc
My first guess would be you have the wrong magneto , particularly as it has the same symptoms with both carbs, but a new plug correctly gapped is cheap and if not needed becomes a spare for latter on .
#26
Hammermechanicman
Hammermechanicman
What was post #17?Why dont u use all your knowledge and help this guy get his trimmer working?. Nobody was helping him, so I gave him some ideas and all I got was how my ideas were wrong. Im here to help if I can.
#28
StarTech
StarTech
First I don't usually fool with curve shaft string trimmer as they are so cheap and it takes just as much time to troubleshoot as the straight shaft brush cutter models.
Even through 2 cycles are simple engines everything has to be working in unison. Just about anything to intake, compression, and exhaust can cause one not work. Among things tested is compression and a pressure/vacuum tests.
Even through 2 cycles are simple engines everything has to be working in unison. Just about anything to intake, compression, and exhaust can cause one not work. Among things tested is compression and a pressure/vacuum tests.
#29
B
BillCT
B
BillCT
I put it back together and tested the spark, visually. The spark is fat and purple. I used a rod in the plug wire grounded on the muffler. I didn't measure the gap but it was substantial. . I also tested the plug which is a new NGK grounded against the muffler and saw lots of spark, same color and not a weak thin yellow. Gap is set to .020.
I tried the suggestion of spraying a half second of starting fluid in the carb and starting. It did not rev up any more than usual and when it started it was pretty rich for a few seconds.( I know you did say to remove the carb but I thought this would be OK)
Since this engine ran exactly the same with the original carb as with the new carb I'm thinking the carb isn't the problem. And other than replacing the fuel lines and filter the only other new part is the coil.
It has 120 psi compression, if the crankcase seal was bad would it still have good compression? Are you referring to the crankcase cover gasket?
I've checked the wiring with a meter and neither the switch nor the wiring to the coil appears to be faulty.
Man it makes me grit my teeth to buy another coil but I hate to give up and set this thing out for target practice after all this. Also, both these coils I bought were made in China by the same company. I'm sure MTD could have had them made in China also.
Several parts places sell this coil (753-04336) for around $100 vs the eBay/Amazon $20 versions.. Sure wish I knew if that was it but it does kind of lead in that direction I guess.
I wish I hadn't thrown out the original coil, I can't believe I did that, I usually keep stuff forever.
I tried the suggestion of spraying a half second of starting fluid in the carb and starting. It did not rev up any more than usual and when it started it was pretty rich for a few seconds.( I know you did say to remove the carb but I thought this would be OK)
Since this engine ran exactly the same with the original carb as with the new carb I'm thinking the carb isn't the problem. And other than replacing the fuel lines and filter the only other new part is the coil.
It has 120 psi compression, if the crankcase seal was bad would it still have good compression? Are you referring to the crankcase cover gasket?
I've checked the wiring with a meter and neither the switch nor the wiring to the coil appears to be faulty.
Man it makes me grit my teeth to buy another coil but I hate to give up and set this thing out for target practice after all this. Also, both these coils I bought were made in China by the same company. I'm sure MTD could have had them made in China also.
Several parts places sell this coil (753-04336) for around $100 vs the eBay/Amazon $20 versions.. Sure wish I knew if that was it but it does kind of lead in that direction I guess.
I wish I hadn't thrown out the original coil, I can't believe I did that, I usually keep stuff forever.
#30
B
bertsmobile1
B
bertsmobile1
Inside the coil is a timing chip that basically replaces the points .
You can have 10 identical looking coils with 10 different chips that will cause the ignition to throw the spark at different times.
If the factory makes the entire magneto then it would be relatively safe to assume that two units with the same number on them were the same units.
However if that factory just stamped the metal laminations then assembled the unit from bought in parts then the 173 could be nothing more than a type 173 coil which could be fitted with a dozen different chips . we don't know.
Next a lot of trigger chips are fitted with a rev limiter so your "new" coil could be one of those where the limiting chip is cutting off the spark at 5000 rpm in place of 15,000 rpm
We don't know and this is the problem with unbranded parts from an annonomus source, way too many unknowns .
Now if it ran fine on the old carb and you did not fiddle with it then it should run fine with the new coil unless you did not hook up the throttle wire properly.
And yes this easily happens so the cable is not anchored properly thus does not open the throttle butterfly fully , which will of course limit the revs .
You don't have to buy everything from a dealer but you do have to buy them from some one who actually knows what they are selling you
SO these are places like,
e-replacement parts
Small engine warehouse
Barretts
K & C Mowers
Parts Tree
JacksSmall Engines
etc etc etc
GO back to the place you ordered it from and have a look at what else that vendor sells
If they are selling everything from maternity bras through to Condoms including trimmer parts then they are a residual / surplus seller and usually have less than no idea what they are actually selling
And if that includes both condoms & maternity wear then better than average chance what they are selling is defective .
You can have 10 identical looking coils with 10 different chips that will cause the ignition to throw the spark at different times.
If the factory makes the entire magneto then it would be relatively safe to assume that two units with the same number on them were the same units.
However if that factory just stamped the metal laminations then assembled the unit from bought in parts then the 173 could be nothing more than a type 173 coil which could be fitted with a dozen different chips . we don't know.
Next a lot of trigger chips are fitted with a rev limiter so your "new" coil could be one of those where the limiting chip is cutting off the spark at 5000 rpm in place of 15,000 rpm
We don't know and this is the problem with unbranded parts from an annonomus source, way too many unknowns .
Now if it ran fine on the old carb and you did not fiddle with it then it should run fine with the new coil unless you did not hook up the throttle wire properly.
And yes this easily happens so the cable is not anchored properly thus does not open the throttle butterfly fully , which will of course limit the revs .
You don't have to buy everything from a dealer but you do have to buy them from some one who actually knows what they are selling you
SO these are places like,
e-replacement parts
Small engine warehouse
Barretts
K & C Mowers
Parts Tree
JacksSmall Engines
etc etc etc
GO back to the place you ordered it from and have a look at what else that vendor sells
If they are selling everything from maternity bras through to Condoms including trimmer parts then they are a residual / surplus seller and usually have less than no idea what they are actually selling
And if that includes both condoms & maternity wear then better than average chance what they are selling is defective .
#31
StarTech
And the coil should only cost $81.81 at a dealer. Below is my cost and resell price.
Now with the compression at 120 and the fact that the starter fluid caused the engine to run rich I would say that eBay coil is defective. Though it is a pain to get get to it would hurt to check the flywheel key. On this unit it made as part of the flywheel so if the damage a new flywheel would be needed. Be careful as it can look bad when it is not.
StarTech
Yes it would still have compression. There several seals and gasket involved. A two cycle uses the crankcase as part of the intake system/It has 120 psi compression, if the crankcase seal was bad would it still have good compression? Are you referring to the crankcase cover gasket?
Several parts places sell this coil (753-04336) for around $100 vs the eBay/Amazon $20 versions.. Sure wish I knew if that was it but it does kind of lead in that direction I guess.
I wish I hadn't thrown out the original coil, I can't believe I did that, I usually keep stuff forever.
And the coil should only cost $81.81 at a dealer. Below is my cost and resell price.
Now with the compression at 120 and the fact that the starter fluid caused the engine to run rich I would say that eBay coil is defective. Though it is a pain to get get to it would hurt to check the flywheel key. On this unit it made as part of the flywheel so if the damage a new flywheel would be needed. Be careful as it can look bad when it is not.
#32
B
BillCT
B
BillCT
Thanks for all the good info and sources, I’ll report back on the results. If I get this thing running I’m going to paint it gold!!
#33
B
BillCT
B
BillCT
Thanks. Yes I did pull the flywheel and checked the key, everything was fine, the key was not damaged and was aligned in the keyway. Flywheel keyway was not damagedYes it would still have compression. There several seals and gasket involved. A two cycle uses the crankcase as part of the intake system/
And the coil should only cost $81.81 at a dealer. Below is my cost and resell price.
View attachment 61957
Now with the compression at 120 and the fact that the starter fluid caused the engine to run rich I would say that eBay coil is defective. Though it is a pain to get get to it would hurt to check the flywheel key. On this unit it made as part of the flywheel so if the damage a new flywheel would be needed. Be careful as it can look bad when it is not.
#34
B
BillCT
B
BillCT
Thank you! I'll get one on order from one of these guys.Inside the coil is a timing chip that basically replaces the points .
You can have 10 identical looking coils with 10 different chips that will cause the ignition to throw the spark at different times.
If the factory makes the entire magneto then it would be relatively safe to assume that two units with the same number on them were the same units.
However if that factory just stamped the metal laminations then assembled the unit from bought in parts then the 173 could be nothing more than a type 173 coil which could be fitted with a dozen different chips . we don't know.
Next a lot of trigger chips are fitted with a rev limiter so your "new" coil could be one of those where the limiting chip is cutting off the spark at 5000 rpm in place of 15,000 rpm
We don't know and this is the problem with unbranded parts from an annonomus source, way too many unknowns .
Now if it ran fine on the old carb and you did not fiddle with it then it should run fine with the new coil unless you did not hook up the throttle wire properly.
And yes this easily happens so the cable is not anchored properly thus does not open the throttle butterfly fully , which will of course limit the revs .
You don't have to buy everything from a dealer but you do have to buy them from some one who actually knows what they are selling you
SO these are places like,
e-replacement parts
Small engine warehouse
Barretts
K & C Mowers
Parts Tree
JacksSmall Engines
etc etc etc
GO back to the place you ordered it from and have a look at what else that vendor sells
If they are selling everything from maternity bras through to Condoms including trimmer parts then they are a residual / surplus seller and usually have less than no idea what they are actually selling
And if that includes both condoms & maternity wear then better than average chance what they are selling is defective .
#35
J
Jeff P51
J
Jeff P51
I put it back together and tested the spark, visually. The spark is fat and purple. I used a rod in the plug wire grounded on the muffler. I didn't measure the gap but it was substantial. . I also tested the plug which is a new NGK grounded against the muffler and saw lots of spark, same color and not a weak thin yellow. Gap is set to .020.
I tried the suggestion of spraying a half second of starting fluid in the carb and starting. It did not rev up any more than usual and when it started it was pretty rich for a few seconds.( I know you did say to remove the carb but I thought this would be OK)
Since this engine ran exactly the same with the original carb as with the new carb I'm thinking the carb isn't the problem. And other than replacing the fuel lines and filter the only other new part is the coil.
It has 120 psi compression, if the crankcase seal was bad would it still have good compression? Are you referring to the crankcase cover gasket?
I've checked the wiring with a meter and neither the switch nor the wiring to the coil appears to be faulty.
Man it makes me grit my teeth to buy another coil but I hate to give up and set this thing out for target practice after all this. Also, both these coils I bought were made in China by the same company. I'm sure MTD could have had them made in China also.
Several parts places sell this coil (753-04336) for around $100 vs the eBay/Amazon $20 versions.. Sure wish I knew if that was it but it does kind of lead in that direction I guess.
I wish I hadn't thrown out the original coil, I can't believe I did that, I usually keep stuff forever.
I could possibly be either the crank seals, or a crankcase gasket.. Not really compression so to speak, but it will affect gas fuel mixtures and intake cycling. Depends on how bad the leak isI put it back together and tested the spark, visually. The spark is fat and purple. I used a rod in the plug wire grounded on the muffler. I didn't measure the gap but it was substantial. . I also tested the plug which is a new NGK grounded against the muffler and saw lots of spark, same color and not a weak thin yellow. Gap is set to .020.
I tried the suggestion of spraying a half second of starting fluid in the carb and starting. It did not rev up any more than usual and when it started it was pretty rich for a few seconds.( I know you did say to remove the carb but I thought this would be OK)
Since this engine ran exactly the same with the original carb as with the new carb I'm thinking the carb isn't the problem. And other than replacing the fuel lines and filter the only other new part is the coil.
It has 120 psi compression, if the crankcase seal was bad would it still have good compression? Are you referring to the crankcase cover gasket?
I've checked the wiring with a meter and neither the switch nor the wiring to the coil appears to be faulty.
Man it makes me grit my teeth to buy another coil but I hate to give up and set this thing out for target practice after all this. Also, both these coils I bought were made in China by the same company. I'm sure MTD could have had them made in China also.
Several parts places sell this coil (753-04336) for around $100 vs the eBay/Amazon $20 versions.. Sure wish I knew if that was it but it does kind of lead in that direction I guess.
I wish I hadn't thrown out the original coil, I can't believe I did that, I usually keep stuff forever.
#36
B
bertsmobile1
B
bertsmobile1
Not trying to be arguementative Don, but bad seals generally make the tool hard to start because at cranking speeds there is a lot of time for the fuel to leak out and air to leak in.
The faster the engine spins the less effect the leak has part from making the mix too lean and causing overheating then seizure if the piston does not hole first .
Lean mixes tend to cause over reving with little to no power not limiting the top speed.
If you repair these thing regularly you should be able to hear the difference between a lean burn ( hard sharp & high pitch ) exhaust note and a rich burn ( deeper & muffled ) exhaust note .
From the get go, the engine just stopped then was found to have no spark
The coil was replaced then it developed the new low reving problems
Motor mechanics 101 is a fresh problem will most likely be cause by the last part replaced .
And a fat blur spark at cranking speed tells me the timing chip is firing way too late unless it is a short stroke big bore engine as used on concrete & demolition saws or it is a professional grade engine and has a capacitor discharge ignition which it is neither
Remember the spark has to be at the right time and when you are talking 7000 to 9000 rpm that most of these units run at that timing is down to pico second accuracy
A retarded spark will very effectively limit the peak revs and if the coil is producing a fat blue spark at 300 rpm cranking speeds I doubt it will be producing a good spark at the right time for 7000 rpm .
Just about all of the hand held engines I have worked on have a faint spark that is very hard to see at cranking speeds that gets bigger , better & stronger the faster the engine revs
The faster the engine spins the less effect the leak has part from making the mix too lean and causing overheating then seizure if the piston does not hole first .
Lean mixes tend to cause over reving with little to no power not limiting the top speed.
If you repair these thing regularly you should be able to hear the difference between a lean burn ( hard sharp & high pitch ) exhaust note and a rich burn ( deeper & muffled ) exhaust note .
From the get go, the engine just stopped then was found to have no spark
The coil was replaced then it developed the new low reving problems
Motor mechanics 101 is a fresh problem will most likely be cause by the last part replaced .
And a fat blur spark at cranking speed tells me the timing chip is firing way too late unless it is a short stroke big bore engine as used on concrete & demolition saws or it is a professional grade engine and has a capacitor discharge ignition which it is neither
Remember the spark has to be at the right time and when you are talking 7000 to 9000 rpm that most of these units run at that timing is down to pico second accuracy
A retarded spark will very effectively limit the peak revs and if the coil is producing a fat blue spark at 300 rpm cranking speeds I doubt it will be producing a good spark at the right time for 7000 rpm .
Just about all of the hand held engines I have worked on have a faint spark that is very hard to see at cranking speeds that gets bigger , better & stronger the faster the engine revs
#37
B
BillCT
B
BillCT
Sorry for the late reply on this, I've been away on vacation.
Well you guys were correct on the coil, I ordered a factory replacement and it revs right up now. Carb needs a little adjustment for the high speed but not bad, it'll work fine the way it is.
Hope this thread helps out somebody else with a similar problem. Thanks to everyone who replied with all the helpful input!!
Bill
Well you guys were correct on the coil, I ordered a factory replacement and it revs right up now. Carb needs a little adjustment for the high speed but not bad, it'll work fine the way it is.
Hope this thread helps out somebody else with a similar problem. Thanks to everyone who replied with all the helpful input!!
Bill