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Briggs & Stratton Model Number: 123K02-0258-E1 03012456
Craftsman 6.5 HP Self Propelled Mower Model Number: 917.377660
I have tried absolutely everything to get this mower started, and it will not start. This mower belongs to my mom and hasn't ran in two to three years. I knew the carb would be varnished and gummed up. I performed the following before attempting to start the engine:
1. I cleaned and rebuilt the carburetor, including cleaning all the ports and blowing them out with air; replaced the welch plug; the float needle and seat; the float bowl gasket and the air filter housing gasket; fuel hose; and tested the float seat by both blowing and sucking on the fuel inlet nipple to make sure it was seating. Please note, this carburetor does not have any adjustment possible... no fuel mixture or idle screws... no choke... the only moving part is a throttle plate.
2. I cleaned the mower and engine thoroughly from top to bottom, inside and out.
3. Changed the engine oil.
4. Removed and cleaned the gas tank, inside and out. I blew it out with compressed air and made certain it was clean.
5. Found the flywheel key sheared; removed, cleaned and replaced with new aluminum key.
6. Set the coil air gap to .006" (Spec is 6 - 10 thousandths).
7. Replaced the spark plug (three times). Checked the coil lead for cracks or damage. Checked and cleaned the kill switch wiring and switch.
8. Checked the cylinder compression and found it to be at 55 psi and holding.
9. Replaced the air filter and primer bulb.
10. I checked the spark and had a nice blue spark.
11. Filled the tank with fresh premium gasoline.

I tried starting it with starting fluid, carburetor cleaner, and WD40 with no luck. Then, I finally managed to get it running once by squirting brake cleaner in the spark plug hole and it ran perfect. After shutting it off, it wouldn't start again even with the brake cleaner. I tried squirting the fluids in both the carb and the spark plug hole. I tried using a known good spark plug out of another mower and three other brand new plugs with no luck. Finally, one more time it started, but only for a few seconds and then it quit again, not to be re-started. I pull and pull on the rope to start the engine, and it doesn't even seem like it's trying. I am so frustrated with this thing I can hardly stand it. I am a mechanic by trade and can't believe this this is kicking my butt! I am desperate for an answer... please help.

The question is, and I may have missed it, did you actually check for spark. On a push mower it is hard to do by yourself. So remove the spark plug, put it against a good ground on the engine with the wire attached, and have somebody crank the mower and see if you have spark.

I thought I heard somewhere that 60 psi is the minimum psi for a Briggs to be able to run. I could be wrong.

An internal combustion engine requires 3 things to run :

1. Fuel .... ( you obviously have that covered ) ( vented gas cap ?? fuel shut-off open ?? )

2 Air .... Thats a given ... provided the air cleaner / filter is NOT restricted

3 Fire .... Spark is where I'd look ( sometimes when a coil is about to " go on extended vacation " it'll work itermittently )

PLEASE keep us informed ........ its kickin my "set- down" along with yours !!! BEST of Luck, I hope SOMEONE can find the solution !!! Boobala :confused2: :confused2:

Air- I can imagine people blowing in the spark plug hole right now:laughing:
Let's trade that for Compression & also throw in Timing as a 4th.

Thank you everyone for your quick replies. Yes, ILENGINE, my wife helped me and we did it just as you described. We had a thin blue spark - right through the plug to a bolt in the head. From what I have seen, this thin spark is pretty common on these newer engines. I was told that as long as the spark is "blue", then, it is a good spark. The compression may be the problem. I couldn't find any specs on what the compression is supposed to be, but I know it was holding the compression (not leaking off) until I released it.

So when you put starting fluid or choke cleaner in cylinder, it will sometimes start? Any backfiring when trying to start?

mtnlovrs said:

Thank you everyone for your quick replies. Yes, ILENGINE, my wife helped me and we did it just as you described. We had a thin blue spark - right through the plug to a bolt in the head. From what I have seen, this thin spark is pretty common on these newer engines. I was told that as long as the spark is "blue", then, it is a good spark. The compression may be the problem. I couldn't find any specs on what the compression is supposed to be, but I know it was holding the compression (not leaking off) until I released it.

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briggs doesn't publish compression specs for their engine. I like to see 90 or above on most engines, but have seen new briggs engines on push mowers run fine with 55-60 psi.

Problem is they all have automatic decompression.
The amount of pressure this will bleed off will vary with the speed the engine turning over and the amount of valve lash.
This makes compression figures not much use and why you keep hearing "Leak down testing" tlked about on the forum.
I use wet/dry compression testing for confirmation of rings but that is mainly becuse I broke the leakdown gear & have not had time to replace it as I don't like most of the modern stuff.

Mikel1 said:

So when you put starting fluid or choke cleaner in cylinder, it will sometimes start? Any backfiring when trying to start?

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I actually had no luck what-so-ever with starting fluid (may be too old) or anything except the brake cleaner, and then, only a few times did it do anything at all... usually just a single puff. A couple times it did start, and it ran good the first time, the second time it ran good for about 15 seconds and then quit. Today, I pulled the head off and found the bolts to be slightly snug. I think 140 inch pounds should have felt tighter than it did. I should have used a torque wrench to remove them, but it's too late now. I cleaned the carbon off the head, but didn't have time to get it back together before going to work. I want to clean the top surfaces of the piston and valves, as well, since they have a pretty thick coating of carbon on them too. No backfire.

ILENGINE said:

briggs doesn't publish compression specs for their engine. I like to see 90 or above on most engines, but have seen new briggs engines on push mowers run fine with 55-60 psi.

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Hopefully, loose head bolts were the problem. I will find out tomorrow when I get it back together. If it still doesn't start, then I will know this mower is simply possessed!:confused2:

mtnlovrs said:

Hopefully, loose head bolts were the problem. I will find out tomorrow when I get it back together. If it still doesn't start, then I will know this mower is simply possessed!:confused2:

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My wife says you probably have "the-pixies" problem ......... she has the "calories-problem" ..... you know , those things that go into your closets at night .... and magically make ALL your clothes fit TIGHTER !!
She said sometimes if you put a BIG hammer and BIG screwdriver in front of it ... it gets so scared .... it fixes itself ! I don't need Encyclopedias ......my wife knows it all !! Boobala :laughing: :laughing:

Boobala said:

An internal combustion engine requires 3 things to run :

1. Fuel .... ( you obviously have that covered ) ( vented gas cap ?? fuel shut-off open ?? )

2 Air .... Thats a given ... provided the air cleaner / filter is NOT restricted

3 Fire .... Spark is where I'd look ( sometimes when a coil is about to " go on extended vacation " it'll work itermittently )

PLEASE keep us informed ........ its kickin my "set- down" along with yours !!! BEST of Luck, I hope SOMEONE can find the solution !!! Boobala :confused2: :confused2:

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Don't forget timing

reynoldston said:

Don't forget timing

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Crankcase has never been opened and everything is moving as it is supposed to, therefore, I don't believe the mechanical timing could have been changed. I replaced the flywheel key and have gone back to make sure it hasn't sheared again... so that takes care of the ignition timing. Thanks again. I'm heading out now to get it back together. I'm a second shifter, so I don't get going very early in the morning.

Boobala said:

My wife says you probably have "the-pixies" problem ......... she has the "calories-problem" ..... you know , those things that go into your closets at night .... and magically make ALL your clothes fit TIGHTER !!
She said sometimes if you put a BIG hammer and BIG screwdriver in front of it ... it gets so scared .... it fixes itself ! I don't need Encyclopedias ......my wife knows it all !! Boobala :laughing: :laughing:

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Thank your wife for me! I don't need an encyclopedia either because my wife has been to the end of the Internet and back several times now. Tell your wife I will include those tools in my arsenal when I head back out there today!!!:thumbsup::laughing:

Recheck your work, you missed something. Spark, fuel, compression, timing. You are missing one of these or it will run. How are you making your test? You are checking your spark under compression right? Checking compression with a gauge or a leak down test ? Installed flywheel with proper torque? Give carburetor a really good cleaning? Just stop and think what you are missing?

At the risk of looking like an ignorant fool ..... by all accounts this engine should be running, I mentioned in another forum or thread ...... one last thing I finally remembered from a Loooong time ago ......... a guy told me he had a similar issue ..... drove him crazy , forget why .... but he removed the muffler and it fired up..... found his muffler was clogged with carbon !! at this stage of the game , MAYBE , it's worth a look-see ?? I really really want to know what the problem is ( I'm sure some others following this thread would also )
I really was thinkin the coil , but ............ Boobala :confused2: :confused2:

mtnlovrs said:

Briggs & Stratton Model Number: 123K02-0258-E1 03012456
Craftsman 6.5 HP Self Propelled Mower Model Number: 917.377660
I have tried absolutely everything to get this mower started, and it will not start. This mower belongs to my mom and hasn't ran in two to three years. I knew the carb would be varnished and gummed up. I performed the following before attempting to start the engine:
1. I cleaned and rebuilt the carburetor, including cleaning all the ports and blowing them out with air; replaced the welch plug; the float needle and seat; the float bowl gasket and the air filter housing gasket; fuel hose; and tested the float seat by both blowing and sucking on the fuel inlet nipple to make sure it was seating. Please note, this carburetor does not have any adjustment possible... no fuel mixture or idle screws... no choke... the only moving part is a throttle plate.
2. I cleaned the mower and engine thoroughly from top to bottom, inside and out.
3. Changed the engine oil.
4. Removed and cleaned the gas tank, inside and out. I blew it out with compressed air and made certain it was clean.
5. Found the flywheel key sheared; removed, cleaned and replaced with new aluminum key.
6. Set the coil air gap to .006" (Spec is 6 - 10 thousandths).
7. Replaced the spark plug (three times). Checked the coil lead for cracks or damage. Checked and cleaned the kill switch wiring and switch.
8. Checked the cylinder compression and found it to be at 55 psi and holding.
9. Replaced the air filter and primer bulb.
10. I checked the spark and had a nice blue spark.
11. Filled the tank with fresh premium gasoline.

I tried starting it with starting fluid, carburetor cleaner, and WD40 with no luck. Then, I finally managed to get it running once by squirting brake cleaner in the spark plug hole and it ran perfect. After shutting it off, it wouldn't start again even with the brake cleaner. I tried squirting the fluids in both the carb and the spark plug hole. I tried using a known good spark plug out of another mower and three other brand new plugs with no luck. Finally, one more time it started, but only for a few seconds and then it quit again, not to be re-started. I pull and pull on the rope to start the engine, and it doesn't even seem like it's trying. I am so frustrated with this thing I can hardly stand it. I am a mechanic by trade and can't believe this this is kicking my butt! I am desperate for an answer... please help.

Click to expand...

You really do need a spark tester when checking for spark.
A blue spark means nothing. It could be pink with an aluminous yellow dress on it would make no difference.

I would expect that the metal suppressor cap on the end of the spark lead ay be causing your issue.

The easiest way to set the coil to flywheel is with a business card.
Also the date code of the engine depends on what spark plug to be fitted.

Is fuel being push up the main jet when primer bulb being used?
Remove the air filter cover and look in the carb. Fuel should be squirting up.

Boobala said:

At the risk of looking like an ignorant fool ..... by all accounts this engine should be running, I mentioned in another forum or thread ...... one last thing I finally remembered from a Loooong time ago ......... a guy told me he had a similar issue ..... drove him crazy , forget why .... but he removed the muffler and it fired up..... found his muffler was clogged with carbon !! at this stage of the game , MAYBE , it's worth a look-see ?? I really really want to know what the problem is ( I'm sure some others following this thread would also )
I really was thinkin the coil , but ............ Boobala :confused2: :confused2:

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I find as a rule a plugged muffler you lose high speed unless maybe nothing go's through it. This is what I have found when I come across a plugged muffler.

reynoldston said:

Recheck your work, you missed something. Spark, fuel, compression, timing. You are missing one of these or it will run. How are you making your test? You are checking your spark under compression right? Checking compression with a gauge or a leak down test ? Installed flywheel with proper torque? Give carburetor a really good cleaning? Just stop and think what you are missing?

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Believe me, I have done that many times and I have double, triple, and in some cases quadruple checked my work before ever coming to the forum. I know this defies all logic. That's why I came here asking for help. As I mentioned earlier in this thread, My wife helped me check for spark. I do not have a spark checker. First, I pulled the rope while she held the sparkplug against a head bolt. Then, we swapped places so that we both could see the spark with our own eyes. The spark was a thin blue spark. The carburetor could not be cleaner. I have taken it apart now four or five times. I used the correct drill bit sizes to clean every orifice, thoroughly cleaned all surfaces inside and out with carburetor cleaner, and blew out all the orifices with compressed air, making sure that air was coming out the other end of each orifice. I replaced the float needle and seat. I pressed the seat (ribbed side down) all the way down into the recess with a 3/16" drill bit and made sure it was flat in the bottom of the bore. I checked the float and seat to make sure it was seating by blowing and sucking air through the fuel inlet. The float is hanging horizontally to the carb body, as it should. I replaced the welch plug and seated it in place using a 1/4" extension because the rounded end of the extension fit the plug perfectly. I replaced the gasket, O-ring, air filter and primer bulb. There are no adjustments possible on this carburetor - no idle or mixture screw, no choke. When I checked compression, I used a cylinder compression tester. I now realize that the next step is a leak-down test. Yesterday, I checked the flywheel key again (not sheared). I found an incorrect torque of 138-150 foot pounds in an old book, so I torqued the nut to 110 foot pounds because that seemed too much for this engine. I have since found the correct torque for the flywheel on this engine: 55 foot pounds. Next, I replaced the intake manifold tube gasket, removed the head and cleaned out all of the carbon. I checked the cylinder bore and did not see any signs of scoring or damage, but it was pretty oily. I checked the valves to see if they seated snuggly during the compression stroke, and they were nice and tight. There was no sign of any damage to the valves or their seats. I cleaned everything and re-torqued the head to 140" lbs. I used copper spay-on head gasket sealant on both sides of the gasket. Today, I tried starting it again and, unfortunately, still the same story. Once again everyone, thanks for all the help. Please keep the ideas coming... there must be a reason this simple little motor won't start.:thumbsup:

Boobala said:

At the risk of looking like an ignorant fool ..... by all accounts this engine should be running, I mentioned in another forum or thread ...... one last thing I finally remembered from a Loooong time ago ......... a guy told me he had a similar issue ..... drove him crazy , forget why .... but he removed the muffler and it fired up..... found his muffler was clogged with carbon !! at this stage of the game , MAYBE , it's worth a look-see ?? I really really want to know what the problem is ( I'm sure some others following this thread would also )
I really was thinkin the coil , but ............ Boobala :confused2: :confused2:

Click to expand...

Thanks, Boobala. That sounds reasonable. The only thing is... it ran perfect that one time and seemed to run on its own until I killed the engine. Would it have done that with a plugged muffler? Nonetheless, I will definitely try that.:thumbsup:

I removed the muffler and tried starting the engine, but it would not fire. I looked the muffler over and did not see any significant carbon build-up. I cleaned it anyway and put it back together. Today, I tried starting it again on the freak chance it would start... it didn't. I removed the armature and cleaned the rust off of it. (I was going to try an armature off a different engine, but the bolt holes were not the same and it would not fit.) So, I figured since I had it off, I might as well clean it before I put it back on. I set the gap at .006" again and put the engine back together. I pressed the primer bulb six times and pulled the cord once, and the engine started! It ran perfect!!! I took it out and mowed the front yard, but before I could finish, the engine began to slow down like it was running out of fuel. I stuck my finger inside the cover and pressed on the throttle to try to keep the engine running, but it died as soon as I pressed on it. I checked the fuel level and it still had half a tank. I pulled the rope again and it started with the first pull. I continued mowing for a while and then it did the same thing again. I lifted up on the handle bar and raised the rear of the mower and the engine immediately sped back up again. I continued mowing and it happened again and again. Each time I was able to keep it running by lifting up on the back of the mower. Finally, I wasn't able to keep it running with the previous method. I rechecked the fuel level and had about a quarter of a tank left. I restarted the engine and it sounded like it was going to stall again. I immediately began pumping the primer bulb and the engine sped up again, but then sounded like it was running out of fuel again. I kept pumping the primer, but couldn't keep it running long enough to finish mowing. It began to rain, so I called it quits, but before I put the mower away, I decided to see if it would start one more time... and it did (one pull starts it every time now), but it would not continue to run.:confused2:

Next time it's starts to die quickly remove the gas cap. If it continues to run, the vent in your cap is plugged.

Rivets said:

Next time it's starts to die quickly remove the gas cap. If it continues to run, the vent in your cap is plugged.

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I agree. Every other Briggs engine I have ever seen has a vented gas cap... this one does not. There are no holes in this cap for venting. I tried removing the cap to see if it would help, but all it did was slosh fuel.

While mowing yesterday, the height adjustment handle fell off and the mower dropped to its lowest adjustment. This was the "final straw", as they say... it was raining, the engine kept stalling, and now this. I quit mowing at that time and I didn't mention it before because I thought it was no big deal. I went out today to put the handle back on and discovered that the right hand drive axle had been cut in two by the handle. The hardened spring steel of the handle acted just like a blade and cut all the way through it. My wife found the drive axle on the Internet for $35 bucks, so I guess that's the next hurdle. I called my mom and let her know the good news and she said she wants to go get a new mower, but she still wants me to fix this one so that she has a back-up mower.:ashamed:

I work on a ton of these Briggs flat heads and love fixing them up. So easy to get them going (usually). Couple of things for future reference.

1) Never rebuild these carbs. Rebuild kit is like $12, while a new carb is barely over $20. My time is worth more than $8, and a rebuilt carb doesn't work right 50% of the time. Just replace them for a much smaller headache. I've used a bunch of OEM carbs as well as the Chinese Oregon ones and they all run the same.

2) I personally only use Champion RJ19LM in these. Made in USA and good quality. Have had bad luck with other brands for some reason.

3) Gap at 0.020 if you think your coil is getting weak or if unsure you have spark. Run the gap at 0.030 for a good running engine, but knock it down to .020 for coil diagnostic or to limp along a dying coil.

4) I'm almost positive that your problem is a clogged up carburetor. It is really hard to clean behind the welch plugs. I'd put a new carb on it and chock it up as a lesson learned. Should start right up and run perfect with a new carb.

5) Replace the fuel line at the same time. I've seen them get spongy inside and slow fuel down.

Two bits...Don't put gasket seal on a head gasket which does not call for it. My old song on spark...The modules contain transistors or other electronic devices that fail at hot, but will spark at cold. A spark guru recently posted that some excellent sparks are invisible. "Thin" and "thick" descriptions of spark, as well as color are not useful. Try a white paper as a background for the spark at hot. The intek factory manual published 60-65 psi as compression spec. This is for the V engines. Does not state take hot or cold. I once used an automotive inductive timing light on my Intek. The spark is so weak it barely strobes weak orange, but was at least a way to determine a rough measure of timing. You can set in a TDC ref prick punch mark on your engine to help you if you try the light. Shroud removed,

bubbatime said:

I work on a ton of these Briggs flat heads and love fixing them up. So easy to get them going (usually). Couple of things for future reference.

1) Never rebuild these carbs. Rebuild kit is like $12, while a new carb is barely over $20. My time is worth more than $8, and a rebuilt carb doesn't work right 50% of the time. Just replace them for a much smaller headache. I've used a bunch of OEM carbs as well as the Chinese Oregon ones and they all run the same.

2) I personally only use Champion RJ19LM in these. Made in USA and good quality. Have had bad luck with other brands for some reason.

3) Gap at 0.020 if you think your coil is getting weak or if unsure you have spark. Run the gap at 0.030 for a good running engine, but knock it down to .020 for coil diagnostic or to limp along a dying coil.

4) I'm almost positive that your problem is a clogged up carburetor. It is really hard to clean behind the welch plugs. I'd put a new carb on it and chock it up as a lesson learned. Should start right up and run perfect with a new carb.

5) Replace the fuel line at the same time. I've seen them get spongy inside and slow fuel down.

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1. Easy to work on... yes, that was my experience also, until I met this one!
2. Where do you get your parts? The Carb overhaul kit cost me $16 and the best price I saw on the Internet for a new carb was $35. We have only one store in town that sell these parts and they have bankers hours. I have never heard of Chinese Oregon. Where do you buy these?
3. I started with a brand new Champion RJ19LM spark plug. I tried three different brand new plugs, (2 Champion, 1 Briggs), and a used "known good" Briggs plug. I finally got it running with a new Briggs plug gapped at .030". I will try your idea of the .020" gap in the future.
4. I know I don't have any clogged ports. I was able to blow compressed air through every port after cleaning the carb - confirming the ports are clear. The carb has only one welch plug, which I removed and was able to clean the port (or orifice) with a drill bit matching the diameter of the port, and then I blew compressed air through the port and had a strong blast of air coming out the other end. This was the primer bulb port that sucks fuel from the float bowl. Then I applied a new welch plug from the overhaul kit. I may still end up buying a new carb before this is all over, but this carb is such a simple design, I really don't understand why it is not performing as new.
5. Lastly, I replaced the fuel hose before I ever attempted to start the engine the first time.
Thank you for your ideas, keep them coming!

motoman said:

Two bits...Don't put gasket seal on a head gasket which does not call for it. My old song on spark...The modules contain transistors or other electronic devices that fail at hot, but will spark at cold. A spark guru recently posted that some excellent sparks are invisible. "Thin" and "thick" descriptions of spark, as well as color are not useful. Try a white paper as a background for the spark at hot. The intek factory manual published 60-65 psi as compression spec. This is for the V engines. Does not state take hot or cold. I once used an automotive inductive timing light on my Intek. The spark is so weak it barely strobes weak orange, but was at least a way to determine a rough measure of timing. You can set in a TDC ref prick punch mark on your engine to help you if you try the light. Shroud removed,

Click to expand...

Yes, I know you aren't supposed to use gasket sealer on the head gasket, but I had no choice. The parts store was closed for the weekend and the gasket was damaged. I have used the Permatex copper spray-on gasket sealer in the past with great success. You use a cardboard box or box lid. Place the cleaned gasket into the box and paint a thin coat on both sides of the gasket. Wait for it to get tacky before applying the gasket and reassembling. Of coarse, make sure all the mating surfaces are clean before hand.
I have seen plenty of old warn-out Briggs engines run well with low compression, burning lots of oil and smoking like crazy! If it were a diesel, I would agree. Maybe it's the weak spark these newer engines produce with the solid-state ignition. Cleaning the rust off the armature definitely seemed to help.