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Hi!

First post on this forum. I'm writing from Sweden so please be gentle if my English isn't perfect. :smile:

So, I have a Tecumseh TWM140 6.0 HP motor on a riding mower that have me really stumped. I can usually fix engines that won't start or I'll be able to determine that it's a lost cause...but this one is an enigma to me. I bought it as a non runner and the plan was to fix it and sell it with a small profit. So far it owes me about $80.

The previous owner was given the mower in another deal and had gotten a carb kit for it. He told me it was leaking fuel from the carb after he put it back together. I took the carb apart and found that the needle seat was missing. I got a new kit, cleaned the carb and put it all back together. The engine was given new fuel, spark plug and oil before I tried to start it. It did start and after some tweaking of the carb i was able to run it for awhile. It didn't run perfect and suddenly it just died, like the spark was killed. I checked for spark and it was there, so was the fuel. I tried to prime with some fuel directly into the cylinder and it fired but wouldn't run.

After several attempt to get it to run I gave up and ordered a replacement carb with new air filter from China. It took forever to get here, but it finally arrived last week. I had to modify the fitting for the fuel line since it needed to be 90° angle and the carb had a straight fitting. I also used the old shaft for the choke to be able to use the linkage arm.

Today I tried to start it again. First try was encouraging...it started after a few pulls and ran pretty good for a few seconds...then it just died the same way again, just like the kill switch was activated. I tried all my tricks: fuel directly in the cylinder, turning the mixture screw in or out, ether (starter fluid?), choke/no choke, full throttle/half throttle/no throttle. It will fire and sometimes even run for a few seconds but I haven't been able to get it to run. I can't identify one thing that makes it fire...it seems to be completely random. Aaaaargh!!! My arm is numb and my hand is blistered after pulling the pull cord 100 times!

I checked the compression and it was about 90 PSI. I don't know what it's supposed to be but I don't think that it's that bad. I have checked the spark and it is there, but I have a feeling that it's not that strong. The ignition is solid state so there are no points to check.

Any suggestions what I can do? I can't sell the thing if it's not reliable to start and run fine.

I'm guessing it's heat related. I'd try a new spark plug first, then the coil. Might have spark with no real compression acting on the spark plug but failing when in the cylinder.

If for some reason you tried to remove the flywheel, you might have sheared the timing key.

tom3 said:

I'm guessing it's heat related. I'd try a new spark plug first, then the coil. Might have spark with no real compression acting on the spark plug but failing when in the cylinder.

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The plug is brand new. I don't think heat is relevant since it just ran maybe 10 seconds until it just died.

Fish said:

If for some reason you tried to remove the flywheel, you might have sheared the timing key.

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I haven't touched the flywheel...but the key might have been sheared before I got the mover. Should I remove the flywheel just to check? The strange thing is that the engine have been running just fine in (short) periods just to be really obstinate later. It's just so weird...

Won't hurt at all to check the flywheel key.
It should line up to make a perfect square.

P.S. I think your English is better than most Americans who post on here!

Scrubcadet10 said:

Won't hurt at all to check the flywheel key.
It should line up to make a perfect square.

P.S. I think your English is better than most Americans who post on here!

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Well, I'm out of ideas so I might as well pull the flywheel and check. Is it possible to do that without a puller? Putting some tension from below after loosening the nut so it lines up with the crank shaft end and tap with a hammer?

P.S Thank you! :redface:

Tecumseh made several different shape flywheel keys, removing the nut would tell you, worth a peek. But the nut must be torqued down enough when you re-intall it, or it will shear pretty soon.

Looks like yours is the one that is a regular woodruff key.

Thanks!

I'll remove the nut and take a look. I guess I'll see if the key is sheared with it gone.

Hello,

Remove the spark plug and rotate the engine by hand to verify the valves are opening and closing,,,could be a sticking valve.

I'm thinking the valves might be working, but the slightest amount of heat is causing them to bind. If the valves open and close cold, try heating the cylinder hole with a propane torch to see if it fails hot.

Does the kill wire and it's connection to the throttle plate look ok? These Tecumseh's I think short out with the throttle lever.

Regards

Jeff

Hi Jeff!

Since there is compression I guess the valves are OK at least. I haven't taken any tins of this engine, so I don't know how to access the valves. Is there a cover?

The kill function is under the plate. There is a thingie that looks like a bent paperclip that a lever operated by the throttle cable contacts when the throttle lever is pushed to the stop position. It looks to be OK. I don't know about the ground wire though, since it goes in under one of the tins.

Guess I should remove the tins and check that everything looks OK under there.

I tried to prime with some fuel directly into the cylinder and it fired but wouldn't run.

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Compression, fuel and spark are the three things needed for an engine to run. That is evidence that fuel is the missing ingredient.

This is what I suspect also...but why? The carb is brand new and I know the float bowl fills up.

it's not firing well when I prime, but it fires. Other engines revs up and dies, but this one sputters and sometimes it doesn't fire at all.

Hello,

If this is a valves in block engine (not 100% sure as I can't find a TWM140 Tecumseh engine in checking the partstree.com website), you should be able to see the valves through the spark plug hole. Look off to the side with a powerful flashlight.

You'd have to remove the recoil starter to check the ground wire, not a big job, only 4 or so bolts hold it on. Sometimes mice chew through it, or the plastic abrades against a cooling fin, causing an intermittent short.

This statement is leaning me towards an ignition issue - I have checked the spark and it is there, but I have a feeling that it's not that strong. The ignition is solid state so there are no points to check.

It could be fuel related, but I'm not entirely convinced.

Regards

Jeff

Paxman said:

This is what I suspect also...but why? The carb is brand new and I know the float bowl fills up.

it's not firing well when I prime, but it fires. Other engines revs up and dies, but this one sputters and sometimes it doesn't fire at all.

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A brand-new Chinese carburetor means nothing. How much did it cost? About the same as a rebuilt kit for a Tecumseh carburetor? Because fuel is sitting in the bowl doesn't mean it's flowing through the passages and jets it has to flow through to mix with air in the correct proportions for the engine to run.

To be able to remove the big tin I had to remove a couple of head bolts. One of them were really oily, so I decided to remove the head. Several bolt were the same, so now I suspect the head gasket. Obviously the gasket is crap now that I removed the head, but do you think my problems could have been a blown head gasket? Even if a new gasket is not that expensive, at some point I have to stop throwing money at this thing...

I could now inspect the valves and they looks pretty good. There is a lot of carbon deposits but they move nicely and it looks like they are seated well.

The flywheel is rather rusty (surface rust) but the key and the slot for it shows no damage.

Jack,

Here is a link to a parts diagram.

Obviously the gasket is crap now that I removed the head, but do you think my problems could have been a blown head gasket?

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I don't think so. You had 90 psi compression; that is more than enough to run.

cpurvis said:

A brand-new Chinese carburetor means nothing. How much did it cost? About the same as a rebuilt kit for a Tecumseh carburetor? Because fuel is sitting in the bowl doesn't mean it's flowing through the passages and jets it has to flow through to mix with air in the correct proportions for the engine to run.

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Since the problem is pretty much identical with the new carburetor as with the old one I actually don't think it is the carb now that I think about it. There is no fuel pump, it's gravity feed with the tank above the float bowl. I know fuel in the float is not a guarantee that the fuel system is working. I only wrote that to inform that fuel is getting to the carb.

cpurvis said:

I don't think so. You had 90 psi compression; that is more than enough to run.

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So where did the oil on the head bolts come from?

You might be making the erroneous assumption that because the carburetor is "new" and the engine displays the same symptoms, that the problem lies elsewhere.

You might be overlooking the possibility that the "new" carburetor has exactly the same problem as the old one--a clogged passageway or jet. Chinese carburetors are not known to have the best quality control.

It didn't come from a blown head gasket. Probably from the piston rings being worn.

cpurvis said:

You might be making the erroneous assumption that because the carburetor is "new" and the engine displays the same symptoms, that the problem lies elsewhere.

You might be overlooking the possibility that the "new" carburetor has exactly the same problem as the old one--a clogged passageway or jet. Chinese carburetors are not known to have the best quality control.

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Yes yes...but now I have these carbs and can not get a new original one, so the only way forward is to eliminate all other sources for the problem.

cpurvis said:

It didn't come from a blown head gasket. Probably from the piston rings being worn.

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How can oil get to the bolts if the rings are worn? I should have mentioned that the oil is on the threads. I'll see if I can upload some pictures...

Here are some of the bolts.




And this is how it looks under the head. There are signs of escaping gases on the muffler and on the yellow chassis.

There are only a few ways for oil to get in the combustion chamber of a flathead engine: Worn rings or cylinder, excessive blow-by being routed into the carburetor or through a worn out intake valve guide. There is no way a blown head gasket on a flathead engine is a source of oil. It does not seal off any source of oil from the combustion chamber. The threaded holes for the head bolts would have to extend into the crankcase itself to reach oil. It doesn't look to me like the head gasket was blown anyway.

None of this is keeping your engine from running. It may use oil and smoke, but it will still run if it has fuel (and air in the proper amount), compression, and ignition (at the proper time).

Paxman said:

Yes yes...but now I have these carbs and can not get a new original one, so the only way forward is to eliminate all other sources for the problem.



How can oil get to the bolts if the rings are worn? I should have mentioned that the oil is on the threads. I'll see if I can upload some pictures...

Click to expand...

No, but you can easily rebuild your carb to like-new condition, eliminating the chance of bringing in defective castings, passages, etc. from an unknown source, which it looks like you did. The Chinese carb, as expected, accomplished nothing.

I had a similar case with an old Tec, and the fuel line was breaking down amd dropping finenparticles intonthe carb, clogging a jet. Letting it sit for a while would let the cycle repeat, as did cleaning the carb. The fix tonget it to keep running was a tank flush and new fuel line. On the oil, I've also had engines that had good compression, started on one pull consistently, and would fog the neighborhood. A hone and new rings had it back to zero oil use like new . . .

The staining on the deck is heat from the muffler and the fact it is in lines is from the breeze created by the cooling fan.
It might just be a shadow but I see what looks like a crack between the inlet & exhaust.
As previously mentioned, nothing stops a flathead from running.
I run motorcycles dating back to 1917 most are flatheads and provided that the spark is happening at the right time they will run with all sorts of problem.
I have ridden 600 miles on an engine with a cardboard head gasket because the composite one crumbled and fell apart.
I had another that broke a chunk out and we had to start that by pushing because it lost so much compression at kick start speed it could not be started .
I rode that bike every day of a 6 day event, just had to stop on a hill.

On the subject of the bolts.
Screw then in till they bottom out then measure the space from the cylinder to the under side of the head
Now measure the depth of the hole through the head including the head gasket.
The head hole needs to be 2-3 full thread lengths longer than the free length of the bolts to enable proper clamping.
If this is not the case then either you have a build up in a blind hole or the bolts have stretched.

bertsmobile1 said:

It might just be a shadow but I see what looks like a crack between the inlet & exhaust.

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I see what you mean...just checked, it's a shadow made by quite a bit of flash from the moulding.

bertsmobile1 said:

On the subject of the bolts.
Screw then in till they bottom out then measure the space from the cylinder to the under side of the head
Now measure the depth of the hole through the head including the head gasket.
The head hole needs to be 2-3 full thread lengths longer than the free length of the bolts to enable proper clamping.
If this is not the case then either you have a build up in a blind hole or the bolts have stretched.

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I will definitely check that!

jp1961 said:

https://youtu.be/iyyy-JE7cPg

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Very informative video! I just checked the valves and they both felt pretty good when I spun them. I did spray some lubricant along the stems and it felt like they freed up a little more. However I found one thing that I don't know if it supposed to be or not. I rotated the flywheel one full revolution and paid close attention to how the valves moved. On the compression stroke the exhaust valve opens a tiny bit (0.4 mm, 1/64") during the first half on the stroke and then closes again at about 75% of the stroke. Is it supposed to do that? If not, what would cause it to? It's like there is a bump on the back side of the camshaft lobe for the exhaust. I have never seen that in an engine...

Hello,

Yes, the engine has a built in decompression feature built into the cam inside the engine.

Try rotating the valves when they are open (as per the video), they should spin freely. Now that you have the head off, this should be really easy. Try a rust penetrating oil like WD40 or PB Blaster, because if the engine sat for a while the valve stems probably have corrosion on them.

When working on anything,,,YouTube is your best friend.

Now I'm thinking out loud, but I wonder if the decompression system is shutting off, once the engine catches? One step at a time I guess.

Regards

Jeff

As I wrote: both valves felt pretty good when I spun them and after spraying some lubricant along the stems it felt like they freed up even more.

Good to know that there is a decompression feature. That means that as fas as I can tell the valves are good to go. Now I only have to source a new head gasket so I can move along with the trouble shooting. I have emailed my local small engine shop with the part number but they haven't replied yet.

The head gasket doesn't look bad, I would reuse it.

Don't try to remove it from the block as you'll undoubtably tear it.

Your engine looks like it is a vertical shaft unit, so the penetrating oil won't trickle down the valves like a horizontal shaft engine (unless you can tip the mower on it's side).

Part of the gasket was stuck to the head so a new one is a must. The valves are fine.

Hello,

With the head off how is the condition of the cylinder walls and if there is a ridge at TDC?

I realize you don't want to sink a ton of money into it.

Jeff

Find tdc on the compression stroke
Two ways from here
1 shine a strong pencil beam torch into the intake & exhaust ports while looking down at the valves.
If you see light then the valves are not seating.
Or tip the engine cylinder down and pour water into both ports one at a time.
If the valve face / seat is good it will not leak out.

Today I had some time to inspect the head and the head gasket. To me it looks like it was blown.


Gasket on the bottom (turned upside-down) and mating surface on the top. The cooling fin is much greasier than any other. I think it's the one facing downwards when installed on the machine.




Same placement here. There is a clear track of black from the combustion chamber to the bolt hole. The two bolts that where grimy was in these respective holes.

A new head gasket is ordered. It'll be interesting to see what the compression is after I put everything back together.

The bore is so so...there is no lip, but there is an area that look a little different on one side (right side looking into the cylinder). I suspect this is from the side force the con rod puts on the piston. I can't feel anything when I run my fingertips along it. The same goes for the whole cylinder surface. The hone marks are still visible except on that side area.

OK, so today I replaced the head gasket and reinstalled the head. Weirdly enough the compression was lower now! The torque spec I found was lower than I could dial in on my torque wrench, so I went a little higher. I thought f*ck it...I'll just put everything back together anyway.

Before I reinstalled the carb I squirted some gas straight into the intake and pulled the cord. It started straight away and revved up and died. Encouraging!

With the carb back, without the plate (that sits on top with the choke linkage), I pulled the cord again...nothing. A little squirt into the throat and the d*mn thing started! With a little fiddling with the mix screws I had it running well enough to put the plate back. That thing is not that intuitive, but I have seen a video of how to set it up and was able to get it pretty good. More fiddling with the main and idle mixing screws and it was running sweet! :biggrin: I ran it back and fourth on the street doing small adjustments on the main mixture screw, stopped it and started it again with no effort! I think it's fixed!! :thumbsup:

The only thing that I'm not super happy with is the governor. When I engage the mower deck the rpms dives and I can't really see the governor arm moving that much. When I had it running before all this fixing the arm moved much more and you could clearly hear that it worked the way it's supposed to. It's not super critical, with enough throttle there the engine copes with the load but it would be nice if the governor kicked in when needed.

Hi Paxman,

Good to hear you got it running, without too much invested.

Regards

Jeff

Thank you Jeff! :smile:

In retrospect maybe the new carb was not needed since the head gasket seems to have been the culprit the whole time. I will not try the old carb now that the engine seems to be running well. I'll keep it for spares for future machines. The new carb was around $35 to my door and I think it will be a good selling argument when it comes to selling the mower in the spring.

Goes to show that not all from China is sh*t, even if it's cheep.

I will do some more testing tomorrow. I have a patch of grass that is on the higher side that I can mow. I found some youtube vids regarding the governor so I'll see if I can adjust that a little better.

So far I think the mower owes me around $150. I'm hoping to get $350 for it in the spring so a profit of $200. It won't make me rich, but so far I have had some good fun and learned that a blown head gasket can give symptoms that points to carburetor issues and even give good compression numbers! :thumbsup:

Hello Paxman,

Yep, working on engines is a work in progress. No matter how much you think you know, you still learn with each project. Nobody is an expert.

Good luck in flipping the mower for a profit.

FWIW, I installed a Chinese carb on a Troy-Bilt tiller and it performed well as the original carb was corroded beyond repair/rebuilding.

Regards from the U.S.

Jeff

Paxman said:

... but so far I have had some good fun and learned that a blown head gasket can give symptoms that points to carburetor issues and even give good compression numbers! :thumbsup:

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Don't kid yourself. Your head gasket WASN'T blown, nor does a blown head gasket mimic carburetor issues. Don't spread that around, 'cause it ain't true.

OK...I need to close this thread since non off the different theories that have been mentioned was correct!

I really needed to get rid of this machine this spring to make some room in my garage so I cleaned it up and tested it some more. Do you think it ran perfect? You fricking son of a b*tch of a crap machine!!!!! The same problem as before!! It started up fine...I ran it for a while and it just died again. More tinkering and the exact same behaviour...it would sputter and die, fire but not start, totally dead and so on. Frustration overload!

I started to suspect bad spark after all and now I have one of those lights that you put inline with the spark plug to check if there is spark. The engine was totally dead when I installed it. I used a drill on the flywheel nut and spun it up...it started right away!! The light in the tester flickered. So I stopped the engine, removed the tester and spun it up again...nothing. OK, tester back on...started right up again!!? Now I could see a pattern for the first time!

After some inspection I could see that someone at some point had used vulcanising tape on the wire from the coil. This was in the part where the wire goes through the fins of the head so it was not easy to see if you were not looking for it. Removed the tape and put double heat shrink tube over the minute damage of the insulation and put everything back together again. I was so convinced that I had found the illusive fault I even reinstalled the pull starter. Gave it a pull and it fired right up and ran like a champ! I did some extensive testing with start/stop, mowing for half an hour, letting it cool down and do a cold start...it just worked!

My verdict is that the damaged insulation of the spark plug wire shorted the spark intermittently. It was juuuuuuust in the sweet spot for working and not working, so sometimes it was a fraction away from shorting and then something shifted and the engine died. Sometimes it was on and off, many even arcing from time to time, which made the engine run rough. When I used the tester the cable got far away the "sweet spot" so it worked just fine.

Anyhow, I sold the machine (with a healthy profit) about a month ago and haven't heard anything from the buyer...so I guess it's still working as it should! ?

Thank you all for your help and support! I guess that if I hade followed [B]tom3[/B]'s suggestion in his first post of trying a new coil I would have saved myself a lot of trouble and head ache! ? Well well...hindsight is 20/20 right?