# Tecumseh question



## Rentahusband (Aug 25, 2008)

TVT691 600401A. Engine pops and backfires when running. Am I looking at a carb, valves or ignition issue? 

Thanks


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## usmcgrunt (Sep 16, 2007)

Just my opinion,I would check valve clearances first and then,as rare as it might be for a rider engine,a sheared flywheel key.A real mechanic should be along shortly with the correct diagnosis.

Just in case,you don't have it.
http://www.barrettsmallengine.com/manual/tecumsehvtwinmanual.pdf


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## Rentahusband (Aug 25, 2008)

I adjusted the valves and cleaned the carbs. Ran better. No more puffing/backfiring. After running, I noticed on one side, the valve cover was barely warm. The other side was hot to touch. When I removed the valve covers to adjust, one side had oil drain out, the other did not have a drop drain out. Did not look like there had been any oil in the valve cover. This is the side that was barely warm. Both sides have spark and 100+ compression. The engine will not start with the plug wire removed from the (hot side) and runs fine with this side is hooked up. It runs fine with both wires hooked up. When I spray carb cleaner in the carb of the (hot side), it reacts as it is choking out, which is normal. When I spray carb cleaner in the (cold side) it does not react at all. What am I missing??
Thanks


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## usmcgrunt (Sep 16, 2007)

I would say the coil on the warm side is not firing.Try a spark tester first on both sides.Pull the kill wire off the coil and see if that makes a difference.Last resort,switch coils from side to side and see if the problem cylinder changes sides.My guess - bad or shorted coil.


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## Rentahusband (Aug 25, 2008)

usmcgrunt said:


> I would say the coil on the warm side is not firing.Try a spark tester first on both sides.Pull the kill wire off the coil and see if that makes a difference.Last resort,switch coils from side to side and see if the problem cylinder changes sides.My guess - bad or shorted coil.


I tested for spark on the warm side by grounding the tip of the plug to the engine block. It had good spark, even switched plugs (that are new) with the same results. Would the spark be different when actually seated in the engine? Why would there be no oil in the valve cover of the side that seems to not be firing? Would'nt it run rough with one side not firing? It runs pretty good for one of the cylinders not working. I will try the kill wire next then the coils if needed. 
Thanks usmc!!!


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## usmcgrunt (Sep 16, 2007)

I'm not sure why only one valve cover has oil in it.I think the oil pump only feeds the crank and cam bearings.I believe the rocker arms are lubed with oil vapor from the engine.

You could have good spark outside of the engine and loose it when under compression.Briggs and other manufactures make air gap plug testers that are far more reliable than the in-line neon testers.I have a home made air gap tester that I use.I just cut off the small ear on a good plug and if the spark jumps the gap between the center electrode and the plug threads,then I'm pretty sure the coil is working correctly.Hope this helps

Afterthought- Is the spark plug on the non firing side wet with fuel ? If not,maybe a carb blockage??


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## Rentahusband (Aug 25, 2008)

When I spray carb cleaner in the carb of the bad cylinder, the tempo does not change. The other cylinder reacts to the extra fluid being sprayed in. Both valves are opening/closing on this cylinder. Flywheel key is intact. Bowl has fuel and jets are clear. I cannot figure out why carb cleaner does nothing on this cylinder. The plug does not look overly wet but is kind of a glossy black color. Does not smoke. I sprayed carb cleaner down the center hole of the bowl with the main jet in place and cleaner flowed through.


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## usmcgrunt (Sep 16, 2007)

I still think there is no spark on the bad cylinder.Have you tried switching coils to see if the problem changes sides?


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## 30yearTech (Sep 14, 2006)

If the engine will not run when only the spark plug on the cooler side is hooked up, then that side is not firing under compression. Placing a good load on the engine will probably show that the cool side is not firing, as the engine will likely run rough and bog down under the load.


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## burheelwilles (Sep 12, 2013)

Rentahusband said:


> TVT691 600401A. Engine pops and backfires when running. Am I looking at a carb, valves or ignition issue?
> 
> Thanks


Hey,, why don't try out to check valve clearances, it sounds like there might be some particle of carbon that might be giving the problem??


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## Rentahusband (Aug 25, 2008)

I will try switching the coils tomorrow. Being there was spark I figured switching would not help. Would rust on the coil laminations where the magnet passes be a factor? I engaged the mower deck and the engine ran fine. Unless the coil started acting up after the last time I engaged the deck. 
Thanks for your responses usmc and 30yr!!

burheewills, I did check the valve clearances, set at .004. 
Compression on both cylinders is 105-110psi.


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## usmcgrunt (Sep 16, 2007)

Rust on the laminations won't stop the magnetic field from being created,but if your pulling the coils,might as well clean them.


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## Rentahusband (Aug 25, 2008)

Ok, I switched the coils with no change. What am I missing!!??


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## 30yearTech (Sep 14, 2006)

Rentahusband said:


> Ok, I switched the coils with no change. What am I missing!!??


I guess I am confused, what makes you think you are missing something. 

Do you know if you actually have a dead cylinder??


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## Rentahusband (Aug 25, 2008)

30yearTech said:


> I guess I am confused, what makes you think you are missing something.
> 
> Do you know if you actually have a dead cylinder??


If the cylinder in question was actually firing, it should get to operating temp like the other side and when I spray carb fluid in the carb of this cylinder, it should choke out like the other side right? I can completely close off the carb on the cylinder in question with no change in engine operation.


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## 30yearTech (Sep 14, 2006)

Rentahusband said:


> If the cylinder in question was actually firing, it should get to operating temp like the other side and when I spray carb fluid in the carb of this cylinder, it should choke out like the other side right? I can completely close off the carb on the cylinder in question with no change in engine operation.


Alright, *with the engine running*, unplug the spark plug wire from the side that gets hot. What happens?


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## Rentahusband (Aug 25, 2008)

It dies. This is after I switched the coils.


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## 30yearTech (Sep 14, 2006)

Rentahusband said:


> It dies. This is after I switched the coils.


If you switched the coils and the same side is the one that's still not operating, and since you indicated that both cylinders have good compression. I would think the issue is fuel delivery into the dead cylinder.
Looking at the IPL I see that this engine has (2) carburetors, both with after fire solenoids. I would check the carburetor on the dead side to see if the after fire solenoid is working.


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## Rentahusband (Aug 25, 2008)

I have verified that the solenoid is working on the dead side. Why wouldn't the cylinder in question react to carb cleaner being sprayed in the carb? It should react to this if it was firing. When I block off the throat of the carb for the cylinder in question, there is fuel.


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## 30yearTech (Sep 14, 2006)

Rentahusband said:


> I have verified that the solenoid is working on the dead side. Why wouldn't the cylinder in question react to carb cleaner being sprayed in the carb? It should react to this if it was firing. When I block off the throat of the carb for the cylinder in question, there is fuel.


You need fuel, compression and ignition for an engine to run. 
Based on what you have reported, you have ignition, you have compression, and you have fuel, so the engine should run off of that cylinder. Since it's not running on that cylinder, you need to investigate the reason that it won't.

I would start systematically eliminating any possible reasons for this cylinder not to fire. 

I don't know if this engine uses diodes in the kill switch wires to the ignition modules, but just to be sure, I would test it with the kill wire removed from at least the dead side to see if it will operate that way. If it does then the problem could lie in the kill wire allowing feedback into that module and causing ignition timing to be off.

Next I would check the valve operation, making sure both the intake and exhaust valve are opening and closing properly, and double check the valve lash. 

I would then check the intake manifold on the dead side to see if there were any cracks, or massive air leaks.

I would move on to the carburetor (perhaps even swapping sides to eliminate each carburetor as an issue) making sure all jets are open, and fuel delivery to dead side carb. is good.

There is a reason this cylinder is not working, we just need to find the reason.


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## Rentahusband (Aug 25, 2008)

I did remove the kill wire from the coil on the dead cylinder still nothing. This one is trying my patience!!! 
Thanks for your advice!!!


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## Rentahusband (Aug 25, 2008)

Well, I figured it out!! Not sure if I want to admit what the problem was!!!


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## 30yearTech (Sep 14, 2006)

Well the suspense is killing us... A bad spark plug???


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## usmcgrunt (Sep 16, 2007)

Please,Please,Please!


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## Rentahusband (Aug 25, 2008)

It was that @#$%&%$ o-ring for the main jet!!! Same issue I had with the same carb on another mower!!! I switched carbs and the "dead" cylinder came alive!!! After putting the carb back the way it was, I could not see any fuel coming out of the emulsion tube when running. So, I took it apart, looked at that o-ring and found it was pretty squishy. Could have saved ALOT of time and FRUSTRATION if I would have just replaced that o-ring!!! 
Thanks again for your help!!!


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## usmcgrunt (Sep 16, 2007)

Well,at least this story has a Happy Ending.:thumbsup::thumbsup:

We all learn something new from each others experience and mistakes.


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