OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk Tecumseh 13.5 hp

Right now the best "it could be ..." is the head gasket, Paul.

So far as spraying fuel into the carburetor is concerned, I don't see it as having much different effect from partly closing the choke, which we already know, made it run better. However it also made it wet its spark plug and plaster its air filter with puffed-back fuel. As a general rule, don't spray fuel into the intake of an engine that is puffing back through the carburetor, for safety reasons. A faceful of burning petrol is definitely not something to look forward to.

As an aside, when you are opening the throttle is one of the times engines are most likely to puff burning fuel back through the carburetor. It is called a "spit", and is a symptom of lean mixture. The old guy may or may not know what he is talking about in general, but in this case, simple prudence should tell you not to do it.

At the moment the engine will not run at steady speed, so doing tests while opening the throttle simultaneously is rather irrelevant. It mixes two variables: steady state running conditions, and acceleration conditions. His test would be relevant (though excessively dangerous) if the engine would run at steady speed, but would not tolerate an opening throttle situation. Poor running then would indicate insufficient acceleration enrichment. By the way, the classic sign of mildly inadequate acceleration enrichment is the engine hesitating. Severely inadequate acceleration enrichment is often indicated by a spit. Spits are a bit disconcerting when the air cleaner is in place, but with it removed, they are rather frightening. No matter how well an engine is running, never stand in front of the air intake with the air cleaner removed. Have you ever seen anyone who's had a faceful of burning petrol, even several decades before? It's a sight you won't forget.

Hi Grumpy,, dont stress wasnt really going to do it, just feels as though we arent getting anywhere. I know we have in reality, just this not wanting to rev out is bit fustrating.

Have put motor back together, setting it up the same way as when tearing it down. Fresh oil, couple of turn overs without sparkplug lead on, just making sure to have everything lubricated. Gave it a run hasnt made any difference.
When i explained to you that the air filter casing was getting wet from fuel, could this have something to do with the inadequate acceleration enrichment that you are talking about. How would we go about fixing this problem, or do you think it could be something else.

You fixed the blown head gasket and it made no difference?

At this point I'm concerned about not actually hearing and seeing this engine, Paul. Let's focus on this for a minute: how well can you get it to run, by applying some choke? Does it run "better" or "properly"? Choose one.

Hi Grumpy, with the motor idling there is a very very slight surge, nothing to be worried about. When i try to rev it out to at least half throttle i need to apply approx 1/4 choke it will run properly, but at the same time it seems to be running/reving to hard, almost as if it is on full throttle plus a bit more. Hope this is understandable, if not i will try again.

What you have said seems clear Paul, but what is causing it, less so.

You said several posts ago, that when you advance the speed control without applying choke, not only does it run badly, but it develops a wet spark plug and a wet air filter. Can you check if the plug and air filter are wet after you run it on the right amount of choke, then verify that it does those things consistently (in other words, run the test again with no choke, and with choke, and see if it always shows wet plug and filter with no choke, but not with the right amount of choke to make it run properly).

Hi Grumpy, have done as suggested, hope you are ready for this.
Gave the motor a run with airfilter on, missing slightly on idle, but now i am able to rev it up to full throttle. Turned engine of , checked for any fuel around airfilter and spark plug, all was dry. Done this 4 times just to be sure it wasnt playing tricks on me, same outcome each time!!
Cannot understand why it went from not wanting to rev out to now reving out when i havent changed anything or done anything different. It is making me come back to a problem with the governor again, not so much in the way it is working but in the way the governor arm should be set up. Am wondering if someone else has tried to adjust it originally and i just havent found the correct setting for it.
Do you want me to also try running it with the choke partially on or would this now be not needed.
Talk about going around in circles.Maybe this is why some people stay away from Tecumseh motors, you never know what they are going to do one day to the next.

I can't see how the governor can be implicated Paul, since you found that it wouldn't run properly when you removed the governor's link to the throttle, and operated the throttle by hand. The result you got by doing that, was exactly the same as when the throttle was operated by the governor. That is the way I read the previous posts, but please confirm whether that is correct.

Because the problem, whatever it was, was consistently overcome by partly closing the choke, it had to be mixture-related. That almost certainly means it was caused by a carburetor fault or an intake air leak. An intake air leak is unlikely to have been the problem because it would idle: it only went lean above idle. Therefore, a carburetor fault, or fuel supply to the carburetor. I think I recall that you checked the fuel flow to the carburetor at the beginning of this process, but please confirm that.

What can cause intermittent lean mixture when the carburetor has been cleaned out? Perhaps some loose crud or loose component was still in there after cleaning, and caused the problem, so a moving mass could move from being a problem to not being a problem without human intervention. If so, it is still in there now, just not causing a problem. My favourite explanation is that your float arm is binding on its pivot sometimes, or the float needle is sticking sometimes. That might result in passing enough fuel all the time for idle, but not enough to rev the engine. Now the needle or float pivot has unstuck itself, so all is well until the next time.

It is a Tecumseh carburetor, and those have an evil reputation. Whether this problem would not have happened on a better carburetor is difficult to say.

H Grumpy, yes i did get the same results with governor linkage both connected and not connected.
What i am trying to figure out with the governor arm, itself being 2 peices, is should one peice be set opposite the other peice an angle or should they both be straight. Will get a photo if you would like me to.

And yes i have checked the fuel flow rate, not sure if i did mention it, but it is a consant steady flow.
Can understand what you mean about the needle/ float being partially stuck. Most defiently understand you when you say that Tecumseh carbys have an evil reputation,, dont i know it.
Should i now reconnect the governor and see what happens or is there something else i should try first.

Here are the things I'd like to know for sure Paul:
1. Can you always make the engine run well, whether or not you have to apply the right amount of choke to do it?
2. Does that apply whether or not the governor is connected to the throttle?
3. If you apply that amount of choke, and set the engine at a fixed speed, is it stable? That is, will it still be running perfectly five or ten minutes later?

If the answer to all three questions is yes, it seems to me we should be focusing on making the mixture stable and correct, if possible without modifying the carburetor.

All that is based on the idea that the engine having "come good", is temporary and will not continue if the wind changes or something equally irrelevant happens. In that connection, you might try a crude and brutal trick. If you can get it to go lean again, try tapping the carburetor body once or twice with a rubber hammer while it is running, and see if that makes a difference. If you can't get it to go lean any other way, tap it and see if it goes lean.

It may be that whatever the problem was, it has now gone away forever, but I doubt it. More likely the situation is unstable. Unless we can find what the cause was, it will be a long time before you'll feel comfortable that you are going to be able to use it when you want to.

My favourite guess is that the needle was slightly jammed where it fits into the top of the float lever, and it has now come unjammed. You can help clear this up by answering two questions:

1. Had you just dismantled and reassembled the carburetor when this problem began?

2. When you put the float mechanism back together, did you gently lift and lower the float a couple of times before you re-attached the float bowl, and did you then keep the carburetor the right way up afterwards?

Question 2 relates to something you should do every time as a matter of habit. Float mechanisms are always tinpot, even back in the days when they were used on cars.

Hi Grumpy,hope your ready for this..
In previous post i had the motor running with the governor linkage connected and ran good.. Now it wont run at all even if i give it a bit of choke. With the governor linkage removed it will run with partial choke, coughing spluttering and spitting ( felt one on my hand ). I did give it a tap with my rubber hammer, didnt make any difference. Talk about one step forward three steps backwards. Your not wrong about them being evil carburetors, its testing my patience really well.
Didnt play with the carby until we got to that part, and i always lightly lift the floats up a couple of times just to make sure there are no sticky points in any of the mechanism and yes i always hold carbys upright, unless dismantling them.
After trying all this while sitting there deciding the fate of the motor i did notice that between the two halfs of the carby, were the gasket is, there were small air bubbles popping out and when i wiped it with my finger, you guessed it, fuel. I am guessing this could be a slight bit of my problem.

Paul, would you mind trying this again first, with your in-line spark tester?

This is a change in behaviour, since it no longer pays attention to the choke. From your comment about fuel coming over the top of the float bowl sounds as if it is now flooding, which again points to a float bowl problem. Bear in mind that a float bowl problem could have caused your previous lean mixture situation.

Hi Grumpy, have done previous test but with in-line spark tester and this is what i came up with.
Will only run properly with throttle held just above idling with nice constant spark. If i try to drop the revs or up the revs it will cough, splutters as you know, what i did notice was as soon as the motor started to play up so did the spark, it was almost is if it had a constant miss until i brought the throttle back to were it was running best. The spark was still there it just seem to loose some so of it punch so to say. Let me now if i have explained this properly Grumpy, if not will try again.

The question is whether the stream of sparks remained completely steady, Paul: not whether the intensity may have varied, but whether instead of looking at a steady stream, you were looking at a ragged stream - which would indicate misfiring due to spark insufficiency. It may not be easy to tell.

Hi Grumpy, have done it again and yes there is a constant steady spark.

I have been thinking of what i wrote yesterday and i am thinking i was jumping the gun,, it wasnt until the motor was coughing/spluttering wanting to shut down did the spark lost some of its intensity.

I'm not clear on what you mean, Paul. If the engine is running at the same speed, whether or not it is coughing and spluttering should have no effect on the stream of sparks. Does the spark lose intensity when it begins to cough and splutter, but always has full intensity when it is not coughing and spluttering?

Hi Grumpy, yes thats right. When the motor is running smooth there is no change in spark, only when the motor starts to cough and splutter will the spark loose intensity, you have to look hard but you can see it. There is a difference between the "good" spark and the "lost its intensity" spark.

Paul, I suspect that the "loss of intensity" is that the spark becomes intermittent. With the engine running at 2-3,000 rpm you can't see individual sparks, it looks like a continuous spark. In other words, your problem now might be ignition failure.

I suggest you disconnect the kill wire at the ignition module, checking the module's grounding and the gap between module and flywheel while you are at it. Then repeat the test with the in-line tester. If none of that makes any difference, it will be time to check the module's primary and secondary resistance, and/or look for a spare module.

Hi Grumpy, sorry for time limit, am snowed under at moment.
Have not connected kill wire on ingnition module since you asked me to remove it. Have repeated test again, some outcome.. Modules grounding is good and gap to flywheel is good, couldnt get it any smaller if i tried. Have tracked down another module, hopefully will be able to give it a try in next day or two. This should let us know if my original module is no good.

That is the best way to find out, Paul, I agree. I don't know why the spark intensity in the tester would vary when it plays up if there isn't a spark problem, but there have been so many twists and turns in this investigation that I think the only way to go, is overwhelming evidence.

Hi Grumpy, sorry been a bit long, but after reading this you will understand. ( hopefully like me you will let out a bit woooohoooo )
Put on other module i told you about and tried to run the motor, guess what, jumped to life straight away. From idle up to not quiet full revs, didnt want to stress it out to much. This was done with no governor linkages attached. Attached all linkages to carby and gave it another run, from idle up without any sign of hunting/coughing, nothing...
So i thought maybe the motor is trying to trick me so i let it sit till the next day, tried it again, whammo, up and running like it had never stopped..Done this for five days straight, each test went for upto 20-25 mins.. Let it sit for two days no test, tried again, whammo, up and running...
So it seems like all this time it has been the ignition module giving me trouble. Talk about a long stroll through stressville.
Should i now connect all unattached peices now and see how it goes.

I think it all makes sense, Paul. Essentially, I think you had two problems in succession.

First, in the long ago, you acquired the engine with a worn-out decompressor pin. In the first part of this thread, that was replaced and the decompressor then worked.

Second, while testing the decompressor, you fitted the engine to a different ride-on which had a mysteriously malfunctioning engine. You hoped that, because the Tecumseh was running by then with its new decompressor pin, it could be a suitable engine for this second ride-on, which had a chonda copy of the Honda GXV390 engine in good condition except for a malfunctioning ignition module. The Tecumseh soon malfunctioned on that second ride-on, and you resolved the problem by disconnecting the ignition kill wire. Meanwhile the chonda engine worked perfectly once it was removed from that mower. So, it seemed highly probable that the second ride-on had tenant-improved wiring which may have been doing something like applying 12 Volts to the kill wire. With its kill wire disconnected, the Tecumseh engine worked well for a short time, then malfunctioned. The malfunction was somewhat erratic and intermittent, which made diagnosis difficult. Ultimately, having established that nothing else was wrong, you tested the spark while the engine was running. It turned out that the spark quality was changing when the the engine malfunctioned, suggesting that the ignition module had been permanently damaged by its time with the tenant-improved kill wire connected. So, you tried another ignition module, and the engine then operated correctly, supporting the theory that the original module had become damaged.

This has been one of our longest threads ever, and I think easily the longest thread ever that was solely concerned with fault diagnosis. Just in case there is yet another unexpected twist or turn in the case study, I'll leave this thread open. Since it will be open I suggest that you use it to trace the actual wiring fault in the ride-on mower. If you give us a full identification of the mower, we can try to get hold of a wiring diagram, and start making some tests.

Hi Grumpy, sorry its been a while again,, but have finally found the wires at fault.. I did track a mower down, exact same model, motor, everything the same,, except this one ran properly. After a number of days tracing wires here and there and everywhere, the only difference between the two mowers wiring was ,on mine, the wire that came out from under the flywheel had actually been joined up with the wire to the ignition module,, on the donor mower it was not. Other than that, there is no difference at all. I set up my wiring the same way and with fingers crossed tried to start the motor. Kicked over first go, ran beautifully from idling all the way to full revs. Again left it for a day tried again, same result, ran perfect..
I cant believe that after starting with a simple problem of a decompression unit, we ended up on a couple of months wiring hunt.

I would like to thank you heaps for you help on this one Grumpy, it is greatly appreciated.

Hey, it all worked out in the end, Paul, which means the whole process was a pleasure.

I haven't seen the wiring diagram, but it sounds as if that other wire from the flywheel area was the alternator/generator output, so as expected, the previous tenant was applying 12 Volts or so to the kill wire whenever the engine was running. The world is full of people who don't know there is a difference between magneto ignition and Kettering ignition: cars need 12 Volts on their coils to run, so mower engines must also. I wonder how he thought it started, if it needed 12 Volts on its coil for the ignition? Oh well, as a rule of thumb, never expect previous tenants to have been logical.

I'll close this thread.