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

Is the linkage the same as in the manual's illustration, Paul?



I'm asking because I can't see the choke linkage in your picture, but it is shown in the illustration. You now have the spring in the correct notch according to the diagram.

You have reported that the governor is cycling, but with some new and very important information: the spark plug is wet, and fuel has been spraying back through the carburetor onto the air filter. I think this makes it unlikely that the problem is lean mixture. My new guess as to what is wrong, is based on that piece of information. Let's go back to the Tecumseh diagnostic procedure for governor-cycling:


When I read that the first time, I thought it was a clear admission that the performance of that governor is marginal at best, and it is prone to cycling. Now that you have said that the plug and air filter are wet with fuel, a possible explanation comes to mind. When the throttle opening increases on a carburetor, a design feature called "acceleration enrichment" comes into play. If the throttle actually flutters, the mixture is likely to become very rich. So, what I suggest you do, is follow Item 1 in the diagnostic: hold wire link between the throttle and governor arm perfectly stationary with a pair of pliers, and see if the engine then runs steadily, and changes speed when you move the throttle slightly. If it does, you will have proved that the problem is governor instability. Of course we then have to try to figure out the cause of the instability, but at least we'll have a focus.

Hi Grumpy, sorry about the time delay,, after x-mas rush is on.

The reason you are not able to see the choke linkage in my photo is i removed the throttle set up so i was able to get a good clear shot of the governor arm for you, and yes my set up is excatly like in the diagram you supplied.
Have done as suggested and held the governor wire with pliers and gave the motor a run.. It will only do this in idle mode. I am not able to open up the throttle to far as it will conk out straight away. Going by the governor arm on the carby it is running in idle mode but to me, just listening to how it runs, it seems to be running to fast as if on half throttle. Would it worth trying the governor in a few different set ups, might snag a winner.

I don't really understand what you've just told me, Paul. Why not try removing the wire link from the throttle butterfly, and controlling the engine with fingers on the butterfly lever? Don't let go of it of course, or it will probably blow the engine. As an alternative, you could rig a piece of stiff wire from the throttle butterfly to a stationary part of the engine (not part of the governor) and try to vary the engine speed by bending the center of that link. The idea is just to see whether the engine runs properly when the whole governor system is eliminated. If it won't run properly with the governor excluded from having any effect, we have an engine problem of a fairly unusual type, and I think you are going to have to go back into the crankcase to re-check the camshaft timing and inspect the decompressor mechanism.

Just to ensure you are as uncertain as I am, I'm pondering what the symptoms would be if the decompressor is stuck in the start position. Some years ago I worked on a couple of veteran cars which had manually-controlled decompressors because at 4.6 litres and with a high compression ratio (they were factory-team racing cars), there was no way you could crank them without decompressors. I even verified that by using a starter motor to rotate the crankhandle without decompressing: it immediately sheared the cross-pin in the front of the crankshaft, where the crankhandle engages. The Hulk himself could not have cranked those engines. So, the point in this story is, when you started the engine in its decompressed state, you had to move quickly to disable the decompressor, or the engine would stop. Meanwhile, it ran absolutely atrociously.

So, if your decompressor is stuck ...

Hi Grumpy, have done as suggested, removed the wire governor arm and controlled the carby myself. Did not make any difference, still not able to increase revs past idling.. I guess now i have to tear the motor back down, something we were hoping not to have to do. Will get the camera ready.

I agree Paul, it is time for that. I can't guess whether it will be that the decompressor is stuck on, or the camshaft timing is a couple of teeth out. If it isn't either of those, I'll be waiting for a useful clue from what you do find out.

I just thought I'd throw this in, it's the butterfly stuck in the manifold as is when I pulled it apart. The engine (12.5 briggs) would still run and I don't know how but only at idle and have never come across it again since. I found the two butterfly screws in the muffler . Lucky it didn't pop a valve seat or even worse wreck the engine .

Perhaps that carburetor had been serviced the way we are told to do it in the carburetor manuals, Rob: remove the choke and throttle butterfly plates, and pull out the shafts they mount on. I literally never do it unless the screws are already loose. As a lad many, many years ago I took some car carburetors apart, and was never happy with the security of those screws afterward. Because the shaft is normally brass, I ended up soldering the screws in, getting them hot enough so that the solder penetrated the threaded section. None of them ever came out after that, but I stopped taking the screws out anyway.

I've never had an engine eat a butterfly valve plate screw, but once again way back, I drove an old 800 cc OHV Morris Minor. One night I was putting along through the suburbs when suddenly the engine rattled and lost a cylinder. I think I had the ignition off in considerably less than a second, and caught a tram home to pick up the spare car and drive back, with a rope and a co-driver, to tow it home. Next morning I pulled off the head and found I'd been very lucky. A disused weld-nut had fallen off the inside of the giant oil-bath air cleaner, and slid down the intake manifold straight into the cylinder. The loose nut in the cylinder had immediately hammered the spark plug gap closed, and hadn't done any other damage in the brief time it had been running. So, it was going again in about half an hour at no cost. It could have been a great deal worse with another few seconds of running: a broken piston crown at least.

Hi Roebuck , thanks for that, but it isnt my problem, as much as i wish it was. Have had carby apart and it all works well. Have had similar problems on smaller B&S motors, but not on a bigger motor yet, touch wood. Thanks for the input Roebuck.
Hi Grumpy, have broken down motor and got some photos for you. As when i first broke it down i set it on TDC, dont ask why i just do, and as you can see from photos all timing marks are lined up.
First photo is crankshaft and counter weight.

Second photo is crankshaft and camshaft.

Have also got a few photos of decompression unit which is still in good working order,(thanks Grumpy),pin moves freely with no sign of sticking.


Did find something though. After doing what i have done so far i noticed some oil on the underneath of the head, which i have not noticed before. Got some photos so you can see what i am thinking.


I am wondering if while the motor is only idling everything is good but when i try to increase the revs some of the compression is actually be pushed out past head gasket which could be causing the burn mark and oil build up,, and lack of power . ( yellow circles ) Correct me if i'm wrong.

The mark is suspicious Paul, but not definitive by itself. It looks as if the gasket has delaminated somewhat when you took the head off the first time, and that does usually cause leakage when you put it back together. You should always scrape the surfaces of head and block so they are smooth and shiny, then inspect the gasket and if one of its surfaces is damaged, you need to replace it. I don't think the gasket was blown when you got the engine, but it may be now. You did take the head off at the beginning of the project, didn't you? That could be where the problem came from.

The first think to do is look closely at the surfaces of the gasket that correspond with the mark, and see if they show carbon, or are eroded by gas flow. Look carefully around the carbon ridge around the cylinder bore side of the gasket, and see if it is missing in places where there might have been leakage. Then see if you can get the layer of delaminated gasket material to flake off the surfaces of both head and block, without actually scraping it, by sliding a sharp blade underneath it on both sides of the suspected blow-mark. If you succeed, see if the blow mark runs across the surface where the gasket was. If you find a mark across the gasket area on either head or block, it was blown. Similarly, if you find carbon deposits on the split gasket surfaces, it was blown.

Hi Grumpy, have gotten abit of the old head gasket off the block where the "blow out " is and yes there was a blow mark across it as you mentioned there would be. ( sorry forgot to get a photo ). Have cleaned up both sides and got a new head gasket.
I will cut this next bit short,, while doing this this morning i had an old timer turn up to question me about his generator, asked what i was doing, explained the situation from the start and he proceeded to tell me to put it back together give it a run while spraying a light mist of fuel into carby throat , at same time up the revs, if it goes hard that will tell you if your carby is playing up or not. Even when i told him i have checked carby a couple of time, he stubbonly told me to try it. Walked away mumbling something about young blokes not wanting to listen...
What do you think, should i give it a go?
I am leaning towards giving it a go as i cannot think of anything else it could be.

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.