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

Hi Grumpy, have done the test, built an in-line tester as i said i would, not pretty but works. Made the tester so i can open the spark set from approx 1mm to 20mm, after that the spark has to jump to far and motor will stop. While doing the test i had a constant strong spark, there was no missing at all. Did not stop it from surging/hunting though, but as with the Millers Falls motor was able to close choke up a bit of the way and smooth it out.I guess this means there is nothing wrong with the ignition module.

Yes, it sounds as if the ignition module is in the clear. However you should still have the engine isolated from the mower's electrical system when testing it: the more irrelevant variables you can eliminate, the more likely we are to find the actual problem.

Have you had the Tecumseh hunting previously? We started out dealing with a decompressor problem: did it also have a hunting problem all along, or has that just begun since you got it running again?

Hi Grumpy, when i first got the mower it wouldnt turn over properly due to decompressor problems, so never had it running until we fixed that problem. Did contact previous owner,regarding the way it used to run, apparently it hasnt ran for over 1 year and being an older gentlemen ( no offence to him ) he cant remember exactly how it used to run. All he can remeber was his sons abusing it and him fixing it until he said no more, and thats were its been sitting since.
Would you like me to get some photos of carby, complete and broken down, governor linkages etc, or are we going to go in a different direction.

If it is hunting, it either has friction in the governor linkage, or lean mixture. Lean mixture would probably be either an intake air leak, or a carburetor fault. I suggest you begin by checking that the linkage moves freely and doesn't rub against anything, and post some pictures of it. I'd like to check that it doesn't have a stretched spring or other damaged parts, since it has reportedly been abused systematically by kids.

Once we are happy with the external governor bits, the next step would be to check the fuel flow to the carburetor, by checking whether it runs freely from the pipe when you disconnect it at the carburetor end. If there is no problem in that area, it will be time to remove the carburetor for examination and cleaning - which also gives you a chance to look at the insulator gaskets, and check that the clamped joints are clean and properly clamped. If there are no suspicious items in all that, next step will be to dismantle and clean the carburetor. The idea is to avoid dismantling things that might not need to be dismantled - start with the easiest things first.

Hi Grumpy, have some photos for you, sorry they arent the best, trying to get behind the throttle mechanism is a pain.




I know the governor arm looks a bit beat up but it is not rubbing on anything and it only takes a bit of pressure to open and close governor, feels about the same as other bigger motors i have worked on. Curious question, should there also be one of those long skinny springs around the governor arm as well, or would that one big spring be all it needs.
Have gone ahead and checked fuel flow rate and it is good, runs at a nice steady flow. ( Not trying to jump ahead, just done it while taking photos ).

Let's start from the manual if we can. Here is an illustration of the OHV13 (your engine I think) governor linkage, correctly set up:


Does yours look like that? I'm wondering if various bits are attached in exactly the right places, especially the governor spring.

Hi Grumpy, looks to be the same set up. In the picture the governor spring is attached on the bottom of governor arm, hope you dont mind but i gave it a try there, no difference. Tried it up higher,just in case, made no difference. Have got some photos of carby with gaskets still on it.
This first one is the airfilter side. Is original gasket and still looks good.


Next photo is back end of carby which bolts onto inlet manifold. Gasket is homemade i'm guessing, but still looks good without no signs of wear and tear, but should it continue all the way into mouth part of carby ( around bottom left side ). With it this way would that be enough to make the motor hunt/surge.


Have included a few photos of carby itself just so as you know what we are working on.

Is there an insulator, with another gasket on the other side of it, between the carburetor flange and the intake port?

The carburetor flange gasket looks rather woeful, Paul. If it is of uneven thickness, it will leak air. It can be difficult to tell without running fingers over both sides. I think I'd make a better one, partly because it might leak, and partly because it is hardly something to be personally satisfied with.

Here is the workshop manual's advice on hunting:


It sounds rather defensive to me: I suspect they think their governor tends to be a bit unstable. However without having actually heard your engine, I think lean mixture is a more likely issue than a governor fault.

Your carburetor is a Series 7, as shown here:


Please check the illustration and description against your carburetor to confirm that identification. It seems we have to face up to the unlovely task of cleaning a Tecumseh carburetor.

Hi Grumpy, no there isnt an insulator and gasket on intake side of carby just the one gasket between the carby and intake. I have noticed there are no air ports as on other carbys either. And yes i will most defiantly be changing that gasket, i'd like to think i could do better.
The picture of carby is the same as mine, they seem a bit of a weird idea, but each to their own. Will strip carby down asap, with photos to go with it.

that is very similar to a tecumseh vector carb, does it have O rings sealing the bowl to the carb body?

Paul, cleaning a Tecumseh carburetor is fraught with difficulties. Please look at these instruction pages first:




Remember, you have a Series 7 carburetor, which is a slightly odd one. The objective is to clean your carburetor, in particular the main jet and the "main nozzle emulsion" (that is, the emulsifier). Don't dismantle more than necessary, and don't adjust anything without discussing it first. Tecumseh's quaint approach to carburetion is probably the main cause of their engines being scrapped as unfixable.

We had a fairly long thread recently on an OHV Tecumseh carburetor:
https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=55609&page=2
The main problem in that case was that the emulsifier was pressed in and could not be removed. However your Series 7 has a removable emulsifier. Let's go at this carefully, though.

Joe, this is one of the large engines, specifically an OHV13 with a Series 7 carburetor. It has an O ring on the bottom of the emulsifier, and another one on the end of the main jet.

Hi Grumpy, thanks for the info, was able to print it out and take out the shed.
Have stripped down pretty much the whole carby, given it a blow out and followed up with some carby cleaner





Before i put it back together whats your opion on this gasket, it sits between the carby body and bowl.Looks as if it had been sand blasted doesnt it. Think i had better change it.

Very nice pictures as usual, Paul. That makes it much easier to see what is going on.

The float bowl gasket looks OK, it has a design that doesn't call for it to have a smooth surface as long as it is slightly soft. The top of the float bowl appears to have a raised up ridge all the way around it, and this ridge presses into the deformable gasket material. You can see the impression it has made in the gasket.

How did the main jet and emulsifier look before you cleaned them? Unless they were slightly gummed up, the cleaning you've done won't make any difference to how well the engine runs.

Hi Grumpy, thanks for the compliment.

Good to hear the gasket is good, it is soft and slightly flexible. I was thinking that with all the pits on the top side it might of been able to let air leak in around it. Thats sorted now. Your not going to believe me but the inside of the carby was virtually spotless, it looked as if was had been cleaned recently. Should i put it back togehter and give it go now or should i go deeper.
Curious question, the way it sounds to be running could i have put the motor back together maybe 1-2 teeth out. I am 99% sure i done it right, piston at TDC and all timing marks lined up just as it was when i took it apart, just starting to second guess myself. I supose if it comes to it i'll have to pull it down to check, not yet though.

It is difficult to be confident about what is happening without actually seeing and hearing the engine, Paul. You will recall that we investigated your Millers Falls chonda problem as if it were hunting, when it actually was ignition cutting in and out. They sound different, but until you've practised for quite a while, you would describe them both the same way. That is why I am not really confident that your problem with this Tecumseh is lean mixture. I do not think it could be a retarded camshaft: I'm regrettably familiar with the symptoms of that, from driving old cars with worn out timing chains, which occasionally "jump" their timing. It makes the engine very gutless rather than causing any other drivability problem (though of course it overheats the exhaust valves and destroys them if you try to drive it in that condition). An advanced camshaft, on the other hand, is mainly characterised by lousy idle quality and poor off-idle acceleration, rather like the behaviour of a racing camshaft. We need to be satisfied with your carburetor before pursuing camshaft timing as a possibility.

You have dealt with the main jet and emulsifier, which are the most likely causes of lean mixture in the upper and medium speed ranges. However while you are working on the carburetor, I think it might be as well to clean the main air bleed, just by squirting carburetor cleaner through it. Look through this instruction set on the Series 7 carburetor:
http://outdoorpowerinfo.com/repairs/tecumseh_series7_carb.asp

Go to Item 14 for details of the air bleed. Do not remove the choke plate from its shaft, just see if you can blast the cleaner into the hole outlined in pink in that picture, and verify that clean carb cleaner comes out from the vent, outlined in blue. If crud comes out from the vent, it was worth doing. If perfectly clean carb cleaner comes out, it was a waste of time except that now you know it is clear. Then put the carburetor back together carefully and give it a test run.

Hi Grumpy, having a bit of trouble understanding whats happening. Will try to explain it with pictures from link you provided.

When i spray carby cleaner into the main air bleed ( pink hole ) it comes out the bottom of carby body via the " white hole ". (picture two )
When i srpay it into the bowl vent ( blue circle ) it come out the bottom of carby via green holes. ( picture 2 )

That is no problem, Paul. I was actually taking a guess/making an assumption. If the cleaner comes out freely and clean, it is all good.

Because you reported that the hunting happens at high speed, and the idle is fine (at least that was my interpretation), there is no point in assaulting the idle system with carb cleaner. As long as you are confident the main jet and emulsifier are really clean, it is time to put it back together and try it out.

The main jet and emulsifier on that carburetor are both made from plastic, so the use of carb cleaner on them should be kept to a minimum. However I have never been able to get hard gum out without using either cleaner or a jet drill. Since we don't know the sizes of the holes, we seem to be limited to carb cleaner in this case. I suggest you measure the main jet size, and the size of the tiny holes in the emulsifier, with jet drills, and report the sizes here. Put the drills in blunt-end first of course, so you don't make the holes bigger - it is only plastic you are dealing with.

Hi Grumpy, sorry it been awhile been flat out, sheds been full of generators.
Got some measuremnets for you, have had to use my missus sewing needles again, i dont have drills small enough ( i know i need some, funds are a different story ). Did do it carefully, not trying to shove an oversized needle through.
Main jet came to 0.90mm.
Top hole on emuslifier is 0.55mm,, the bottom two holes are 0.80mm.

Thanks Paul, those numbers will give people a reference when they grapple with their own Series 7 carburetors. Now all we need is for you to demonstrate that the hunting problem has gone away: otherwise, we don't know for sure that those sizes give good results.

Hi Grumpy, gave the motor a run but had no difference. Done some research and found a number of cases same as mine, most of the answers pointed to the governor not being set correctly. Hope you dont mind but had a play with governor restting it in different positions, did have it running without hunting but it was reving way to hard even in fast mode. Tried adjusting it a fraction more , back to hunting, other times it sounded as if it was getting to much fuel, when i took airfilter case off it was wet and spark plug as well. Have tried to find the corrct setting for governor but unable as yet,, wondering if you could help out please. Will keep looking myself. Let you know if i can find it.
Have included photo of governor arm, it is a two peice. I am wondering if one peice should be set one way, the other peice set another.

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.