# Tecumseh Engine Modification



## strogg

I've got a Tecumseh HMSK80 engine, installed on a snowblower. It seems to be mechanically VERY similar to the more powerful models (it puts out 8 hp, but there are 9, 10, and 10.5 hp models that are very similar). From this, I'm wondering if it's because they're all the same engine, but with a smaller jet in the carb on the less powerful models? I've heard of that before on engines, to limit power output. With that said, would it be possible to install a jet from a more powerful model, and effectively convert it to that model with just that modification? Or are there more differences?


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## justin3

I have an HMSK80 on my snowblower as well and I have been wondering the same thing. My idea is to get the model number of of a 8hp and 10.5hp Tecumseh of the same year and compare part numbers especially in the carburetor. Different carburator jets is how Briggs and stratton manages the power between a 10hp I/C and a 13hp I/C engine on some riders, I found that out by comparing model numbers.


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## strogg

I got the idea from when I heard about Yamaha doing that on outboard boat engines. I knew someone that had a 9.9 hp motor, but it was identical to a 15 hp model, except for the jets. That person successfully installed the jets from a 15 on it, and got the same performance as it.


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## paulr44

justin3 said:


> I have an HMSK80 on my snowblower as well and I have been wondering the same thing. My idea is to get the model number of of a 8hp and 10.5hp Tecumseh of the same year and compare part numbers especially in the carburetor. Different carburator jets is how Briggs and stratton manages the power between a 10hp I/C and a 13hp I/C engine on some riders, I found that out by comparing model numbers.


Most of the large-frame Tecumseh engine adjustable-carbs. use the same kit - a 632947, so there's other differences you'd have to look for. Having been close to the sources for years, I'll let you in on a secret. Many series of engines are built at one HP, then de-tuned for other markets and applications. HOWEVER, sometimes the cams and or valves are different, and many times, THE BORE size. The Tecumseh HM/HMSK(SK means Snow-King) and plain H series are fairly interchangeable as far as externals are concerned, but the bore sizes are different. The HS series basically only differ on bore size. On the other hand, if you have a Kohler CH18 (18hp), simply remove the throttle bellcrank limit screw on the side of the carb. and you have a CH20. Add a different flywheel a, spark-advance module and different coils, and you have a CH22. So, there are other differences besides just carbs. The easiest comparison is to look at the short-block part numbers and with overhead valves you have to compare them too.


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## justin3

Paul what you say does make alot of sense, but im still convinced that the newer Tecumseh engines use carburetor jets as a means to limit horse power. If you purchase a rebuild kit for a newer Tecumseh you notice it doesn't come with the plastic main jet, or idle jet? I believe those 2 items will have an effect on engine horse power. I will full around when i get my MTD out of the shed as I need to repair it anyways. Will post the results of what I find.


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## 30yearTech

justin3 said:


> Paul what you say does make alot of sense, but im still convinced that the newer Tecumseh engines use carburetor jets as a means to limit horse power. If you purchase a rebuild kit for a newer Tecumseh you notice it doesn't come with the plastic main jet, or idle jet? I believe those 2 items will have an effect on engine horse power. I will full around when i get my MTD out of the shed as I need to repair it anyways. Will post the results of what I find.


Usually it's not just the jetting, you have to increase the air volume with the fuel as well, so the venturi size is also different. On some engines it's just the carburetor that's different. Like Paul noted on some engines it may also be camshaft, valves and or bore and ignition modules. I do know that on many current Kawasaki engines, it's just the carburetor.


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## paulr44

justin3 said:


> Paul what you say does make alot of sense, but im still convinced that the newer Tecumseh engines use carburetor jets as a means to limit horse power. If you purchase a rebuild kit for a newer Tecumseh you notice it doesn't come with the plastic main jet, or idle jet? I believe those 2 items will have an effect on engine horse power. I will full around when i get my MTD out of the shed as I need to repair it anyways. Will post the results of what I find.


Justin, strogg has an HMSK80. They haven't used the "HMSK" designation for awhile, and a there's a high probability it has an adjustable jet.
When Tecumseh changed the model designations, they went from a horse-power indicator (HM80 = 8 horse, HS50 = 5, etc.) to a displacement indicator. Eg. LH195SA would be 195cc. The displacement, if the same, then it PROBABLY just has different peripherals. I could elaborate but I'd fill the page up. I used to do a lot of re-powering research for dealers.


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## strogg

Just for reference, I have the other model numbers, as listed in my manual: HMSK80, HMSK90, HMSK100, HMSK105, OHSK120. The manual claims to apply to all of those models.


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## strogg

Another thing that I would like to add is that the oil sump capacity is identical for all of the HMSK80, 90, 100, and 105 models. That's one of the major pieces of evidence that I picked up on.


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## justin3

Oil capacity doesn't really matter in this case, it is possible for the bore and internal parts to be different but still require the same amount of oil. 

I was mistaken and believed you were talking about the newer Tecumseh engines with the fixed plastic jets and not the older ones sorry. Though I do believe on the newer engines, the plastic jets in the carburetor have some kind of effect on engine horse power. It just makes sense as it would be alot cheaper for Tecumseh to manufacture one engine and use cheap plastic jets to limit them. I will post my findings as soon as I get my hands on some model numbers....to Home depot!!!


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## andyvh1959

I have the same HM80 on my snowblower. I bought the engine for $20 with a thrown rod. I installed a new piston, rings and rod kit, so for $50 total I got a great running, one pull to run engine. Been using it for three winters now. But after reading this thread, I wonder if I can get a bit more power from it. I found out the HM80 and HM90 use the same piston, rod, valves, lifters, cam, but a different crank and carb. Like was said above, perhaps the HM90 carb has a bigger throat. Bigger throat means more air per stroke, plus a bit more fuel = more power. 

So does anyone know what else I could easily change to boost the power a bit? When I installed the engine, I slightly up-sized the engine pulley to get a bit more speed in the 2nd stage impeller, and bit more ground speed. Works good, but can I get more? I also fabbed a small shroud over the outlet of the muffler, which then is routed into a length of conduit to direct the exhaust down, just ahead of the left tire, about 4" from the ground. That way I don't stand right behind the exhaust fumes coming out of the engine. 

The govenor setting is stock for all I know, I never messed with it. But a bit higher engine rpm might help too for the heavy wet snow, if I don't crest the torque curve doing it. To me it "sounds" like the engine speed could be a bit higher.


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## justin3

I did look into this but never got around to posting my results, on the older tecumseh's and newer ones it looks like Tecumseh uses bore sizes to change horsepower, in some cases different jets were used to comply with EPA standards but they didn't effect horse power. 

However, if you put an older adjustable carburetor onto a newer Tecumseh engine that originally had a fixed jet carburetor, you can squeeze out a little extra horse power because you can fine tune the engine. However this isn't recommended because it goes against the EPA and has said penalties.


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## i need help

*helpp!*

im in a class at school thats teaching me about small engines. i am currently working on a techumsa 5hp that came off a snowblower. i am not sure of the year but i i would assume it to be of the late 80's. i need to find tons of specifications for this thing. please send as much links as possible that will help me! please!?!?

-colton


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## relics

Andy i have the HM80 on my Ariens ST824 which is a 1982.You want to run the HM80 at 3600 RPM.This would be Max RPM as stated by tecumseh.A lot of these engines do not run at there max RPM.And you will find a very noticeable difference running a HM80 at 3600 RPM.A lot of these engines only run 3150 to 3300 in factory trim.


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## indypower

i need help said:


> im in a class at school thats teaching me about small engines. i am currently working on a techumsa 5hp that came off a snowblower. i am not sure of the year but i i would assume it to be of the late 80's. i need to find tons of specifications for this thing. please send as much links as possible that will help me! please!?!?
> 
> -colton


You need to get ALL the numbers off the engine, including DOM (date of manufacture). Then you can find all the specs you need.


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## i need help

i have the model and the serial number. i couldnt find where the DOM is. do you have any idea where to look?


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## indypower

i need help said:


> i have the model and the serial number. i couldnt find where the DOM is. do you have any idea where to look?


In the same area that you found the model number. It will say DOM and have a number under it.


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## i need help

alright. i will get back to you on monday if i need more help. thank you.


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