# Tecumseh HM80 1550xxx Rev too high



## beriksson (Jan 5, 2013)

All kinds of issues after I took the carb off for a rebuild, cleaned the head and top of piston of carbon deposits, etc...Everything back together and wants to rev really hi and only runs on full to half choke. I looked up the service manual and made sure I had all the linkages and governor set correctly. Head bolts maybe a little over 200 in/lbs but don't think that would have an effect. 

Still wants to take off. Even with over revving, hitting a little snow to put a load on it simply dies.

Have great spark, but only runs on choke makes be believe it's getting to much air somehow? Would the idle mixture have something to do with this? I know I've cleaned the carb out very well and the needle and seat are replaced also the o-ring for the idle mixture correctly and float is level with the world. Governor set according to spec then tried tuning the angle from there (no difference). This thing revs so hi I think it might blow. Huh...


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## GustoGuy (Nov 19, 2012)

beriksson said:


> All kinds of issues after I took the carb off for a rebuild, cleaned the head and top of piston of carbon deposits, etc...Everything back together and wants to rev really hi and only runs on full to half choke. I looked up the service manual and made sure I had all the linkages and governor set correctly. Head bolts maybe a little over 200 in/lbs but don't think that would have an effect.
> 
> Still wants to take off. Even with over revving, hitting a little snow to put a load on it simply dies.
> 
> Have great spark, but only runs on choke makes be believe it's getting to much air somehow? Would the idle mixture have something to do with this? I know I've cleaned the carb out very well and the needle and seat are replaced also the o-ring for the idle mixture correctly and float is level with the world. Governor set according to spec then tried tuning the angle from there (no difference). This thing revs so hi I think it might blow. Huh...


The revving high (surging) and dying (indicates it is running lean) when you hit a load along with the choke needing to be on 1/2 way indicates some sort of air leak such as between the carburetor and manifold or manifold and block. Also how was it running prior to removing the Carburetor? I would suggest cleaning the carburetor jets again (both idle jet and main jet) and then using permatex manifold gasket compound on the carburetor gasket and the gasket between the manifold and the engine. If it has an adjustable carburetor play around with the adjustment until it starts to run a tad rich then just back it off towards the lean until it runs real smooth. Then test it again under a load to see how it runs. If its running well it will run smoothly with out any sputtering/popping from the exhaust which could indicate too much unburnt fuel leaving and combusting on the hot exhaust (running rich)


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## beriksson (Jan 5, 2013)

Gustoguy,
I did have the manifold off and now thinking about it I will check the gasket between the manifold and the block. For argument sake...say there was a leak there (i.e. forgot the gasket) would that make the engine want to rev that high with the throttle not having much of an effect on slowing it down? Wouldn't the governor try to slow it down? Maybe the two don't have an affect on each other. I'll check it out tonight...Appreciate the feedback!


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## GustoGuy (Nov 19, 2012)

An air leak there would cause it to run lean. Spray a small amount of WD40 on the manifold to carburetor gasket and the manifold to engine gasket while its running and if it smooths out and slows down (WD40) temporally plugging the leak then it is leaking air. I would also check to make sure the head gasket is sealing correctly. Usually on an air cooled small engine a blown head gasket will cause it to run poorly and will make low power and could eventually overheat if left running. You can test for a leak with a compression tester that threads into the spark plug hole. When pulling it over quickly you should see at least 60psi or may be a bit more. If compression is much less or near zero than that your head gasket could be leaking. Put a small amount of oil (about 5ml) into the spark plug hole and if compression goes up then it could be rings. If no change in compression it could be the head gasket. Did you use Permatex copper head gasket spray with a new gasket to help to seal it better? Also make sure you clean off all the old gasket material carefully with brake cleaner so it can make good contact with the gasket to prevent leaks. Try not to use any thing sharp to scrape off the gasket that could leave gouges in the metal where the gasket meets such as a razor blade.


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## HCBPH (Mar 8, 2011)

*Overreving*

Something not mentioned, are you sure you go the linkage on correctly and any return springs in the proper holes? I've seen linkage put into the wrong hole on the carb. Another is the governor to carb linkage, I've seen that bent so it opens the carb alot more and overrevs the engine.\
Does the engine idle at all or does it just 'take off' when you start it up?

One test I've done that's cheap, just remove the sparkplug wire and pull it over till you're on the compression stroke and listen. If you have a leak in the head gasket or sparkplug you should be able to hear air leaking if you listen carefully. 

I suspect it's in the carb, linkage or gasket area based on what I've run into so far.
I didn't go over points and timing because you didn't mention touching them.

Something I always do is take plenty of pictures when taking something apart plus use some masking tape and a marker to mark each piece as it's taken off (or baggy them) so there's no doubt where something came from and where it goes back to. It's saved me alot of headaches over time.


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## beriksson (Jan 5, 2013)

Thanks for the trouble shooting tips!! Still frustrated, engine is a hm80 155013G. Last night I re-cleaned the carb including taking the welch plugs out and taking a fine wire and carb cleaner to everything, even took the butterfly flaps out. Followed every orifice to where it goes to make sure carb cleaner then air would freely pass through. I know it's clean and set correctly. Re-assembled and started. Runs a little better with the same issues as before (hi rev and won't idle). Carb settings I started with were the standard 1 1/2 on the bottom and the air-fuel (side) 1 1/4 turn out from lightly set.

Ran really rough with gas spitting back out of the carb tried to fine tune to no avail. Note: Muffler was tight, almost to the point of deformation from the last time I installed it with the tabs bent on the flats of the two bolts. It came somewhat loose. Also when running it was red hot, even the bolt heads. Hot like welding hot with blue flames sometimes coming out of the muffler (was dark out). 

I'm sure the linkages are correct as I marked them and can see the slightly worn holes they were in (also double checked with diagram). Governor set with according to service manual - carb wide open, gov wide open, then set arm. When done it is slightly angled back toward engine a few degrees.
Compression, manifold seals-gaskets are fine. Checked springs and keepers on the valves-good. I doubt there's anyway i could've inadvertently changed the timing? I don't think it can be done. Valves move as they should TDC they are both closed tightly.

Uff da, really don't want to bring it in... Wonder if the muffler is acting up cause it's running so rough? Even used loc-tight red. probably doesn't make a difference due to the hi-temp. Thanks guys.


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## nt40lanman (Dec 31, 2012)

Post pictures of the carb, linkages, etc. Maybe we can all compare them to Tecumseh's of our own. When I revs high, is the throttle open wide and can you manually close it? I have to say it does sound like an air leak bieng compensated by the closed choke.


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## HCBPH (Mar 8, 2011)

One thing I just noticed that was noted, I think the initial carb settings are 1 turn open on the main jet (bottom of the bowl) and 1 1/2 turns on the idle jet (side just above the bowl) for Tecumseh's, then adjust as needed. I adjust them in and out and find the sweet spot, then adjust in and out till the engine starts bogging and split the difference. The one in the side I usually have the throttle set about 'mid range' in rpms. 

By the way, any chance that's not the correct carb for the engine?


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## beriksson (Jan 5, 2013)

Ok, talking to a few guys here at work, one who used to race with briggs motors, say that when I cleaned the valves i affected the way they seat. Huh, didn't occur to me at the time. 
I'll have to 'lap' them. As it's explained to me it doesn't sound too difficult. This would explain fuel being spit back out of the carb and flames shooting out the muffler. Good thing there's no smoking around this ol' john deere. I'll work on this over the weekend and let you guys know. Also I'll take and post a few pictures....


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## beriksson (Jan 5, 2013)

Yep correct carb. Still working on this machine. Rev too hi, slight engagement of auger and it dies. Going to replace the head gasket. I've lapped the valves for a good seat. Compression was at around 60 so hopefully there was a leak in the head gasket. Don't know if this would explain the hi rev? I suppose if this doesn't work I'll have to pull the side of the engine and take a look at the governor mechanism? Don't think that's the problem but out of ideas. Here's a few pictures.


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## HCBPH (Mar 8, 2011)

Here's the info from the Tecumseh manual on governors: 
*ENGINE OVERSPEEDING​*1. If the engine runs wide open (faster than normal), shut the engine off​​​​*immediately.*​*
*2. Check the condition of the external governor shaft, linkage, governor spring, and speed control assembly for
breakage, stretching or binding. Correct or replace binding or damaged parts.
3. Follow the governor adjustment procedure and reset the governor - see "Service" in this chapter.
4. Run the engine. Be ready to shut the engine off if an overspeed problem still exists. If the problem persists, the
engine will require disassembly to inspect the governor gear assembly for damage, binding, or wear.
5. See Chapter 9 under "Disassembly Procedure" to disassemble the engine.​6. Remove the governor gear assembly. Repair or replace as necessary.

It's entirely possible you have something stuck in the governor. Can you run the engine at part throttle now or is it all or nothing?


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## beriksson (Jan 5, 2013)

Well finally got around to taking the sump cover off and low and behold guess what was lying in the bottom of the engine oil compartment....the governor weights. Have new one on order along with a gasket. Wonder how the weights off that plastic gear came loose? It does look like the tabs that hold the weights in place came into contact with the gear thus broke them off. Huh.


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## Midwest Mower Pro (Mar 13, 2013)

Unfortunately those little fly weights just come off after time. No real good way of preventing aside from normal preventative maintenance.


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## Pythons37 (Nov 9, 2012)

I sure hope I never have this problem. Thanks for all these postings and the final report on the ultimate problem.


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