# Tecumseh HM80 surging under load



## ejames13 (Oct 19, 2018)

I have a 1979 Ariens 924040 blower that I recently acquired. Starts on first pull and runs smoothly with throttle fully engaged or at idle. However, once it's under load the motor starts to surge. Last storm I blew the 6 inches of wet snow we had without much issue, but once I got to the EOD pile it started surging and would eventually stall. Funny thing is that once it starts surging, it won't stop even if I disengaged the drive and the auger. I can usually get it to settle back down if I engage/disengage the choke several times. If I just let it surge and stall, I'm able to start it back up immediately with no issue. 

In the absence of snow, I've been able to reproduce the issue by engaging the auger and putting it in 5th gear. I did this a handful of times up and down my driveway. Started in my garage, went to the end of the driveway, turned back, and every single time right when I went over the lip of my garage it would start to surge again. Not sure if it was related to the bump going over that lip or if it was just a timing thing. In any case here's what I've done to troubleshoot so far:

- Put some Iso-Heet in the gas, which didn't help much.
- Drained the gas entirely and put fresh gas in. This didn't help either.
- Adjusted main jet on the carb. I was able to get it to run slightly better by enriching the mixture, but eventually it would surge and stall anyway.
- Removed main jet and carb bowl. Cleaned bowl and cleaned both large and small holes on the jet. No difference. In fact it seemed worse after this step, but I might just need to tweak the setting a little.

The owner said he was having some issues previously (can't remember exactly what they were). Said he cleaned the carb (the bowl and jet were very clean when I removed them), and put a new spark plug in and his issue disappeared. I'm wondering if this is just a continuation of what he was experiencing and he didn't fix it completely. Any help is greatly appreciated!


----------



## leonz (Dec 12, 2014)

About your snow mule,

You may have dirt in the tank that moves around when the snow mule moved back and forth. 
More than likely the fuel tubing is collapsing on you as the carburator works pulling fuel in.

The fuel tank cap may be plugged and you can check that with the engine running and working to see if running with the cap loose eliminates the surging.


A few pieces of pea gravel and some rubbing alcohol or hydrogen peroxide will help clean the tank

Buy the largest cloth type fuel filter you can and a fuel shut off valve if the tank does not have one to help protect the fuel system.

Checking the condition of the crankcase breather rubber tube is always a good idea as well and replace it if the rubber is cracked. 




If you have old fuel tubing it would be worth your while to invest in new tubing as the reinforced tubing has a woven core that prevents the rubber fuel tubing from collapsing which can and does happen.


----------



## 132619 (Nov 20, 2018)

a 1979 machine so i'll beat it is running lean, making for the gov surge, look at the bottom of the crab,if it has a adjuster in the middle that is the high speed screw, in and out till you find it runs the best mid way between lean and too rich


----------



## ejames13 (Oct 19, 2018)

leonz said:


> About your snow mule,
> 
> You may have dirt in the tank that moves around when the snow mule moved back and forth.
> More than likely the fuel tubing is collapsing on you as the carburator works pulling fuel in.
> ...


The previous owner replaced the fuel line and installed a petcock somewhat recently. It seems like fuel is getting to the carb OK since the surging stops when I increase choke. I looked inside the tank when I siphoned it and it was pretty clean with only a few dust sized particles. 

The gas cap leaks somewhat when the tank is over half full, so maybe it is bad? I'll try it with the cap off and see if that makes a difference.

Not familiar with the crankcase breather rubber tube. I'll check the service manual. If you have a pic that would be great.


----------



## ejames13 (Oct 19, 2018)

33 woodie said:


> a 1979 machine so i'll beat it is running lean, making for the gov surge, look at the bottom of the crab,if it has a adjuster in the middle that is the high speed screw, in and out till you find it runs the best mid way between lean and too rich


Yes, I tweaked the high speed screw. Tried both leaner and richer. No matter how I adjust it the surging still happens under load.


----------



## JLawrence08648 (Jan 15, 2017)

I would disassemble the carburetor, remove the Welch plug on the side, soak the carb in a carb dunk solution preferable, if not spray carb solution in these holes, then using a welders tip cleaner through all the holes, then reassemble. For difficult carburetors, the carb dunk is critical. I use Berryman's. It gets in all the holes and passageways. The carb comes out looking like new.


----------



## 132619 (Nov 20, 2018)

ejames13 said:


> Yes, I tweaked the high speed screw. Tried both leaner and richer. No matter how I adjust it the surging still happens under load.


?? have you tried making the adjustment under load?? needing to partly close the choke,it's running lean, do as above give it a good cleaning,

check the carb number look on amazon,they are cheap these days for the china clones if unsure of one's capabilities


----------



## SimplicitySolid22 (Nov 18, 2018)

Always make sure that oil is at the top of the dipstick mark on the HM80.


----------



## bigredmf (Jan 16, 2018)

Check your carb and intake manifold gaskets even if they look good after 40 years its time



Are the bolts that hold the carb on tight?



I have a similar machine one year older and I experienced this issue last year. New gaskets and all is well at the moment


Red


----------



## vinnycom (Nov 6, 2017)

your motor is running too lean, the motor wants/needs more gas but carb cant feed it fast enough or you might have an air intake leak.
adjust mixture screws if equipped.

depending on why carb is not performing sometimes just spraying cleaner internally or using products like seafoam might "fix" the problem. if not then a further detailed cleaning is required.

mainjet removal, float and needle valve removal, mixture screws removal, if any, cleaning of said items and using a cleaner into every orfice, holes carb has and using a thin wire to make sure orfices are clear of debris and using compressed air into all orfices. using a ultrasonic cleaner to further clean also helps.

if u have an air intake leak using brake/carb cleaner or propane can reveal itself if using these around the intake pipe and gaskets to see if rpms change as motor is running.

how far you are willing to take it apart and clean the carb will determine how well the carb will perform. or just buy a new oem, aftermarket or clone carb.


----------



## ejames13 (Oct 19, 2018)

Thanks for the tips everyone. I haven’t had time to do any work on the carb, but got a few inches of wet snow today so I took her out for a spin to do some more tweaking/testing. 

I loosened the gas cap, but that made no difference. I had only about 1/3 of a tank in there and it was surging a lot more even with no load now, but I looked in the tank and the gas line was fully covered. Anyway I filled the tank up and that made a big difference. It was still surging under load, but I finally found the sweet spot. Adjusted the main jet about 1 1/8 turn from fully tightened and pulled the choke out to 50%. With that combo it was chugging through loads of wet heavy snow with no issues. 

I figured I could open the main jet a little more and then the choke off, but that didn’t work. When I opened it up even to 1 1/4 it surged whether the choke was on or not. ??

Guess the carb probably just needs to be cleaned, rebuilt or replaced as many have suggested. Though possibly there is some obstruction preventing fuel from getting to the carb? As I said though the fuel line is somewhat new. 

I don’t really want to put a Chinese carb on there as I’ve read a lot of mixed reviews on them. Also not sure if it’s worth buying a new OEM carb since they’re around $90 and the engine is quite old. Probably rebuilding is the best option, but I don’t have the expertise to do that.


----------



## Grunt (Nov 11, 2013)

Here is a link to OUR favorite small engine mechanic, donyboy73. This is part #1 of a four part series he has, so make sure you watch them all.


----------



## ejames13 (Oct 19, 2018)

Grunt said:


> Here is a link to OUR favorite small engine mechanic, donyboy73. This is part #1 of a four part series he has, so make sure you watch them all.
> 
> 
> https://www.youtube.com/watch?v=dJzasng2_EU


Thanks for that. Watched the whole thing and it doesn't look too bad.

Something I noticed is that in the video he shows a washer and an o-ring that go on the main jet screw along with the spring. Mine only has the spring. I wonder if someone disassembled and lost those two parts. Could that be causing my issues?


----------



## tadawson (Jan 3, 2018)

The O ring is not as much a seal, but used to keep the needle from moving. I suppose if the needle is really loose, it might allow a leak, but not likely.


----------



## Toro-8-2-4 (Dec 28, 2013)

Check out all of those instructional videos. Lots of good info.


Try the easy stuff first. Try opening the main jet just a hair (1/16 of a turn) to make the mixture a bit richer.


----------



## cranman (Jan 23, 2016)

ejames13 said:


> Thanks for the tips everyone. I haven’t had time to do any work on the carb, but got a few inches of wet snow today so I took her out for a spin to do some more tweaking/testing.
> 
> I loosened the gas cap, but that made no difference. I had only about 1/3 of a tank in there and it was surging a lot more even with no load now, but I looked in the tank and the gas line was fully covered. Anyway I filled the tank up and that made a big difference. It was still surging under load, but I finally found the sweet spot. Adjusted the main jet about 1 1/8 turn from fully tightened and pulled the choke out to 50%. With that combo it was chugging through loads of wet heavy snow with no issues.
> 
> ...


I have tried over 20 Chinese carbs in the last three years, and only had one I wasn't happy with...but I'll use it for parts. I keep three of the big block and two of the small block ones on the shelf all the time. $11 is a bargain.


----------



## ejames13 (Oct 19, 2018)

So I ordered the entire main jet assembly replacement kit. For kicks, I left the old assembly on and put just the new o-ring and washer for the needle on, since those components were missing. I am now able to run it with the choke wide open. I’m thinking air was seeping past the threads of the needle in the absence of the o-ring when the engine was under heavy load, and that’s why I had to choke it down half way to even out the mixture. 

One thing I’m still puzzled about is that it runs smoothest when the needle is 3/4 of a turn out, instead of the recommended 1 1/2 turns. Any thoughts on why that could be?


----------



## tadawson (Jan 3, 2018)

If that's the old needle, someone may have closed it too tightly causing the passage to enlarge. And sometimes you just get one that's different . . . after all, the engine never read the manual, and 1-1/2 turns is nothing more that a starting point at which it will run. Also, if the idle is not set correctly, fuel can bleed through it as well . . .

Odd though, that you went from crazy lean and needing choke, to running best at a rather lean needle setting. Have you tried the new needle and seat to see if it behaves the same?


----------



## ejames13 (Oct 19, 2018)

tadawson said:


> If that's the old needle, someone may have closed it too tightly causing the passage to enlarge. And sometimes you just get one that's different . . . after all, the engine never read the manual, and 1-1/2 turns is nothing more that a starting point at which it will run. Also, if the idle is not set correctly, fuel can bleed through it as well . . .
> 
> Odd though, that you went from crazy lran and needing choke, to running best at a rather lean needle setting. Have you tried the new needle and seat to see if it behaves the same?


I haven’t tried that yet, but will do so when I get a chance. Will be interesting to see if that makes a difference.


----------



## 132619 (Nov 20, 2018)

1 1/2 is a basic bench start setting, with the engine running turn the screw in and out till you get the smoothest sounds in the middle and leave it there


----------



## ejames13 (Oct 19, 2018)

tadawson said:


> If that's the old needle, someone may have closed it too tightly causing the passage to enlarge. And sometimes you just get one that's different . . . after all, the engine never read the manual, and 1-1/2 turns is nothing more that a starting point at which it will run. Also, if the idle is not set correctly, fuel can bleed through it as well . . .
> 
> Odd though, that you went from crazy lean and needing choke, to running best at a rather lean needle setting. Have you tried the new needle and seat to see if it behaves the same?


Put the entire new jet assembly in today and it runs smoothest at exactly the same needle setting as before, 3/4 of a turn out. I noticed it was idling a little rough, so I adjusts the idle needle and increased the idle speed a bit. That, however, didn’t make a difference as to where the main jet needle needed to be when on full throttle. 

Puzzling, but if it runs smooth once I have a chance to put it through some snow I’ll be happy.


----------



## ejames13 (Oct 19, 2018)

Thought I was out of the woods, but I fired it up today and it was still surging. I took the cover off the carb and I noticed that even at full throttle the butterfly does not open and the main jet is not being used at all. I can confirm the jet is clear as I stuck some wire through the bottom and I could see it come through the jet into the Venturi.

I don't have a tach on the engine, but it sounds like it's revving to full RPM when at full throttle. But it seems like it's running off of the idle circuit??


----------



## tadawson (Jan 3, 2018)

Are you sure you are seeing the throttle plate and not the choke? The throttle plate proper isn't very visible from the intake side (but the choke is right there). The throttle plate is under the point where the gov linkage attaches, and no, I doubt you could get anywhere near fulll speed out of just the idle circuit. Do any of the linkages move when it surges?


----------



## ejames13 (Oct 19, 2018)

tadawson said:


> Are you sure you are seeing the throttle plate and not the choke? The throttle plate proper isn't very visible from the intake side (but the choke is right there). The throttle plate is under the point where the gov linkage attaches, and no, I doubt you could get anywhere near fulll speed out of just the idle circuit. Do any of the linkages move when it surges?


I am positive because I was manipulating the choke lever and saw it move, then beyond that I see the main jet and beyond that the throttle plate. I also see it open wide when I throttle up with the engine off. But when I throttle up with the engine on the governor prevents the throttle plate from opening. Maybe this is intentional? But it seems odd there’s nothing coming out of the main jet and into the throat of the carb.


----------



## ejames13 (Oct 19, 2018)

tadawson said:


> Are you sure you are seeing the throttle plate and not the choke? The throttle plate proper isn't very visible from the intake side (but the choke is right there). The throttle plate is under the point where the gov linkage attaches, and no, I doubt you could get anywhere near fulll speed out of just the idle circuit. Do any of the linkages move when it surges?


And yes the linkages do move when it surges. Oddly enough it looks like what causes the surge and eventually stall is when the governor causes the throttle plate to open all the way. It opens, flutters a little, at which point I see fuel coming out of the main jet, then it eventually stalls. It only stays running when the throttle plate is closed and nothing is coming out of the main jet.


----------



## tadawson (Jan 3, 2018)

Have you checked the gov linkages and done the setup procedure? IE loosen the screw holding the arm on the gov shaft and push it as far in the direction to open the throttle as it will go while also holding the throttle full open, and tighten the screw? If that's wrong, the gov won't have correctco trol of the throttle. Also, if it dies when the throttle opens, the main jet may be set too rich as well. (This is all assuming the linkage is correct . . .)

One more thought: If it is running at high speed with the throttle closed, about the only way that can happen short of the throttle plate falling off is a large air leak somewhere, and the carb dialed very rich to try to compensate. You just can't get high power/speed with no air!


----------



## ejames13 (Oct 19, 2018)

tadawson said:


> Have you checked the gov linkages and done the setup procedure? IE loosen the screw holding the arm on the gov shaft and push it as far in the direction to open the throttle as it will go while also holding the throttle full open, and tighten the screw? If that's wrong, the gov won't have correctco trol of the throttle. Also, if it dies when the throttle opens, the main jet may be set too rich as well. (This is all assuming the linkage is correct . . .)
> 
> One more thought: If it is running at high speed with the throttle closed, about the only way that can happen short of the throttle plate falling off is a large air leak somewhere, and the carb dialed very rich to try to compensate. You just can't get high power/speed with no air!


I have not adjusted the governor linkage at all yet. Air leak was one of my suspicions. I have to run the idle screw turned out at least 2 full turns or it won’t run when I increase throttle. Where should I look for air leaks?

One more thing for clarification. Right now I have the main jet turned out about 3/4 of a turn and the idle screw about 2 full turns. When I go from idle to full throttle the throttle plate does not open at all and it appears no fuel is coming out of the main jet emulsion tube. It seems to run OK with these settings for the most part. But something isn’t right. 

If I set the screws to factory spec, 1 and 1/2 for main jet and 1 for idle, it idles fine but as soon as I throttle up it dies. Interestingly in this scenario I see the throttle plate open and fuel flow out of the emulsion tube and into the carb throat. So the engine doesn’t like that throttle plate being open and receiving the mixture that way for some reason.


----------



## SnowH8ter (Oct 8, 2018)

tadawson said:


> Have you checked the gov linkages and done the setup procedure?



Definitely worth a look. The HMSK100 engine on my "wounded" MTD started surging bad under load when the beast was about 10 year old. Spent too much time looking at everything but the integrity of the governor linkage assy. That was ultimately the culprit - it was loose. Downloaded the Tecumseh manual and performed the governor set up procedure and Bob's yer uncle! That was the only problem I had with that engine in over 20 yrs of blowing.


----------



## ejames13 (Oct 19, 2018)

SnowH8ter said:


> tadawson said:
> 
> 
> > Have you checked the gov linkages and done the setup procedure?
> ...


I checked the governor linkage according and it looked like it was already set correctly. For kicks I went ahead and followed the steps in the manual to recalibrate it, but it ended up being set in the same place as it was originally.


----------

