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Tecumseh HMSK80 surging


garandman's Avatar
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11-19-05, 08:59 PM   #1  
Tecumseh HMSK80 surging

When I started up my snow blower yesterday to test after new friction disk and belts, it started surging fairly dramatically.

At a rate of about once per second, it accelerates to full throttle, then cycles back almost to idle. I took the cover off and you can see the governor mechanism moving back and forth.

Putting on a little choke moderated it a little but didn't sop it. What trouble shooting steps should I take? It didn't do this at the end of least season, when I drained the tank and carb.

I took the bolt and float bowl off. The bowl was clean, the bolt didn't look bad but I washed it a while in carb cleaner. Also addes some Seafoam to the gas (which is fresh).

It now runs steadily at full rpm but still pulses at part throttle? The drops are rainwater, not fuel.

<img src=http://www.geocities.com/theseventhfirst/HMSK80carb.jpg>

 
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cheese's Avatar
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11-19-05, 10:46 PM   #2  
Remove the brass bowl screw from the carb and clean out the tiny holes in it. There should be 3. 2 oppose each other near the head, one runs straight down the center, and the 3rd is a tiny one that usually causes your problem located in an unthreaded section of the screw.


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11-21-05, 11:02 PM   #3  
It is starving for fuel or the other thing that can cause it is an improper setting of the governor. Pretty well covers it.

 
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11-22-05, 12:07 AM   #4  
Posted By: cheese Remove the brass bowl screw from the carb and clean out the tiny holes in it. There should be 3. 2 oppose each other near the head, one runs straight down the center, and the 3rd is a tiny one that usually causes your problem located in an unthreaded section of the screw.
Thanks! I chased the holes with a needle and will give it a try.

 
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11-25-05, 09:07 AM   #5  
Hmmm, cleaned holes, runs pretty well at full throttle but still surging at partial throttle.....

 
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11-25-05, 01:43 PM   #6  
If i read the post correctly, it sounds as if you cleaned the main jet but nothing else. You need to remove the carburetor and soak it in your carb cleaner. Be sure to remove all jets (two) and rubber parts before soaking, paying particular attention to the low speed fuel jet.

 
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11-26-05, 12:06 PM   #7  
OK, got a #30 Torx and got the manifold and carb off. Removed the float and choke linkage.

FWIW the # on the casting is 5002G7G. Is that any reference to part #?


Last edited by garandman; 11-26-05 at 08:22 PM.
 
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12-11-05, 04:30 AM   #8  
As Winter is here I bought a new carb ($53) and a rebuild kit for the old one.

Apparently on this carb there are two O rings that can go bad and create thsi problem. The rebuild kit includes them.

 
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12-12-05, 03:48 PM   #9  
Garandman
Not to be a nit picker but one thing you should do is position the float bowl on the carb in the right spot. If you look at your picture,the bowl is in the wrong position. The indent or high spot of the float bowl is facing the choke end of the carb, it should always be facing the fuel inlet. Reason being is that you will now have the full swing of the float in the bowl allowing the most fuel that is needed. It's a common mistake because the bowl can be put on in any postion but only one position to work effectively.

snoman

 
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12-13-05, 01:39 AM   #10  
Great point, I'll check it on the new carb as well.

 
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12-13-05, 03:00 AM   #11  
Based on your carburetor ID number (5002***), you should have gotten Tecumseh part number 640349 as a replacement carb. The 2 o-rings that can go bad and do are on the emulsion tube. Note that it is very common on these, fixed jet, carbs that they will hunt (surge) until the carburetor body is up to a sufficient temperature - usually about 4-5 minutes of run time.

 
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12-13-05, 03:15 AM   #12  
Yes, that's what I got, works fine. Haven't torn in to the old one yet.

 
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12-15-07, 10:23 AM   #13  
Hi there- first time posting.

First, thank you all for the wealth of information posted here. I have an older MTD with an 8hp hmsk80 that surged like crazy. It drove both myself and the neighbors nuts. I cleaned the bowl screw (there was brown varnish all over everything) and now it runs great! Thank you. Saved me from having to pay for a tune up.

One question though, why do these engines not have an air cleaner? I understand that there is not as much dust around as with the use of a mower, but isn't this just more invitation for wear? Is there a way to retrofit a cleaner? Am I just being paranoid?


Scooter

 
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12-15-07, 12:53 PM   #14  
Is this what you mean by surging?

http://www.youtube.com/v/fY87ijdfhOs&rel=1

Mine will surge up-n-down. Choking it helps a little, but not at high RPMs. This thing has maybe 2 hours on it at the most. This is my 3rd season with it. The first season it was fine. The second season it started doing what you see in the video. I took the carb apart, blew it out with compressed air and soaked it in a coffee can of carb cleaner overnight. I also ran some carb cleaner additive through it by adding it to the fuel. Still surges.

If new carbs are only $50 I may go that route. It's a Techumseh Snow King 8 HP. The first season I let the gas sit in it (like I did every year for 15 years with my Craftsman w/ a B&S engine). Last year I put Stabil in the fuel as well as some carb cleaner.

I think I'll take it apart and look at the orifices described above. Any other suggestions would be appreciated.

 
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12-16-07, 12:30 AM   #15  
Scooter, snowblowers don't have or need air filters. No need to worry about them.

Jimmy, your carb is still the problem. I'd bet the tiny hole near the end of the bowl screw is clogged. You might not even see it if it's clogged because it's so small.


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12-25-07, 08:42 PM   #16  
Wow, always figured an aircleaner was a must. Guess there is not that much dust to worry about on a snowy day.

Cleaning out that hole took care of the surging on mine, but I do have a new problem. It runs fine when idling or running fast with no load, but when I put a load on it (run it through snow), it bogs down and puffs some black smoke. Seems like it is over rich. I turned the screw on the bottom of the carb in by small increments and it seems to help a little. Am I working in the right direction or is this a float adjustment?

Scooter

 
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12-26-07, 02:54 AM   #17  
I put the carb off of my dad's HKS80 on my machine and it worked flawlessly. My dad's had eaten a belt so it was out of commission anyway.

While picking up parts for his machine, dad talked to the local small engine guy. He said that once the seals disintegrate like mine did you have to rebuild it and do it correctly. His advice was that the cost of the kit (which was nationally back-ordered with no ETA) plus the time to do it right wasn't worth it. He suggested a new carb and gave my dad the P/N.

Online, I found the original carb and the carb associated with the part number we got. The original carb is $50, the other is $70. Trusting the advice of the small engine guy I bought $70 unit. Turns out the difference is whether you get an adjustable ($70) or non-adjustable ($50) carb. I now have a needle valve in that screw at the bottom of the float bowl as well as some other adjustments. I think I'd have preferred the 'fool proof', non-adjustable carb for $50 but maybe these adjustments will prove useful in the future. Just more stuff to goof up, IMO.

I didn't put the new carb on yet - been busy with other stuff. Hopefully it'll run right out of the box.

Jim

 
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12-27-07, 05:17 AM   #18  
Scooter, you are working in the right direction just a bit off. You need to richen the adjustment, not lean it. The black smoke is a rich issue but what is happening is that because the carburetor is starving for fuel, during load operation, the governor opens up the throttle well past normal to compensate for need. If you richen the main jet (bottom of fuel bowl) you will be already providing the needed extra fuel and there will be a smooth transition between no-load and load operation.

Jim, the adjustable jet carb will be quite useful in the future and they are much less likely to aquire a governor hunt (surge). Post back with your engine's ID numbers including the model (HMSK80), specification (155 something) and serial number (4 digits and a letter) as well as your dad's engine ID numbers. What was the local small engine guy's part numbers for the repair kit as well as that of the replacement carburetor as well as his estimated cost to recondition your carburetor? I've yet to have a repair kit backordered to me this year and I've ordered hundreds of various Tecumseh kits this season. I'm just curious because we rarely ever replace a carburetor at my shop and the cost to recondition one is generally half the cost of a new carb. And, furthermore, I think my carburetor rebuilds are better performing than a new, out of the box, carb. The proper carburetor bath cleaner is, by far, the key to getting a good performing carburetor, post reconditioning.

 
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12-28-07, 02:21 AM   #19  
Posted By: puey61 Post back with your engine's ID numbers including the model (HMSK80), specification (155 something) and serial number (4 digits and a letter) as well as your dad's engine ID numbers. What was the local small engine guy's part numbers for the repair kit as well as that of the replacement carburetor as well as his estimated cost to recondition your carburetor?
I don't have my dad's info, but here's mine:
LH318SA
156553H

The local guy wanted $15 for the rebuild kit (if he were able to get it) and $80 for the carb. I found the carb online for $70. I don't know how much he wanted to rebuild it - I was going to do it myself.

The carb he recommended is 632334A (this is the one I got) and the rebuild kit was 632760A.

I haven't installed the new carb yet. It's a 15-minute job but I've been bogged down in other stuff. My lofty goal today is to unearth the snowblower from the debris in the garage and slap that carb on it.

Thanks,
Jim

 
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