Snowblower surging up and down

[viperv10]

Hi guys.
I went to start my churches' snowblower and it wouldn't start by hand. I forgot that it had a fuel shutoff.
It did start with an extension cord, but the rpm's surged up and down.
I took it home and cleaned the carburetor and I thought that might help but it that didn't help at all.
It is a Tecumseh 8.5 hp 4 stroke. The carb is part 640349. It does have pilot jet or something with a plastic cover.
When I screwed it back in I wasn't sure if it was to go in all the way or turned out a little.
It set all year with old gas in it. I drained it and put a little seafoam in the tank
Does anyone know a cure for this problem ?
Thanks
Jerry

 

[Rivets]

Two things most often cause surging on those Tecumseh engines, Most common cause is that the float needle seat has swelled, due to sitting with old fuel, which now is allowing the needle to shut off prematurely. This results in a lean running condition and can be repaired by replacing with a new needle and seat, plus adjusting the float level properly. Second cause is the idle jet, under the plastic cap you found. This jet has both a vertical and horizontal holes. The one coming up from the bottom plugs when it has old gas around, again resulting in a lean mixture. Needs to be cleaned and opened.

 

[bkeller500]

I have a 10HP version of that same engine on my Cub snowblower. I found a replacement carburetor on Amazon for about $20.00 which took all of an hour to install. Solved the RPM surge and a occasional backfire..

 

[viperv10]

Ok Thanks Rivets.
I think I do have a new needle and seat. I did clean out the holes in that idle jet with a wire and carb cleaner and blew it out with compressed air.
The only thing I didn't take out was the plastic emulsion tube with the little rubber o rings. I don't know if this could be part of the problem or not.
But I will do that now since it's got to come off again. The float level looked good to me, it ran fine last year.
If you have any other thoughts, let me know.
Thanks
Jerry

 

[Rivets]

The float may look fine, but it is the float level which you must check. It must be level from the pin side across or slightly lower on the side opposite the pin. This is with the carb held upside down.

 

[viperv10]

Ok, I took the carb back off and the float did tip down quite a bit on the opposite side of the pin. I bent the little tab that the big end of the needle sets on.
now it is level. I found out that this is not the original carb. This one has a metal emulsion tube and also a metal seat, kind of like the ones on a plastic lawn boy
carb. I talked to the guy that worked on it before and he said he put on an after market Oregon carb.
Any way I cleaned out every hole again and put it back together and it still surges like crazy. I was watching the throttle linkage going back and forth,
or maybe it was the governor linkage I don't know. I thought sure it would run but it is no better at all.
Any more thoughts?
Thanks

 

[Scrubcadet10]

Does it run smoother if you apply choke?

 

[Rivets]

Sorry, but I don’t know how if I’ll be able to help you more?? Having a knockoff carb, which probably not the correct one for that engine, is probably the main cause of your problem. My memory is not the greatest, but I don’t think I’ve ever seen the type of carb you describe on a Tecumseh engine. Is it possible for you to post a couple of pics of that carb, plus all the engine numbers? Might have a better guess if I have more info.

 

[viperv10]

I don't how to take pictures and post them. I don't even have a cell phone. It does run better on half choke than on open choke.
My friend says he has the original carb and it has been rebuilt. This one has been running good for the last 5 years but it doesn't get used much.
Maybe I'll try putting the rebuilt one on and trying it.
The engine number is LH318SA and the carb replacement number is 640349
The 2 look identical except for the seat and the center tube with the two o rings is brass looking material instead of plastic that the original has.

 

[Scrubcadet10]

I wouldn't call Oregon knock off, however your engine is definitely running lean, too much air or not enough fuel. I would get some WD40 in a spray bottle and soak the carb mount area down while running, if it blows white smoke or runs better, you found the leaking gasket letting in excess air. If that doesn't change anything, the carb still needs cleaned or there is inadequate fuel flow into the carb.