Engine Surges/Falters Under Load

[SkiFletch]

Hey all, have a 10hp Tecumseh HM100 engine off a John Deere Snowblower that's giving me some trouble. As winter is coming and Lake Erie is giving me that leery look, I did my usual maintenance on the snowblower. Checked belts, changed spark plug, replaced oil, added fresh gas, and even removed and cleaned the carb. Didn't find any junk in the carb, which was promising. Got her all back together, and did the carb adjustment procedure in the manual. Dialed needle valve till finger tight, backed off 1 1/2 turn, choked, primed, fired right up. Turned needle in till she got rough, out till she got rough, split the difference. She sits fine at full throttle. Slowed her down, did the idle speed adjustment needle on the carb (same procedure).

Throttle back up to full and now that she's nice and warm drop the drive lever, engage the belt and the engine starts slowing and returning to full throttle. I can see the throttle linkage going in/out. Problem gets more pronounced when I hit the auger as well putting more load on the engine.

What would you guys do? Tweak the carb a little first? Or might this be a governor problem? Or perhaps some nefarious fuel or exhaust trouble?

 

[mechanic mark]

Tecumseh Service Manuals Locate your manual & see troubleshooting section, let us know what you find, thanks.

 

[Rivets]

Posted this earlier today,but it also applies to your problem.


Take the carb off and remove the float bowl. Tip the carb upside down and look to see if the float is level. I'll bet that the side opposite the hinge pin is higher. If it is I would follow this procedure and replace the float needle and seat with kit number 631021B. We're getting snowblowers ready around here and I do at least one of these carb rebuilds a day.

Needle and seat replacement

Remove the carb, and then remove the float bowl. Check the float bowl jet (which is the bowl screw) and make sure the jets both horizontal and vertical are clean and open. Tip the carb upside down and remove the float pin and float with needle attached. Look in the float needle passage and you should see the red float seat at the bottom of the passage. This is where a #5 crotchet hook would come in handy as you need to remove this seat. If you have no hook, but compressed air, you can blow through the fuel inlet and try to pop the seat out. Put your thumb over the passage to prevent the seat from flying who knows where. No air or hook try bending a stiff paper clip to dig the seat out.

I would either give the carb a good 24 hour soaking or have it ultrasonically cleaned at this time.

With the seat out clean the passage way with carb cleaner. Now you must find a drill bit slightly smaller than the passage way, to be used to press in the new seat. Apply a very, very small amount of a very light lube to the new seat. 3-1 oil or lighter, to help seat it better. Carefully insert the new seat in the passage way with the rings on the seat down toward the carb body. Slowly and carefully force the seat down with the back end of the drill bit. Once it is seated, check to see that it did not flip and the rings are up. *Next check to make sure that the float does not have any liquid in it. *If it does, replace. *If everything looks correct, attach the new needle to the float and install with the float pin centered. It everything is correct, the float should seat level to the carb body, when looking at it upside down. If everything looks good reattach the float bowl, making sure that both the bowl gasket and the nut gasket seal properly. Reinstall on the engine and test unit. Remember to have patience and take your time. Good luck, but I don't think you'll need it.

PS: *On the side of some Tecumseh carbs you will find a plastic cover. *Under this cover will be an idle jet. *Remove it and check to see that the jet is open both horizontally and vertically. *You should be able to push the old float needle wire through the vertical opening.

 

[SkiFletch]

Thanks guys. Will start with a carb rebuild and then move to governor adjustment I guess? Parts in on saturday so wish me luck.

 

[primerbulb120]

Why rebuild and adjust the carb when you can get a new one for $25?

 

[Rivets]

I would love to know where you will find a good carb for this engine for $25????

 

[primerbulb120]

http://www.google.com/aclk?sa=L&ai=...%2Flike%2F281215553476%3Flpid%3D82&adtype=pla
http://www.google.com/aclk?sa=L&ai=...%2Flike%2F231109590577%3Flpid%3D82&adtype=pla

 

[Rivets]

Don't know how they got those prices, as they are well below dealer costs. Are they Tecumseh carbs or knockoffs?

 

[primerbulb120]

I doubt they are genuine Tecumseh carbs, but they could be. I don't think it matters whether the carb is OEM or not. So many things are made in China these days that the aftermarket and OEM could be the same quality.

 

[Rivets]

If they work fine, but for $5 they can clean the carb and rebuild and get back to work. The posters on this forum are looking for help and have more time than money. I know cleaning carbs with my procedure works, because I average one plus carb cleaning every day and can do it cheaper than what it costs me to replace it. I will admit that it is cheaper to replace Honda carbs, but all others I clean first.