H35 Hunting at Full Throttle

[Bob372]

Hey all, I've got an H35-45593S engine on a Troy-Bilt Junior tiller that seems okay at idle and half throttle, but hunts a bit at full throttle.

I don't use this thing much and it hasn't run well for several years. I did replace the carb a while ago after cleaning the old one didn't help. No joy.

Spark and fuel are fine. I just ordered new gaskets for the carb and manifold thinking maybe an air leak.

I won't know for about a week and was wondering if you thought I was on the right track.

Thanks!

 

[sgkent]

does it do better under load or does it do worse?

What comes to my mind is either the govenor is hunting or the mixture is lean. If the mixture is lean, it should do worse under load. If it is the governor, it will hunt more under no load.

 

[Rivets]

Clean and rebuild the carb, replacing the float needle and seat. Part number 631021. This is the procedure I taught my students to use.

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

 

[Bob372]

Thanks all!

The gaskets are being delivered today, but since the real feel temp outside is 114°, I'll prolly wait a bit to try them.

I'll try a new seat and float needle, plus a good cleaning again if they don't work. I wish I had an ultrasonic cleaner, but the need only arises once every few years. I'm on good terms with my Exmark dealer. Maybe I'll ask him if he'd drop it in his tank for a few.

Would pulling the welch plugs help in cleaning? I've always found that to be kind of a pain...

 

[Bob372]

OP here.

I've been messing with this thing for a while and I can't figure out what the problem is.

I thoroughly cleaned the original carb and installed a new float needle and seat. I can get it to idle great and at full throttle (I have it at 3100 rpm) it sounds good except there are quiet 'coughs' every 1-3 seconds.

After I put a load on the engine, it'll go for 5 or 10 seconds and die. When I open up the main jet a bit, the coughs get a bit better, but it will die the moment I engage the tines. It dies fast too - like the coil was grounded.

I'm about ready to try a new clone carb, but was wondering if maybe this was something else. A failing coil? I set the gap, but didn't put a meter on it. I have an old one the reads 6.2k that I could swap in.

Any ideas?