Engine Dies When Given Throttle

[Gokarts4Life-11]

A few days ago I bought a 6.5hp Powerfist (Honda clone) engine off of kijiji for $50 that I have intentions on putting on my doodle bug. Seller said that it came off a rototiller and ran a bit rough. So I figured I would buy it cheap and get it running right.

I brought it home and it fired right up however when I give it mild throttle it starts to stall/sputter and dies if I don't let off the throttle. I figured that one of the jets was plugged so I took off the carb and gave it a good cleaning. All the jets were clear and the carb looked practically new. I started the engine up again and there was hardly any improvement, still would not rev up. It seems like the choke is always on even though it is not. if you know what I mean

I proceeded to open up the crankcase and check the timing - all is good. (I removed the low oil sensor while I was in there)

Checked the valve lash and removed the cylinder head to check the cylinder wall. Smooth and looked brand new.

The only part I haven't checked is the flywheel key to see if it is sheered or not (don't have the correct socket size to remove the flywheel).

If anyone could give me some insight on what may be the issue with my engine that would be great.

P.S I also changed the spark plug to eliminate a variable. The new plug built was covered in carbon after a few minutes


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[fowler]

It sounds like its flooding
Too much fuel is getting in

Either the needle and seat or the float

In some cases fuel tank location
But if that's stock then we can rule that out

Make sure the needle and seat is in good contrition
It may pay to just replace the needle
It's cheap and they do wear our

Also make sure the float is floating
Submerge it in liquid for a little while
When u pull it out it should not have any of the liquid inside it

Lastly u say it sounds like the choke is on
Well is it?
Make sure the mechanism is actually turning the choke off


EDIT
Oh did u or the pervious modify the engine
Change the jet or anything
Also what does the air filter look like?
Clean?

 

[Doc Sprocket]

Is it blowing black smoke? The plug would seem to indicate a rich condition. Have you tried running with the air filter off? Is the inlet needle valve (float) sealing?

Just for kicks- does it run any better with the choke partway or fully on?

EDIT- I guess Fowler was already typing...

 

[Gokarts4Life-11]

Thanks a lot of the input guys, I finally figured out the issue! After doing pretty much everything you guys suggested one of my buddy's suggested to check if the valves are seating properly so we took the head off and sure enough both valves needed to be re ground and lapped. I guess all the carbon build it cause them to open slightly and not create a good seal. After lapping the valves I reassembled the engine and we go it started. Finally it rev'd up to full rpm and was much smoother overall. It would still only run with the choke closed which means that it is running to lean correct?

Really appreciate the suggestions!

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[Doc Sprocket]

It would still only run with the choke closed which means that it is running to lean correct?

Yup! And of course, if you have to keep an engine choked to compensate for a lean condition, you can end up with a plug that looks rich as a result. This is why I asked (despite lean comments) if it ran better choked.

Glad you've got it sorted out!

 

[Gokarts4Life-11]

Yup! And of course, if you have to keep an engine choked to compensate for a lean condition, you can end up with a plug that looks rich as a result. This is why I asked (despite lean comments) if it ran better choked.

Glad you've got it sorted out!

Sweet good to know. Now in order to solve this problem do I need to buy a larger jet? Also what does the pilot jet behind the throttle flap do?

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[mckutzy]

If you do in fact get a new jet for you carb, and if it is a Honda part, let us know how it fit and does. The lawnmower repair guy where I went to get my new jets for my motor(a Champion brand clone) he was pretty insistent on non compatibility with these motors. So at least we have a potential start of cross compatibility chart or thread going.

 

[Gokarts4Life-11]

I will certainly let you know if I do buy a larger main jet. However I think my problem is just an air leak somewhere between the carb and intake port because the engine is all stock and idled find before I took the carb apart. One of my gaskets is either missing or in the wrong place. If I were to buy a new jet I would probably get it at affordable gokarts.com

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[Doc Sprocket]

I will certainly let you know if I do buy a larger main jet. However I think my problem is just an air leak somewhere between the carb and intake port because the engine is all stock and idled find before I took the carb apart. One of my gaskets is either missing or in the wrong place. If I were to buy a new jet I would probably get it at affordable gokarts.com

Agreed.

And, FWIW, I'd BET a standard GX jet will fit the Champion engines. I think what you have McKutzy, is either an ignorant OPE dealer, or one that has a hate-on for chinese stuff.

Also- In my research on Champion (I have a Champion generator powered by one of their GX340 clones and it's bloody brilliant) is that they're built to American QC standards in china. Take is for what it's worth, but they do seem very legit. Check out the weebsite.

 

[mckutzy]

Oh mine works I just now have other issues on my thread it explains there. It is a good motor.

I found Honda numbers if needed for a new jet. The ones I got came from a dealer in Ontario shipped out to me.

 

[BigThieme]

Maybe you should check the throttle