I've posted about this before, the last time I think was last winter. We have a 2008 M/Y Craftsman 26" with a Chonda 208CC OHV engine. The engine has great power, and runs pretty smooth overall. The one problem I have with it is that at high throttle, it surges very badly, especially under load. I honestly don't know what to do about it. I've run Techron through it, it has a new spark plug... Do any of you have any suggestions on how to fix this? Adjust the mixture or something maybe?

look for vacuum leaks.

Governor?

Could a governer not work properly in such a way that it would cause this? vacuum leaks? Could that cause surging?

If you can adjust the mixture, I'd guess it's running a little lean.

I would vote for the fuel mixture adjustment also. I had this problem on a portable generator.
turn the adjustment screw clockwise, if this starts to shut down the engine, turn it ccw till the surging stops. I also poured in 2 oz of stabil fuel stabilizer should there be any water in the tank. Ethanol attracks water. I got rid of the surging with the adjustment screw setting .

Nick, I vaguely recall your issue with this last winter. Did you change out to a quality spark plug? These engines can be set to run lean right from the factory, which is what this sounds like. Does it have a choke? Does it settle out if you choke it a bit? The carb probably doens't have much if any adjustability, but if it did, I'd try to give it a tweak. Could be crud in the carb jetting as well. I've seen that on brand-new stuff.

Joel

Yeah I replaced it with an NGK plug, I posted a thread about it a week or two ago. And yes, it does smooth out if I turn the choke on a little bit.

Worst case, I wonder if you could swap the carb out for a generic 6.5hp carb. They can be had for under $30.

http://cgi.ebay.com/HONDA-CARBURETOR-GX2...=item41535507b6

Joel

Wow that honda carb looks identical to the one that is on the snowblower... Chinese honda clone no lie. Though I would wonder if a 6.5HP carb would be big enough for this engine, which I would think is more than that.

Did it ever run good at high speed?

My 6.5hp Honda had a bad surging problem that was caused by a cracked intake gasket.

Lean causes the surging because as the engine accelerates to top speed the carb's main (high speed) circuit mix goes lean. Unable to sustain full speed because of the lean mix, the rpm drop down until the mix gets rich again from the idle (slow speed) circuit. because the rpm has dropped the governor pulls the throttle wide open and it's then able to accelerate again, due to a better mixture, until it gets to high speed and the cycle starts over.

If it has an automatic choke it also plays into the cycle of lean/rich surging.

Well, since it is a honda engine, made in china... I'll look into that, maybe that is the problem. And no, it's done this from the first time we used it.

Before you buy a new carb, remove the nut on the bottom of the float bowl and clean the main jet (it's proberbly the nut itself)

From reading your posts sounds like high speed adjustment is needed, most snowblower carbs come with adjustment screws to adjust the blower under load.

Has the carb ever been removed and disassembled for cleaning? If the jets or fine passages are occluded with crud it can easily lead to surging. Running Techron isn't necessarily enough to rule cleanliness out as the problem.