Huasheng 4-stroke revs up and down on it own...

[Max-M]

I finally took my new build out of the house yesterday. It's a cruiser with a Huasheng 142F four-stroke and a Q-Matic drive. The bike is new, but I used the engine/drive kit previously for a short period of time on my first MB build. I basically removed the whole kit from one bike to another.

On the previous bike, the engine always ran great.

On my new build, I've changed the stock spark plug to the proper (and properly gapped) NGK plug. I also have a new, rocker-type kill switch from Sick Bike Parts, a better fuelcock, and a higher-quality fuel line with an inline sintered bronze fuel filter.

The engine sat, drained of fuel, for about four months before I started the new build.

Yesterday, it took only three pulls to start the engine (full choke). After a brief warmup, I turned off the choke and I had a decently smooth idle. With my rear tire off the ground (I've got a center stand), I twisted the throttle, but the engine wouldn't rev very high at all. The centrifugal clutch would engage, and the rear wheel would spin, but not with enough power to ride the bike.

At this point, when I tried applying the choke even part way, the bike would rev at full power. I tried this a couple of times, and then I turned off the choke, and the engine returned to a decent idle. I stood around with a friend watching the engine idle as we tried to figure out what was going on. Then after about ten minutes, the engine would - on its own - rev up very high, then settle down to idle, then rev high again -- repeating the same pattern over and over. Then after a high rev, the engine stalled. I was able to easily restart it, and the pattern would continue for a few cycles until a stall. While all of this was happening, we weren't touching the bike, and the throttle arm on the carb was sitting firmly in idle position.

I'm baffled! Help!

 

[GoldenEagleChris]

I will not help you. I will only revel in the fact that you are having a bad day.

I wish I can be allowed to type profain remarks but his highness will punish me further if I do....so I do not dare test the powers of the kingdom.

Ps buy a japenese engine.

 

[Max-M]

Hey, thanks for the kind words, Chris. That's nice.

By the way, the spelling is "profane" and "Japanese."

 

[motorpsycho]

have you cleaned the carb?
it sounds like possibly the float is sticking, or you have a massive air leak.
Any time that you use the choke, and the engine revs like crazy, normally it's because there's an air leak.
but, with it sitting drained of fuel, scale and crud in the carb could have loosened up and fallen into the float bowl, possibly clogging the main jet partially. (which would make it run lean).
There could also be crud keeping the needle & seat from opening fully to allow the float bowl to fully fill with fuel.
I'm imagining that the bowl is only partially full, because the float can't drop all the way down due to crud and scale. and then as the float bowl runs empty, the engine leans out, which causes it to rev up. Then the fuel bowl gets some more fuel which causes the rpms to go back down because the air-fuel ratio gets richened back up. any time an engine runs out of gas, the idle will go way up because the air-fuel mixture goes really lean. also, no power when you throttle it could indicate a partially clogged main jet.
I'd clean the carb and see what happens.

 

[Max-M]

Thanks, motorpsycho. What would be the possible sources of air leaks, besides the main gasket where the carb mounts to the engine?

And as far as cleaning the carb, how would you go about that? I've cleaned and rebuilt Rochester Quadrajet four-barrels on various cars, but I'm not quite sure what to do with this little Huasheng carb!

Also, somebody here at work suggested to me that the time that the engine was sitting on a shelf for those four months, it might have still had gas in the carb bowl, and that that could have gunked things up in the carb before the fuel fully evaporated. He thought that maybe I should try a product called "Sea Foam": www.seafoamsales.com

Are you familiar with this stuff? Their MSDS says that it contains three parts:
1. 60% pale oil (a highly refined mineral oil with no wax content)
2. 30% naphtha
3. 10% isopropanol alcohol

Thanks again...

 

[VROOM]

Get some spray carb cleaner and blow it out with compressed air afterwards.

 

[motorpsycho]

if you've rebuilt rochester quadrajets, then this carb should be a peice of cake. I'm surprised that you haven't torn it apart yet!
you'll have to take the float bowl off, take the float out, take the needle & seat out, take the main jet out, and that should be it. there shouldn't be more than that in the carb that will come out.
just spray carb cleaner in EVERY little hole you can see (wear safety glasses). clean everything else with a toothbrush and carb cleaner (float, float hing pin, needle & seat and main jet.) get some tiny wire and run it through the hole in the main jet to clear out any built up gunk.
if the carb sat for 4 months with fuel in the bowl, the gas probably evaporated and left deposits behind. I wouldn't be surprised if you find a white scaley substance in the carb. I doubt that you'll find "gunk" or bad gas because it probably evaporated before it had time to turn to gunk because it was probably only a small amount.

an air leak can be coming from where the carb mounts to the intake manifold or where the intake manifold mounts to the cylinder (a bad gasket). An air leak could also be coming fro the top of the carb where the throttle cable goes (if it has a screw on top).
I'm not that familiar with that carb, so I have no idea how it's designed. I'm just using basic carb rebuilding / cleaning techniques to help you out.

 

[Max-M]

Thanks, motorpsycho. I tried running some "Sea Foam" through the carb. That didn't help. I then cleaned the "slow jet/idle jet" which is easily removed without removing the carb. No change.

So I've got the carb off of the engine now, and it looks like it should be a pretty easy cleaning process.

But I just have one question for you: When remounting the carb onto the engine, should I use any kind of sealant on the gasket (between the carb body and the intake)? The gasket looks good, and it's really quite new. But since my symptoms seem to possibly relate to an air leak (revving super high when the choke is turned on), I'm concerned about getting this little carb reattached with a good seal.

Thanks...