Huasheng 4-stroke revs up and down on its 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!

 

[Quenton Guenther]

Hi Max-M,

Sounds like a common problem. Because of the small jets in the carburetor, they are easy to "stop up".

Please let me suggest that you don't run the motor on the stand at full throttle, as the HS motor doesn't know when to stop and can easily rev way past the redline. If the HS or Honda motor is run past 9000 RPMs for any length of time you can plan on buying another motor as the rod will not survive.

I normally use Gummout carburetor/fuel injection cleaner in the gas tank. I add the additive about every 6th tank, and mix VERY heavy [3 to 4 ounces in a tank of gas].
If you store the motor for more than 30 days it might be wise to treat the gas with "Stabil" to stop it from leaving resdiue inside the carburetor.

Sadly if the jets are seriously plugged, it may be necessary to remove the float bowl and clean all the jets and passages with spray cleaner. Never use a drill bit to clean the jets, but can use fine wire [from a wire brush] to reove any stubborn deposits from the jets.

If you live in FL or CA you should stop using regular gas and switch to Hi-test, as it works better than the over modified regular blend.

What is the part number of the new plug?
Have you removed or disconnected the new parts to make sure it isn't a fuel flow issue?


Have fun,

 

[Max-M]

Thanks, Quenton

Many thanks for your thorough response, Quenton.

I removed the carb a couple of days ago, and will have time to buy some spray and clean it tomorrow. In the past, I've rebuilt Rochester Quadrajet four-barrels on small-block Chevys that we hot-rodded, so it was actually kind of fun removing the simple, little Titan carb and opening it up. I now feel a bit more acquainted with my bike's inner workings, and I enjoy that.

Before deciding to remove the carb, I did check that the new fuel line components were allowing fuel to run freely. And I also unsuccessfully tried running some "Sea Foam" (seafoamsales.com) through the carb (a couple of ounces in my 1.5L gas tank).

Finally, before removing the carb, I removed the carb's "slow jet" (or "idle jet") and used a tiny strand of copper wire to clear anything from the jet hole. I found a video on thatsdax.com describing this procedure.

I'm in Connecticut, so I guess I don't have those CA/FL gasoline issues. But I used 93-octane when I fired up this new bike. Would you recommend that I continue with 93, or would the 87-octane stuff be a better choice for the HS engine? When this engine was on my previous bike for a short period of time (when it ran well), I can't remember which octane I used. The Honda GHX50 manual only says "pump octane rating 86 or higher."

My new NGK plug is CR5HSB (as recommended in the GHX50 manual).

When I buy my spray cleaner tomorrow, I'm going to buy some Gumout, as you recommended, and establish that regimen.

Again, thanks for your help.

 

[Old Bob]

Connecticut is on the same smog standard as Calif.You don't need and can't utilize 93 octane in your GXH 50.CT gas is as bad as anyone elses, the MTBE gas Lowell P Whacker stuck us with absorbs water and causes rust in tanks.(thank you you worthless liberal commie scumbags)
It will not not make the engine run better or different.It will not keep the carb cleaner, it will not not burn cleaner, hotter or any thing else the uninformed claim.
The condition you describe is caused by the following 1 foreign objects in the carb, dirt or water or both 2 is a fuel flow issue, tank vent comes to mind

Seafoam is worthless, it is naptha, you can use coleman fuel to the same effect.

 

[Max-M]

Thanks, Old Bob.

It sounds like after cleaning my carb and reinstalling it, the engine should be back to normal. Geez, I hope so!

Many years ago I had a Toyota Tercel, and for some reason, one day I decided to "splurge" and fill it up with high-test (probably 93-octane, or whatever was the highest in 1982). As it turned out, the engine RPMs dropped so low at idle that it wouldn't idle; it would just stall out. So for several days, I had to keep my foot lightly on the gas pedal when stopped in traffic, when I pulled up to stop signs, stop lights, etc. I told my brother about this, and he laughed as he told me about octane; how the higher the octane is, the slower the fuel burns. He said that high-octane was a requirement in high-compression engines, but that it was a waste in my Toyota.

I'm wondering if the 93-octane in my current bike contributed at all to my present bad idle woes. I guess I'll know after I get my newly-cleaned carb back on the engine.

 

[Quenton Guenther]

Hi Max-M,

I only suggested using the higher octane blend becuase of feedback from motorbike owners in CA & FL. I always use regular in all my bikes [Whizzers, EZM, etc] because regular actually ignites quicker on stock motors compaired to high test. Unless the motor has a high compression ratio, the hi-test actually runs worse. Having said all this, reports from motorbikers, esp. In CA and FL tell me the bikes idle and start easier using hi-test [not sure why this is true]. Several have told me that cleaning the carburetor often is the norm, however switching to the higher grade reduced the need to do so [also don't understand why, just reporting from feedback].

The Honda motor uses the NGK CR5HSB, and manual says to run 86 or higher, however the HS manual doesn't suggest this. It is important to note that the HS motor has a higher top RPM level, lower compression, and the stock main jet is 3 sizes larger than the Honda. You might try a colder plug in the HS motor, as I do so on the motors tested on the Dyno.

If you have been running 93 octane, I would suggest you return to regular as the higher octane doesn't appear to produce the same results as the feedback from other riders.

Have fun,

 

[Old Bob]

The flame front of high octane fuel travels within a few m/s of low octane.Higher octane only has more knock resistance. It is formulated to reduce the formation of unstable peroxides.
The use of tetraethyl lead in the old days would prevent knock by the easily oxidized lead molecules attracting the oxygen that would form the peroxides, so instead of forming the peroxides it would oxidize the lead.