Adjusting the HuaSheng 142F (49cc) carburetor

[azbill]

I have had a few members pm me for help adjusting their HS carbs
this info was posted by Quenton (pres of EZM)
I am reposting because I couldn't remember where it was located

"Adjusting the HuaSheng 142F (49cc) carburetor

In order to adjust the carburetor it is necessary to warm the motor up first. The motor should have at least 5 minutes running time before any adjustments are made.

On the left side of the carburetor near the front is the idle mixture screw.

On the HuaSheng motor the idle mixture screw is a fuel adjustment, not an air adjustment.

Simply adjust the screw for maximum idle, and then turn the screw approx 1/16" counter-clockwise [slightly rich].

Check the throttle response, and adjust the mixture if there is a hesitation. Turn screw clockwise if it "bulks" and then catches on [rich], or adjust screw counter-clockwise if it accelerates and then drops off quickly [lean].

Have fun,
__________________
Quenton "Lee" Guenther
EZ Motorbike Company
www.ezmotorbike.com"

 

[thirstybike]

Thanks for sharing this info!

 

[Mr. Minecraft]

This is the method I use to tune, but the problem is the black idle screw. I get drastically different results depending on the position of this screw. For example, if I set the black screw so my bike is barely staying on, then adjust the mixture screw for highest idle, I have to turn the mixture screw a lot more than if I adjust the mixture screw at 1/4 throttle. Is there a recommended RPM to run at when adjusting the mixture screw? I called Phantom Bikes a while ago to see how they tune, and Sterling told me to turn the black screw all the way in, then adjust the mixture. I used this method a few times only to have my engine overheat and die due to the high rpm's without having the extra air flow running over the cylinder. Obviously there are many different methods, but which one gives the best results?

 

[Trey]

I successfully did this today- (following advice I received on this site by the way!)
[Stock engine and carb. Aftermarket air filter. 5,500' altitude.]

1) I began by seating (screwing in clockwise until gently tight) the idle mixture (fuel) screw. I then turned it counter clockwise two full rotations.
2) I set the curb idle screw until it barely touched the throttle lever bracket. I then turned it clockwise two full rotations.
3) I started the engine normally.
4) Briefly test rode bike to determine idle mixture adjustment needed, as per the information given in azbills post. Because it was obviously revving high, I almost immediately adjusted curb idle screw counter clockwise 1 full rotation- perfect.
5) Adjusted idle mixture (fuel) screw counter clockwise two full rotations- perfect.

Fuel screw two turns out, idle screw two turns in, seems to be the best starting point on these small engines.
All my adjustments were made 1/4 turn at a time to harmonize it all, and after warming up.
Tinker, tinker, tinker- Good luck! Let us know how it goes.

 

[Vince]

mine wont even start unless the idle screw is out about 3 turns and my plug looks white i assume that its running lean am i right on this ????

 

[scotto-]

mine wont even start unless the idle screw is out about 3 turns and my plug looks white i assume that its running lean am i right on this ????

You are correct, your engine is running lean.

 

[Vince]

So do I need to turn it out more ?

 

[The_Aleman]

Best way to figure that out is to keep testing. Get the engine warmed up, run a section of road near you at full throttle, shut the engine off. pull the plug and inspect it.

This is called a "plug chop". It's possible that no amount of adjustment will get your engine to optimum air/fuel adjustment tho. This depends on engine mods.

Your setup may very well require a different-size jet. For example I have a stock Huasheng with an aftermarket intake and exhaust and I had to rejet my carb to get the optimum fuel/air adjustment. What I did was buy a micro drill bit set and drill out a spare jet I had 1 size larger than stock. Then it takes 6 turns out of the mix screw to get it to run properly. Does run slightly rich.

Your results will likely vary. From my experience, an unmodded engine requires about 2-3 turns out, but will vary quickly depending on mods.
The carb itself isn't really consistent, either. You'll have to perform a "plug chop" to be sure, IMO. A different heat-range plug makes a difference too!

 

[Vince]

Yes makes sence I did put on a long exhaust with an expansion chamber

 

[GearNut]

An expansion chamber on a 4 stroke?
Only 2 strokes benefit from one as a 2 stroke does not have valves to control the intake and exhaust.
There is no harm in running a 4 stroke with one but it will not have any performance effects.

 

[scotto-]

An expansion chamber on a 4 stroke?
Only 2 strokes benefit from one as a 2 stroke does not have valves to control the intake and exhaust.
There is no harm in running a 4 stroke with one but it will not have any performance effects.

Ditto what GearNut said......a straight pipe with a muffler on the end will be much more beneficial than a 2-stroke expansion chamber.

 

[Vince]

thats good to know ty for that info

 

[Vince]

Ditto what GearNut said......a straight pipe with a muffler on the end will be much more beneficial than a 2-stroke expansion chamber.

yeah thats what ill probly go back to

 

[JeremyD]

This is the method I use to tune, but the problem is the black idle screw. I get drastically different results depending on the position of this screw. For example, if I set the black screw so my bike is barely staying on, then adjust the mixture screw for highest idle, I have to turn the mixture screw a lot more than if I adjust the mixture screw at 1/4 throttle. Is there a recommended RPM to run at when adjusting the mixture screw?

I am definitely a novice when it comes to carburetors, but it seems to me that the fuel mixture screw is part of a high speed circuit, not an idle circuit. I don't think the HS 142 has an idle mixture adjustment (although my high speed mixture screw came from the manufacturer buried under a brass plug so who knows!)
So I had to give it a little throttle to test my adjustments; adjusting the mixture screw did not have much of an effect on idle speed. This is the procedure that worked for my bike:

Gently seated,
out one turn (richer)
try to start
out half a turn, etc. until it starts.

then try a little throttle (probably too lean and dies)
out a quarter turn

repeat until you can reach all the range in the throttle without hesitation or sputtering.

 

[GearNut]

The factory HuaSHeng carburetor does not have a high speed mixture screw. The Idle speed mixture screw is in fact capped by a brass plug. It is capped because the powers that be do not want you to be able to fine tune your carburetor. They believe that the factory can somehow magically tune the idle mixture perfectly for all situations.

 

[KCvale]

I don't know if it's the elevation here (1086') or the fact that I use NGK 7544 (CR7HIX) Iridium spark plugs, but I have NEVER had to adjust the carb other than idle.

Just for giggles and grins, how do you guys get the brass plug out?

 

[SlickChik]

KC, that is NOT the plug you want to remove. It's the flush one to the left. I drilled a little hole in the center, inserted a wood screw until it caught and pulled the plug out.

 

[KCvale]

KC, that is NOT the plug you want to remove. It's the flush one to the left. I drilled a little hole in the center, inserted a wood screw until it caught and pulled the plug out.

Thanks man ;-}

 

[Kustomized Hypnosis]

I got a 49cc Huasheng 4-stroke from bikeberry (done with them now, long story) and among some of the broken parts was the choke lever. They sent me a complete new carb, and I got a filter from SBP. Just put both of them on this morning, and I noticed the brass plug (which the damaged carb had) was not in the new carb. That should make adjusting the screw convenient!

 

[cliptwings]

I want to thank all the good folks in this forum thread for their knowledge and experience with the 4-stroke carb. I've been testing out my new bike, going further and further with each ride. The cold motor started right up each time, but after about 10 minutes of operation, it would stall when I slowed down or stopped for a light. With the info I found here, I was able to drill and pull out the brass plug for the idle mixture. I found the idle mixture screw to be completely leaned out against the stop! No wonder the motor wasn't getting any fuel! I adjusted it according to the instructions found here, and fixed the problem with 2 full counter-clockwise turns of the idle mixture screw. It runs as long as I want it to now! Thanks again to all of you for your help.