Troubleshooting a Huasheng 4-stroke Engine

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#1
Hello MotorBikes.com I'm Matt, a new member to this forum, however I've been working at this motorized bike for close to 3 years now and I've only got it running a hand full of times unfortunately. First a little bit of background about the bike. I first purchased the Huasheng 4-Stroke engine kit at GasBike.net along with the 4 stroke shift kit at Sickbikeparts.com back in 2015. Also purchased a mountain bike and upgraded Shimano hydraulic brakes. After having assembled the bike in the summer of 2015, I did manage to get it running a hand full of times with the top speed clocked at 45mph. After about 2 rides on it I noticed the engine mount was sliding downward on the frame thus putting slack in the chain, fixed the issue with the mount.

After having the motorized bike sit for quite a while roughly 2 years, I tried to start it up again recently and it wouldn't fire up. So I took apart the carburetor cleaning every part meticulously (tons of old fuel lacquer inside the carb), cleaned the fuel tank, put in new fuel lines, new fuel filter, new on/off fuel valve and new fuel. I also replaced the cheap chinese spark plug included in the kit with an new NGK plug.
IMG_20180315_160922.jpg

This boils down to the current issue that I'm having with the Huasheng 4-Stroke 49cc engine not wanting to start no matter what I try. After replacing most of the fuel components, new spark plug and carb cleaning it's still a no go. I've even tried pulling the throttle a little bit to put some fuel in the cylinder when pull starting it, but it still doesn't start up. I've also looked at the engines compression and it looks good.
IMG_20180315_160951.jpg

After doing some research online I've come to the point that I think the reason for the bike not starting is that the air-fuel mixture is off. Doing some research I've found that the mixture can be adjusted with a screw located on the back of the carb(pictured above). It appears that the carb that came with my motor has a brass plug in the place of the adjustment screw.

Would this be a problem with the air-fuel mixture? If so should I replace the carburetor, and what carburetor would you guys recommend?

Hoping to get this motorized bike project up and running as soon as possible!
 

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CrazyDan

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#2
Carefully drill a small hole in that brass plug then tighten a screw in there. Use the screw to twist that plug out. Enjoy being able to adjust your a/f mix.
 


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#4
Carefully drill a small hole in that brass plug then tighten a screw in there. Use the screw to twist that plug out. Enjoy being able to adjust your a/f mix.
Thanks for the tip Crazy Dan! I have a few questions lol. First I drill a hole in the brass plug and somehow get it to pop out with the screw. OK great! How do I know if there's going to be a adjustment screw behind it for the A/F mixture. For all I know this cheap carb doesn't have the mechanism to adjust the A/F and put a brass plug in place. Don't want to sound cynical but I don't want to put in all that work and there not be anything behind the carb or just destroy it trying to get the plug out. Also should I just get a replacement carb with a A/F adjustment screw?
 


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UPDATE: So after much testing I've come to the conclusion I thought I would come to but had to make sure! So after purchasing some starting fluid at a local auto parts store, I sprayed about 3seconds worth into the carb (directions from the starting fluid ). After about 3 pulls...BAM! It started up and slowly died :(. So what I'm thinking is, it's getting air, spark, and compression is good. The fuel line is letting fuel in. I know this because after taking the fuel line off and opening the fuel valve, the fuel was flowing fine. So this leads me to believe that the A/F mixture is completely off and/or there is a problem with the jet.

So I think the best way to go about this is to purchase another carb. This is where I will need your help everyone. I'm looking for a new carburetor to put on the motor, one with A/F mixture adjustment. If it's a racing carb, even better. I hear those can give better air flow. The motor is a HuaSheng 49cc Honda clone.

Looking forward to have this project up and running soon, so please comment your carb recommendations for this motor!
 

CrazyDan

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#7
Just yank out the brass plug on the carb closest to your engine, the idle a/f mixture screw is hiding behind that.
 


CrazyDan

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#9
To prevent folks from tuning it outside epa restrictions. Lean engines burn cleaner, but too lean = no fire. I prefer slightly on the rich side, engine runs cooler.
 

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#10
To prevent folks from tuning it outside epa restrictions. Lean engines burn cleaner, but too lean = no fire. I prefer slightly on the rich side, engine runs cooler.
Gotcha! Alright well I'll give it a try. Just frustrating that they put that plug there. I'll try to take the plug out might save me a couple bucks if it works rather than replacing the carb.
 


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#12
I removed the brass plug too. It was fairly simply and allows adjustment now. A lot easier than fitting a different style of carburetor. Turn the screw to adjust the rpm where you like it.
 


CrazyDan

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#14
Turn screw clockwise for leaner, counter clockwise for richer. Try setting it with the idle rpm screw (the black plastic one) set at about 1 1/2 turns in and turn the screw behind the plug all the way clockwise then turn counter clockwise 2-2 1/2 turns. Do minor tweaking on this screw till its where you like. If you gotta turn the rpm screw in a bunch then you are too rich.
 

CrazyDan

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#15
Idk why I haven't suggested it yet, but you let it sit for 2 years. Perhaps old gas gummed up your carb. Get carb cleaner and take your carb apart. Unscrew the idle jet and spray in there. Remove the float bowl and spray in every hole you find including the one the float plunger covers. Try not to lose any parts, do it in a bright clean area.
 

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#16
I have had the same problems as you. My Huasheng 49cc would have a hard time starting and the idle would waver all over the place. I definitely recommend cleaning the carb as old gas gums up this carb fairly quickly. I would look into replacing that carb with an NT carb. I replaced mine a few weeks ago and the idling is super smooth. I even gained some acceleration as the older carb would bog down before starting to accelerate. I have had great success with the NT carb and have never looked back. Also, I would make sure your valves are adjusted as well .004" intake and .006" exhaust. My valves were pretty off from the factory and my engine ran so much better after that as well.
 


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#18
UPDATE: Ugh beat and tired lol! Has not been fun lately getting this thing to try to run. OK so here's the breakdown I did everything CrazyDan recommended and a few others. Got the brass plug out and lo-and-behold there's a A/F mixture screw there. So I do the tuning instructions that CrazyDan recommends and.......no luck. I was spraying starting fluid into the carb and the engine would fire briefly but never stay running. Would only run for the amount of starting fluid sprayed into the carb. So here I am now, beat and tired lol. My arm is sore from pulling the pull start so many times and doing changes to the idle screw (black one) and the A/F mixture screw. I tried every possible combination for tuning and no luck. Not sure what to do at this point just feel frustrated and beat :/.
 

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#19
Idk why I haven't suggested it yet, but you let it sit for 2 years. Perhaps old gas gummed up your carb. Get carb cleaner and take your carb apart. Unscrew the idle jet and spray in there. Remove the float bowl and spray in every hole you find including the one the float plunger covers. Try not to lose any parts, do it in a bright clean area.
That was one of the first things I did BTW, think I had it in the original post. Took the whole carb apart and got every nook and cranny clean. There was a lot of lacquer from the old fuel and gunk! Glad I did that deep cleaning.
 

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#20
I have had the same problems as you. My Huasheng 49cc would have a hard time starting and the idle would waver all over the place. I definitely recommend cleaning the carb as old gas gums up this carb fairly quickly. I would look into replacing that carb with an NT carb. I replaced mine a few weeks ago and the idling is super smooth. I even gained some acceleration as the older carb would bog down before starting to accelerate. I have had great success with the NT carb and have never looked back. Also, I would make sure your valves are adjusted as well .004" intake and .006" exhaust. My valves were pretty off from the factory and my engine ran so much better after that as well.
I've done a deep carb clean, one of the first things I did. There was so much lacquer from the old fuel in the carb and gunk that I'm surprised it didn't run previously. But now I'm kinda stumped as to why it's not wanting to run. Even after tuning it and trying to kick start it with some starting fluid.

Thanks for the recommendation for the NT carb. I'll have to take a look at it, looks like a safe bet if you had success with it. I'm just tired of messing with this carb and not having the engine fire.

As for the valves I've never looked into doing an adjustment on them, I don't know if that might be the issue. But the motor hasn't run that much since I've gotten it. Probably like a total of 2 hours at most.

I'll definitely look into the NT carb though!
 


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