Too rich at half throttle

[AE86]

Hey guys, this problem has been bugging me cause i cant figure it out. I have a Japanese carburetor on my 80cc bike engine with a motovelo tuned pipe exhaust. I was riding along a few days ago, everything running smoothly, then out of nowher it starts acting like its running rich and starts four strokeing and smokeing. At half throttle it stops smoking and runs smoothly again. But annything more than half throttle results in it going rich and loosing all of its top end. I was wondering if its a problem with my carb, which i just cleaned and serviced last night and is working properly, or maybe my CDI? The CDI i am useing is the stock one i got on my first bike, i bought a new engine from ebay and used the original coil on the new motor...maybe its just old and is loosing spark or timing at top end? anny help will be GREATLY appreciated.

 

[motor_bike_fanatic]

an electrical problem shouldnt affect throttle response, at least not to my knowledge. I would clean and re-gap your spark plug. if that doesnt help, then you're probably flooding your engine.

 

[AE86]

I actually replaced the sparkplug hopeing that would make a difference and it didnt

 

[Bikeguy Joe]

Er, "an electrical problem shouldn't affect throttle response"........then "I would clean and re-gap your spark plug".

Yes, it may be the plug (electrical)......or, it sounds like too large a main jet. Could it have been partly blocked then after you cleaned it, it became too rich?

 

[Bikeguy Joe]

BTW- welcome to the forum AE86.

 

[AE86]

What confuses me is it ran just fine with the carburetor for 2 months and it just barley started doing this...i have re-adjusted the A/F mixture multiple times, trying to lean it out to see if the problem goes away but im on the leanest notch and it still four strokes at top end.

 

[Bikeguy Joe]

What kind of carb do you have exactly?

Like I said, it may have been partly clogged in the main jet, and when you cleaned it....

 

[Bikeguy Joe]

Finally, sometimes a partly clogged exhaust will cause the same type of symptoms...4 stroking, bogging on the top end.

 

[AE86]

Its a HUAGUANG carb with remote choke

 

[Greg58]

What type of air cleaner are you using? One way to tell if the jet is too big is to do a test run without the air cleaner, if it runs better you need to rejet. I installed a high flow sbp filter on my cns2 and had to drill the main jet to get the mixture right.

 

[AE86]

It has a 1.5 inch K&N style high flow conical filter on it right now.

 

[Greg58]

I went from a b6hs to a bp5hs which is one step hotter with a extended tip to cure a rich problem on one of mine. After warmup the engine runs alot better.

 

[AE86]

I am currently running a champion J8C Small engine plug, I think I might try that bp5hs, and if that doesn't fix it....I'll be back with more questions. Thanks for all the tips guys you are a really big help!

 

[tooljunkie]

any chance the jet is loose?
maybe a dirty needle /seat,or seat missing?

 

[ivan H]

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Like Bike Guy Joe said, it sounds like ur main jet is too big. Check ur plug, wot color is it,,, it'll tell u wots happening in there. BTW, I thought that carb was Chinese, but I could be wrong. Cheers

 

[Bikeguy Joe]

Taking a wild guess that yes, it's Chinese.
http://www.google.com/search?sourceid=chrome&ie=UTF-8&q=HUAGUANG

 

[ivan H]

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Yeah, I aint positive but I think that Zbox, a company that sells chinagirl kits etc in Australia, offers these carbs as an upgrade to the NT & speed carb. Supposedly a lot more "tuneable" & over the whole range, not just main jet. U could check them out at zbox.com.au. Cheers

 

[AE86]

Hey guys just a little update on my bike. I bought a brand new stock carburetor on Ebay and an NGK bp5hs (thanks to Greg58) and WOW! For some reason every problem went away! It has MUCH better throttle response and revs cleanly from idle all the way up to top end at 40mph. I guess I learned the hard way about aftermarket carbs for these engines, according to a buddy of mine that tunes snowmobiles he said the motor is running too rich because its not designed to run with a carburetor that has a large main jet AND a pilot jet. In this case the stock carburetor out performs the huanguang. I'm sure with a proper jet and better intake the big carb might perform better, but at the level my bike is built its not needed. TO EVERYONE LOOKING AT PERFORMANCE CARBS you may hurt your performance rather than help it if you don't have proper A/F mixture. I learned the hard way don't let it be you!

OH! and before I forget, yeah I think the Huanguang is chinese, but on the throttle barrel it says "Technology of Japan" so Thats what confused me...thanx again guys for all your help!

 

[ivan H]

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the BP prefixed plugs will also give u a very slight compression increase with the extended tip taking up a little more area in there, & it puts the spark closer to the piston. Cheers

 

[Greg58]

The reason I went to the bp5hs is what I learned in the 70s, on most engines that had breaker point ignition with weaker spark the extended tip put the flame deeper in the fuel mixture. Anything that lowered my E/T I would try.