real bad problems 72cc kit plz HELP

[07jonway50]

i have an 07 jonway 50 i have a 20mm carb with a 88 main jet racing coil racing cdi iridium spark plug uni filter full exhuast and 5 gram slider wheights i had the 72 cc bbk installed by a mechanic recomened to me by scrappydogs where i got the bbk they installed it i went picked it up rode it real quik and it was real sluggish he said it had to break in so 150 miles later same thing wont go past twenty almost backfiring and blowing some black smoke out the exhaust i know its running way to rich and thats my problem but no matter what i do it wont lean out i down jetted to a 75 and then even a standard and nuthing played with the mixture screw on side of carb and same thing took filter completly off and no difference adjusted the valves and no diference im so fed up im about to just sell the parts and say forget it plz help

[90GTVert]

First off, it should go back to the mechanic again. I think. I dunno if I'd want a mechanic that thinks running pig rich is just a side effect of break in messing with much though.

Is there something clogging the intake tract or filter? If it's running rich and downjetting has no effect, that would be my first thought. Also, do yourself a favor and check your oil. if the level has gone up and or it smeels strongly of gas, change it. That can happen if they run way rich and then your fuel thins out and engine damage can result.

[Fox]

I think it's actually running lean and you've burned a valve. #88 jet is actually kinda small for a 70cc IMO. My 50cc scooter came with a #95 stock.

[scooterrebel]

How was it running before the BBK. If it was actually running good, I don't know how the BBK would have damaged the valves but stranger things have happened.

A new BBK done by a professional mechanic should be running great from the start. I'm wondering if it has the valves properly adjusted, if the timing marks were lined up properly. Check it to see if it has any kind of vacuum leak. A vac leak can make it back fire but not run rich.

[tomcas]

Aug 26, 2010 13:51:19 GMT -5 Fox said:

I think it's actually running lean and you've burned a valve. #88 jet is actually kinda small for a 70cc IMO. My 50cc scooter came with a #95 stock.

WOW, that sounds way off. Most stock 50s come with anything from a #72 to a#80 with #78 most common. I've installed a few 72cc kit and find an#85 to #88 is more then enough. I'd imagine a #95 would drown a 72cc because the flow in not proportional, that is flow increases with the square root of the diameter and it's not a linear relationship.

[Fox]

I think it all depends on the factory, year of mfg., carburetor type/maker, air filter etc.. These scooters may be the same on paper but different mfg's. use different parts. I know on my scooter I removed the little tube inside the stock air box cover and it ran better because of the larger jet. I've tried removing that tube on customer scooters w/smaller jets and the scooter bogs down without it. It's all about the sum of the parts.