Bike runs rough with air filter

C

Chris7420

Member
First time posting on here I’ve built 15+ of these bikes, have never had a reason to post before cause I’ve never had any issues I couldn’t figure out but this bike I built for my friend runs like crap with the air filter, when you take it off it runs fine. With the filter on it’ll run fine to a certain rpm/speed then it just bogs out super hard and would only go half as fast as the others I’ve built. When it was new and we assembled the top end we noticed a big gouge in the cylinder head (casting defect) and we thought that was the issue so we actually replaced the cylinder but it still ran the same so I was stumped, was going to swap parts out with ones from a good running bike till I found the issue I put the carb from another bike on it and didn’t bother putting on the air filter and took it for a ride to see if it was fixed and it was it ran good so I thought it had a defective carb but then I put the air filter on the other carb and it ran the same as before, switched back to the original carb but didn’t put the air filter on and it ran good. Anybody know what could cause this? Also by the way here are the engines that I use https://mobettabikes.ca/collections/frontpage/products/zeda-firestorm-80-motorized-bicycle-kit
 
Venice Motor Bikes said:
It sounds like it needs a slightly smaller main jet
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Do you think that would fix it? I considered that but it’s weird cause I’ve ran a bunch of these engines and never touched the jetting. This is 1 of 3 of the same engines I ordered at the same time the other 2 have no issues I even tried the carburetor from one of the other ones and had the same results.
 
Chris7420 said:
Do you think that would fix it? I considered that but it’s weird cause I’ve ran a bunch of these engines and never touched the jetting. This is 1 of 3 of the same engines I ordered at the same time the other 2 have no issues I even tried the carburetor from one of the other ones and had the same results.
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I'm almost certain this will fix it... These engines can be very weird like that.
Be sure to only go one size smaller on the jet at a time (& then test it ).
 
I had that problem on my 20 inch build. I think it’s probably due to some differences in the port timing of the cylinders. Put the little clip in the top notch on the needle and see if it is better.
 
Larry Trotter said:
I had that problem on my 20 inch build. I think it’s probably due to some differences in the port timing of the cylinders. Put the little clip in the top notch on the needle and see if it is better.
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I usually don’t touch the needle clip until the motors are broken In, this one is still pretty new. Isn’t the top notch leanest position?
 
Yes it is and it the air filter being on makes it run bad then it running too rich. Move the clip to the top and see what happens. Mine had the same problem and I had to take even more steps to cure it.
 
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