A quick fix for my fuel mix! m

H

Huffathump

New Member
I bought several "80cc" motors from BGF and both of the ones that I have mounted have the same problem- after a few seconds at wide open throttle &high RPM the motor would just fall on its face.
It would lose all power until I gave it a few seconds rest, then pull hard again for a few seconds only to fail again.

Reading the many threads about this and similar problems, I found conflicting opinions as to whether the stock jet was too large or too small. I was just about to drill the thing out on one carb and solder/ drill another just to see what difference it would make when I noticed something- neither of the needles I was looking at had much taper at all. Nothing like the needle on a Holley carb like what I used to work on. So I took one of the little boogers to the drill press and put some sand paper to it- concentrating on the area near the tip. I didnt even measure it before or after, I just went by instinct and removed more metal where I figured more gas was needed. Back in the motor and it runs a bit rich. Wont idle at all. I lower the needle one notch. Whamo! my power band is even throughout! great idle and no sputter even at WOT downhill!

This might just be a bad batch of needles, but if anybody else has the same problem, it si worth a shot- I didnt even have to take the carb off the bike! Just dont take off too much metal- I think I came close on mine with the stock intake and no porting. Thats ok though because these motors wont stay stock for long! A little port and polish + improved air filter should increase airflow enough to compensate for the extra fuel. Or I could build the dual RAM air intake I have been dreaming up....fly
 
I have re-shaped a few of the jet needles just to tailor the carb since there is no mixture adjustment.
 
Yes. You make the taper much "shallower" than a knitting needle though.
I usually taper the last 1/3 of the needle, not just the tip.
 
Bikeguy Joe said:
Yes. You make the taper much "shallower" than a knitting needle though.
I usually taper the last 1/3 of the needle, not just the tip.
Click to expand...

Yeah, thats what I meant to say. Just the last 1/3 of the needle. In my hurry I got up a bit higher than that (hence, my need to drop the needle by a notch.) Luckily I have extras. My advice is go slow and have an extra needle handy- just in case you sand off too much metal.

I will post a pic, but right now the needle is in my bike, it is a nice spring day, and I wanna RIDE!

(OK, I admit it- I was riding every day even when we had 12 inches of snow and minus 5 farenheight. At least the fuzz could only spin their tires and glare at me while i rode by!)
 
oooh, good to know. i do have an extra needle in fact, so i will try this.

i've experimented with top notch, 2nd from top, and 3rd, without noticing any difference, my idle stays pretty low even tho my idl screw is all the way in, why is that? the air filter isn't blocked, the choke isn't stuck... its strange.
 
some of the needles I checked start at 0.070 up by the clip slots and taper to 0.068 at the tip if that will help anyone. I did Pablo's carb a long time ago and got his carb to working it would not rev up at all only idle.
 
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I tried a few things on the 67cc,smoothed ports,piston skirt mod,tapered needle.carved an extra groove in the needle to lean it further ,this cleans up idle to mid range then with the modded needle richens up top as to not seize,then made a 36t sprocket out of a bmx front cog fixed everything ,runs sweet like my 48cc + more top speed these motors need more load to run good!
 
Just put the needle in a cordless drill and use some wet or dry 400 grit paper with a tiny drop of oil. Let the needle spin and concentrate on the bottom 3rd of the needle where it goes into the jet. I usually take a little off ( you'll see it on the paper) and try it, take off a little and try it. It's very trial and error, and you can go too far, so be careful.
 
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