Originally Posted by ducedave
Road up and down the block to chex the tune all's well-I would like to try a #77 or #78 jet I'm running with a #76 4th clip slot down on the metering rod - I have no drills smaller then a #76 it's fine the-problem is the exhaust-I'm scavenging fine but port blocking and any" back flow " can't remember what that's called, is not good after 7/8 throttle 35mph+ up slight hill a little better down that street
maybe if I crimp down the 3-3/4 out side circumference head pipe just before the muffler body it would help with some back pressure the stinger is tuned good I think the head pipe is the problem at top end
Wow #76 - #78 those are some verty small bits (jets)..!
Are you running a 48cc or a 66cc engine?
I went with a #74 on one engine the other day after replacing the NT carb with a different (NT) one, and the engine was way lean on the jet plug run light gray and engine had a bad low end dead spot with no torque at all, I went up to a #72 bit and that got me a nice medium brown plug with the mtering needle clip set second notch from the top, the engie has been ported, port matched, shaved head, SBP expansion chamber exhaust,this may be the reason it needs the jet size it settled in on.
This is were I get my wire gauge bits, they have the replacements for cheap or the sets for cheap and they are good little bits, been using mine for almost 2 years now and they are still nice and sharp.
Link: Widget Supply: Wire Gauge Drills