I have my 1975 RD250 converted over to a 350 fresh bore with Jim Lomas street retro pipes and an Economy Cycle crossover tube (large fuel line style) and manifolds. As well I converted her to electronic ignition with a Vintage Smoke Dyna setup at 1.8 btdc (1.81 left and like 1.79 right. As close as I could get).
The air filter that came out of the bike from stock was unbaffled and the jets were 120 mains on a 30 pilot. Stock needle and 0-8 needle jet.
I replaced the main jet with a 190 main to start , left 30 pilot in it. Then ran it around the block a few times. It seemed kinda all over the place. Initially started fine after rebuild, but seemed to not like idling the other day. Turned idle screws up half a turn and raised idle to about 1400. Still stalls on occasion. Tried setting air screw to 1 and 3/4 out from 1 and 1/4, still died when cold. Seems to idle fine when hot.
I know I made a lot of changes to the bike all at once so it's a rough start with tons of new info, but the main thing was it seemed to be running rough, surging at slow speeds every now and then, not taking throttle well. Carbs were synced before taking off bike and a quick check with my finger inside carb bells showed they matched each other at full throttle when I put them back on. Top end felt lax as well.
I have to pull plugs to see but I wonder if its lean? 190 seemed a good spot to start since it is 5 main sizes over stock.
This is cross posted in ac rd club. Suggestions so far have been larger 35 pilot and main jet, and plug the EC crossover. Also pressure test motor. Which I might be able to do but for now I'll check with propane or ether around motor.