- Wed Sep 22, 2021 6:18 pm
#98368
No, it's not normal to keep adjusting the idle screw all the time. I've never touched the one on my 350 except when I've made alterations to the engine. So something is wrong with either the slow running circuit itself (is it unscrewing itself? Maybe mark the screw position?) or the overall setup. As I say, an air leak at the inlet manifold will cause erratic idling.
An old test for an air leak is to get the bike idling then spray some starter fluid over the inlet manifold area, if the revs increase when you do this, there's an air leak (be aware doing this is a fire risk!).
Backfiring through the carb isn't likely to be carb setup, that'll be more likely to be ignition timing. If it's too far advanced, it'll be a pain to start and do a lot of backfiring or kicking back when you start it. Maybe worth a check, and make sure the auto-advance mechanism is in good order and not sticking or malfunctioning. Or maybe even just retard it a touch and see if there's an improvement. I had issues with the auto-advance on my 350 once because there was so much lateral play on the distributor shaft, the bob-weights were sometimes catching on the points plate.
A leak at the inlet valve could also cause backfiring issues, either the valve itself, or an over-tight pushrod. Is the rod straight? Backfiring can bend the rod itself or the adjuster as I found recently. Spinning the rod in position would usually make any bends obvious.