Idle Problem

Not open for further replies.
May 27, 2006
I don't remember this as being a problem last summer, but I'm now finding my '71 roadster tends to stall when I slow to a stop at junctions. Unless I blip the throttle when coming to a rest (clutch in and/or neutral) then the fire goes out. I've adjusted the idle to about 1100 rpm and it will work fine on the driveway, just not in practice on the road.

I don't find it at all easy to kick the engine over without putting the stand down, so some junctions can be untidy.. :oops:

I'm running a pair of standard Amals & have electronic ignition. Otherwise the bike has plenty of power when going. A bit rough/noisy on overrun though.

Any suggestions on where to look?

I think it's a 3.0 - should be standard for the 750 ( anyway, that's what I asked for they're fairly new)

My 850 runs rich with a #3 slide. The classic symptom of this is the engine stalling when comming to a stop.

But according to an old Haynes manual I found stuffed on a shelf above my work bench, your 750 should have #3 slides. So, perhaps your needle is positioned too high?

If you have some #3.5 slides, you might give them a try. Debbie, who also has a 750, should be able to provide some tried and proven throttle slide size suggestions.
I'd be looking for an air leak on the inlet side. The noisy overrun could be an indicator of this.
If your engine is popping or banging through the exhaust on overrun, then as Pommie John suggested, you probably have an air leak. Double check the balance pipe between the manifolds as well as all manaifold/carb gaskets.
The key here is it ran properly the previous summer. What has changed? I would suggest starting out by completely readjusting the carburetors.

Start by making certain the cables are adjusted so the slides lift together. Turn the air screws out 1 1/2 turns to start. Use carb stix or a Twinmax (my favorite) to set the mixture and idle.

I find some old timers can set the carbs "by ear", but it using a set of vacuum gauges or Twinmax lets you get them spot on.

If this doesn't get you where you need to be, then check the state of your battery. Maybe you aren't getting enough juice when the alternator isn't supplying it.
Thanks for the suggestions!

Thinking back, air leak is probably favourite as I took the carbs off earlier in the summer to lengthen the tickling sticks (technical term) - Anyone else notice that new Amals use cheepo dowel pins that are about 3mm too short to make contact with the floats? I put a couple of M2.5 screws into the ends which helped.

I'll clear through the idle jet too - I sealed the fiberglas fuel tank, but it's not really a pretty sight in there, plenty of old lining held by the bostik or whatever it was. Hope to afford a replacement metal item sometime - possibly of slightly larger capacity if thats posible.

Snow forcast for tonight, but I hope I'll have the carbs off & on again by the weekend.

Not open for further replies.