Momentary loss of acceleration

[Phil C]

I set the throttle stop to a quite high tickover. Wound in the mixture screw until ran unevenly, then out again searching for highest revs. Kept winding out, and revs kept increasing. Having wound about two full turns I thought is this right? How many turns would be too many?

[Phil C]

Aaargh.  I've lost track of where I was with the screws. Could someone give me a starting point for the mixture screw please?  Phil

[JulianS]

1 1/2 turns out usually a good starting point.

[Phil C]

Further to my previous post, my carb is a Concentric 626, and the bike a 1965 B40F. I think a starting point for the mixture screw is found by winding it fully in, and then out by a certain amount? Is it 1.5?  Don't know what makes me think that. Phil

[Phil C]

1 1/2 turns out usually a good starting point.

Just seen this. Thanks Julian.  Phil

[Phil C]

By the way, craigc11g, just to say that I haven't ignored your suggestion of the advance mechanism.  It's on my list of possibilities.  Thanks.  Phil

[Rog1]

If all else fails, check to see you haven't got a damaged wire that moves under acceleration. It might have an internal break which may be difficult to spot, or damaged insulation and it's earthing out intermittently. In the second case, it won't blow the fuse if it's the wire from the coil to the points, but either fault could cause the plug to spark at the wrong time.

[Blackthou]

Phil,
Before you go too far, drop the needle one groove and try the mixture screw scenario again. You should be able to achieve a greater degree of response, ie not winding it out and needing more.

[Phil C]

Well I've tweaked the screws again using Julian's recommended starting point and it sounds okay when stationary. I'll take it for a short run later if the weather improves s bit (with empty pc to try to find the leak.)  Fingers crossed! Phil

[Phil C]

Mixture, connections, fuel, advance...all good ideas, but you weren't to know how stupid I can be where motorcycle maintenance is concerned.  I noticed when I was out on the bike this morning that when the little pause happened there was a slightly odd feeling at that moment in the twistgrip.  Remembering that this afternoon, I checked the cable route, and look what I found!  I've now altered that, and the issue has gone away!

Thanks for your help anyway, and sorry to have wasted your time!

I'm learning. Honest!

Phil

[Rog1]

Well done. You haven't wasted our time.

[hoogerbooger]

Well I'm a bit disappointed Phil....I was hoping to find out the settings on your 626... .But I guess  it'll be more useful to know if it runs ok on them 

[Phil C]

Haha, yes, well if and when I take it apart - which I confess I'm tempted to out of interest - I'll let you know.

[Blackthou]

Great news Phil and really pleased you got to the bottom of it.