H2C Idle - over run?

[Nigel Thorpe]

Hi. Just got one of the H2C's going after some work - carbs etc. Starts fine and idles OK. If I push the revs up to 2500 or 3000, then let go, it takes 15 seconds or so for the revs to drop back down to the idle. Would anyone have an idea why please? Thanks. Nigel

[Wolfie]

Have the Carbs been balanced as per the manual? It may be that just one is pulling the others along.

On my own, I found that lowering the tickover just a little helped it drop quickly back down although there is still just a slight delay.

[Nigel Thorpe]

Hi wolfie. Sent the carbs off to tangoman, who went through them. Set all of the slides even when off the bike and marked the knurled throttle stop screws so I could increase/decrease the tickover evenly over the carbs. With carbs back on the bike, set the throttle cables to sychronize the slides opening. Air screws are 13/4 turns out. The choke cables, or should i say 'fuel enrichment', were each adjusted at the carb to give approx 2mm of slack with the valve closed. Idle is around 1500 at present so will try reducing it when i next run the bike. I wonder if a sticking 'choke' valve may cause the overrun - if it isn't closing properly.

[TallyB]

Maybe oil the throttle cable as the bike has been sitting a while.

[Nigel Thorpe]

Hi. Throttle cables are all free - slides return to stop the instant the grip is released.

[Triple Parts]

The other think that can cause it to "hang" is an air leak.

[Tilly H2C]

As said above an air leak will do this whats referred to as 'slow to idle down'

The heat gasket and paper gasket can be a pain to seal 100%, I use a smear of RTV on every side of the various parts there, If you over tighten the 2 nuts that hold the rubber manifold on they will generally 'bend' the rubber manifold and leak, carefully squirt some WD on them and see what happens to the idle, brake cleaner evaporates too quickly and finds it's way into the inlets giving a false indication

Basically it's a weak mixture, If you haven’t got an air leak just twiddle the air screws in until it returns to idle, Be wary of getting the engine far too hot messing around as that puts everything out

The correct adjustment for air screw is to get the cylinder you want to adjust 'leading' (Basically turn that idle speed adjuster (throttle stop) in for that cylinder in and the other 2 cylinders out, maybe 1/2 turn but be carefull not to get lost and lose your carb sync) then set the air screw for highest rpm setting, some then say turn the air screw back in 1/8th, note all your air screw settings as they are generally different by up to 1/4 turn, some times slightly more

^ That works great in theory and your idle will be sweet until you either ride it or rev it and you get the slow to idle down issue or a 'jerk' forwards as you close the throttle when riding to the end of your road, this is generally caused by fact that it's easier to pull air through the Pilot circuit than fuel so it goes ‘weak’, so turn air screws in 1/8th at a time until it idles down nicely and/or the horrible 'jerk' disappears. This will upset the idle a little but unfortunately everything carb wise on these is a little of 'robbing Peter to pay Paul'