Carb problems ?

[lzsteve]

Problem,
         Well I cleaned out my carbs yesterday after a long soak in solvent/carb cleaner and a blow out with an airline, all jets were clear. I've reassembled, synchronized and replaced the inlet boots ( lots of cracks), checked mixture screws with infra red temp on exhausts and adjusted to 280°C. Revs well very clean but it won't tick over without a little choke( about 5mms out) even after it's hot. Went for a ride and runs well no hesitation anywhere in the range up to 10000 revs.Ticks over fine at 1200 but only with a little choke after run. No choke and it stalls, cannot adjust idle screw to tick over still needs very slight choke. Initially I thought an inlet leak or slow run jet blocked but it ticks over nicely at 1200 rpm but only with very slight choke. Had carbs off again, tops off,  all diaphragms intact on splits,pistons rise and fall smoothly, checked all jets clear, no rise or fall in rpm if I spray carb cleaner on inlets or carbs.

Any Ideas ??

I have no problem running it with this small amount of choke but I'd rather sort the problem.

Thanks
           Steve.

[crickleymal]

First guess is either you have a leak around the new carb rubbers or the mixture is weak.

[HRHpenfold]

Did you check float heights?

[lzsteve]

Thanks for the reply's.
Yes I've checked the float heights, spot on. I agree it is probably a weak mixture but I'm satisfied the inlet rubbers are not leaking in air. However I've just noticed a piece of 4 into 1 tubing with a funny S shaped plastic bit in it on the bench, is this important ? Haynes manual doesn't say much about this and is only fitted to early models (mine's a 1993/1994) model).

Cheers,
Steve

[GAv]

It's probably a balancer system so equal amounts of air go into each of the 4 Venturis. I guess that may be the answer to your problem(I did wonder about that before you mentioned it,)however you haven't stated which model it is 6 or 900? Presumably it's a Divvie either way.

[lzsteve]

Hi gav, thanks for the reply. Trouble is where does it fit and what to ? (600s divvy by the way )

[bobh]

Is it for attaching vacuum gauges to synch the carbs? Also, are the vac gauge connections properly blanked off? If not, that would allow extra air in on tickover.

[lzsteve]

Thanks for the reply Bob.

I've found out that the hose with the S shaped plastic bit inside is actually a drain from the float chambers and it is not necessary.

Good suggestion about the vac guage connections I'll double check the screws are sealed and the pipes haven't got any holes in them.

Cheers,

[marshallman72]

Sounds like a weak pilot mixture to me. I'm guessing you have the Haynes manual already. You will need a gunsons colour tune to set the pilot mixture strength. A colour tune is a glass top spark plug which enables you to see combustion taking place inside each cylinder when the engine is running. Starting with no 1 cylinder, remove the spark plug and screw in the colour tune in its place. Start the engine and you will see combustion taking place. The colour you see should be blue like that on a kitchen gas stove. If the mixture is too rich it will be yellow. If its too weak the colour will be very light blue almost white. With the engine running turn the mixture screw on no1 carb a little each way and see the colour change. With a little choke on I'll guess its blue. Adjust the screw so that the colour turns yellow. Make a note of how much you have turned the screw and in which direction. Replace the spark plug and adjust the renaming 3 pilot mixture screws by the same amount. Turn off the choke and the engine should idle fine with no choke. A leak in the exhaust system may cause weakness but not hardly at all at idle.

[lzsteve]

Thanks for the reply Marshallman.

I've tried opening the mixture screws a little at a time but it runs rough after 3.5 turns out on each. Also at that setting Temp on the exhaust headers is down to 200C and still won't run without a little choke.I'm now pretty certain there is no inlet leaks or leaks from the vac gauge connections.Looks like I'll pull them off again and re-check everything.Anyone know of any cheap carbs going ?

Thanks to all.

Steve.

[HRHpenfold]

Did you blow through the passages in the mouth of the carb and take out the idle screw and blow through, and clean the end, and replace the o ring?

[marshallman72]

Probably a daft question but did you try turning the screws in rather than out? I think the standard settings are about 1 1/2 turns out. When I had mine dyno'd after replacing the exhaust system the dyno guy said the standard settings were too rich for optimum power so weakened off. The result is although she is 4hp better than before, she does take longer to come off the choke. The pilot screws are now 2 1/4 turns out, weaker than before. On that basis the screws need turning in to richen. I'm sure you'll get her singing good soon! Jon.