Just finished rebuilding my 1964 B40B SS90 and got it running. All seems well except the idle speed seems to vary and is difficult to set.
This engine has the 10 degree advance plate and I've timed it as per the service sheet at 5 degrees BTDC fully retarded (or pretty close).
The carb has been completely dismantled, cleaned throughout and reassembled by me. I've used new fibre washers but kept the jets and needle that were there. They may be original but I can't be sure.
Pretty sure I have no air leaks.
The bike starts OK with the pilot screw 1.5 turns out but idles unevenly and is slow to return to idle after a 'blip' even though the cable is slack. I'm pretty sure the slide is not sticking and is sitting tight on the top of the idle adjuster screw.
Turning the pilot screw in results in a faster idle with it fastest at about 3/4 turn from seated, but still the idle speed varies when left at tickover for no apparent reason.
I'm currently running without an air filter - mainly because I haven't got one yet!
It may also be running a bit hot as the new exhaust is already staw coloured at the head after about 10 mins running on the stand.
Any thoughts on the cause or what to check please?
Thanks,
Bernie
My new exhaust downpipe turned a straw colour very quickly after the engine was rebuilt. I think it is pretty much normal for it to do so.
I also had to set my idle to a "fast idle" to stop the engine from cutting out if left to idle for long. I did change the advance springs in the distributor ( early B40) which did help but it will still cut out when left running after a while. I also have a brand new Amal monobloc fitted so was confident it wasn't the fueling. I have not done many miles on mine yet so am hoping that the idle issue will improve as the engine loosens up.
As you know from my previous posts about the C15 rebuild I carried out, I could not get a good tickover with either brand new Monobloc or new Concentric, changing the jets etc. In the end I bit the bullet and installed a new OKO carb and all my problems were gone. I took it out last night for a couple of hours and it never missed a beat, it was a pleasure to ride around the lanes even in 4th doing 30mph without it missing and coughing. I've always been one for originality but this one beat me, but I'm not fussed anymore, I just wanted a bike I can jump on and ride.
do you have enough of an insulation plate between head and carb, if its getting too hot it may be due to running on stand as road use will help keep temperature down.
straw colour usually a sign of weak mixture, or excessive air mixture, of course, could be a thin walled exhaust pipe
Can you time the bike with a strobe to make sure if timing?
With regards to carb. Mine took a bit if ine adjusting to get to a reasonable tick over. The methos I used was get bike running and warmed up. Adjuat the pilot screw to get tick over as fast as possible. Then adjust throttle stop to slow it down. The repeat cycle two more times. Pilot as fast as it will go. Stop as slow as it will go.
Thanks for your replies.
I'll see if I can make up a strobe to check the timing - it's interesting that on this model the service sheet specs it at 5 degrees fully retarded when mostly the specs are for fully advanced.
I was also wondering if a worn slide might cause this although visually it seems pretty good. If uneven tickovers have been experienced with new replacements then maybe I'll look for other solutions before resorting to that!
Cheers,
Bernie