erratic idle?

My bike idles fine – smoothly at 1000rpm – when I start it and for the first half hour of riding, but when it gets really hot, esp after open road riding the idle becomes erratic ranging quickly from between 500 – almost 2000rpm. What causes this? Is it to do with my ignition? I'm running a Boyer.

Headfullofsnakes said:

My bike idles fine – smoothly at 1000rpm – when I start it and for the first half hour of riding, but when it gets really hot, esp after open road riding the idle becomes erratic ranging quickly from between 500 – almost 2000rpm. What causes this? Is it to do with my ignition? I'm running a Boyer.

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Might help to list your carb types.

My first vote is carbs heat soaked to expand for slide air leaks. If you can cold start w/o choke of heavy tickle then suspect too rich a tune state. Could be heat increasing resistance to smoke volts to what ever ignition system you have. If it was mine it'd usually be both at once. Once in a while it can be spark plugs.

Sounds like some air gettin there. Check the manifold mounting fastenters. Neither too tight not too lose.
While yer at it, check yer voltage.

... and make sure the float bowls on the carburetors are cinched up



Tim Kraakevik
kraakevik@voyager.net

Oh yeah had that happen this year. How soon we forget ugh. On that note better make sure you have a screw driver that can reach the top screws as well as bowl screws in the tool kit. There is no other screws on bike to steal if float is found hanging by a thread. Check carb head fasteners too of course.

With a Boyer you'll chase the idle around forever. A Tri-Spark ignition cured this with all else the same. Mikuni VM 34 fitted.

way 2 much over analyzin

i think the clue that the bike runs good @ start up and then not so much when warms suggests carb adjustment problems - sound 2 rich -

read/search about carb adjusting and learn about your bike - pilot screws need to be turned in proper direction - needles maybe -
there are a shit=load of bikes w/ boyers and amals that rubn OK - start small - work up
also looking at photo - did you miss burning man festival (thats a joke)

Clapped out Mk 1 Concentrics with the choke mechanisms still in ? ?
Viton tip float needles mandatory for regularised behavior .We could go on . :wink:

Ok ok... single Mikuni. I've been having other electrical problems so was just wondering if this was related. Those problems seem to have been fixed though, so I'm thinking after reading this that i need to look at the carb. I'm a total amateur, but into learning and getting my hands dirty. Will pull the carb off, read up, and strip it to see what's fuckin what anyway!

Headfullofsnakes said:

............. I'm a total amateur, but into learning and getting my hands dirty.............

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good! your on your way to becoming able to sustain your Norton -

turn a few nuts here and there and you can start making post like some of the experts here! :mrgreen:

Fullauto said:

With a Boyer you'll chase the idle around forever. A Tri-Spark ignition cured this with all else the same. Mikuni VM 34 fitted.

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I'll second that statement, trispark (with twin amals) on mine now. Sorted.

We all assume you keep your battery fully charged, very important with any electronic ignition.

Single Mikuni should idle perfectly all the time, assume you have everything set up as recommended, needle in middle clip, jet sizes correct, etc.

Assume the cable is not kinked or not fully seated in to the top of the carb body, and that there is no looseness in the threaded cable adjuster up near the handgrip.

Assume you have a #35 or 40 pilot idle jet in there and that the air screw on the side is set about one and one quarter turns out from fully seated.

Assume you do need to depress the choke lever to start from cold, and that you immediately pull the lever up as soon as you are started and control a very brief warmup with your throttle hand.

All above checked and ok, then I would take the tank off and take the carb off and check everything listed above, then take the fuel bowl off the bottom and see if any bit of grit is stuck anywhere, maybe blow out everything with carb cleaner and compressed air, and report back!