1978 Bonneville T-140V

[Nige W]

The only way the timing can have altered is if you've moved the ignition back-plate or the timing gears. Seeing you only mention rebuilding the carbs and the top end it seems very unlikely that the timing will have changed. High revs are caused by a wide throttle opening (or, more correctly, a high volume of fuel and air getting into the cylinder(s))- either you have something holding the slides up (mechanical) or something else causing a high volume of fuel/air mixture to get into the cylinders. Wrong timing would give you a spark at the wrong point and lead to (most likely) a non-running engine. A big air leak on the intake side could create this problem as a weak mixture will push revs up (ever noticed how the revs rise if you run out of fuel?) - if you're sure cable routing/seating has been addressed then check the idle mixture screws... these should each be out one and a half turns for a datum setting. the new needles shouldn't affect idle speed as fuel is drawn through the pilot jets, not the mains - until the slides start to lift.

 

[Nige W]

Sorry - re-read your earlier post and noticed new float needles, not main needles. Badly worn slides will cause weakness, but this sounds quite dramatic in terms of revs. I still think that seeing you've had the carbs off that this is where your problem lies. Spitting can mean either rich or weak mixture so isn't definitive on its own. As a point of interest - if you've backed the throttle stops all the way out as you say, then the bike shouldn't idle at all! Are you totally sure that the slides are seating fully?

 

[The Seeker]

I too was going to mention an air leak in the intake side. Are the carbs mounted correctly and are the rubber intake hoses not ripped or the clamp not tight?

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