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Me again – the one with the noisy 400/4. Mechanic got it quiet but it still has a very poor pull away and wont tick over less than 2k. It then gets a bit vague here – The bike then starts loosing revs whilst on tick over and then finally stops. Takes messing with the tickover/air screw to get it going again, and then repeat above! Mech suspects an air leak posibly from the stubs. Also we know the motor has been bored to first o/size. Anyone with any ideas – If its down to the rebore do we lift the needle? / adjust floats (if so how much) or does it all sound like an air leak to you guys? All advice appreciated.
Sounds like an air leak to me as well.
A good way to check is to get it running at what ever speed then spray where you suspect the air leak to be from with (a little) WD40. The engine note will change when you find the air leak.
Be carefull about spraying WD40 around exhaust – might be wise to have a fire extinguisher handy.
Good luck let us know how you get on.
It may be worth going back to basics. Timing, plug gaps, plug condition (check health of each plug’s spark visibly by grounding to engine), mixture and balance of carbs.
A visual check of the likely culprits for air leak would be useful too as would an inspection of the carb diaphragms. Does it feel like it’s running on 3 cylinders when riding (or revving to say 3000rpm and holding it there if you can’t ride it)?The ironic thing is once the revs were up it ran OK. 2.5 – 3k onwards… We’ve changed the stubs and the O rings but as per your last line are starting to suspect something more fundimental . It has Boyer Bransden ignition on it. The battery is getting 12.5 v and the coils get 11.5. Not too sure if this is pointing to the regulator or the rectifier. Generator is putting out 17-18v and the plugs get very sooty. It has also now taking to back-firing Getting to the “sod it – break it and sell it” stage now.. New exhaust system, timing chain da de dah ..lady owner, etc
I think that would be the rectifer, but could be wrong as I am electrical numpty
Do you have a standard exhaust and airbox fitted to the bike?Yep brand new OEM system.
Will give your suggestion a try – Its not like its not cost me anything so far [
] !, Electrics and me dont get on either -Anything I can’t see is evil!Battery when running the engine should get a bit more than 12.5v usually. Expect to see around 13 – 13.5v. If your battery is flat then it may be ‘dragging the engine down’ with it. You could try a known good battery, even a car one with jump leads, just to test.
Dead cells on batteries give some weird faults.
17-18v output also sounds a bit high unless this is without a load on it, ie battery disconnected.Think that the sooty plugs are your best clue here though. If they are sooty then the fuel mixture is definitely suspect. Clean them up, ride the bike a bit, do a ‘plug chop’ and pull them out again. If they are still sooty then get your mixture sorted. You’ll never tickover correctly without the right mix.
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] !, Electrics and me dont get on either -Anything I can’t see is evil!- You must be logged in to reply to this topic.