OK here's the problem bike starts lovely and runs very well then after about 3 mile she starts missing, appears to have a fuel starvation then cuts out. I then have to leave the bike until it cools off completely before it will start again bike will not start despite godd spark fuel etc. I have changed the coil and condensor, no joy, its not fuel starvation and I have got a good spark on both cylinders, with fuel showing on the plugs when removed.

I would be grateful for any ideas on what to check next. please help!!.

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Honestly officer I WAS only doing 60

Possibly weak battery. When you shut the bike off it builds back up enough to start again.
Measure battery voltage with lights off. Should be about 12.5 or so. Turn lights on for two minutes. Should stay above 12. If not battery might be going bad. How old is it.

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Htown16, Houston, Texas
1978 T140E Bonneville, 2004 XL 1200R Sportster

Everything will be alright in the end.
If its not alright, its not the end.

Please state the age of teh bike, in particular I need to know if your bike has a distributer behind the cylinders or a twin coil /twin points setup in the timing cover.

For a bike to stop, both cylinders need to stop working. The common thing is carburetter and this is classic air vent symptoms. try riding with filler cap loose or even off. Plugs being wet is no proof the carburretor isn't running low on fuel. it just means it failed to light. Alternatively, the bike could be gassing up, maybe the choke is on when it should be off, the fuel level is too high, broken or missing carburettor needle or main jet fallen out.

You say you changed THE coil, so I am assuming distributer.
Check that the distributer cap is clean and dry and also the the carbon plunger inside is free to move and is contacting the center of the rotor arm. Clean the contact s where the rotor arm meets metal in the cap. also clean the rotor arm ( centre and outer edge). Failing that fit a new capacitor and plugs, I have known plugs to fail when hot and to fire fine outside but not inside cylinders, but is unusual to get both stopping. Check also the HT lead coming from the coil to the centre of teh distributer, in fact change it. Fit known good stuff, or as second best new parts.

as a final grasp at a straw... check your tappets are not too tight

well, a final final grasp.. you are turning to 'ign' and not 'emg' arn't you ?

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A wise man learns from his mistakes..
A genius learns from other peoples mistakes.

Panda yes I am turning to ign, the bike is 1960 model with single carb and 6 volts battery is good. Not too much fuel and I have tried with the fuel cap off, remember the bike will not re start until it is stone cold. Battery is good and holds charge well. It has a single coil and single points setup, i have checked and cleaned the distributer arm and cap HT lead is fine.

I have thought it might be a valve gap problem or possibly tappits ie as the bike heats up valves expand and close off iether input or exhaust ports, once bikes cools right off valves contract and bike starts fine again. Is this possible? I just don't know enough.

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Honestly officer I WAS only doing 60

Faulty coils can work okay when cold, then the windings open up as they heat up, causing the engine to die.

Often will not "fix themselves" until totally cold where the material between the windings can conduct once again.

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GrandPaulZ
Author of "Old Bikes"
Born Again Bikes
My Photos

GP is correct, but you said you changed the coil and have good spark........

There is a possibility of corrosion under the points plate. When cold it conducts ok but not so hot, as teh rust forms a sort of temperature sensitive diode. Take the pints plate out and clean out in there. check also the ground connections of the points. Spray the distributer cap with wd40, there may be tracking going on, make sure the distributer cap is clean and dry inside.. make sure no black lines going anywhere.

Re the tappets... when the bike stops check via the kickstart that you have good compression. When hot the kickstart should just about support your body weight on either compression stroke.

Tell us what you find ...

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A wise man learns from his mistakes..
A genius learns from other peoples mistakes.

Hi

My 60 5TA did something similar on one occasion and it turned out to be a dodgy battery. Mind you mine did misfire a bit just before it stopped

clutching at straws list
is the tank breather blocked?
points closing
sticky carb float

sorry i cant be more help

clive

Thanks for all your suggestions, luckily the dealer I bought it from has taken it back and it will go into the workshop for repair before it's returned.

Most of the possibilities highlighted have been checked and discounted, ie new battery holding its charge and charging well, good clean distributor cap, rotor arm clean, points good and properly gapped, fuel cap breather not blocked, earth's checked no apparent problem. Loss of compression was apparent when trying to restart prior to the engine cooling, did I mention that before?

I'll let you know what was wrong when I find out.

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Honestly officer I WAS only doing 60

Originally Posted by RDE

Loss of compression was apparent when trying to restart prior to the engine cooling, did I mention that before? I'll let you know what was wrong when I find out.

No you did not It will be too tight tappets setting... maybe now valves burning a bit also

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A wise man learns from his mistakes..
A genius learns from other peoples mistakes.