too hot, cuts out

[blacklav]

Hi all. My xs D model has started to cut out, it happens when ive been for a ride and then have to idle in traffic for a while ( getting very hot ). It will not start again for about 20 seconds and then its fine. Its done this the last three times out and always on a hot day. Now ive checked the ignition wiring for any loose connections that could seperate due to the heat and all ok.
Someone suggested its the fuel evaporating in the carbs. It certainly seems like a temporary fuel blockage, but why would it happen on both carbs at the same time?
If its evaporation, surely the fuel would instantly refill the carbs from the tank as the floats go down, or am i missing something about the workings of the carburetors.
Any suggestions appreciated.

 

[RustiePyles]

Is your cap venting? Try opening the gas cap next time it does it. Also could be a vacuum issue, try turning the petcock PRI next time and see if that helps.

 

[blacklav]

Thanks for the reply.
Tried that, it only does it on idle not when riding. There isn't a prime on my taps, just on and reserve.

 

[RustiePyles]

What's your Idle set at? these bike dont really like anything <1300rpm

 

[blacklav]

About 1100. Only does it when the weather is really hot. I've left it idling in the garden for 10 mins on a cooler day with no probs.

 

[gggGary]

If they are "vapor locking" Try full throttle for bit while cranking. a vapor lock is pretty much like a flooded cylinder the fuel vaporizes and displaces all the air so no combustion can occur. WOT will pump the vapor through, let in some air. Typically normal starting throttle, ie just a bit above idle, then slowly go to WOT, crank for a few seconds then back to normal starting throttle, try again. Lot of times the motor will catch as you open throttle,
This could be a sign of leaking float valves or high fuel levels in the float bowls.

 

[Paul Sutton]

When I first added an inline fuel filter the extra tubing was closer to the engine and the line would vapor lock. Petrol starts forming vapor bubble at about 30 - 40 Celsius. I had to relocate the filter and fuel lines further back to solve the issue.

 

[Paul Sutton]

Forgot to mention the vapor lock was particularly bad where the tubing made a U bend down then up to the carb T connector between the BS34s (81SH). So try to keep the tubes as direct as you can to the carbs.

 

[blacklav]

Thanks Paul. All the tubes run down wards so no air block and are away from the heat.

 

[blacklav]

If they are "vapor locking" Try full throttle for bit while cranking. a vapor lock is pretty much like a flooded cylinder the fuel vaporizes and displaces all the air so no combustion can occur. WOT will pump the vapor through, let in some air. Typically normal starting throttle, ie just a bit above idle, then slowly go to WOT, crank for a few seconds then back to normal starting throttle, try again. Lot of times the motor will catch as you open throttle,
This could be a sign of leaking float valves or high fuel levels in the float bowls.

Thanks Gary I will check the float levels.