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Sudden partial power loss - bitten by vapor lock? Petcock flow rate on reserve?

roeme

roeme

Forum Mentor
Past Site Supporter
Just recently I lost a fair amount of power on the highway, again.

Some power losses could be chalked up to the wind, some to running out of gas. However, the last time I switched over to Reserve, she still had problems to go above 6 rpm (5/6th gear, at around 120km/h).
Had this issue already once, but wasn't too sure if I was just imagining things.

Now, the questions are; is it possible that the Petcock flows less on reserve, with low gas remaining in the tank? Or is is possible that the carbs sucked in vapor prior to running out of fuel on the regular setting, and
then have a hard time providing a proper mixture?

Unfortunately I don't have a transparent fuel line on this bike, so I couldn't check.
 
It is good that you DON'T have a transparent line, unless you are willing to change it often.
All of the transparent lines I have seen get hard rather quickly, making it difficult to remove the line to do any maintenance and even more difficult to get it back on and sealed.

Vapor lock? Highly unlikely. Vapor lock happens when fuel turns to vapor, which the fuel pump can not pump to the carbs. Our "fuel pump" is gravity, which has not failed in recent memory.

Yes, it is possible that flow might be reduced on PRIme. Remove the petcock from the tank, inspect the filter, see if it is blocked at all. The REServe portion draws from a lower area on the petcock, there might be something blocking it, while still allowing full flow to the upper tube that supplies the RUN function.

.
 
Thanks!

If I'm going to take off the petcock, is there a gasket or anything I need to replace in any case? Whatever I'm going to find, I'd like to be able to put the petcock right back on, the weather has really cleared up these days :cool:
 
There is a rubber "gasket" under the petcock. Would't be a bad idea to replace it. Look at a parts fiche for your bike to get the part number.
 
There are also two special washers under the bolts holding the petcock to the tank. These washers have a rubber portion on the inside of the washer, to prevent fuel from leaking down the threads of the bolts. The parts fiche also shows these washers.
 
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