Tank vent follow-up

Ped pedmail at dbmail.dk
Sun Jul 8 00:52:39 PDT 2007


Sorry that I didn't reply to your original message. I was away on vacation.

I had had exactly the same problems with symptoms of fuel starvation, 
especially after longer laps at motorway speeds. I used to lift the tank 
bag slightly as I thought it might restrict the tank vent. Sometimes it 
worked, some other times it didn't. Other times I turned the petcock to 
prime for a few seconds, then turned it back again. Sometimes it worked, 
some other times it didn't. However, I didn't consider the problem 
severe enough to really go into deeper investigation.

The inline fuel filter was installed shortly after I bought the bike as 
new back in 1997. It was a glass type of filter - the only filter I 
could find with 10 mm pipes. A no name filter. At a motorcycle market 
this winter I found another no name glass filter, slightly different but 
also with 10 mm pipes. I thought it might be time to replace the old 
filter and bought the new one. Now the fuel starvation problem seems to 
have gone completely. So you are right: The problem seems to be caused 
by a substantial restriction of fuel flow in some types of filters. A 
pity that these (cheap) filters come without any specifications at all - 
it would have been nice if there had been a standard for measuring the 
flow through the filter so that one could make a comparison. But anyway: 
Thanks for the info!

'96 "Black Stealth" GPZ

Larry Zoia skrev:
> Taking all advice into consideration with regard
> to my apparent fuel starvation issue, I decided to
> test the gas flow in the Prime position with and
> without the filter.
> I found a pint of Popov vodka in a plastic bottle
> and drained it.
> I disconnected the gas line from the distal end of the
> fuel filter, turned the petcock to prime and let the gas
> drain for 15 seconds.  It yielded a quarter pint.
> I removed the filter and placed the fuel line in the bottle
> and turned the petcock to Prime, expecting to leave it
> open for 15 seconds and compare volumes.
> In approximately five or six seconds the bottle was overflowing.
> Apparently the gas filter was causing more than substantial 
> restriction of flow, thereby starving the carbs
> upon sustained high-speed riding.
> I had it installed correctly.  It's a glass type filter. I've
> spliced the gas line together with no external filter for the time being.
> Larry in Michigan

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