Quote from: Kerry

Quote from: FlashI removed the other P.O.S. petcock (On/Prime/Reserve) and all the vacuum tubes and put a straight fuel line to my carbs. That is how I know the fuel tank petcock is to blame.

Somebody said something the other day that gave me a new perspective on the whole fuel starvation problem.  The gist of it was something like "When the throttle is wide open there is less of a vacuum to operate the ON/RES diaphragm in the frame-mounted petcock".

If this is true, then the following may NOT be true:

1) The tank-mounted petcock simply can't pass enough fuel through.
(Flash, you removed the vacuum system along with the tank-mounted petcock, so how do you know for sure where the problem was...?)

If the fuel from the tank-mounted petcock was able to keep up & the problem was inside the carbs (i.e. float bowl), then wouldn't my fuel line from the tank to the carbs be totally filled with gasoline? What I actually observed (via the clear fuel line) was the meniscus would actually travel from the top down. Wouldn't this mean the gasoline could not get down fast enough?

2) The hoses have a too-small inner diameter to satisy the high-speed fuel demands of our rip-roaring 487cc twin.
I replaced mine with 5/16" ID clear-vinyl tubing from Home Depot; I'd go bigger, but it would be difficult (if not impossible) to affix it to petcock stem

3) The frame-mounted (ON / RES / PRI) petcock simply can't pass enough fuel through.
(It MAY be able to in the PRI position, which is not affected by the presence or absence of a good vacuum.)
I only removed the frame-mounted petcock, not the tank-mounted one. However, I was just thinking: would having the main & reserve stem connected to the carbs via a T-connector somehow be fighting each other? Should I try to cap one of them off? If so, how?
[/list:u]
Can anybody confirm the assertion that

WOT = significant drop in vacuum?[/size][/b][/i]

I don't think my throttle was totally wide open. Once it happened while I was in 5th gear & another in 6th gear (both while sustaining 80-85 on the speedometer; nothing excessively like doing 100mph)[/list:u]

Now, Ive gotten so paranoid I look down every so often while I'm riding to make sure the fuel line is totally filled with gasoline. So far, it hasn't happened lately.

Quote from: mp183You are right about varying the engine speed.  I do that as a matter of principal.  Cuts down on the boredom.  It's also the key to successful speeding on the Thruway.

yes, yes it is. :mrgreen:

Quote from: xaeniacSince the GS500 has a 10% speedo increase can you run the bike at 80-85 on the speedo (really ~75 mph)for about 1.25 hrs without hurting the engine in superhot  humid Louisiana weather?

I had the same question when I first broke my bike in. My brother (he's a mechanic) told me it shouldn't hurt at all.  He said you can run the bike at whatever RPM you want (under the redline) and it should be fine.  

Flash!  ("He'll save every one of us!")

Without re-quoting our conversation:

* Oops!  I jumped the gun.  Somehow I got it in my head that you had gone to a Pingel tank-mounted petcock.  :dunno:

*Are you saying that the changes you made didn't solve the problem?  That would explain your conclusion that the tank-mounted petcock was the major cause.

* It's interesting to me that the 5/16" line stays full better than the 1/4" line.  I haven't figured that one out yet.[/list:u]
Sorry for the confusion!

Quote from: KerryFlash!  ("He'll save every one of us!")

Without re-quoting our conversation:

* Oops!  I jumped the gun.  Somehow I got it in my head that you had gone to a Pingel tank-mounted petcock.  :dunno:

-- Boy, do I wish; a couple of members have gone this route, but its like a $90 upgrade

*Are you saying that the changes you made didn't solve the problem?  That would explain your conclusion that the tank-mounted petcock was the major cause.
-- No; so many people complained about the crappy fuel lines & frame-mounted petcock, so I replaced it (apparently it didn't help)

* It's interesting to me that the 5/16" line stays full better than the 1/4" line.  I haven't figured that one out yet.
-- Huh? I increased the ID so as to reduce any possible fuel restriction.[/list:u]
Sorry for the confusion!

No problem