I know this has come up before, but I don't remember if we ever got a definite solution.  Cruising at highway speeds the bike will start to buck a bit like it is out of gas and needs to be switched to res, except I have a full tank.  Did it twice yesterday.  The first time I pulled in the clutch to lower the RPM and maybe let the fuel delivery catch up a bit, but it just stalled and I pulled over.  Switched to PRI for 30 seconds and then it fired right up.  The second time I decieded i would try to switch to PRI during the fuel starvation and teh engine evened out and I continued on my merry way.  
This leads me to believe there is a vacuum problem.  Is this just inherinet to teh bike or do I have a vacuum leak somewhere.

Thanks

Matt

I would assume it's caused by a block in fuel delivery.

Consider removing the tank and draining it.  Examine the components from the internal filter down into the carburetors.  If the problem persists, there could be an internal carburetor blockage likely requiring disassembly.

But hit the easy stuff first.  My 2 cents worth -- crossing my fingers for ya.

If it was a blockage in the fuel system, switching to PRI would not cure the problem.  But switching to PRI solves it which lead me to believe it is a vacuum problem.  PRI is gravity feed and the others are vacuum.  Am I right on this or am i totally missing the mark here.

matt

Quote from: Jasco.................. PRI is gravity feed and the others are vacuum.  Am I right on this or am i totally missing the mark here.

matt

My meager understanding is that in the ON position the engine vacuum opens the fuel valve to allow gravity feed to the carbs.  In the PRI position the vacuum valve is bypassed to allow fuel to flow to the carbs, engine running or not.

In both cases it is gravity feed.

Any engine gurus confirm this? :dunno:

Quote from: JascoIf it was a blockage in the fuel system, switching to PRI would not cure the problem.

Unless the blockage was in the ON hose circuit.  (As far as I know, the PRI setting pulls fuel through the RES hose.)

Quote from: JascoBut switching to PRI solves it which lead me to believe it is a vacuum problem.

You won't know for sure until you have tried running on RES after it smooths out on PRI.

Quote from: JascoPRI is gravity feed and the others are vacuum.  Am I right on this or am i totally missing the mark here.

Yep, that's how I understand it!

do you happen to ride with a tank bag....??

Finish that thought about the tank bag. . .

Quote from: Jake DFinish that thought about the tank bag. . .

It blocks the air entry via the gas cap. Especially those rubber bottom bags that seem to stick to the tank ... He ran his SV that way and had it die 30 mins from home. He waits 15 mins and it runs great again till it hits the 30 min mark ... However a CA tank I believe will take in air via that funky vent in it. You may be OK. But maybe that is blocked and the cap was the main entry point for air ...
Cool.
Srinath.

Same thing happened to me this Saturday, this is the first time I experienced this on this bike. I was doing 60, steady throttle, and she started hesitating, a little at first and then it got worse and worse. I totally forgot to switch to Prime, and instead proceeded to find a safe place to pull off and shut down. If the bike is fine everywhere, and there is a fuel delivery and a vacuum problem, what is happening? There is a few parts that use vacuum for fuel delivery. The vacuum actuated fuel selector being one of them. In the ON position the vacuum drawn by the piston opens the diaphragm in the selector to allow fuel past; when it's working properly. What causes the loss of vacuum? Does something (fuel?) block or clog the vacuum port from the left carb to the selector?

When I opened my gas cap I didn't hear the "whoosh", so for me, I don't think the vent is clogging temporarily.

The gas cap has an O-ring and is designed to be air tight anyway. . . and vent through the hose on the bottom/center of the tank.  Correct?  

When I read this post, this was my initial thought.  Correct me.

That's the overflow/tipover drain. The tank would still have to vent to allow fluids to drain. The gascap vents though...gosh, I don't know...I haven't looked at it!

ya what buda said
the tank vacuum locks
no air coming in as the fuel leaves causes problem


next time you ride and the bike stalls
quickly shut it off
remove helmet
open gas lid slowly and listen for a sucking noise

my SV tank was broke when i got it from PO
the tank drain under the cap was broken away from the tank
and was letting rain water in the tank
i thought that was weird.....
so i repaird it
and 30-45 min into a ride...it would fuel starve
if i WFO the throttle it would last an extra min or so before die-ing

it kicked my ass for weeks.
the last time i removed my tank bag i noticed that there was a perfect form of the cap on the bottom of the bag. and got the sucking noise.... I took a bandana and placed it between the cap and the bag and out to one side....never had the problem again

I've got a GSX-R cap on my tank (I think that is what it is from).  The seven bolt style.  Anyway, I think it fits tighter than the old GS cap.

I had a vacuum problem at the cap and it would make the highest pitch whine, like rubbing a wet finger around the top of a wine glass, except at like 96dB.  Pop the cap open, whoooooooosh!

Plus it would get a lean condition and start running crappy, no rev.  That is what I thought was the problem when I read this inital post.  And it is still my theory.  Even today.

Quote from: werase643ya what buda said

Duuuude Buda is just the way its sounds ... Buddha is the right way to write it  ... Buda = old ... Buddha =  enlightened ... OK Just nit picking ...
Cool.
Srinath.

No I don't have a tank bag.  It is n't a serious issue and I can live with it.  Doesn't happen everytime i ride, just everyonce and awhile.  Atleast now I know that I can switch ot PRI and keep going.

Later

Matt

Has somebody said to check your diaphragms yet for tears?  If not, check your diaphragms for tears.