That's right, folks.  As I've mentioned to you in the past, I got around the problem of my bike starving for fuel at high speed by riding it on prime, then returning it to reserve or on after I shut it off for safety.  I didn't mention that I have been putting 2 ounces of Marvel Mystery Oil in my tank after I fill-up since I bought it last June.  I've been using MMO in other vehicles for 30 years.

Well, now it's spring again, so I'm riding again.  I decided to wring it out to see what it'll do  and forgot to put the petcock on prime.  It was left on reserve.  Well folks, the problem is gone!  The vacuum operated fuel valve is opening all the way so the engine is no longer starving for fuel at any speed.  I made 3 high speed attempts to make the fuel starvation problem return, including a 3-mile run at 90-100+ mph.  I was not successful. 

Awesome 

The fuel starvation problem is likely most noticable at low RPM and higher engine loading, like puttering about in slow traffic on hilly roads.  I imagine it could also be more likely with bikes that have been sitting with dry gas tanks where the rubber dries out a bit -- your fuel or MMO may h ave make the valve parts more supple.

prs

Quote from: Pigeonroost on March 21, 2009, 09:18:41 AM
The fuel starvation problem is likely most noticable at low RPM and higher engine loading, like puttering about in slow traffic on hilly roads. 

Um... Not in the GS.. its most common a Carb or petcock problem, usually over 50Mph at a sustained speed.

My guess is that it cleaned your carbs.. You could have taken them off and done it... Some try seafoam and have similar results.

Scott, it's the petcock I'm talking about.  It's a vacuum-operated valve unless you set it to PRI.  Didn't you read what I wrote?  If I left it on prime the problem would never occur.  If I rode on RES or ON the bowls would run dry at high speed.  The problem is now gone, and my carbs were clean to begin with.  The bike would always run fine at 70 for extended periods on the highway.  Dirty carbs won't allow that.  The problem would never occur unless I was doing at least 90 with the petcock set somewhere other than PRI.  We don't have any long, steep hills where I live, or I likely would have noticed it under those conditions as well.

Quote from: bill14224 on March 22, 2009, 06:45:03 AM
Scott, it's the petcock I'm talking about.  It's a vacuum-operated valve unless you set it to PRI.  Didn't you read what I wrote?  If I left it on prime the problem would never occur.  If I rode on RES or ON the bowls would run dry at high speed.  The problem is now gone, and my carbs were clean to begin with.  The bike would always run fine at 70 for extended periods on the highway.  Dirty carbs won't allow that.  The problem would never occur unless I was doing at least 90 with the petcock set somewhere other than PRI.  We don't have any long, steep hills where I live, or I likely would have noticed it under those conditions as well.

dirty carbs usually have trouble at idle, or slightly off-idle conditions. WOT conditions usually show petcock problems, ya, but dirt = poor lower speed (engine) conditions.

you can do the JBWeld thing (there is a thread here somewhere) about how to do it, and turning the petcock into an ON/OFF setup. it means you'll never again starve your bowls. Provided your float height is right, it won't leak down into your engine when the bike is off either. Remembering to turn to OFF isn't that big a deal. Habits are formed quickly, and last long.

I have not run any Marvel Mystery Oil or Seafoam in mine, but my petcock issue only rears its ugly head in windy high-speed conditions.  Since I live and do most of my riding in the plains, wind is a frequent issue!

A few things have lessened my petcock issue.  One is valve adjustment.  I theorize that engine vacuum is increased with better adjustment.  Another is being sensitive to throttle position in sixth gear.  I downshift a little more frequently than I used to and the problem is lessened. 

With those minor adaptations, I only have to run in PRIME about 10% of the time.

I don't have any idling or low speed fueling or ignition problems.  Never did.  The problem WAS my fuel valve.  I love how that sounds in the past tense... WAS!     My bowls would never run dry unless I was doing over 90, and riding in the prime position prevented it from happening, which is why I was in no hot hurry to fix it.

I didn't change anything mechanically on this bike.  I took the tank off and looked everything over, looking for cracked hoses, dry rot, and the like, missing hoses and/or buggered-up modifications, and found none.  There is no evidence of dry-rot anywhere on this bike.  Not surprising, this is NY, not NM!  Checked the fuel filter, still clean, no rust in tank, removed the carbs, took-off the bowls and they were clean as a whistle inside, noticed my stock carbs also still have the plugs in, so I put everything back together.  That was last summer.  Then I began to ride on prime to prevent my bowls from running dry.  Last week I began riding again and forgot a few times to put it on prime.  Then I realized the problem was probably gone so I took it up to 100 a few times and sure enough, it is!

It's true you use more fuel when accelerating from a stop, but you don't do it for enough time to allow the bowls to run dry.  For that happen you have to be climbing a long steep hill, which we don't have here, or running flat-out, with a fuel valve that's not opening all the way, or poorly adjusted floats.  My float bowls are fine, and the bike runs like a top.  Some of you sound disappointed!

Trumpetguy:

I hear you on windy conditions!  I happen to live in the windiest city in the United States!

Quote from: bill14224 on March 22, 2009, 11:27:09 AM
I hear you on windy conditions!  I happen to live in the windiest city in the United States!

But do you have over 100 giant wind generators within a 10 mile radius of your house?  I do!  Another windfarm an hour north and another an hour south.  Yes sir, it's windy out here in Western Oklahoma.

And, I always thought it was crosswinds sucking the air out of the floatbowl vent hose, thus removing the atmosphereic pressure from the bowls.

Whenever I have a hesitation, I notice the wind is coming from my right, and whenever I shift back my left foot on the peg, the problem goes away.

Hi Scratch:

If there was enough crosswind to suck air from the carb vent tube, it would reduce air pressure in the bowls, yes?  That would cause gas to flow into the bowls more easily, not harder.

Yes, but the lack of pressure in the floatbowl would not "push" the fuel into the venturi.