Flow issues with '92 GSPD tank

[DonW]

Hi all, Thanks for all the conversation. I didn't mention in the original post that I did the "flow test" with a pretty low tank- about 2 gallons left. That said, it was a "static" test, and I do wonder what other factors come to play while actually riding- vibration, incline, tilt, heat, etc. I also didn't mention that I very recently cleaned the filters and petcocks, and have cut down the reserve tube on both sides. If the problem persists, I might swap on one of my spare tanks, a stock R100GS unit.

I'm going on 200 mile ride today, just filled the tank, and will see what happens.

[daz]

The antique tractors that I used to restore had three fuel filters. One on the petcock, one on the sentiment bowl, and one on an elbow that screwed into the carb. You would not believe how much was spent on ignition parts and carburetor parts before someone would do that simple test to figure which filter was clogged. Duane, you are one smart cookie.

[DonW]

Update- The bike ran with no stumbles for the first 165 miles yesterday. Cool morning, mostly flat and easy riding (with a group). Then, on the way home (riding alone, and faster) I got that "running out of gas" hesitation. It was warm (the bike had been running for about 15 minutes), I got on the freeway going uphill on Hiway 17 leaving Santa Cruz, and with pretty wide open throttle, it started to sputter. Switching to reserve seemed to cure it, but then the sputter came back. (It occurs to me that when I switch to reserve, I also slow down and use less throttle as I'm moving petcocks). Engine keeps running, just seems to be missing. Slowing down seems to cure it (maybe refill the float bowls??). Rode easy for a minute or two, problem solved. All good for another 20 miles, then it returns. DAMN I hate intermittent problems!!

Got home with 200 miles ridden, and drained the tank- about 4 gallons left. I've switched tanks (and therefore filters and petcocks) to one of my stock GS tanks. Will see if that makes any difference...

[Bamboo812]

Classic symptom of fuel starvation at WOT. Did you adjust your floats yet?

[Kurt in S.A.]

Sounds like the early riding was more sedate while the latter riding was more aggressive, "pretty wide open throttle". I've not been following this completely, but that basically sounds like a lean float setting or a fuel flow problem. On high demand, the fuel can't get into the bowl faster enough or the float setting is too low. A low float settings is more difficult to pull up into the throat than a higher setting. Switching to reserve creates more "head" on the fuel column, therefore pushing the fuel a little more down the fuel lines. Then you slow down and things are OK? Less demand, the bowls are able to fill up enough to keep up.

You may have both things going on.

Kurt in S.A.

[DonW]

Noooo, not yet. Will do today. Another factor in this formula is the frontal area of my GSPD. The model probably has the largest, least aerodynamic front of any of the airheads, and I've made it worse with a 24" windscreen. Pushing a lot of air will take more horsepower. Sure is nice to ride though...

[DonW]

Jeez! Why didn't someone mention adjusting the floats?? Anyway, thanks Bamboo. The right side float was WAY low, and the left looked OK (parallel with the carb base, and about 24 mm of fuel from bottom of bowl). Heading out for a ride to test...

[Bamboo812]

No applause, just throw money! From the old saying, "Strippers work for the money, but burlesque dancers do it for the applause."

[DonW]

Clap clap clap... And, I owe you a beer. Come to the Manchester Airhead Campout next weekend, and I'll pay up.

Just got back- 80 mph, 5K RPM, pretty good headwind, slightly uphill, full windscreen and elbows out.... no sputter. Even left one petcock closed, the other on "on", not reserve. Will ride to work tomorrow which is when it has happened in the past... hoping.

Also, smoother idle, but not sure it's related.

Thanks again, to all.

Don

[robert]

Check your float adjustment; wide open throttle can lead to fuel starvation if the bowls aren't full enough.

Post #2. Aparently you missed it.