Fuel starvation feel when low on fuel

[mentalshark]

I bought a dead 04 GS500F and with a lot of help from this forum, I have fixed most of the problems and I am now starting to ride it daily. I have recently just passed my road test with it too.


The only problem I have with this bike right now is that it died once when I was on the highway. when I gave it throttle the rpm dropped till the engine died. Turning the petcock to prime and reserve didn't change anything. there was still some gas in the tank at that time. eventually, I realized the bike would run when the choke is on, except the idle RPM stays at 4k. I rode the bike to the closest gas station(about 3km) and fill it up, and all problems go away. What could be the possible causes here? is this a fuel starvation problem?

[The Buddha]

Yea we routinely try to run our bikes without putting gas in it too.
Somehow most of us are smart enough not to boast about what happens after that.

Cool.
Buddha.

[mr72]

Buddha I think you missed where he put it on RES and it didn't fix itself. And it wouldn't run on choke if it was out of gas.

My guess is that when the fuel gets low enough, junk in the tank gets past the tank filter screen from the reserve pickup and clogs the pilot jet. You refilled it can pick up cleaner fuel from higher in the tank. You might even have junk in the reserve fuel line.

If it was me, I'd do this, which is worthwhile anyway:

1. pull the tank off. Drain the gas, take the tank petcock off, check/clean the screen, and flush/clean the tank.
2. pull the carbs off and clean them with the prescribed process, you can check my signature for a link that might help
3. replace all of the fuel lines and vacuum lines when you put it back together. Be sure the vent is facing rear.

Then when you put new gas in it, be sure you are using ethanol-free fuel, and I'd put some Seafoam or B12 or some other carb cleaner additive in it to run the next tank of gas.

[The Buddha]

Maybe the fuel filter in the tank has been installed backwards.
BTW I run it in reserve, and I fill at 100 or close enough on the trip and reset it every fill. So all these reserve etc etc makes no sense to me.
Cool.
Buddha.

[mr72]

Maybe lines reversed at the petcock. Either way, good time to service the whole system.

BTW with the '04 tank, I routinely go 150 miles before refilling. Only ever had to use reserve twice.

[HPP8140]

^ that doesn't sound like mileage for stock bike jets

My E style tank bikes went ~150 before reserve. My 02 Can go ~220 before reserve

[mr72]

well that sounds odd. I guess my 14t sprocket has something to do with it?

I have 125 main jets, '04 tank should be 4.5 gallons. Reserve is about 1 gallon. I am getting about 150 miles or more on 3.5 gallons which puts the mpg in the 40s. I calculated as high as 51 once. 220 miles on 3.5 gal before reserve would be 63mpg. That's pretty freaking high. My wife's 125cc scooter barely gets that.

[mentalshark]

It is totally possible that the lines were reversed... but why would choke help in this case?

Maybe lines reversed at the petcock. Either way, good time to service the whole system.

BTW with the '04 tank, I routinely go 150 miles before refilling. Only ever had to use reserve twice.

the bike came with gas in the tank, and I have ridden on this bike for about 400 miles (650km), I fueled it up twice, which sounds about right.

[mr72]

the choke working, TO ME, makes it feel like a clogged pilot jet. The "choke" actually opens an extra jet. Pilot jet can be completely clogged and it'll still run on choke.

That's why my theory is that junk is getting into the pilot jet through the reserve fuel path and it gets washed out miraculously when you switch to non-reserve. But that theory is very limited in its validity. I would still do a fuel system service and carb clean just to rule all that out at least. And if something is installed wrong, you'll discover it.

[The Buddha]

The choke sucks through the pilot atleast in the 89-00 carbs.
So does air screw passage.
However pilot being free (unblocked) but air screw passage downstream of pilot jet can be blocked, especially with rusty tanks.
Then the choke which pulls through the pilot but not the rest of the air screw passage will supply fuel where there was none without choke.
Cool.
Buddha.

[mr72]

choke is an extra jet on the '01+ carbs, right? this is an 04.

Anyway. like anything else with the carbs, the right fix is to just clean everything, replace all of the rubber parts, and reset to known good condition.

[The Buddha]

Choke sucks through the mid mains on the 01/02 - I just checked the one I got sitting around.
Let me see if the diagram shows something else. If a diagram is even available.
Cool.
Buddha.

[mr72]

Right on. So choke makes it work could mean clogged pilot jet. Esp. on those bikes with teeny pilot jets. I'm always shocked they could be not clogged.

[The Buddha]

Right on. So choke makes it work could mean clogged pilot jet. Esp. on those bikes with teeny pilot jets. I'm always shocked they could be not clogged.

Yea and when you open the carbs, they look bluish and have a weird gel around them. They sure FIXED what wasn't broken.
Cool.
Buddha.

[mentalshark]

Alright! Tank coming off again! Thanks guys!