New GS500 owner - fuel tap Question!

[DavidR]

Hey all,

Good to be with y'all, from rainy England !

I just bought a '90 GS500, mechanically perfect but a dog cosmetically.

I've just spent the last week and a half (about 14 hours total), painting the bike and she looks great now!

When the bike was delivered to be (from the eBay seller), it had very little fuel in it and the fuel tap was set to RES.

I filled the fuel tank to about 3/4 full and set the fuel tap to the main 'ON' position.

But the bike coughed, spluttered and stalled, and then would not start.

I suddenly noticed the PRIME setting, so I set this and bike started and ran beautifully (for a 16 year old bike).

However, after 4 miles I tried to set the fuel tap from PRIME to the main ON position but again, the bike refused to run and stalled as soon as I let the clutch out.

So....... at present the bike runs great in PRIME setting, but I figures I ain't supposed to leave it there forever!

So my question is, how long do you need to leave the fuel tap in the PRIME position, after an empty tank and subsequent refuelling ?

When should I be able to set the tap back to the main ON position, and have it run ok ?

I did try to search the forum and view the FAQ but this seems too simple a question and I couldn't find it covered!

Thanks so much y'all !




David R,
Durham,
UK

[Wrecent_Wryder]

G6

[DavidR]

Hi WW,

Thanks for that info - really useful !

I have just spent some more time on the bike and there definately seems to be a problem with the fuel flow when ON is selected, the bike is still coughing, spluttering and mis-firing in this mode.

However things improved a lot at the RES setting although the engine is still somewhat hesitant - contrastingly, as soon as I switch over the PRIME mode, the bike runs perfectly with no hesitation, just nice smooth power.

So I guess there is some problem with the vacuum system.

My next question is therefore, will I do the bike any serious harm (the bike was only $600 so minor harm is ok!), by running it in PRIME mode ?   

Thanks, 

Dave R

[pandy]

I rode my commuter GS for a year, and eventually I just figured that he liked to run in PRI best. He definitely had the fuel-starvation issue, so if we were hitting the highway, or if he coughed at any point, to PRI he went. I got VERY good at adjusting the petcock at freeway speeds (sometimes I'd forget to put him on PRI before getting on the freeway, but he'd remind me  ). When I parked him, I'd change the petcock back to ON. I had to be careful to know when to put fuel in, because running in PRI, you have no reserve. It wasn't that much of a problem for me, though, because my commuter GS would choke and sputter if I didn't fill him  up every 100 miles.  He was quite a character!

[DavidR]

Cool - thanks for that!

Yes, my GS is 16 years old, with 36,000 mles on the clock, and I think she also has a bit of a fuel starvation prob, so think I'll risk it too and run it on PRI, but turn to ON once the engine's off   

[MarkusN]

No problem having using the Petcock like that; it's just the way a traditional non-vac petcock would operate.

Two potential problems though:

You lose the Reserve warning. PRI draws from the  reserve hose, so when you run out of fuel you run out of fuel.

If the needle valve in the carbs doesn't close properly (quite common) and you forget the petcock in Prime the carbs will overflow when she is parked.

[Wrecent_Wryder]

b6

[mjn12]

I hesitate to mention it, but... as we've said, if the symptoms are similar in "On" and "Reserve" but clear up on "Prime", it's probably a problem with the vacuum line to the carbs or the petcock. However, if they really are similar on "On" and clear up on "Reserve" and "Prime", the simplest explanation is usually that the bike is just low on petrol. Is that a possibility here?

DavidR says the tank was 3/4 full.  If it didn't run significantly better on reserve I'd say the simlest explanation is already eliminated since res and prime draw from the same height in the tank.

[Toledo Jim]

Did he fill it till it "looked" 3/4 full, or did he he put in 3 of 4 gallons?

If he went by "looks to be 3/4" he may still be too low to run on "On". (don't ask me how I know.  )

Also, if the fuel lines from tank to frame petcock are reversed it may not work on Res. I would check that right after filling the tank up all the way.  (Where is that fuel hose routing diagram?)

Found it! http://www.bbburma.net/FuelHoseRouting.htm