Fuel/carb? problem

[Nata Harli]

This one's got me baffled (doesn't take much, though).

I can be riding down the street with my petcocks in the normal position and the bike just quits on me, like it's just run out of gas. I turn my petcocks up to the reserve position and I can start it back up and it runs fine. This even happens with a full tank.

So, over the winter I emptied my tank and cleaned it out and installed brand new pectocks. But, I continue to experience the same problem.

I've opened up the gas cap so it is not sealed to see if that helps and it does not.

Don't know if this is relevant or not but the PO "rebuilt" the carbs last year. I picked up the bike in NC in the fall and rode it home. I experienced that problem all the way home.

Anyone got any ideas?

Thanks.

[ignatz72]

So the PO rebuilt the carbs, but have YOU?

Don't trust the work unless you paid for it or did it yourself. I'd say check the float levels and the float needles first.

But it's hard to say much else w/o knowing what bike you have...

[boxerboy81]

Floats came to mind, but also blocked jets. Easy enough to check.

[Stagehand]

Maybe the float bowls arent filling up fast enough, or keeping enough fuel in the bowls.

I would try and check the float heights if you suspect carbs. You can do some really rough checking with them still on the bike.


Edit: DAmn, you guys type fast! Hey I also only assume this is an airhead.

[mykill]

Originally Posted by stagehand

maybe the float bowls arent filling up fast enough, or keeping enough fuel in the bowls.

I would try and check the float heights if you suspect carbs. You can do some really rough checking with them still on the bike.


Edit: Damn, you guys type fast! Hey i also only assume this is an airhead.

+1

[Nata Harli]

Originally Posted by ignatz72

So the PO rebuilt the carbs, but have YOU?

Don't trust the work unless you paid for it or did it yourself. I'd say check the float levels and the float needles first.

But it's hard to say much else w/o knowing what bike you have...

Sorry, left out that info - it's a '92 R100GS.

The carbs were my first thought since I can tell from some other work done that the PO was definitely a "shadetree" mechanic.

I've thought about sending the carbs to Bing and have them rebuild them but for the life of me I can't make a connection between the bike not running when the petcocks are in the normal position/running when they are pointed to reserve and the carbs.

I'm not the most mechanically inclined person so could someone tell me what the relation is between the position of the petcock and the carbs?

Thanks to everyone for all the help so far.

[Stagehand]

say what? lol

In answer to your question, when the handle is down, they are in the nortmal running position. When they are up, you are on reserve. and when they are horiztonal, they are off.

[Renegade_Azzy]

Not familiar with the GS, but seen it on a few other bikes, are you confident in your fuel hose? Ive had them collapse and switching either jostles it enough or relieves some pressure to spring them back into shape.

[Nata Harli]

Originally Posted by Stagehand

say what? lol

In answer to your question, when the handle is down, they are in the nortmal running position. When they are up, you are on reserve. and when they are horiztonal, they are off.

I'm not sure what I said that indicated I didn't know that, but I am aware of that. Sorry for any confusion.

[Stagehand]

Originally Posted by Nata Harli

I'm not sure what I said that indicated I didn't know that, but I am aware of that. Sorry for any confusion.

Originally Posted by Nata Harli

so could someone tell me what the relation is between the position of the petcock and the carbs?

Sorry i got confused I thought that was the question you were asking, here.

OK, so what is it you are trying to figure out?

[mykill]

Do your fuel lines go directly from the tank to the carbs?
My California model GS has solenoids under the starter cover that shut off the fuel when ignition is off. Those solenoids might have a questionable electrical connection. If you do, bypass and go straight from tank to carb and report back! Now you will NEED to remember to shut off your gas when parked.

[supershaft]

I was getting ready to say ride on reserve all the time. The symptoms don't make any sense to me unless his new petcocks have the same problem his old ones did.

All US bikes had that setup. BMW Advised all non-Ca. dealers to disconnect them. They would often cause problems AND they are a huge drain on the charging system.

I not only disconnect them but I reroute the fuel lines the good old fashioned way and take out all that junk.

[ignatz72]

Well if you've got brand new petcocks with the straws in the correct holes (sounds like you might) then I would definitely check the carbs. Jets, needles, and floats. Dig in and clean it all with Berryman's carb cleaner. Replace any questionable looking jets, etc. and possibly the floats if they look badly shriveled and yellowish orange.

Measure the gas in the bowl after opening both petcocks for a minute. From the center circular divot in the bowl to the top of the gas should be close to 24mm of fuel for 32mm carbs. Anything lower than about 21/22mm you might have the "takes too much time to fill the bowl for the main jet" syndrome. A bad float needle could (or crud in the seats) could prevent bowl filling too. Both of these issues may rectify themselves in the timeit takes you pull over to fiddle with the petcocks.

And yeah ditch the shed solenoid setup if you still have it. Just a bunch of extra parts to go wrong there...

To add more fuel to the fire, I think JDMETZGER had a similar problem that he swore was fuel related (shed vapor lock) but it turned out to be ignition related (bad ICU/ICM and coil). Got a multimeter and a Clymer's manual?

[hardwaregrrl]

On the subject of fuel lines....check your crossover line that runs beneath the airbox. Could have some crud stuffed in it. Out of sight, out of mind.

[ignatz72]

Sorry, back to your question as to the relationship btwn the petcocks and the carbs:

In the simplest form, the petcocks provide the flow of gas to the carbs. You have two avenues of flow from the tank with these petcocks - primary and reserve. Primary runs until you have a level of gas below the primary "straw" in the petcock. When you get no more gas via the primary straw, switching to reserve sucks gas from a much smaller straw that barely pokes above the bottom of the tank's inner liner. The difference in height between the two straws in the petcocks determines your "reserve" fuel level, which varies by bike (but usually 1.5-2 gallons).

That's all the primary and reserve circuits do, and they both do the same job - providing fuel flow to the carbs.

Now if the primary doesn't work but reserve does you might just not have enough gas in the tank (or the primary circuit is clogged). If primary works and reserve doesn't then your reserve channel is probably clogged. And if you have a problem with the petcock in either position, and you have verified fuel flow, then the problem is elsewhere in the gas/air/spark equation(carbs, plugs, ignition, or air intake).

Is that close to the info you were looking for?