Starves for fuel on main, OK on reserve

[Old Mechanic]

94 GS500E recent purchase just over 10k miles. Tank is immaculate inside, runs fine on reserve but if I switch to main it will run out of fuel, even with a full tank. Hit prime for a few seconds, leave it on reserve starts right up and runs fine again. I'm bringing this bike back to good operating condition and would like to get this working properly. I haven't been into the carbs but did replace the air slide springs (one was broken in half-replaced both). Good power top end still a little trace of stumble in transition from low to top end. Motor is immaculate undet the valeve cover clearances are good. New iridium plugs (previous owner). Is this a typical petcock issue?

regards
Mech

[mustangGT90210]

Make sure the lines are routed properly first! If they are, could be the petcock.

[weedahoe]

Two things..........

1) What air filter are you using and
2) why not leave it on PRI

Thats where mine stays.

[adidasguy]

Probably dirty main fuel line or it is pinched.
Also possible the tank and/or frame petcock is dirty. Open them yo and clean them.

[EdChen]

Is there a fuel filter installed on the bike? Coul be a potential cause.

[mustangGT90210]

Oh make sure not to leave it parked in PRI! When everything in the carb is in perfect working order, it causes no issues. But as soon as the needles or seats start getting old and don't seal perfect, sitting in PRI will cause it to flood.

[Old Mechanic]

The fuel lines from the tank to the petcock and petcock to carb (the one you can select postions) were reversed. The tank hose was in the front and the carb hose was in the back, just the opposite of their proper locations. I switched them around and it is working fine. One of the reasons I bought this bike was the tank was basically spotless, like brand new inside. I replaced the two hoses from the tank to the petcock and put them in the same positions they were when I started working on the bike. They were wrong, probably a previous owner mistake, Combined with the broken air slide spring on one carb the bike did not run very well at all. Last tank was 62.38 MPG and it runs great now, just a little lean until you hit the secondary circuit which is the way it is supposed to be from what I have read.

regards
Mech