Problems after replacing petcock

[Guest]

After I replaced the petcock on my 1980 GS550L I flooded the #2 cylinder. At the time I didn't know that it was lacking it's guts. No diaphragm no spring. After resolving this issue, by simply taking the guts from the old petcock and putting them into the new one, I have taken the bike back out and can't get over 50MPH. I've noticed, while in 3rd I don't get over 5k RPM max and then checked 1st, 7k rpm max, and 2nd, 6k rpm max. As I continue to check what I can get from the throttle I realize each gear I go up I looses 1k RPM and she won't go faster than 50MPR. Any suggestions for this newb?

[tom203]

"After resolving this issue, by simply taking the guts from the old petcock and putting them into the new one, "

Taking parts from a 38 year old petcock and sticking them in defective new unit seems like a bad strategy. Your issue sounds like fuel starvation as load increases - the petcock is the first link in supplying fuel, so I'd get another one.
I'll assume that you have the dreaded 1980 leverless petcock like in this pis?? Where did you get the defective unit?

image.jpeg

[Gorminrider]

turn the petcock to "prime". This disables the vacuum-activated function and gives full fuel flow. you can test for flow with fuel line disconnected... Now run the bike and see if the problem is fixed.

If this fixes it, that indicates a problem with the old parts..likely a sticky o-ring or inadequate vacuum ...you can also suck on the vacuum line as a test, but yours is working somewhat so it's a finepoint as to how much suction is wanted to run it "properly" ..

a full tank of gas has more pressure on these than a 1/4 empty tank also relates to the vacuum system...sometimes, these work better with a full tank.
also full fuel flow may point out issues with floats and the inlet needles if carbs overflow...again , a full tank being the better test.

[ScubaSteve]

I'll give that a try tonight

[ScubaSteve]

yes the picture is an exact match. I'm not sure where my brother ordered the replacement from. But I'll be sure to give them an ear full for all the trouble they caused.

[tom203]

This style petcock and its replacements seem trouble prone...but this guy sells them. Always test any replacement!

http://www.georgefixs.com/1980-gs550-gs750-gs850-gs1000-gs1100-petcock/

[OldVet66]

I had a factory petcock fail after many years on the '80 tank I had bought to replace the original when I put my bike together. It was starving the bike for fuel. I replaced it with one from Z1 Enterprises that is supposed to be a K&L product. It came in a red box from Japan (no markings indicating K&L) and it had the same milling on the petcock body as the factory petcock. It works nicely. https://www.z1enterprises.com/motorc...l/petcock.html