Almost there...1981 GS550 help

[Kris V]

Pingel.com

[Kris V]

Pingelonline.com

[khardrunner14]

Maybe I should have been more specific...

Which petcock and which adapters do I need. They have a ton of H-D stuff and drag stuff, but I don't need that.

[Nerobro]

Spend the $20 on a petcock rebuild kit. Or take yours apart and clean it.

You can also easily test your current petcock with some vacuum line and fuel line. Set the petcock to on, point the fuel line into a cup, and suck on the vacuum side of the petcock. No fuel? Take it apart and clean it. If that doesn't work, a $20 rebuilt kit will make itwork like new. And you don't need to futz with adapters.

The only reason I've ever seen a petcock fail is from crap building up in it. That only happens if you let a bike sit for a decade or so. :-)

[KEITH KRAUSE]

That still doesn't explain why it struggles to run correctly even on Prime. It does idle much better on prime, but it isn't quite right. I don't know much about the Prime setting, but here is my theory...correct me please if I'm nuts. Since Prime is gravity feed, there is no control over how much gas reaches the carbs (save for the overflow valve). Because of this, the bike runs lean or rich (not sure which) on Prime. This causes the bike not to idle well.

Prime doesn't deliver any higher flow rate than on or reserve. The amount reaching the carbs is controlled the same as any other position. All positions are gravity fed. Only difference is that when on/res, the vacuum overcomes the spring keeping the diaphragm closed. On prime, the fuel goes straight through because it bypasses. It can't run richer or leaner because of petcock position. The flow is ultimately controlled by the float needle valves that regulate the fuel level in the bowls. The sole purpose of a prime position is to fill the bowls after the carbs have been serviced and there's no fuel in them yet. Makes initial starting a lot easier.
Before replacing or rebuilding, be sure the petcock is clean. If it's dirty, it can fail.

[KEITH KRAUSE]

I am still struggling with getting the bike to start/idle properly. It will start and idle pretty much on PRIME and with at least some choke on. I tried the air mixture screws at 1 turn and 1.5 turns with the 1.5 turns being a little better. Either way it will not idle anywhere below about 3 grand. Is this related to fuel, air, or even the new pilot fuel jet? What do I do?

- The bike will only run/ride with the petcock on PRIME. If I am careful with the throttle, it will limp along on run/reserve. Does this mean I have a petcock problem, or is it more likely a problem with the vaccum?

I still wonder about the new pilot jets. Did the problem show up right after the carb work?

[khardrunner14]

I bought the bike running VERY rough after sitting for 2 years. Needless to say it needed work. From the sound of it, you would suggest that I pull the carbs again and replace the new pilot jets with the older ones. With the information you provided about the petcock, this sounds like the jets could be my real problem. I know the pilot jet controls the fuel flow from idle to about 1/3 throttle. This is where the bike runs a little rough. If I can correct the petcock problem and replace the jets I think I have a shot at finally getting the bike to run properly.
THanks again!