running lean

[Anonymous]

I am putting together an 81 GS550 and have yet to witness it running. I finally got done rebuilding the carbs and i think i got everything right (after 4 times) I double checked the float height and air screw settings, but i can't get it to start unless i hold on to the choke lever (the cable won't pull it out far enough). When i do, it will run fairly well, however let go and the engine dies. I did install an aftermarket 4-1 exhaust since the original was rusted out. I am thinking I may need to re-jet, but I don't know what size to go to or if this is the solution. I need some help with this now as I'm quickly approaching the limit of my knowledge.

Also, could someone verify that my fuel level is correct? I stuck some clear tubing up the bowl drain and looped it up the side of the carburetors to see the fuel level with the carbs on the bike - then I marked the level, this is what you are seeing in this picture:

 

[frosty5011]

Your carbs

Your carbs

Hey,

I don't know what size tubing you used to check "fuel level" in the carbs, but if it was a "homemade" job, it's possible the tubing was too small. With tubing that is too small (diameter), you could be seeing some capillary action - meaning the fuel in the tube will actually be drawn up higher in the tubing than the actual level is.

If this is the case, that would mean your fuel level is really lower than what is "marked", and could explain the lean condition.

I would advise checking the float height just for kicks, to see where that is....measure without the float bowl gasket. I'm curious if it is actually in spec when measured that way.

Good luck,
Ron

 

[Anonymous]

It was a home-made job, and the tubing was about the diameter of the hole in the bottom of the bowl, so there wasn't much capillary action - plus I tried to account for the "meniscus" i think it's called - i remember that from taking measurements in chemistry class. I did a little more reading and it seems that i wouldn't see any problems with the main jet unless I was at 50% throttle or greater. I have problems just idling so i guess it's something with the "pilot circuit"?

 

[Anonymous]

oh, and i checked the float heights from the gasket surface (without the gaskets installed) to the absolute top of the float on both sides and it's between 22 and 23mm. The specs I got for my bike was 22.4mm float height and 2.5 turns out on the mixture screw.

 

[KEITH KRAUSE]

If you adjusted the floats correctly, the level should be good. Just looking at your mark on the bowl, I think the level should be right at the bottom of the upper carb body. Or, just a little higher than your mark. But you said you measured...
As for the mains, a full size up (5) may work for the 4-1 pipe. You have to test.
As for starting, I assume you've turned up the idle adjuster enough to allow it to idle? Also, spark is fat and blue at all plugs? If so, then you most likely need to do a good bench synch to the carbs and follow that with a vacuum tool synch. You should have a manual.