Yamaha FJ 1200 Carb Problems

[DesertDrifter]

Hey guys, so we are trying to get my engine fired up, all the fuel lines are in, wiring harness is semi sorted out , we are getting spark and everything seems fine, but when we power up the fuel pump, it *floods the carbs and fuel starts coming out of the overflow valve. I took apart the bottom float chambers, checked the floats, they work fine; tried to remove the foats but couldnt get the pins out so we couldnt get the needles out to clean, but we did flush them out with gunk remover, and they do seem to move freely. When a gravity-flow fuel line is connected and we hold the carbs up and it doesnt seem to flood, when we hold the carbs with out the float chamber on, we can move the float up or down and allow and block the flow of fuel, so the needles do seem to be working.

Questions:
1.- Can the seats and needles of a MC carb hold the pressure *of the flow from a fuel pump?
2.- Could it be something else besides the float needles?
3.- Where can I find reasonable new or rebuilt carbs, if I need 'em?

This is basically the last thing that I need to do before she can be fired up and tested out, so I really need to fix this BAD!
Thanks.

[plkracer]

What kind of pressure is the pump putting out? The MC carbs, if made for gravity fed, can only hold about 4 lbs safely. if you are using a 7lb pump from a vehicle, it could be too much. Does it run on gravity feed?

[DesertDrifter]

Originally on the bike, yes it did run gravity fed. The fuel pump I bought is from an auto parts place so it is for a car, it doesnt come shooting out but it does just keep a nice constant flow of fuel.

[plkracer]

See if you can rig up a pressure gauge.. I have one and it just plugs onto the metal outlet of the pump, and it is fuel safe. If you can run a gavity fed line to them, and they don't flood, and the engine runs fine, then the pump is too strong. Most cars use a pump from 7-11 lbs, or up to 40+ is they are FI.

[DesertDrifter]

OK I can do that, I will check and provide feed back. I will also try to find out the rate pressure floe rate for the pump I have. Thanks plk.

[DesertDrifter]

I talked to the guy that sold me the engine and he says he thinks the pump is too strong, that many bikes cant handle the higher pressure that a car fuel pump puts out. He says that he thinks if its over 4 lbs, that its probably too much.

[bdkw1]

4#'s is a lot, 2-3 would be more like it. Any atuomotive pump is going to put out to much pressure. You need a regulator.

[plkracer]

I've run a motorbike with a keihen carb at 4 lbs, max. It had a little stumble when it got really rough, but it should be okay. I think that was just from the fuel splashing around. Anyone know what pressure a gravity fed system has? I think 32 feet of water is about 15 lbs, so if it were around a foot, maybe 1/2 lb/in?

[bdkw1]

Originally Posted by plkracer\";p=\&quot

I think 32 feet of water is about 15 lbs, so if it were around a foot, maybe 1/2 lb/in?

The specific gravity of fuel is a little less than water. Water is about 1/2LB per inch, the specific gravity of fuel is around .75 to .85 of water. So on a bike with the tank 1' above the carbs that would give you about .4 of a pound of pressure........

[DesertDrifter]

I am going to La Paz today, I am going to pick up a motorcycle low pressure fuel pump and a regulator, just to try them both out. *Whcih are the best or most recommended regulators?