Xs400 No Gas Help!!!!

[big_dave]

I have been working on a 1979 XS400. I am not getting gas to the cylinders. I have cleaned, and set the floats in the carbs. Replaced the rubber intake boots and gaskets on the cylinder with NEW ones. When I turn the gas to prime or on, gas comes out of the rear of the carb like it is flooding. I did recheck the floats to see if they had a hole, and where filling with gas, Nope not that. I reset the floats again. I can put my hand on the back of the carb, and it will suck gas through ok. I cracked the drain plugs, and there is gas there. I checked the compression, and there is 160lbs in one hole, and 150 in the other. 156 is what it says in the FACTORY manual. I pulled the plugs, and they are DRY. I did put NEW plugs in the bike (NGK), and there is good spark. Any ideas? I am stumped at this point. I did not replace the needle and seats in the carbs. I very much doubt there is a crack in the cylinder causing a air leak. The bike has 10,000 miles.

Big_Dave

Thanks in advance

[prometheus578]

needle and seat : new needles will stop the over flowing carbs. You may also have the vent for the carbs plugged.. that will cause them to over flow, too.
Put in new needles, flip the carbs over and run gas to them. Watch if they still leak(with the bowls off) Bowls back on, flip right side up and watch again. no leaks.. put them back on the bike.
The idle circuit may be plugged. Putting your hand over the carb throat will bring up lots of gas... but you don't know from which circuit. Is the air cleaner on? Sometimes, as demonstrated by putting your hand in front of the carbs, bikes needs the air flow restriction that an air filter provided in order to have enoigh suction to draw up fuel.
Also... if it isn't cranking fast enough... it may not draw properly.

[big_dave]

xs400 no gas problem

I will get new needles, and try what you have said. I DID have the airboxes on the carbs when I tried to start the bike. As for not cranking fast enough, I was jumping the battery with my car as it was running, and it turned over quickly. It is a NEW battery also.

Thanks for the ideas... Dave

[John]

When jumping the battery from a car, do not run the car engine. The car's alternator will put out too many amps for the battery to absorb.

[big_dave]

xs400 no gas

I have since charged the motorcycle battery with a trickle charger. I never liked jumping a bike battery with a car, but I just wanted to see if the engine was getting gas, it wasn't. Thanks for the reply.

Dave