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#2 carb flooding

  • Thread starter Thread starter davey550
  • Start date Start date
D

davey550

Guest
Hello, this is similar to some previous posts, but it seems every situation is slightly unique when it comes to carbs. So here it goes:
Bike is a 1981 550T w/ BS carbs. I am leaking fuel from #2 carb with petcock on prime. Takes a few seconds and fuel starts to flow out from somewhere above the float bowl. Have new petcock and just put in a new (aftermarket) float needle and seat and adjusted float level. Im not sure what else could be causing this besides the float not closing off the fuel properly. Is it possible the relatively cheap float needle and/ or seat are defective? If so, could anyone direct me to a good source for reliable carb parts? Any help appreciated, thanks
 
One of these pages has the seats and needles.

http://www.siriusconinc.com/search_...art=1&partno=&x=20&y=13&search=search&start=0

BUT FIRST..tap on the carb with a socket ratchet right where the bowl and body come together to see if the float frees itself up. If that doesnt do it, take them back off and check that the float itself is in stalled right. On the egde of the brass flange youll see a tab bent at a 90 degree that lines up with one of the float posts.When the float is in correctly, youll see that tab from above looking at it. If you dont see the tab the float is in upside down. And TEST them before you put the bowls back on. The float should fall till the tab hits the post...but not allow the needle to bind from dropping too low. Follow me here? If the float drop and the needle binds as you try to lift the float..then adjust the tab till it move the full range and the needles dont bind.

Second scenario is the gasket itself is scraping on the float ..trim the gaskets back a little so the floats dont get snagged up there.
 
It is somewhat normal for the needle to leak if the petcock is left on prime for an extended time. Run it on 'run/on' or 'reserve'. Prime is just for filling the bowls after you have had the carbs off or it has sat a while. You can easily verify that the petcock is functioning correctly, and it won't cost you anything: Set on "on", put the gas line coming out of it in a container, then suck on the end of the vacuum line. It should flow gas when you suck on it, and stop when you don't. On prime it should flow, and flow, and flow no matter what. If the carb #2 is not leaking with the petcock on 'run/on' you are good to go. If still leaking follow Chuck's advice to a "T".
 
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If you're trying to figure out if it is in fact a flakey needle and seat drop the float bowls and simply swap it with the needle and seat from another carb. If the problem follows the needle and seat then it's a bad needle and seat. If the problem stays with the original carb then the problem is something else. In an ideal world they shouldn't leak when left on prime but it's not really ideal world is it? If the leak isn't bad then don't leave it on prime and don't worry about it. Me, I'm stubborn and would want to fix it.:confused:
 
I agree with Sandy. Even in the PRIme spot the floats should shut off fuel when the bowls are full. The problem with EXTENDED PERIODS of SITTING with it on PRI is that ever so slowly the floats tend to weep a tad.

When you leave it on PRI, the excess eventually finds its way into the cylinders, past the rings, and fills the crankcase with fuel...which is a very bad deal if you dont catch it.

Thus, the vacuum fucntion of the petcock coupled with the floats seating the needles act in concert to prevent the fuel failure situation.
 
Thanks for the ideas everybody. I will try the tests and if I have to take the carbs off again, this time I will set up the carbs and tank off the bike so I can do a real test of the floats. Im 99% sure I put the float on correctly, but maybe it is hanging up on the gasket.

One more question (for now anyway): if the carb is flooding in Prime so quickly, could it not also flood or at least introduce too much fuel to that cylinder when the engine is running with the petcock on Run?
 
PRIme bypasses the "normal" action of the engines vacuum operating the petcock. The float....well float....per the rate of fuelused from each bowl when the engine is at differing RPMs. If the floats are right and the petcock is in the ON position things should be normal. Prime is really only used when the bowls are dry from evaporation or from maintenance such as youre doing.

I will set the petcock to PRIme for maybe 30 seconds if the bike has sat for a longer time to refill the bowls only. Switch back to the ON position, choke, and fire it up. Other than that theres no reason for use of the PRIme spot.
 
One thing that hasn't been mentioned... Test the carbs OFF the bike. Putting the carbs back on and off and on and off is a real PITA. Use a fuel "tank" and some tubing suspended above the carbs. Put the carbs in a bench vise or something to secure them. Check to make sure they're fairly level. turn the fuel on (I like to add an inline valve or fill the tank) and see if the floats hold. I like to use a drilled drain plug with a barb epoxied to it and some clear tubing to verify that the float level is correct and is not creeping up.
 
Use water when doing this, youll get same results as gas. Lay a towel under them to soak up the water. Point being do they stop the flow of the involved liquid. Tape them all up ( closed position ) and do one at a time.
 
I agree with Chuck that testing one carb at a time is great idea. I usually take the bottom joining rail and put it in a vise and level it out. You can then take a carb and screw it to the last position on the rail to hold it securely while testing the floats.

As an alternative to taping them up, you can use one of the tubes that connects between the carbs with O-rings attached and the fuel-T. You then use a couple 5/16" vinyl screw protectors you can pick up at your local Home Depot to plug the sides that you're not using. The protectors you're looking for can be found in the assorted hardware section near the screws. They simply slide over the side that is not used in the carb and seals that end. No leakage of any kind and are reusable. The caps look like this:
tlhmlK.jpg

The caps cost $.67 for two. Everbilt part number: 756475 which is HD's SKU#
 
Yes, what I meant in my last post is that if the float does not work properly when priming, it probably will cause issues when starting and running with the petcock in the normal run position. In other words, I will have to fix this thing before I think about getting it back on the road.
 
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