Carb float level - works on the bench, floods on the bike...

Last fall on my last ride, my 1982 XJ750 Midnight Maxim (Canada) filled the airbox with gasoline and flooded badly.

I finally got to it this riding season, put 4 K&L carb kits into it, adjusted float levels on the bench as instructed in the float level adjustment document, and it still fills the airbox with gasoline and floods out. It runs really nice for a few seconds after starting, but then as it drowns it runs worse. As the engine drowns, it seems to run well at higher (5000 or so) rpm and bog out and choke at low rpm. So I suspect (hope) 1, maybe 2 carbs are drowning.

The oil smells like gasoline, so I've changed it.

My plan is to remove the airbox-to-carb boots, turn the fuel petcock to the PRI position, and see which (if not all) of the carbs overflow fuel to the airbox. I am also going to fit-up 4 level indicator tubes to the 4 floatbowl drains, that should tell me pretty quick which or how many float valves are mis-behaving.

I have become way too familiar with removing/replacing the carb-rack on this bike. I'd like this to be my last time.

I am curious as to why it drowned before I kitted the carbs, and why it still drowns.... is it possible that one of the floats leaks and sinks? Anyone ever heard of that?

Any other suggestions?

Thanks, The geezer in Canada with 2 weeks left in riding season...

 

there is a difference between setting float levels and setting wet fuel levels. setting float height is a ball park setting
Setting the fuel levels

 

The K&L kits sometimes work, and sometimes don't. The float needles tend to be turned slightly undersize (in diameter).

XJ floats can't sink.

 

+1 above, the fuel height is best done wet set. You could get lucky and do the 16mm set and it will work, but wet set is best. That way you know for sure.

 

the floats are solid foamy plastic that can't "leak". i doubt that's the problem

 

Did the kits include new o-rings for the float needle valve 'holder' (brass capsule thingy) ? old dried out o-rings will let by
as if the needle is at fault.

 

I first set the float levels to the 16mm measurement, then checked and re-set several times after checking "wet" with clear tubing attached to the bowl drains. I even hack-sawed and modified and re-welded my carb-holding jig so that the tilt is adjustable to emulate the forward tilt on the bike. After the wet-checks, the float levels measure about 17mm to get fuel level in the tubes 3mm below the carb body casting. I concur with the method of fastening (taping) tubing to the fore-aft center of the float bowls to reduce the level reading error from carb-tilt.

I've used K&L carb kits for single cylinder atv carbs, and in my experience I have never had one not do the job. However, those carbs - for offroad use - are much simpler and less "tuned", so there is more room for error. The carbs on these XJ's are highly tuned for performance and emissions, and everything must be perfect or results will be unsatisfactory.

When I pulled the carbs apart, there were no O-rings under/in/between the brass float needle valve and the carburetor body casting. So I did not put any O-ring there on reassembly. There were O-rings left-over in the kits. That may have been my problem all along, with one or more float needle valve assemblies leaking / drowning before and after I put the kits in. With an O-ring between the float needle valve body and the carburetor body, the orientation will change so I'm back to square-one on float height adjustment.

What makes it all even more challenging is the neighbour, who has a fuel-injected Kowalski Spock Vulcan, sees my shop lights on and comes over to provide an audience, drink beer, cheer me on, and pontificate about the superiority of computter controlled fuel injection. He fails to mention that I have rescued him from broke-down on the highway due to a TP-sensor gone bad, but he's never had to rescue me.

I can't guarantee that a previous owner or mechanic did things correctly, and that the carbs came to me correctly assembled. By all means please chime in on the should or shouldn't have O-rings on those float bowl needle valve bodies where they thread into the carb body casting.

Thanks all for the advice and cheering-on. I need to get this thing running to put an end to the nattering from next door, when its running right its quicker than the Vulcan.

 

I see where the trouble lies. The wet-set is supposed to be done with the carbs sitting perfectly level. By adjusting them to sit as they do while on the bike you changed the reference you're measuring the fuel height against, resulting in an incorrect adjustment.

The 750 does not have an o-ring on the float needle seat, but it does use crush washers between the seat and the carb body. If the crush washers aren't present, then fuel will leak past the seats.

 

Thanks K-Moe, for the info about what should be on those seats. I'm pretty sure the copper washer is there but I will double check. No replacement copper washers in kit.

My first wet-set was with the carbs perfectly level, set all 4 carbs to the 3mm below casting line, and after installing on the bike it drowned in fuel. It was after the flat-level wet-set didn't work that I modified my holding jig to mimic the angle on the bike. Then after doing the slightly inclined - but centered fore/aft - fuel level adjustment and check, it drowned again. 2 oil changes. Vulcan neighbour giggling at me.

 

tell your neighbor to bring that Vulcan around in 37 years

 

Isn't the other issue with the K&L float needle valve kits is that they are about 1 mm longer, which causes an issue with the geometry of the float tang to float needle valve. I know I had a set of longer float needle valves and could never make them work - they would work sometimes but when doing multiple attempts of drain and refill the bowls they would sometimes not seal.

 

This is exactly correct, and $1 says this is exactly the problem that Jiggs is having, which means that they will never work properly...……….

 

Just buy the correct needles and seats from Chacal and do it right the first time. I recommend the brass needles.