Fuel Line Question

Johnny5 · Posted: Tue Sep 02, 2008 7:58 pm Post subject: Fuel Line Question

My bike was running well, but then it started to sputter a little in the right cylinder. When I got home, I noticed the fuel had crept up higher than the carburetor. I tried tapping the side of the carb to see if the float was stuck, but nothing happened. So what would cause the carb to flood?

reserected · Posted: Wed Sep 03, 2008 3:43 am Post subject:

could still be the float,a tap may not have done the trick. if your carbs are vac op the diafram may have a small pin hole.also the passage between carbs may be blocked causing the one carb to build fuel meant for the other carb....although that would be noticed during your last ride. pls post the solution when you find it. good luck Exclamation

Johnny5 · Posted: Wed Sep 03, 2008 5:36 am Post subject:

I'll check it out tonight. The floats and the carb are very clean, I cant imagine it sticking or hanging up anywhere. Really weird.

On these carbs, there's no tube linked to each carb though. I'll also check the diaphrams. They looked good when I checked them on the last pull about a month ago.

cousinoliver · Posted: Wed Sep 03, 2008 12:12 pm Post subject:

I'm intrugued by this. On my 350 the fuel level for the left carb is always higher than the right one and reads slightly higher than the float bowl (??).

Also on our 350 diaphram-type carbs we have a nipple coming out of the float bowl that looks like it should have a hose attached (right Johnny5?). Should the carbs be linked by a hose or is that just to drain the float bowl?

Johnny5 · Posted: Wed Sep 03, 2008 12:17 pm Post subject:

I know what "nipple" you are talking about but I dont think any hose or anything goes there. Possibly it's for air or something.

This is more than uneven floats. My inline fuel filter is about about 2" above the float line and gas is filled pass that. Fuel isnt coming out of the overflow tubes, so it's either a blockage in the fuel line or the filter. Im getting new fuel line tonight regardless. But it just seems weird to just happen out of the blue.

KirkN · Posted: Wed Sep 03, 2008 1:48 pm Post subject:

I'm a little confused: the gas tank is above the carburetors, so wouldn't you expect that the fuel lines would be full from their attachment points at the carbs all the way back to the tank? Sometimes there may be a bubble of air in there, but it doesn't stop the fuel flow. That is, the fuel in the line flows "around" the bubble.

I mean, it's the float that stops the fuel flow (when the petcock is ON or RESERVE).

The carb diaphragms are unrelated to fuel level / flow. They're there to control the throttle slide based on intake vacuum. When you whack the throttle open, you open butterflies in the intake tract rather than directly pulling the throttle slides up, unlike most dirtbikes where the throttle cable directly pulls the throttle slide. Engine vacuum pulls the throttle slides up and it only pulls them open as much as the engine can stand at the moment. Keeps the motor from bogging.

Not sure what nipples you guys are talking about without pix, but generally, nipples coming from the bottom of the bowl are overflow and/or drain ports and are typically connected to hoses that run down behind the motor (along with battery overflow tubes) to route overflow away from the hot motor (and, ironically, they typically spew onto the rear tire!). Nipples that come from the side of the carb body itself are bowl vents. This keeps the air pressure on top of the fuel in the bowl at atmospheric pressure, rather than letting any pressure (or vacuum) build up.

Different levels visible in clear fuel lines at any given moment? Not an issue.

Kirk

KirkN · Posted: Wed Sep 03, 2008 1:48 pm Post subject:

double-post. sorry 'bout that.

KirkN · Posted: Wed Sep 03, 2008 1:48 pm Post subject:

d'oh - triple post. Embarassed

Johnny5 · Posted: Wed Sep 03, 2008 5:33 pm Post subject:

Yep, it was just air in the fuel line. Just never saw that before.