Duromax 440 Leaks Fuel From Behind Carb

[SquidBonez]

Hi, I recently just got my project kart running but I have been having some concerns with how gas is leaking from behind the carb where the "carb insulator block" (black plastic piece behind the carb) is. I just replaced all the gaskets with new gaskets, including the float bowl o-ring. I ensured the float wasn't stuck (has happened once before and it dumped gas out of the intake) and tore down and cleaned the whole carb. Despite this it still leaks. I have circled where it is leaking from in this picture:

Note that gas only leaks when I jump on the suspension of go over bumps. The engine is mounted to the swingarm like how many off road go-karts are built, so the engine does get jostled around. Is this just some sort of carb overflow that dumps excess fuel when needed? Any suggestions?

 

[Master Hack]

Looks like a bowl vent.

Note that gas only leaks when I jump on the suspension of go over bumps.

Fuel sloshing around, slopping out the vent.

 

[SquidBonez]

Looks like a bowl vent.



Fuel sloshing around, slopping out the vent.

Does this happen on all swingarm-mounted engine karts? Is this normal/ok?

 

[Master Hack]

I'm no expert, but I would guess the more bouncing around the worse the problem. I don't think its exclusive to swing mounted situations.
Is it normal? Yes. is it Ok? depends on how much it leaks.

Time for my usual smart a$$ answer:
try putting the carb on upside down, then the vent would be at the top.

 

[Denny]

Is the float sticking or level too high? Is it the stock carb?

 

[SquidBonez]

Is the float sticking or level too high? Is it the stock carb?

Stock carb. It got stuck once but when it did it dumped gas out of the intake, not from the back. I also took it apart and cleaned it to make sure it wasn't sticking.

 

[Denny]

Check your float level again?

 

[SquidBonez]

Check your float level again?

I don't believe these carbs have a float level adjustment anyway. But it's in the stock position.

 

[Denny]

They do actually. You bend the tab on the float that makes contact with the needle. You flip the carb upside down and measure the difference between the front and rear of the float to check height going from the bowl gasket lip.

 

[SquidBonez]

They do actually. You bend the tab on the float that makes contact with the needle. You flip the carb upside down and measure the difference between the front and rear of the float to check height going from the bowl gasket lip.

Huh, never knew that. What adjustment should I be looking for then? Should the bowl be level when I flip it upside down?

EDIT: Looking at it now I still don't see how it's adjustable. The entire carb float is plastic. Most adjustable carb floats have a piece of metal you can bend. I think if I tried to bend it I would just snap it. Plus I managed to find one video online saying that these carbs were not adjustable for float level.

 

[Denny]

Remove the bowl first. Then flip the carb over. There will be a little tab (usually brass) on the float that contacts the needle valve. If the float is higher in the rear or level it is probably too low. Should be about 1/8th” higher at the front (opposite the hinge pin).

 

[Darren]

Basic checks, make sure float isn't faulty, chuck it in some fuel and make sure it stays afloat.
Look for any wear or machine marks on the needle pin, you need a magnifying glass.
Get a feel for the pin moving in and out of the tube, nice and smooth?
Assemble and blow through the fuel pipe and gently push the float until the spring just starts to compress on the needle, is this stopping the air?
If this checks out all okay, then I don't know.
You say you rebuilt the carb, did you use a new needle pin? I thought these come as part of the 'rebuild/refresh' kits.
Carbs for the stationary engine are pretty cheap, you may have one that's badly machined around the needle valve, might be an idea just to buy a new one.

 

[bob58o]

One thing I didn’t see addressed in these posts was checking there are no cracks or deformities in the hard black plastic insulator/spacer thing behind the carb.

A closer look at the plumbing makes me think it’s a gasket type problem (if it is a problem) if it’s not the float/needle.

 

[Denny]

Sure seems like a pi$$ poor way of venting a carb float bowl.

 

[Master Hack]

Sure seems like a pi$$ poor way of venting a carb float bowl

Not an uncommon way. Honda carbs (some) are the same.
It's a labrinth, normally they don't leak much. Not all that different than a hose hanging.

 

[Master Hack]

Is it possible that the angle of the carb is way off level when the swing arm swings its full travel? That in combination with the sloshing/slopping around, maybe lower the float level a few thou??

 

[bob58o]

Carb circuitry is like a foreign language to me. One opening has to allow air for the idle circuit, right?

 

[Master Hack]

Yeah, but even that is filtered, it starts in the carb throat.

 

[bob58o]

Is it possible that the angle of the carb is way off level when the swing arm swings its full travel? That in combination with the sloshing/slopping around, maybe lower the float level a few thou??

Like this gx390 to gx200 carb adapter for engines on 15degree motor mounts. I believe some race karts tilt the forward so the exhaust clears the back right tire.

I suppose a swing arm is similar, but tilted in opposite direction. I guess it depends on its geometry.

The adapter twists the carb to account for the mount.

If the swingarm angle is to great when seated in it, add more mass to your body to level it out. I suggest double bacon cheeseburgers.

6878 ARC Carb. Adapter GX390 to GX200

Carburetor Adapter GX390 GX200 Clone ARC Carb

www.arcracing.com

 

[SquidBonez]

If the swingarm angle is to great when seated in it, add more mass to your body to level it out. I suggest double bacon chcheeseburgers.

I have the swingarm set to be slightly tilted back when I'm not in it so it levels out when I sit in it. The axle sit just slightly backwards of the crank on the engine so the engine moves basically as much as the axle does. Rear suspension travel is about 5", so you can imagine how much the engine moves. It does not leak when it is idling or even driving smoothly, only when I jump on it and cause the rear suspension to move. Looks like this "leak" is just the overflow after all, so it's actually doing its job. Just something to live with I guess.

My eventual goal is to have an electric buggy. Will probably do the rear suspension in the same way (motor on swingarm) because it's light, cheap, simple, stable, and strong. And the added benefit of electric motors is they don't have any fluid to leak, and don't care how they are mounted. Should make my job easier. Until then, however, just gotta deal with some gas leakage.