New/Repro YF carburetor for the 300 six

[Gary Lewis]

So this Amazon YF has been working well for the short little bursts that I've actually been able to run the truck. However, now that I'm able to drive the truck a little bit I am having a problem. It works great when it is cold (choke is tied wide open), but once the engine gets up to temperature the carb starts leaking terribly. I took it all apart thinking the float was stuck, or needle valve stuck, but it was all clean as a whistle. Put it all back together, and again it ran just fine while it was cold...but once it warmed up it started leaking terribly again.

This time when I pulled back up to my garage, it was leaking and I could hear the gas sizzling...on the intake and probably some of the exhaust manifold. It got me thinking though...am I overheating the carb somehow?

There is an valve in the exhaust manifold for heating the intake manifold...and I thought I tied it shut, but maybe I tied it wide open?

Any thoughts from the experts?

If it was a float or needle valve or fuel pressure issue, it wouldn't matter if it was warmed up or not, would it?

Right, if it was float level or pressure then temp shouldn't matter.

So it does sound like you may be overheating the fuel, causing it to boil. I'd tie the valve the other way and see what happens.

[ArdWrknTrk]

So this Amazon YF has been working well for the short little bursts that I've actually been able to run the truck. However, now that I'm able to drive the truck a little bit I am having a problem. It works great when it is cold (choke is tied wide open), but once the engine gets up to temperature the carb starts leaking terribly. I took it all apart thinking the float was stuck, or needle valve stuck, but it was all clean as a whistle. Put it all back together, and again it ran just fine while it was cold...but once it warmed up it started leaking terribly again.

This time when I pulled back up to my garage, it was leaking and I could hear the gas sizzling...on the intake and probably some of the exhaust manifold. It got me thinking though...am I overheating the carb somehow?

There is an valve in the exhaust manifold for heating the intake manifold...and I thought I tied it shut, but maybe I tied it wide open?

Any thoughts from the experts?

If it was a float or needle valve or fuel pressure issue, it wouldn't matter if it was warmed up or not, would it?

Do you have any kind of insulator gasket under your carb?

It certainly sounds like the intake manifold floor is getting heat all the time.

Doesn't the exploded view show which way the flap below is positioned?

[Rembrant]

Do you have any kind of insulator gasket under your carb?

Just the factory style gasket, which is an insulated one, but it just covers the perimeter of the opening in the exhaust manifold.

I'm going to try and flip the exhaust the flap the other way and see what happens.

 

[Rembrant]

Do you have any kind of insulator gasket under your carb?

Just the factory style gasket, which is an insulated one, but it just covers the perimeter of the opening in the exhaust manifold.

I'm going to try and flip the exhaust the flap the other way and see what happens.

I checked some pictures and videos of 300 exhaust manifolds, and it looks like mine is tied closed.

 

[ArdWrknTrk]

I checked some pictures and videos of 300 exhaust manifolds, and it looks like mine is tied closed.

Are you sure the flap is still attached to the shaft, and not rotted through?

It seems odd that your carb would be getting that hot.

I don't think that is any fault of the carb.

[ArdWrknTrk]

Do you have any kind of insulator gasket under your carb?

Just the factory style gasket, which is an insulated one, but it just covers the perimeter of the opening in the exhaust manifold.

I'm going to try and flip the exhaust the flap the other way and see what happens.

I meant is there any insulator where the carb body attaches to the (non) EGR spacer. ?

[Rembrant]

Are you sure the flap is still attached to the shaft, and not rotted through?

It seems odd that your carb would be getting that hot.

I don't think that is any fault of the carb.

Jim,

That exhaust valve flapper was still intact and in good condition when I installed the manifolds, or at least it appeared to be. It has a counterweight on it to close it (on top of the thermostatic spring that was there), so I did have it tied in the closed position.

The only thing between the carb and manifold is a non-EGR aluminum spacer. The trucks never got the feedback carbs up here, but the earlier Bullnose 300's all seem to have EGR systems, while later on they just had spacers like this one (1986).

I was thinking back to the fuel pump...the one I installed was a higher pressure one, but not that high...and even if that was an issue, it should be cold or hot.

Googling around a bit I did find one guy that installed a thicker gasket somewhere for this same reason, and cured it.

The temp gauge on the truck stays pretty low, so I don't know what temperature it is actually running at.

[Rembrant]

Jim,

That exhaust valve flapper was still intact and in good condition when I installed the manifolds, or at least it appeared to be. It has a counterweight on it to close it (on top of the thermostatic spring that was there), so I did have it tied in the closed position.

The only thing between the carb and manifold is a non-EGR aluminum spacer. The trucks never got the feedback carbs up here, but the earlier Bullnose 300's all seem to have EGR systems, while later on they just had spacers like this one (1986).

I was thinking back to the fuel pump...the one I installed was a higher pressure one, but not that high...and even if that was an issue, it should be cold or hot.

Googling around a bit I did find one guy that installed a thicker gasket somewhere for this same reason, and cured it.

The temp gauge on the truck stays pretty low, so I don't know what temperature it is actually running at.

Looks like the float was the culprit. I don’t know how the temperature affected it, but the Amazon carb had a plastic float in it. I swapped in the metal float (which had more heft to it) from the original carb that was in the truck (an original YF that had been reman by Autoline p/n C6077.) works great again, and no leaks. Carb is cold to the touch even when up to operating temp. Thanks guys for listening to me whine LOL.

[Gary Lewis]

Looks like the float was the culprit. I don’t know how the temperature affected it, but the Amazon carb had a plastic float in it. I swapped in the metal float (which had more heft to it) from the original carb that was in the truck (an original YF that had been reman by Autoline p/n C6077.) works great again, and no leaks. Carb is cold to the touch even when up to operating temp. Thanks guys for listening to me whine LOL.

Interesting! I would never have guessed that the temp would affect the plastic float. Obviously it must be made out of the wrong material 'cause billions of plastic floats don't have that problem.

I wonder if it is expanding with the heat? But that would seem to mean it would float easier and lower the fuel level and this would suggest the fuel level was going too high.

[ArdWrknTrk]

Interesting! I would never have guessed that the temp would affect the plastic float. Obviously it must be made out of the wrong material 'cause billions of plastic floats don't have that problem.

I wonder if it is expanding with the heat? But that would seem to mean it would float easier and lower the fuel level and this would suggest the fuel level was going too high.

Well, I'm glad you've got it figured out and it was an easy fix Cory!

If it was a common problem you'd think it would appear in the Amazon reviews.

I've seen 'waterlogged' foam floats before. But it seems this is not that.