Carb problem: Needle Valve vs. Float?

[IDave]

I recently cleaned some gunk out of the SD40 carb in my Fj45 (took it apart and soaked it in carb dip, etc). Since then, I have noticed some hard starting (progressive over the last week) and gas on the outside of the carb (while I was changing the oil yesterday).

So, today I watched closely. While it is running, the gas in the sight window is right on the level line where it's supposed to be.

After stopping the engine the level in the glass slowly rises, over 5-10 minutes, until I can hear it dripping into the intake and I can actually see it overflow the carb and drip down onto the outside of the intake/exhaust.

Not only am I concerned about the wasted gas and the puddle that might form and the starting issue, but I'm worried it might be diluting my oil, ultimately.

So, I figure one of two issues: either the needle valve isn't completely seating, or I have the float maladjusted somehow.

I'm hoping someone can tell me what to adjust/replace/clean/fix. Any way to tell what it is?

 

[IDave]

Ok, looked at it some more. After 25 minutes the gas level peaked and is back down to about half way between the top of the sight glass and the level line. If that makes a difference.

 

[Degnol]

I have at least part of a rebuild kit for that carb. Does you want it?

Ed

 

[IDave]

Thanks, Ed, but I actually just rebuilt it. I have to figure out what's wrong, or I don't think it will help.

 

[inkpot]

Howdy! Sounds like pressure in the tank is forcing fuel thru the pump after you shut down. I'm guessing that a 64 does not have a fuel return line to back to the tank. How about an electric fuel pump with a stuck solinoid? John

 

[IDave]

It's a mechanical fuel pump. Yeah, there has to be a residual pressure problem. I thought it was pump related, but maybe it's the tank. No, it doesn't have any return lines. I suppose I could drive home with the fuel cap off and see if it makes a difference.

 

[inkpot]

It's a mechanical fuel pump. Yeah, there has to be a residual pressure problem. I thought it was pump related, but maybe it's the tank. No, it doesn't have any return lines. I suppose I could drive home with the fuel cap off and see if it makes a difference.

Howdy! That would be a good way to test it, and it's a good test for your neighbors: "Hey mister, your gas caps is gone!" I would defintely be changing out that oil pretty often till you get it figured out. Actually, you could just pop off the gas cap when you stop and park it at home, then just watch to see if that fuel level goes up on the site glass. John

 

[IDave]

Yeah, it IS a vented cap, and I just went out and blew through it to make sure it isn't plugged. I'm still going to try this but I'm not holding my breath...

 

[Pin_Head]

That's some wierd sh*t. Try parking it with the nose up hill .

Or you could try cleaning the junk out of your needle seat so it actually seals.

 

[IDave]

That's some wierd sh*t. Try parking it with the nose up hill .

Or you could try cleaning the junk out of your needle seat so it actually seals.

Guess I'll try cleaning the needle valve again.

This evening drove home with the gas cap off and watched it for a while. The level only rose 2/3 as high as it did this afternoon, and this time it didn't overflow. Don't know if that's because I had the cap off or because the needle valve seated better or because the sun wasn't shining on it and it was 10 degrees cooler.

Thanks for the suggestions! I take it this isn't a common problem.

 

[IDave]

Ok, so what I did was take off the air horn, check the carb screen and checked the needle valve assembly (which was new from a toyota rebuild kit 2 months ago). As far as I could see, everything looked fine, no dirt, no wear, nothing.

Then I compared it to the needle valve from a keyster kit... The actual angle on the needle valve point is a little different between the two (the keyster is blunt-er, essentially, not the point but the angle). So, I swapped the needle valve assembly, readjusted the float, and reassembled. To get the level in the bowl to stay at the line required a couple of more adjustments to the float arm.

So, with that change, the level still rises after I stop the engine and wait a few minutes, but only about 3/16 inch. It hasn't overflowed, at least so far, and it seems to be running better (that's really subjective). Also, it seems like the float bowl doesn't empty out as much or as fast when I open up the throttle. All-in-all, an improvement, I guess, but I don't know why it still seeps and whether that's a problem or not.