Carb is a 48 IDF. Boost prepped.

I have a full rebuild kit on the way and will thoroughly go thru it soon but have been pondering an issue with it.

After the car is turned off fuel is steadily flowing into the bores. It seems to do this until the float bowl is almost dry. It is almost like a vacuum is being created and sucking the fuel right out of the bowl.

I have swapped out the needle and seat for a new one. I have adjusted the float level 10+ times. Fuel is regulated with a very accurate gauge.

Anyone have any thoughts?

-billy

 

Is the fuel coming out of the booster squirters?

 

The only thing I can think of is either you have a crack in the carb body or more commonly a float that has a hole in it and is allowing fuel to enter the float causing it to sink which would allow fuel to enter the bowl.

 

All that has been checked.

I believe we may have found the issue. The fuel tank is building pressure. all the lines are used or capped. I think this is pushing the fuel in. I will remove the gas cap and see if it solves the issue.

-billy

 

Yeah, if your fuel tank is not venting, then it will build pressure and push the fuel through. I was going to mention that but thought that you would have checked that already.

 

Been hectic and had not investigated the plumbing in the trunk. I will go sit in the corner for a while

 

Ha, it happens to the best. I have seen some veteran technicians at my work chase their tails around an electrical problem on a car, spending a day on the a car trying to diagnose when it was just a blown fuse. It's easy to get caught up and forget to check the basics first.

 

Did the fuel cap take care of it? My Weber DCO had a similar issue, turned out I needed a larger idle jet. The idle air mixture screws had to be backed out too far and this allowed fuel to leak past so when I put in the larger idle jets and turned in the idle mixture screws the leaking stopped.

 

hey tom!

thats a fun one....

 

Nope. Still have the problem. I removed the cap so no pressure can build up.

Been reading a bit and have adjusted to carb with the mixture screws 1 turn out. Idle speed 1/2 in from first touch of the lever. Air bleeds fully seated.

Once the car has run a few minutes and is warm I turn it off and the fuel spills onto the butterfly from the progression hole in the front bore only.

3PSI +/- .1 on the gauge ( ) and float level is set.

I am stumped again.

-billy

 

Sure sounds like a float level problem. I would bend the tab on the float level up a little and see if the problem goes away.

 

This may be a dumb question but what fuel pump and pressure are you running? Is there a return line?

 

you read my mind jose

 

 

I thought of that too, but he is saying it happens when the engine is turned off. The pressure would have to be way high. I guess another question would be does it do it when the engine is at idle too or only when the engine is off?

 

Holly pump.
Mallory Regulator. (has return)
Pressure gauge can tell the difference in 3 PSI and 3.1 PSI

Float level has been set. That was my first thought so I messed with it for a while.

As soon as the fuel pump is turned off the pressure drops to zero.

While running everything is fine. If turned off before the engine is warm everything is fine. It only happens once the engine is at operating temp.


-billy

 

It's not a fuel pressure problem, I run my Weber with no regulator and deadheaded, using a pump that does about 7psi. Float problem would make it dribble all the time, not just after turning it off.... What does the fuel spray look like when running? Should be a very fine mist you can barely see.

Screw the idle mixture adjust screws all the way in and see if that problem persists. Some Weber carbs the screw should be out no more than 3/4 of a full turn.



Yeah it was, that sucked. I had that problem for years before I figured it out!

 

^ How would idle mixture screws cause a fuel dripping when the engine is off?

Man, I am stumped now too. Did you figure it out yet? The thing that has me stumped is that it only does it when the engine is off and at operating temps. The only thing I can think of and this is a shot in the dark is maybe your fuel lines up to the carb are getting too hot causing the fuel to boil and when you turn off the engine it drips out . Like I said... a shot in the dark. Let me know what you find, I'm very curious now.

Ps. how long does the dripping go on before it stops?

 

Going by your sig this is in an RX3? I've seen this once before in an Rx3 with an IDA. As soon as the engine was turned off fuel would slowly gravity/siphon feed into the bowl flooding the engine. This would only happen when the tank was half full or above. There was no pressure build up at all. Pump and reg were Holley blue.

 

Not yet. I pulled it apart to fully clean it. Have a new float on the way as well as new mixture screws. Basically replacing stuff to see if it helps at this point

Seems to go on until the float bowl is about dry.

Sounds very close to the same but the tank level is low currently.


Should have it back on this weekend. Will let you know what I find out.

-billy

 

Well.....I completely rebuild the carb. new need/seat, new idle mixture screws and all new gaskets and o-rings.

Set the float level at 15mm (so I know it is low).

Same thing.... I even pulled the top off as soon as I shut it down to see if it was the needle/seat letting the fuel in.....nope. With the top of the carb off, float bowl with fuel in it.... it leaks out the progression holes.

So that has to eliminate the float level, pressure buildup in the gas tank and overflowing the carb......

-billy

 

Man, this carb ran great when I had it. Maybe it just misses being in a RX7

 

billy plugged bleedback jet ftw or you are runnin a 000 bleedback pick up a .10

 

Make sure the throttle is completely closing when the gas pedal is not depressed, oh and the fun part, make sure its wide open when the pedal is to the medal

 

Did you ever try a bigger idle jet and turn in the idle air mixture screws further?