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Fuel pouring out the front of the carbs


Cooper260z

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To set the scene: early ‘74 260z with four screw round tops and a recent l24 swap. 
 

ive been chasing little issues trying to get this l24 that I swapped in, to run. 
i drove the car with these round top SUs on the l26 with the current float level and mixture adjustment. 
Since putting the l24 in and trying to start it, fuel has started to pour out of the front of both carburetors after I stop cranking. 
 

I previously adjusted the float level and recently checked the float level, they are within spec. 
I ran and drove with the carbs set up this way and didn’t notice fuel leaking from the carbs before, and I’m guessing that it would’ve started a fire if it had been leaking previously, because the fuel does land on the exhaust. 
I looked at the floats action in pressing the shut off valve and they appeared to press the little button in, I’ve heard that that could be a problem. 
If it makes a difference, I put the mechanical fuel pump from the l26 onto the l24. 
 

Ive gotten the engine to start running in this configuration but it quickly gets flooded and won’t start again. 
Im just trying to see if there’s anything I can try before just having the carbs rebuilt. So if anyone has tips as to how to fix the fuel leak, please let me know!

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There are filters at the banjo for the SU carbs, steel mesh. My setup would flood because there was crud that would enter through that filter and jam the float needle. Inspect them for debris.

Edited by heyitsrama
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I would put a cheap fuel pressure gauge right out of the fuel filter before it enters the metal hardline. You may have too much fuel pressure? I think 3psi is about the max.

Lowes has cheap gauges in the swimming pool supply section, fyi. Good luck. You want that fixed asap. While you're at Lowe's get a fire extinguisher. They have a metal rechargeable that fits perfect in the tool bends behind the seats.

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I'm having a hard time reconciling these two statements:

On 6/24/2021 at 11:39 PM, Cooper260z said:

fuel has started to pour out of the front of both carburetors after I stop cranking. 

I ... checked the float level, they are within spec. 

About the only way to get fuel to pour out of the carb mouth is for the float bowls to overflow. So if the float levels are withing spec, I'm having trouble correlating that to fuel coming out of the front of the carbs.

Are you saying that you have checked the bowl levels right WHEN the problem is occurring and they are in spec? Even while there is gas pouring out of the carb mouths?

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I wonder if his nozzles are stuck down or the choke wires are in a bind somehow. Would that cause the overflow?

I know when I got my first 240 I would leave the choke lever pulled back after cranking and running it for a few minutes leaving the nozzles dropped down. My upstairs apartment smelt like gas really bad. Girlfriend wasn't happy with the smell and I was glad to be alive with my pilot light water heater downstairs where the fuel was. LOL

Edit for clarity of dumbassedness. 

The choke lever bracket was broken all to hell so I tried not to use it too much until I got the metal holder from Mr Singer. Best $$ spent on a 240 BTW.

 

Edited by siteunseen
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I haven’t gotten out there to check the screen at the banjo bolt yet. 
 

@Captain Obvious I set the floats to .55” I think that’s what the Ztherapy video said to do. That’s why I believe they are within spec. Should I try to set them at less then .55” so that they shut off sooner?

 

@siteunseen I thought that the nozzles might be getting stuck but I did give them a little push upwards after having the choke on, to make sure they were set all the way home, so I don’t think they’re stuck. 

Edited by Cooper260z
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3 hours ago, Cooper260z said:

 I set the floats to .55” I think that’s what the Ztherapy video said to do. That’s why I believe they are within spec. Should I try to set them at less then .55” so that they shut off sooner?

No. You should assume that your .dry 55" measurement got you (hopefully) close to your target, and do a REAL fuel level test using the clear tube method.

The mechanical .55 is just to get you in the ballpark. Sometimes it works straight out of the box without subsequent adjustments, and sometimes it doesn't. You need to verify the level on the car with fuel in the bowl, not dry on the bench.

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Yeah, it unfortunately sounds like the bowl level is going too high for some reason. Either the fuel pump is forcing the valve open, or the setting was always ballpark and never precise. The wet set method is a bit of a pain, but it's the only way to be sure.

If you want to confirm the theory, you can unscrew the air vent nipple on the top of the float bowls and see what happens. Nothing is supposed to happen, but I suspect you're going to have fuel come pushing out of those vents. And the only way that happens is if the bowl level is too high.

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