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Fuel Pump Pressure for Carb??


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9 replies to this topic

#1 Petersubaru

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Posted 08 October 2009 - 02:04 PM

Just wondering if anyone would know what the fuel pump "psi" was for a stock carb '86 ea82

#2 GeneralDisorder

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Posted 08 October 2009 - 02:52 PM

1.5 to 2.5 IIRC.... somewhere in there. Weber's like 2 to 3 so they typically work just fine for those as well.

GD

#3 Petersubaru

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Posted 08 October 2009 - 04:50 PM

1.5 to 2.5 IIRC.... somewhere in there. Weber's like 2 to 3 so they typically work just fine for those as well.

GD

...it suddenly dawned on me today to ask the above question because over the many years and having 3 different carbs on the same car, they all have 2 things in common ...a slight fuel leak onto the throttle plate for about a minute or so after turning the car off..and the fuel pump which is "not" original and puts out 3.5 psi....there is no excess pressure in the gas tank..could the pump be the reason for the dripping fuel after shutting it down

#4 GeneralDisorder

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Posted 08 October 2009 - 05:55 PM

Perhaps - are you using the return line?

What orifice does the fuel leak from inside the carb? Is is leaking from the accelerator pump nozzle or some other place?

I wouldn't think that .5 psi would make any difference and frankly there should be no real pressure present when the fuel pump shuts down. The fuel inlet to the carb is solely controlled by the float and needle valve - 3.5 psi is not enough to blow the needle off the seat.

I think the key is going to be in finding out where the fuel is comming from that's leaking onto the throttle plate.

GD

#5 Petersubaru

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Posted 08 October 2009 - 09:10 PM

Perhaps - are you using the return line?

What orifice does the fuel leak from inside the carb? Is is leaking from the accelerator pump nozzle or some other place?

I wouldn't think that .5 psi would make any difference and frankly there should be no real pressure present when the fuel pump shuts down. The fuel inlet to the carb is solely controlled by the float and needle valve - 3.5 psi is not enough to blow the needle off the seat.

I think the key is going to be in finding out where the fuel is comming from that's leaking onto the throttle plate.

GD

.
..yes, I am useing the return line and the orifice on the front side (radiator side) of the carb can be seen dripping fuel onto the throttle plate..the shut-off valve/switch next to it does work..could it be that the float is set to high

#6 GeneralDisorder

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Posted 08 October 2009 - 09:25 PM

I'm assuming you are refering to the accerator pump nozzle then. I suppose it could be that the float is set too high - I'm not sure if that would cause it or not. Typically the nozzle is way above the fuel level and the fuel is pumped to it by the accelerator pump plunger. Perhaps the plunger is not sealing well....

GD

#7 Petersubaru

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Posted 09 October 2009 - 12:05 PM

Thanks GD for hanging in there..I am beginning to think that the top gasket needs replacement since I can see some wetness along the one side of the carb where the gasket is located..but before I do that...would you know if it is possible useing my mouth to blow air freely thru the return line into the tank (fuel cap off) ..because in my case I can Not....today I attached a toggle switch to the fuel pump hopeing to see some change ..so I manually turned off the fuel pump about 30-45 secs, (until the first stumble), before actually turning off the keyed ignition hopeing to drain the fuel out of the carb bowl ..several attempts of doing this only resulted in the same drip problem but only took a little longer before starting to drip

#8 GeneralDisorder

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Posted 09 October 2009 - 04:04 PM

If the return line is hooked up as stock, then *very* little airflow would be possible while blowing into it. There is an orifice at one of the hard-line connections under the hood that contains a silicone "nozzle" for lack of a better term. I'm assuming it only opens under pressure..... my guess is that the return line is only there to prevent the fuel pump from overheating in the case of the float getting stuck closed. It can only flow a tiny amount with that orifice and the tiny hole supplying the return line hose barb from the main supply line barb at the carb.

Fact is - I have no idea why these cars were equipped with return lines. 80/81 models didn't have them and the pump was under the hood. It was only in '82 that they began putting the pump under the car (to minimize the possibility of fire by insuring that the pump always has liquid in it and never explosive fuel vapor). At the same time they introduced the return line..... I've hookd up Weber's both with and without the return line and never noticed a bit of difference either way.

GD

#9 Petersubaru

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Posted 09 October 2009 - 06:23 PM

If the return line is hooked up as stock, then *very* little airflow would be possible while blowing into it. There is an orifice at one of the hard-line connections under the hood that contains a silicone "nozzle" for lack of a better term. I'm assuming it only opens under pressure..... my guess is that the return line is only there to prevent the fuel pump from overheating in the case of the float getting stuck closed. It can only flow a tiny amount with that orifice and the tiny hole supplying the return line hose barb from the main supply line barb at the carb.

Fact is - I have no idea why these cars were equipped with return lines. 80/81 models didn't have them and the pump was under the hood. It was only in '82 that they began putting the pump under the car (to minimize the possibility of fire by insuring that the pump always has liquid in it and never explosive fuel vapor). At the same time they introduced the return line..... I've hookd up Weber's both with and without the return line and never noticed a bit of difference either way.

GD

Thankyou again and off too exchange the top gasket of the carb..I have kept one many yrs as a spare just for this time..

#10 Petersubaru

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Posted 10 October 2009 - 03:43 PM

..removed the top of the carb (easy enough to do) and installed a new top gasket ,.. also adjusted the float 2mm to sit further into the carb bowl..still leaked but not as much after the ignition was turned off..however it did Not leak after manually turning the fuel pump off as before and running the motor the same 30seconds before turning the ignition off..some change has taken place, but still maybe the float needs further adjustment and/or the fuel pump difference of 1-2 psi is to much..new top gaskets will be ordered up and I will slowly play with this problem whenever...

Edited by Petersubaru, 10 October 2009 - 03:46 PM.





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