Pressure builds up in carb until accelerator pump won't push down

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dmaddox

dmaddox

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Initial problem:

Cold Starting
No "squirt" from accelerator pump.


Fix:

Bought carb kit - replaced air-horn gasket and accelerator pump.

New Problem:

It started great after the reassembly and even idled better than before - but after idling for about 45 seconds, the I thought I'd try to push the accelerator pump down - it was hard as a rock!

I thought for sure it was hung up on something in there - so I started to take the airhorn back off and when I took out the last screw - it sounded like taking the gas cap off on a hot day and I was able to operate the accelerator pump no problem.

I asked a buddy and he said plugged return line.

Sooooo.....I disconnected the return line and I am able to blow in it - but if I blow and blow I can feel it building up until it wheezes air back out at me.

What is going on?

help!

Not sure it's related, but I noticed the line on the bottom of the charcoal canister broke off.

Vehcile: March/1978 FJ40 - completely bone stock - down to the airlines.
 
I would think the return line would have to be blocked at the carb fitting. When you blow in the return line are you pressurizing the gas tank? Try blowing with the fill cap off. If your clear to the tank than it sounds like it's in the carb. Isn't there a regulator in the return fitting?
 
I just started the cruiser and built up pressure again.

I then removed both lines (send and return fuel lines) - nothing squirted out of either of them AND....with both lines disconnected - the accelerator pump STILL had pressure - I can't push it down - unless I break the seal on the air-horn.

So, what would cause such a huge pressure to build up in the carb at the accelerator pump?

There is not a regulator in the return fitting that I know of....
 
I would guess that the outlet from your accelerator pump is blocked
 
Actually the return line only returns the fuel that doesn't go through the float valve into the bowl so I'm going to say the bowl vent is blocked.

What is the fuel level in the sight glass.
 
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fuel level is right on the dot.

I checked BOTH holes that go into/out of the accel pump channel.

1. The main hole just dumps into the fuel bowl.
2. The other little hole goes into the "bb"/"little spring"/"T-valve looking thing. The passage is clear - but the gasket covers the top of it (as did the old gasket).

After checking both channels - ITS STILL building up pressure and I can't push the accelerator pump down until I crack the seal on the air horn.

What else could be plugged? I have the haynes manual open here looking at the "bowl vent" now as you have mentioned Toyo - thanks.

Any other thoughts while I check this?

-dallas
 
I dont see anykind of bowl vent you mentioned.

This is a strange one. I can't figure this out.

I noticed this last time that even WITHOUT firing up the engine, as soon as I snug down the airhorn, YES - I can push the accelerator pump down - but I notice that the rubber boot expands on the top of the pump rod. It is only after I loosen the top of the carb (what I keep calling the air-horn) that I can push it down - and I noticed that it is squirting between the airhorn and gasket - not out any jet anywhere.

I don't know what to do.
 
Is fuel supposed to push out the bottom of the accelerator pump channel? When I look down there, there is a "BB" in the bottom with a retainer.

Second, the gasket (new and old) covers the "stopper" as the haynes manual calls it. There is a "stopper" and then under that a spring (that looks similar to the sring in an ink pen) and another "BB" in the bottom of that channel.

I ran wires (the little "E" string of a guitar) through both channels.

This is really aggrivating.

Thank you for any insight as I research this problem today.
 
Hey Dallas, can you post a picture of the 'stopper' your referring to that is covered by the gasket? Remember that other gasket that we looked at that had a slightly different pattern? I'll pull it out and see if that reveals anything.
 
The stopper I am referring to is "P" in the following picture:
carbfigure1.webp
 
Pin_Head said:
From what you described, I'm not sure there is a problem. You can't just push the accelerator pump rod down; it only moves when you open the throttle.
Click to expand...

thanks for the tip Pinhead - but ....

What happens is that when I button everything up and start the cruiser - you can't push down on the accelerator pump at any point in time.

Even with the cruiser off - you can't push it down.

Only when you break the seal on the air horn, does it go down.

-dallas
 
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I had the exact thing happen to me last week. My carb is a '75 federal model. I would take the horn off and the pump would wrk fine, put the horn back on and it would start, then the acc. pump would not pump, like pumping against a closed valve.Thats when I saw that there was a little rubber O ring on the T shaped valve you talked about that would plug the acc. pump outlet when I tightened the air horn down. I dont know anything about carbs, but my money is less than brain power at this point so I just removed that O ring and now my accl. pump works fine . Also that ball under that G shaped clip was corroded so I cleaned and replaced the ball (they come in the carb kit) I had to use a hemostat to remove the the clip. I hope a carb guy will respond because I want to learn this stuff aswell. good luck.
 
I've had that T shaped valve out about a dozen times. The only thing in that channel is the valve, a spring, and a BB in the bottom.

I did notice however that the BB directly under the pump plunger (at the bottom of that throat where the accelerator pump is) is a bit corroded - I didn't take that apart.
 
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