Holley 390 carb help needed

[gtbrain]

I have a holley 390 carb on my 66 250.

If I let my truck sit for a couple of days without starting it, the accel pump on the carb will not send fuel to the squirters.

For some reason it builds up enough pressure to not allow linkage to work the lever on the pump.

If I pull the carb and loosen the 4 screws on the accel pump housing, it will shoot out fuel under pressure. I can then get the linkage to work the pump.

I am baffled. Anyone have a cure for this?

[blown240]

Maybe you got some gas with some junk in it and the squirters for the accel pump got clogged? That happened to me once when I got some really cheap gas.

[gtbrain]

Thanks. I havent noticed anything when I have taken it off. This last time I took the float bowl side apart and it seemed clean with no debris. The truck has a new gas tank.

I can just release the pressure from the pump housing, remount the carb and it will squirt fuel just fine. The pump lever will work just fine. It does this regularly if the truck sits for a few days. Frustrating the heck outta me.

[chevy_mike]

Sound like some internal check valve or ball is being put under pressure, possibly by the fuel evaporating as it sits. It's not venting this evaporation. I have this carb but have never experienced this problem and I have let it sit for months at a time.

[cdowns]

Is the carb mounted ontop of a phanolic spacer to isolate it from the engine heat?

[gtbrain]

The carb is mounted on an Offenhauser intake with just the adapter plate for the holley 390. I don't have any additional spacer.

['68OrangeSunshine]

I ran a Holley 4160/R8007 390 on my '68 292 for 25 years (before I switched it out for a 1404 Edelbrock).
Offy intake, Clifford headers.
But I never had the gripe you mention.
1] Headers or OEM cast iron exhaust?
2] How long since carb was rebuilt? [Sounds like some passage is clogged]
3] What kinda fuel filter?

I changed out the normal 33CC accelerator pump to a 50CC to clear up a hole-shot problem. Not that it would clear up your problem, but it sure was fun.

[prostreetC-10]

There is NO WAY your accel pump housing is building up pressure and forcing the diaphragm not to move. Especially if it's sitting for a few days. You need to pull off the shooter and check the little plunger that is down inside the main body. How old is the diaphragm? Fuel trickles passed the check ball or valve through gravity to fill the housing. When you activate the pump, they close, forcing fuel through the metering block and into the main body where the shooter passage is. If you're diaphragm isn't old and dry, thus causing it to hang up, you have something blocking the passage through and to the shooter. One of the things that can happen is gasket material, especially if old and coming apart, can get hung up where the fuel bowl meets the metering block. If I had to guess though, your plunger is, some how, hanging up and stopping fuel from getting to the shooter. It's not a pressure problem though......


Oh and there is never ever ever ever a reason to put a 50cc pump setup on a 390 or any other carb than a Dominator or a 660 center squinter. If you put a 50cc pump on a 390 and it cleared up a problem, you have something else going on and the change just went around it. Just sayin'

[gtbrain]

Thanks for the responses, i do appreciate the input.

I have a cast iron header. The carb is only a year or two old. Has not been run too much in that time. Inline glass filter, that is fairly new also. I can see no sediment in it.

Prostreet, it is weird. Just today i had it apart once again. I checked the shooter and the plunger, nothing blocking them. Diaphragm is new. Like I mentioned, when i loosen up the four screws on the pump housing fuel will spray out. This is even after draining the fuel bowl. There is still fuel within the diaphragm. I just can't find any blockage. But i can put it all back together and the pump lever will work without resistance and I can have fuel squirting.

This has happened pretty much since i put it on the truck. Again, I do appreciate the help, and I imagine it is something simple plugging me up but it is getting frustrating having to dingle around with it after it sits for a couple of days. I am, though, getting really good at pulling that carb off and on, so i got that going for me.

['68OrangeSunshine]

Originally Posted by prostreetC-10

Oh and there is never ever ever ever a reason to put a 50cc pump setup on a 390 or any other carb than a Dominator or a 660 center squinter. If you put a 50cc pump on a 390 and it cleared up a problem, you have something else going on and the change just went around it. Just sayin'

Well yeah, the problem was that Cylinders #3 and #4 were not functioning. So the 50CC shot made it a real lopey 4-Banger.
Shortly thereafter, I rebuilt my original 292 block, and after the 500 mile break-in, when the 25 year old Holley 390 wouldn't hold a set, we figured its baseplate was warped. So I R&R'd it for an AFB clone, 500 CFM. It was economics that made me switch. But we're getting off topic.

[prostreetC-10]

So you are saying the carb was new when installed and hasn't had any work done to it?

I have had a thousand or 2 holleys run through my hands and I can say that I have never heard of anything like this. Granted, it can be very easy or very hard to diagnose a problem over the computer with just what you have said. Once again the housing is gravity fed and not under any pressure. If it was the shooter would always dribble. You also have a bowl vent that would/should bleed off any pressure in the fuel bowl. This is a head scratcher for sure. hmmmm.....

['68OrangeSunshine]

Cast iron headers -- like Tom Langdon's "Late Chevy Fenton-style" or OEM manifolds?
Either way, I don't seen the need for a phenolic spacer like a 4 barrel on a V8. L6 carbs just don't get that much heat. Some people in temperate climates add a carb heating set-up on aftermarket carbs/manifolds just for fuel/air equalibrium.
It sounds to me like your squirter is defective. Try cleaning up the bore with a very tiny drill bit, or replace the squirter with a genuine Holley part. You don't want to open the bore too big, or your squirter will be out of calibration.

[gtbrain]

Yep it has the Langdon stove bolt headers.

And yes the carb was new. I did add the quick change secondary housing kit. The squirters have been changed numerous times to get the right ones. Along with the diaphragm, just cause i thought there might be something wrong with it. I also bought a rebuild kit from holley with an abundance of parts. I agree with ya Prostreet, it is a head scratcher. Thanks.

[GASoline71]

How old is the carb? Holley went through a run of carbs that the plating was flaking off in the bowls and the metering blocks basically disintegrated. I know that was some time ago... late 90's maybe?

Gary

['68OrangeSunshine]

What did the experts at the Holley Tech Line have to say?

[prostreetC-10]

Originally Posted by '68OrangeSunshine

What did the experts at the Holley Tech Line have to say?

LOL are you joking?

The few times I called Holley tech it flat scared me. I was trying to get an idle discharge hole size for a certain carb and he kept trying to give me the air bleed size. The really smart guys at Holley all work in the back with the race teams. Maybe it's changed but I couldn't believe some of the things I have been told over the toll free line. There was one older guy there and I think his name was Ricky, that knew what he was doing. They rest? Uh........

Just giving you a hard time Orange Sunshine but you can probably get better help here than Holley Tech.

['68OrangeSunshine]

Originally Posted by prostreetC-10

LOL are you joking?

The few times I called Holley tech it flat scared me. I was trying to get an idle discharge hole size for a certain carb and he kept trying to give me the air bleed size. The really smart guys at Holley all work in the back with the race teams. Maybe it's changed but I couldn't believe some of the things I have been told over the toll free line. There was one older guy there and I think his name was Ricky, that knew what he was doing. They rest? Uh........

Just giving you a hard time Orange Sunshine but you can probably get better help here than Holley Tech.

I don't doubt you can get better help here. This board is amazing. And it just gets better. I have had problems communicating with Edelbrock but I was asking about a Carter AFB Comp Series 9605S [same as a Performer 1405] and I let my 'Edelbrock cover' slip. Dude clammed right up. ''We don't know anything about Carter carburetors."

Back in the day when I bought my first Holley R8007 390 and I took it back to the speed shop in pieces to ask how to reassemble it, the guy just took one look and said "Ya know that was a defective batch, kid. Here's another one." [Now scram] I guess I got my $82.07 worth.
I do think the manufacturer has a duty to his clients, and GT Brain should at least get their opinion. It's free.

[gtbrain]

hahaha. No I have not checked with the holley techs. I have to agree with Prostreet, I get better help and info from you guys on this forum.

As far as the carb, it is sitting on the bench in the back garage. I have not installed it yet. But I will give an update when I get around to messing with it again. It just has to be something simple.