Holley Help !

Bobcat · #1 (**permalink**) 10-06-2009, 06:44 PM

Guys .... about to beat my head against the wall .... again . I have a new ( 300 miles ) Holley 750 double pumper from the Carb Shop on my 482 . I have been fighting a low speed/idle rich condition for a few weeks . Week before last , I tore the carb down and found fuel behind the primary P/V in the well in the throttle body . So I put a new P/V and gasket in and everything was OK .... until last week when the problem came back . Found fuel behind the primary P/V in the cavity in the throttle body again .... and found fuel in the same location on the secondary side behind the P/V plug .
Another P/V went in and the P/V and P/V plug gaskets were changed again.
Same problem again today . Tore the carb down and checked the throttle body mating surface where the metering block mounts for straightness by using 600 grit wet paper on a piece of plate glass to see if I had any high spots . Couldn`t find any .
Fuel pressure is around 5 to 6 psi , using Holley gaskets and I`m not cranking down on the bowl bolts , just snug . I am overlooking something here ..... any and all ideas welcomed !!!

Jerry Clayton · #2 (**permalink**) 10-06-2009, 08:24 PM

I do a lot of carbs and recently had a Holley that did not have a good set of threads in the plate for the PV--so--fuel could and did leak around the threads just like you discribe--holley sent the customer new metering plate but he returned the Holley and got a Demon

rooster · #3 (**permalink**) 10-06-2009, 08:27 PM

Hey Bobcat, I'm having the same problem with my 650 DP.
Gas is weeping out just below the front vent tube when I hit the squirter without the motor running and not getting a good squirt from the primary. Upped the squirter size, pump cam, Same thing. I'm getting fuel behind the power valve also. Contacted Holley's tech to see if they had any porosity issues with there castings and they said - If you have your gaskets installed right you may have porosity. - So bottom line is they didn't answer my question or offer to help. I've been using Holleys for 40 years and I guess It might be time for a change. Good luck, Russ

Argess · #4 (**permalink**) 10-06-2009, 08:34 PM

If the PVs and their gaskets are good, then I'd look at the connection for the accelerator pump passage. I'm not familiar with your carb, but the Holley's I do know sometimes have a brass tube joining the metering plate AP passage to the main body AP passage. I think it is supposed to have sealant on it.......fuel proof sealant. And the other type, the main body AP passage merely presses against the metering block/main body gasket. For this latter type, try holding a straight-edge along the main carb body and make sure there is no clearance on the main body AP passage boss.

Just some thoughts. Sorry I don't know your carb.

Bobcat · #5 (**permalink**) 10-07-2009, 07:34 AM

Thanks for the replies ... Jerry , I hadn`t thought about the threads in the block for the P/V ..... I`ll check that this morning , but the chances of bad threads on both metering blocks ????
Argess .... mine doesn`t have the brass tube , but I`ll check the body for flatness again ... it was late last night when I did it the first time .
I`m going with a Barry Grant P/V this time as it is supposed to be a better one than the Holley .... but that doesn`t explain why the plug is leaking . However , I did find ( late last night ) that some of the plug/P/V gaskets fit MUCH better than others do . I hand selected several and will use those when the carb goes back together .
At least it`s raining so I won`t miss driving time .... and the humidity is so high , the porch and sidewalk is sweating !

Argess · #6 (**permalink**) 10-07-2009, 07:44 AM

If the Accel PUmp check doesn't reveal a problem, it may be the PV gaskets.

The PV gasket should keep out the fuel from the vacuum chamber. Some after-market gaskets are not the best. According to my Holley books, the triangular opening washer is an after-market version of the Holley washer with internal tabs.

They say "Never use the triangular one as you should never use after-market carb parts."

Of the two other types, the regular "O-shaped" one is for PVs with a shoulder and the one with internal tabs is for PVs with no shoulder.

There should be a "step". Look at this pic:

If the gasket were removed, you'd see the step.

Here's two OEM PVs with proper gaskets. The PV without the step, needs the gasket with ears to keep it centered:

This is the kind NOT to use:

Bobcat · #7 (**permalink**) 10-09-2009, 04:46 PM

Thanks for everyone`s input . I think I found the problem . On the metering block(s) , there is a casting stamp . On this carb , the casting stamp/mark is down low and partly under where the gasket for the P/V goes . I measured and it was raised by about .050 inches . When the P/V and gasket were installed , that side was held off the seating surface slightly . It was that way on both primary and secondary blocks . Spot faced the marks so they were even with the gasket sealing surface and so far , no bypass . I talked to a Holley man and he said this was a problem some years ago and the fix was exactly what I did . All I know is that it drove me crazy !

Bob

Cobrabill · #8 (**permalink**) 10-09-2009, 06:24 PM

Holley quality...gotta love it.