Thompson Performance 'Powerblast Plates'

[UNGN]

The Bog starts to happen before the secondaries open, very early in the linkage movement. the "40" I have doesn't look like a 40. I think I'll buy a higher flow screw and larger/smaller nozzle for the primaries, then adjust the cam to come on sooner.

 

[pontiacgp]

If you hook an air/fuel mixture gauge that will let you know what your carb is doing

 

[UNGN]

If you hook an air/fuel mixture gauge that will let you know what your carb is doing

True, but with the accelerator pump squirters you can physically see what the carb is doing and since the bog is less than 1/2 second, it would probably be hard to see on the air/fuel mixture gauge because it would swing from lean to rich so fast.

I will check some things tonight. If the secondary butterfly is opening early, that is the problem, because the secondary squirters are definitely coming on later.

 

[UNGN]

Got the proper drilled screw for 040" squirters, got a proper .040" squirter, turned my Primary AP cam upside down and moved it to position 1 and bog is gone.

The carb probably needs tuning, but it comes pretty hard off an 750-850 RPM idle, now. I have the steering shaft out of the car waiting parts, so I can't drive it, but it seems 100% better, now. Right now most of the credit for it goes to the Accelerator pump tuning video, but the distribution off the plates looks pretty good. Before buying the plates, I would recommend running out of options with AP tuning.

I still need to see how everything works under load.

 

[TURNA]

Did the carb come with 40's in the primaries?

 

[UNGN]

Did the carb come with 40's in the primaries?

I bought it off Ebay for $125 about 15 years ago, so I don't know.

I went to the "hot rod shop" by my work and to get the screws with holes in it, I had to buy a kit from Holley with 2 screws and 2 "40" squirters for $20. It was all he had (and Oreilly's wants $10 per screw and $14 squirter and a days wait if I order them), and I was his only customer so I took it. So now I have 3 40's.

I replaced my old 40 with one of the new 40's and kept the 31 in secondaries. So technically, the squirters are still what has been on the car for the last 14 years and the only change I've made is the plates and moving the primary AP cam to the #1 position.

More, better fuel sooner seemed to fix the problems it was having. Now I have to put it under load to see If its getting too much fuel.

 

[lilbowtie]

Wide band tuning w/ a recorder tells you what your circuits are doing no guessing.

 

[TURNA]

In my 850 I think I have 78's in my primaries and 86's in my secondaries

 

[565bbchevy]

I replaced my old 40 with one of the new 40's and kept the 31 in secondaries. So technically, the squirters are still what has been on the car for the last 14 years

Every square bore Holley I have ever worked on or owned has come with the same size squirter front and ,if there is a difference in pump nozzle sizes the rears would be bigger.so I would guess that yours originally came with 31's and someone put a 40 squirter in the front in an attempt to fix a bog or some other issue, I have also seen people put on 50cc pumps on the front to do the same thing usually trying to band-aid a misapplication.
I would try find out what the original specs where for your carb and set it to that as a baseline and tune from there.

 

[lilbowtie]

Most of the problems I've seen is improper blade to transfer port adjustment.