Let me repeat this is an old Carb, it doesn't have any vacuum ports at all. It is a 750 with vacuum secondaries. I have it on a 383 with GM Hotcam. The problem is that it cuts out, well its more like a miss at around 4000 and up intermittent like, you know it isn't like its running out of fuel. Before I rejetted it the sucker would cut out bad, now I have #70 jets in the primaries and #74 in the secondaries. I am pretty sure it isn't floating a valve because I never had a problem with the previous carb except that it was too small (600 Edelbrock). The floats are set correctly and the pv is 6.5, the accelerator pump is also set correctly, I am looking for suggestions. It has been a few years since I played with a carb and I have forgotten something apparently. Any help or suggestions are greatly appreciated. Thanks!!

 

sounds to me like its leaning out. i would jet it up 2 sizes and try it again.i've always jetted mine the same on the primary and secondaries too.you get the right power valve by dividing your highest vacuum reading by 2 and addind .5 . example , you get 14" vacuum . 14/2=7=.5 = 7.5

 

If the problem you say from 4000 up is while under fairly heavy throttle opening (well into the secondaries) the secondary jets are too lean. If there is no power valve on the secondary side
install a #80 sec jet. I've always used 70/72 primary jet and
80 to 84 sec jet on 750 holleys with good results. You may also need to install sec jet extensions to keep the sec side from starving under acceleration. This may require a notched float.
Hope this helps

 

Sounds like you didn't read my post about the PV. Go to the link on that thread and read what Holley has to say - get it from the horse's mouth.

Also, a Holley carb with primary PV, no secondary PV should have secondary jets 6-8 sizes larger than the primaries. If the primaries run fine with the current jetting, just jet-up the secondaries and try that.

james, no vacuum ports at all? Not even for the vacuum advance?

 

I have tried #78 jets in the secondaries and it didn't make the slightest difference. Now I am playing with the vaccuum canister for the secondaries. Someone cut the original spring so I bought new ones and tried a weaker spring which should open up the secondaries quicker, that helped a little. I think I need one step stronger and that may cure it. This carb has absolutely not one vaccuum port. Thanks guys!! If you have any more suggestions let me know. Also it has a primary power valve, but no secondary. What difference will that make?

 

Check the needle and seats. Some of the old holleys
came with real small needles and seats. Should be .093" to .110"
with 6 to 9psi fuel pressure for a healthy 383.