New FJ40 project struggles under hard acceleration

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Hi everyone!

I picked up my first 40 a few months ago, a 1964 with a three on the floor transmission and a 1969 engine which the PO put in. I am very happy with it so far and am enjoying the project; however, I have encountered an issue that I cannot seem to solve. The truck idles beautifully and does fine under slow acceleration or when I step on it after it's already driving, but when I step on it from a stop, it stutters and wants to die and sometimes backfires through the carb. When I pump the accelerator hard a few times and then hold it, it does not seem to do this though. The carb is a Rochester 2G and the dizzy is a Delco Remy 1112403 9K1. I have rebuilt the carb, replacing the accelerator pump (which is what we thought the issue would be), tried different float settings and different jet sizes (came with 49s, tried up through 57s). I replaced all the guts on the dizzy and have tried the point gap at .018 and .019. I've tried different timing as well ranging from 7 to 14 BTDC. To a certain extent, all of this helped, but the problem still persists. Any suggestions?
 
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Just doesn't send it enough gas quick enough I guess? It should work fine if I don't have the vacuum advance dizzy though right? I wanted to return the carb and distributor to OEM eventually, but I guess I will just have to do it sooner than I was hoping. Thanks for the quick response!
 

Downey

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Being the guy who sold a few thousand "properly baffled" Holley 350's between 1970 and 2009 I think I might be interested in ebay #265143683037- -just saying.
 
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Is your vacuum advance working? Backfiring through the carb indicates combustion didn't finish before the intake stroke in my opinion. During wide open throttle you need a lot more advance.
 
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It seems that this distributor doesn’t have a vacuum advance, something the stock ones do have, correct? I'm debating which one is causing the problem more, the carb or distributor, I think my Rochester could work with a vacuum advance as there are some holes that are plugged on the base of it so maybe I will get the distributor and see if that helps so I can put off shelling out the cash for a different carb. Any thoughts?
 
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I decided to go and get a distributor from @65swb45 first after messing around with it some more and talking to some more carb guys. Eventually, I will return to the OEM carb though! I'll post an update when I install the distributor.
 

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