mikeringland Posted April 4, 2017 Share Posted April 4, 2017 I've noticed when I accelerate from a stop there is some initial hesitation when I step on the gas. It's a very slight stumble and I almost have to feather the gas pedal on that initial acceleration. The stock 4 bbl carb was rebuild last year and the idle mixture screws have been adjusted appropriately, accelerator pump working great The timing is correct Just installed the Pertronix ignition conversion kit (stumbled before the kit was installed) new air filter vacuum is fine at idle plugs and wires were installed last summer Once the car is moving, acceleration is fine, the engine actually runs very well for it's age. I was going to focus on the vacuum advance next, but wanted to get some of your opinions first. Anything else that it could be that I'm missing? Mike Quote Link to comment Share on other sites More sharing options...
Murphy Posted April 5, 2017 Share Posted April 5, 2017 HI Mike, the carb is out of adjustment, specifically the air valve. Is this an automatic trans? electric choke? Any change when the engine is warmed up? Quote Link to comment Share on other sites More sharing options...
mikeringland Posted April 5, 2017 Author Share Posted April 5, 2017 It is an auto trans, and it is all stock, so I think it's just a manual hot air choke. Quote Link to comment Share on other sites More sharing options...
mikeringland Posted April 5, 2017 Author Share Posted April 5, 2017 No change once the engine is warmed up either. Quote Link to comment Share on other sites More sharing options...
Leghome Posted April 5, 2017 Share Posted April 5, 2017 My 72 used to do that. I found my problem was the carb sucking air. My son in-law and I played with it for about 6 months, We found the base of the Holley was bent and not sealing to the intake. So I agree with Murhpy if it is not the air valve check out the base to make sure it is not warped or sucking air elsewhere. Quote Link to comment Share on other sites More sharing options...
rsorg Posted April 5, 2017 Share Posted April 5, 2017 Is the carb a rochester,I had the same ,issues with my stock carb,then a mechanic used a hand held propane bottle and torch, UNLIT OF COURSE ,and slowly turned on the bottle on and waved tip to the base of the carb,after a new carb base gasket was installed (without the plastic sleeves on the bolt holes )and the car was running ,and the rpms went up ,to lead me to believe that the brass bushings in the throttle plate were worn out,VACUUM LEAK, very common on the quadrajet carbs, I had a guy from the web rebuild the carb ,installing new brass throttle plate bushings, runs perfect now, p. s. I have been dealing with this for a long time. Quote Link to comment Share on other sites More sharing options...
mikeringland Posted April 5, 2017 Author Share Posted April 5, 2017 Yes, it's a Rochester Quadrajet carburetor. The stock one that came with the car. I'll have to look into the air valve and see if that's the culprit. Quote Link to comment Share on other sites More sharing options...
stangeba Posted April 6, 2017 Share Posted April 6, 2017 Was the initial timing set with the vacuum advance hose pulled off and plugged? From the factory, the 71 and 72 engines came with a TCS (transmission Controlled Spark) system that prevented vacuum from getting to the dist till the transmission shifted into 3rd gear (or Reverse for testing) Most were totally removed, (mine was in 1971) or the owner thought it was, and or bypassed. After 40+ years, who knows! I prefer using ported vacuum direct to the dist vac advance can vs manifold vacuum. Test the vacuum can on the dist to make sure it is holding vacuum and not just leaking. How did I run my vacuum line? This pic shows a T in the hose from the ported vacuum to both the dist and the emission vapor canister on the left ft of the engine compartment. 71 350 4BBL, automatic no A/C. Good luck, Bruce Quote Link to comment Share on other sites More sharing options...
mikeringland Posted April 6, 2017 Author Share Posted April 6, 2017 I didn't check the timing with the advance hose plugged and capped. I guess I should start with that first. Thanks Quote Link to comment Share on other sites More sharing options...
mikeringland Posted April 10, 2017 Author Share Posted April 10, 2017 Well I ended up bypassing the vacuum cannister and put the vacuum advance directly to the vacuum port on the carb the the cannister comes from. Problem solved. Car accelerates perfectly now. Quote Link to comment Share on other sites More sharing options...
stangeba Posted April 11, 2017 Share Posted April 11, 2017 My vapor canister was leaking, causing the vacuum to be very very low. Back about 10 years ago, I just bought a whole new canister. Happy to hear it's running good now. Quote Link to comment Share on other sites More sharing options...
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