John S Posted August 14, 2016 Share Posted August 14, 2016 I'm hoping someone can help me. I have 70 350/300 with Carter Quadrajet carb #7040203 correct carb for eng. with 350/300 w/4spd. If I gradually floor it I have a slight hesitation. If I hit it hard the car stumbles then takes off. The eng idles great runs excellent at all speeds and the tailpipes burn clean but stumbles on accel. When I move the throttle I can see gas squirting in the primaries. I know these carbs are vacuum secondaries but is there an adjustment on these. In the late 70,s I had a 327 with a Carter AVS that had an adjustment screw to adjust secondaries and I could get it right by increasing or decreasing spring tension. I can see that there appears to be only two holes you can put the pump rod into for adjustment, mine is in the outer hole. I do not know if secondaries are adjustable. If it is the proper carb for the eng it should function correctly. The carb has been rebuilt less than a year ago. I have good vacuum at idle so I am confident there are no leaks. If there is something I can adjust please let me know. I don't want some bonehead in a Honda Civic "chainsaw" car pulling away from me. I like to drive the car the way it was meant to drive which means stepping on it fro0m time to time. John S Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted August 15, 2016 Share Posted August 15, 2016 John, I spent a ton of time on the exact same carb when I did my 4 speed. I could tell you a whole bunch of stuff but the best thing to do is call http://www.cliffshighperformance.com/ your accelerator pump maybe working but it maybe weak, if this carb hasn't been gone thru in a while and with today's ethanol gas, it's time to do a rebuild, Cliff's is my go-to place for quality Qjet parts and advice...hands down! here's some things... it's already lean due to ethanol fuel (carb was tuned for 100% gasoline) throttle shafts worn weak accelerator pump metering rod piston stuck secondary air valve opening to soon low float level plugged passages in carb Quote Link to comment Share on other sites More sharing options...
John S Posted August 15, 2016 Author Share Posted August 15, 2016 Thanks. I'll give them a call. I am not knowledgeable on how ethanol fuel affects these carbs. I know the carb was rebuilt with new bushings and internals.If Cliffs works with them on a daily basis I'm sure he may have an answer. Again thanks. John S Quote Link to comment Share on other sites More sharing options...
lastss Posted August 15, 2016 Share Posted August 15, 2016 You can easily adjust the rate the secondary with a small flat tip & Allen wrench, also change the sec rods & hanger. Quote Link to comment Share on other sites More sharing options...
John S Posted August 15, 2016 Author Share Posted August 15, 2016 After reading up on the quadrajet I believe it is the secondary spring that needs adj. It will be trial and error but I believe that will solve it. Also I watched a video on it. John S Quote Link to comment Share on other sites More sharing options...
John S Posted August 20, 2016 Author Share Posted August 20, 2016 Made adjustment to secondaries. Original setting was one turn clockwise from zero tension. Tried backing off 1/2 turn made it worse. Tightened screw 1/2 turn more from original I could feel the added tension. That took away about 90% of hesitation. Now a very slight hesitation then it takes off. May try going a little tighter but don't want to go too far, if you can go too tight. May also be problem with accel. pump or float level, but that will be for another time. Right now the adjustment made a HUGE difference. I was wondering do the secondaries open slowly or do they snap open? John S Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted August 20, 2016 Share Posted August 20, 2016 try opening your idle screws another 1/4 turn at a time, Qjets idles screws should be out approx 3 full turns or more Quote Link to comment Share on other sites More sharing options...
John S Posted August 20, 2016 Author Share Posted August 20, 2016 try opening your idle screws another 1/4 turn at a time, Qjets idles screws should be out approx 3 full turns or more Alright I will try that. Thanks] Quote Link to comment Share on other sites More sharing options...
wallaby Posted August 21, 2016 Share Posted August 21, 2016 The secondary plates at the bottom of the carb pretty much snap open, but the plates at the top (secondary air valves) rotate more slowly based on engine demand. Normal adjustment of the spring tension keeps them from opening when the car is stationary... so you won't see them working when you goose the throttle in neutral. You need a substantial load on the engine and a drop in engine vacuum to trigger them to open, and you can get that from a test drive. Quote Link to comment Share on other sites More sharing options...
John S Posted August 21, 2016 Author Share Posted August 21, 2016 OK thanks. I appreciate the help especially when it is kept simple. When under a load the vacuum from the intake combined with loss of vacuum at the Choke pulloff that holds plates closed under normal driving must be strong enough to override what vacuum is at the pulloff under hard acceleration. I've got a book on Quadrajets that I saw posted on a previous thread from Cliff at Cliffs high performance. John S Quote Link to comment Share on other sites More sharing options...
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