Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Idle problem pontiac HO 7237262

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Kilraine hoGTO:
 400 ho engine.. .30 over 670 heads HO manifolds 21/2 " exhaust..xe 274 comp can 230/236 duration .. 481 lift at .5 ,roller rockers700 r4 3:90 rear.. Car performs well idles rough and loses idle (stalls). Petronix2 ignition , 14" vacuum idle 2200 stall torque converter ...all newwites , plugs(ac44) .timing 12 deg initial .. Total36 deg.. Opened up idle plugs on top of carb just a little , which slightly improved ... All other components stock ideas?

omaha:
Probably need more fuel and idle air. Like maybe open up the idle tubes and  maybe add some bypass air.The cam is a bit "aggressive" especially in a 400. Think you may need to pull the idle tubes out and enlarge them maybe to .036. I think the idle speed will end up at around 900 (maybe 950). for the idle air I think I would start at two-1/8 inch holes and maybe go up from there if needed. I think the timing should be ok. If anything may need a couple more degrees on the initial but the total mechanical at 36 sounds right. The early casting is nice for a restored car but has its limitations. It can be made to work but I would put it on the shelf because of its originality and find a carb from the '70's to use on the street. those 1967 Q-jets are getting harder to find these days. Good luck!

Ethan1:

--- Quote from: Kilraine hoGTO on January 10, 2014, 05:39:04 PM --- 400 ho engine.. .30 over 670 heads HO manifolds 21/2 " exhaust..xe 274 comp can 230/236 duration .. 481 lift at .5 ,roller rockers700 r4 3:90 rear.. Car performs well idles rough and loses idle (stalls). Petronix2 ignition , 14" vacuum idle 2200 stall torque converter ...all newwites , plugs(ac44) .timing 12 deg initial .. Total36 deg.. Opened up idle plugs on top of carb just a little , which slightly improved ... All other components stock ideas?

--- End quote ---

 Welcome to CHP! :)

Kilraine hoGTO:
Thank you for reply .. I was told to open up tubes , but no one knew how much .. I dont understand what I should be doung to which part of card tol get 1/8 " .... You are correct in that I should look for a later model carb .. But car is otherwise numbers matching ... I should pull cam and switch to comp xe272. ..i had that cam in a ho 2+2 and it ran extreenly well as well as having good idle manners..

omaha:
the 1/8 inch holes are drilled into the base plate. there is a place to drill them in the casting (usually) sometime they are drilled already. the idea is to let some air get passed the primary throttle blades that is not goin through the venturi. this fills the needs of the engine at idle without the need to open the throttle blades too much (causing nozzle drip.)  usually when a larger than stock cam is used the bypass air is needed. how big the bypass air is depended on the size of the cam or size of the engine or both.  If you  look at the bottom of the base plate you will see 2 grooves that extend from the edge of the throttle bore. at the end of the groove is where the holes need to be drilled. one groove is straight and one is dog-legged. these holes will connect with passages in the main body and will eventually connect with a passage in the top casting that lets filtered air in through holes/openings the air horn casting located near the choke. It acts as a metered vacuum leak though the air is filtered cause the openings are within the inside of the air cleaner.

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