wrong q-jet on 430

Discussion in 'The Venerable Q-Jet' started by smooth98, Jul 9, 2004.

  1. smooth98

    smooth98 New Member

    have a '67 electra with a 430 that's idling rough. i tuned it up within the last year and along w/ new wires, points and plugs, timing and dwell are right on point. i suspected carb trouble, so i considered a rebuild of the q-jet. i ran the number on the carb, and to my surprise, the numbers suggest that it came off a '67 chevy smallblock. if i remember correctly, in a past thread someone said that a q-jet for a smallblock won't idle correctly on a big block motor. any suggestions will be appreciated! ( q-jet designed for bb? new edelbrock?)

    this site is the best, man! really feels like family here.

  2. RAbarrett

    RAbarrett Well-Known Member

    Can you be more specific regarding the rough idle? Can you identify the cylinders running rough? I have specific reasons for the questions, especially with my knowledge of these carbs. How does the fuel inlet orient with respect to the engine? Ray
  3. smooth98

    smooth98 New Member

    thanks for your reply, ray. unfortunately, i don't know how to determine what cylinders are running rough. the fuel inlet is oriented in front in respect to the engine. i neglected to mention before that in addition to the rough idle. there is a "flat" spot in the initial acceleration when i hit the gas from a full stop. also,when cold, it takes about 10 sec. of cranking (along with pumping the gas pedal) to get the engine started. that being said she always starts and has no other problems.

    thanks again for your reply and advice

  4. darrenkp

    darrenkp Love that Torque!

    If you can post the number off of the carb., I can double check it's origin for you. Make sure it is on the drivers side, stamped vertically. It will be 7 or 8 digits and begin with either a 7 or 1.
    Last edited: Jul 13, 2004
  5. RAbarrett

    RAbarrett Well-Known Member

    Here is the method of determining the cylinders with the problems. Remove the spark plug wire from the cap, noting whether the cylinder runs rough or does not respond. Knowing which cylinders are affected and which are not will tell me volumes of where to proceed.
  6. John Eberly

    John Eberly Well-Known Member

    Wrong Carb

    Take it from a guy who knows - get a big block carb, preferably rebuilt by one of the better known Buick carb guys.

    I am just working through this problem on my '68. It has a relatively healthy 455 and I've been running the '68 spec Q-Jet that came on the 400 in the car when I bought it in (supposedly) original condition. When I checked the carb numbers, it turns out that this is a '68 Buick carb but it's for a 350!

    The car always idled rougher than it should have. I have a performance cam but not anything outrageous, and the car always shook like a willow tree. This spring, it also started to exhibit surging at part throttle and cruise. I think this may be due to some loose chunks of epoxy from an old fuel inlet thread repair.

    I fought with this carb for 4 years, trying to modify it and get it set up to work on my motor. At the Buicks at Norwalk this spring, I met one of the "gray hair" Buick racers and carb tuners. He mentioned that he could fix my problem, so I bought a big block spec Q-Jet from him. I just slapped the carb on the car Tuesday night, didn't do any tuning because of a thunderstorm rolling in. It appears that the idle and cruise problems are fixed, and once I adjust the choke linkage I should be good to go.

    The small block carbs do not allow enough air or fuel to pass for adjusting idle. I drilled my primary throttle butterflies to allow more idle air, but the curb idle screws didn't have much effect on idle. The flat spot you have is probably because the transition slots are not allowing the proper amount of enrichment as the throttles crack open. They are also sized differently on the small block vs big block cars.
  7. smooth98

    smooth98 New Member

    fellas, thanks for your replys. sorry for the long response time--this is the first chance that i could get access to the computer.

    ray: thanks for the tip concerning the cylinders. i'll use that method this evening and post the results as soon as possible

    darren: the carb number is 7037213. thanks in advance for the double check

    john: thanks for that sound advice. and for the info on carbs, because i am definitely a novice when it comes to carbueration.

    thanks again!

  8. RAbarrett

    RAbarrett Well-Known Member

    Food for thought... the wrong carb will cause its share of problems foer several reasons. The main reason is that the Qjet has more than its share of specialized passages for a specific function, including idle, off idle, low cruise, high cruise, hwy and power. These passages are tuned for the engine "package" used, which includes engine size, trans application, tire size, final drive ratio, and emission package. Whenever using a Qjet, use the one specified for the package, or expect to have problems. These carbs can be tuned, and I have the expertise to do it, but it is in many cases best to have the correct carb, especially in emissions trim. The Qjet is not a one size fits all like the Holey, misspelling intentional. Qjets rule, but must be understood.
  9. darrenkp

    darrenkp Love that Torque!

    You are right. Definately from a '67 Chevy. I couldn't find out which engine, though. The forth digit indicates 1967, the next to last indicates Chevy. This would be a 4 for a Buick carb.

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