Anyone have any stories, good or bad regarding sending your quadrajet away for rebuilding. Costs average about $250 for complete rebuild and testing/tuning on a live engine. I'm attempting to cure the hesitation in my BB chevelle.

Thanks in advance

Good Lord! Don't even send your Q-J to someone for that crazy amount of money!! That is crazyness! You are a motorhead. You must attempt to do these things yourself before you pay for services!

Unless your lazy like me....

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"I been chasing a madman for 700 miles."
-Smokey and the Bandit

Sean Thomas
TC Member #907
Sean's Garage (http://www.chevelles.com/showroom/gorbe1.jpg)
70 Chevelle SS 396/350 hp
71 Chevelle SS (clone) 400/450 hp

Gary, I've sort of taken to doing these rebuilds for friends. Admittedly Holleys are a much simpler mechanism to tweak, but QJ's aren't that bad once you've done a few.

AS far as the "pros" go. I cant remember who, but someone here had a carb done by one of the "pro" shops and , even as an amatuer I could tell the jetting was way off where it should be.

Another "pro" up north in Canada did a carb for a friend ( member here) and put the nastiest seat in I've ever seen. Chatter marks all over the actual seating surface. It ran rich. Jets too big. Yeah, or maybe put a seat in that actually works.

So the "pros" have no monompoly on knowledge and, at worst, screw up just like you and I would. Maybe its bad help I dont know.

My advice to you. Pull your spark plugs and see hoiw the mill is burning, rich,lean or just right. If your plug color is close to the "lightly toasted marshmallow" then your hesitation is not jetting related.

Depeding on the nature of the hesitation it could be one of 4 things.

If hesitation is just off idle , or at cruise where secondaries are not yet opening:

1. Float too low. Should be set so mild pressure to seat needle has the rear of the float sitting 5/16" below the top of the casting.

2. Accel pump needs more shot or is worn in the bore. Either replace the diaphram, or simply move the accel pump rod to the outside hole in actuating arm.

3. The trickiest - your power piston piston is either too weak tor too heavy. The power piston is analogous to a power valve in a Holley. As engine idles and vacuum is high, the spring holding the piston up is overcome and the psiton sucks down, bringing the primary rods with it, into the jets. As vacuum drops, the spring overtakes and raises the piston and the attached rods, and bring them out of the jets, enriching the primaries.

And if the bog is clearly in the secondary side of the carb, either

1. The tension on the air flap is too tight or loose. On the pass side of carb, you will see a screw under the air flap rod, where the pull off connects. Under this is an allen set screw. Back the set screw off and tweak the tension of the tensioning screw. Only go in 1/4 turn increments. This governs the opening rate of the secondary air flaps ( the throttle plates are mechanical down below). As then open they raise the secondary metering rods out of their "jets" ( just machined holes actually). If the flaps are too loose, the rods come up too quick moving too much fuel, and if they are too tight, not enough fuel is metered. If you find that by loosening the allen set screw you have lost all tension, I typically start at 1/2 to 5/8 of a turn for 4 speed/loose converter cars and 5/8 to 3/4 of a turn for stock auto trans cars.

Or the actual rods could be the incorect taper. Again, allowing too much or too litle fuel to flow by. This would be more subtle than the air horn not being adjusted right.

So spend the $15 on a rebuild kit at a good parts store ( I use Carquest), pop the top off the carb ( this will be the hardest part of the whole drill ) and tweak your own QJ.

HPH and best of luck.

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Gene Chaas
Gold Member 62/ACES
67 SS 427 (http://www.chevelles.com/feature/october2000.html)

GREAT advice Gene. , to go along with you advice. I recommend an HP book. " Rochester
Carburetors" by Doug Roe.IF you want to know the in's and out's of the Q jet, And want to tackle the problems that are inherent with this Carb, it's the cheapest 15.00 bucks you'll ever spend. and it's chock full of rebuilding tips for stock carbs , and mods to enhance the carb plus lots of cool carts,
and a comprehensive tuning section.

Wayne

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All good advice here Gary - this is my .02 worth of concurrence. Your hesitation can be caused by any number of things - which a rebuild may NOT correct.

If you seek a simple rebuild, try not to suffer from Quadraphobia - purchase the "Row" book and the aforementioned kit then dive in. If the QJ has never been rebuilt it's probably a good idea to replace the float as well but it can be tested first. You'll also have to pay attention to the throttle shafts where they pass through their bores - they are prone to wear and therefore, vacuum leaks.

If you still choose to send it out, do select your vendor carefully. Keep in mind, however, although testing/tuning on a live engine sounds like the cat's meow it is misleading. Running it on a live engine will show that, yes, it will actually run. It will NOT give you any assurance that it will run correctly on YOUR engine, unless the test engine is exactly like your's (cam spec's, intake, exhaust, compression, ignition, etc) and installed in a vehicle with a similar weight and drive train.

If you'd like more information feel free to drop me an e-mail. I will also share the name of a particular vendor that you should NOT choose if you go that route.

All - here's an interesting link for those who've not see it;
http://www.dapa.org/frazier.htm

Regards,

Dan

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Awww, fer cyrin out loud, there's that IMPALA guy again.

http://photos.yahoo.com/bc/ss3964spd?d&.flabel=fld1&.src=ph