CamaroMan
Petty Officer 1st Class
- Joined
- Mar 18, 2016
- Messages
- 324
Since google brought this page up - I will share my exp of Qjets. I bought one off ebay that was junk (melted by acid dipping) just to familiarize myself with one before I decided.
If you arent aware, quadrajets are spreadbore which means the 4 barrels are not equally sized (like most "squarebore" holleys / eddies / etc)..
Now in a boat one wants low down torque and preferably economy - look no further than a Quadrajet.. The small primaries make UNBELIEVABLE torque because of the velocity, Secondly they have the most advanced booster ring design over just about any other comparable carb out there.. (im not talking 3-400 $ street demons etc). Also - since you will spend 95% of your time in the primaries, you will also net yourself the BEST all round performance and economy out of any other carb. Tan plugs and a smile on your face!
You can find one on Ebay for 25 bucks and with a basic rebuild/tune be in the money for power/economy.
What you NEED to look for / Tune:
Hope this helps someone
*** If someone comes and tell you a 750 Qjet is "way too big" for a whatever motor, they shy of the fact that the Qjet is an "on demand" carb, tiny primaries and whatever you engine can suck secondaries.
On a lame I-6 the secondaries might only open a 1/4", on a mild 350 maybe 70%, mild 350/400 all the way! The carb adjusts to vacuum regardless of cid!!! Thats why its so brilliant, it works on just about any car - even big blocks!
If you arent aware, quadrajets are spreadbore which means the 4 barrels are not equally sized (like most "squarebore" holleys / eddies / etc)..
Now in a boat one wants low down torque and preferably economy - look no further than a Quadrajet.. The small primaries make UNBELIEVABLE torque because of the velocity, Secondly they have the most advanced booster ring design over just about any other comparable carb out there.. (im not talking 3-400 $ street demons etc). Also - since you will spend 95% of your time in the primaries, you will also net yourself the BEST all round performance and economy out of any other carb. Tan plugs and a smile on your face!
You can find one on Ebay for 25 bucks and with a basic rebuild/tune be in the money for power/economy.
What you NEED to look for / Tune:
- There are basically 3 model groups: Pre (74 i think) that have different needles, Post 74 - and the 80s Tbi (usually a blue plastic connector on carb). Ud want the Post 74 non TBI - parts are easier to find! The TBI ONLY work on TBI motors and u cant really do that much.
- Warped top plates: Most people seems to treat carbs like wheel nuts. Make sure yours isnt warped. You can press it flat in a press with wood blocks
- Right - so u have an ok condition qjet.. what next:
- Make sure when u are full throttle the primary blades are at a 90 degree angle (might need to address throttle cable geometry / use adapter)
- The primary needles have a vacuum actuated spring, u need to buy the kits but usually a boat cam has alot of idle vac so u might be fine with stock - otherwise make sure to get one that will keep the needles in position at idle, (spring pressure has to be about 2" more than vac idle iirc)
- The primary needles ALSO have a set screw that sets the "seated" height of the needle in the jets - THIS IS CRUCIAL for idle/low speed! iirc 2 turns back from lightly seated got me in the ball park. *** Some ppl make the mistake of putting earlier needles into the post 74 models and this make the carb UNWORKABLE, you HAVE to make sure your needles are for the right group/family. Ive found 2 instances of seeing the wrong meedles in the wrong carbs. The older qjets are referred to as the "earlier" not "older"
- Check the primary throttle shaft is not worn (actually quite seldom), u can redrill/retap (the butterfly screws WILL break off :/rebush or use a thin nylon strip pushed in from the side.
- Set secondary spring tension
- Correct jets, primary needles (they match up and come in MANY sizes). Use the casting # for stock jetting/needle specs to get u started.
- Secondary hanger and needles (not so important on a cruiser boat).
- The FOUR HOLE adapters work very well to adapt this to a squarebore intake manifold, it will also increase the intake velocity and u MIGHT notice that but prob not - dont bother with the large open adapters, they suck - literally.
- Bonus points for joining the feared qjet club
- If you wanted to get into the power / secondaries you get the right hanger, needles (the come grouped as lean/medium/rich - usually the thicker lean to mid needles give the best power)
- Set and experiment with the spring tension for the secondaries
- If you have a secondary choke pull off (they slow down the secondary opening for a steady climb in power and they are usually very slow - you can get "faster ones that release the butterflies sooner allowing near instant power)
Hope this helps someone
*** If someone comes and tell you a 750 Qjet is "way too big" for a whatever motor, they shy of the fact that the Qjet is an "on demand" carb, tiny primaries and whatever you engine can suck secondaries.
On a lame I-6 the secondaries might only open a 1/4", on a mild 350 maybe 70%, mild 350/400 all the way! The carb adjusts to vacuum regardless of cid!!! Thats why its so brilliant, it works on just about any car - even big blocks!
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