General Category > Quadrajet Carb Talk and Tips

QJet tuning on SBC 350

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Cliff Ruggles:
I can't provide any advice on a carb built from that source, could be anyplace for calibration.  Without knowing airbleed sizes, and what else was done to it, I'd just be guessing.....Cliff

kfa670:
Understood cliff, I'm going to have to take it apart next time I'm home off work, and figure out what they are.

kfa670:
Well, its been a while... but I was finally able to get a few measurements on my carb.  These are approximate but pretty damn close I think.  My Numbered drill bit set is in a little rough shape and I'm missing a few.

17054208

Idle Tubes: .042
Idle Down Channel: .046
Upper Idle Air Bleed (Main Cast): 0.064-0.067
Lower Idle Air Bleed: 0.072
Idle Bypass Air: 0.065
Mixture Screw holes: 0.088

MAB (body): 0.112
MAB (Air horn): 0.112

Main Jets Currently 0.072
Primary Rods Currently: 0.046K

So I'm assuming I have a big MAB carb, but I know for a fact they aren't .125" as that size bit wouldn't fit.  This carb came from an aftermarket source but the only strange thing I found with it is that it had two different main well bleed tubes.  One was much smaller than the other, and wasn't at quite the same depth.  I drilled out the smaller one to 0.042 which matched the other one and put it at the same height. 

Since Cliff mentioned the original specs have much bigger main jets, I put in some 0.074s and gave it a try.  It started up SO much easier and the Mixture screws were way more effective.  I took it for a drive and while the idle and everything is great, off Idle (with .046 rods) has got to be WAY to rich.  Off idle it is sluggish and smokes like crazy.  If I'm in neutral, and I blip the throttle, It isn't very snappy and I get a puff of black smoke out the exhaust.  If I disconnect the accel pump, it is much more responsive and basically doesn't smoke at all.  However, With the .074s in, the top end is MUCH improved.  Actually feels like it has horsepower!

So my question is, do my measurements make sense, and what should I do to clean up the richness off-idle?  I have some .048, .050, and .052 rods coming, but they are all the M style, hopefully that will do the trick?

Cliff Ruggles:
WAY too much idle tube for that carburetor, and most likely why it is rich right off idle.

I'm still confused some, aren't we working with carb number 17058204?

I don't know what 17054208 would be from?.......Cliff

kfa670:
Yep sorry, its a

17058204

I get a little dyslexic with the keyboard sometimes...

I'll order up some idle tubes, what size would you suggest?  And in your book you say to use the .026 inch tip metering rods with these large MAB carbs... I only have 3 sizes in hand, a .046K a .041K and your .044Ks.  Stock for this carb were .052K?  Will M Rods work if I adjust jetting accordingly? 

Thanks Cliff

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