General Category > Quadrajet Carb Talk and Tips

Main air bleed question

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Cliff Ruggles:
Did you change the camshaft during the engine modifications?  If so what are the specs?

What has been done to the distributor?

With the OD transmission and much better heads, plus raised compression you should be getting a LOT better fuel economy, so something or combination of things are way off the mark.

Are you using vacuum advance?

Are you locking up the TCC once the car is up to speed, cruising on the highway, etc?

What exactly have you done to the carburetor?  Did you use one of my rebuild kits in it?

More information/details are better than less, but for sure something is WAY off the mark someplace........

Jim H:
Oh yeah, the cam. Probably the most important part, it's a Lunati 10120702LK: 219 intake, 227 exhaust at .050". Here's a link https://www.summitracing.com/parts/lun-10120702lk. Sorry 'bout that, not too swift on my part to leave that out.

Distributor is MSD 8362, I am using vacuum advance but for now have the lowest setting on the limiter plate at 5-8 degrees. This is because of a high idle that I am also dealing with (I have a previous post on that) which has improved since I tweaked the linkage but I still think some air is getting past the secondaries. This is actually the main reason I am thinking of bringing the other carb into service. I'm using the lightest springs from he MSD kit, all mechanical advance is in before 3000 rpm. 

The torque converter lockout is confirmed to be working.

The carb was rebuilt and modified to your Recipe #2, although we did not restrict the main air bleeds as I mentioned before. And I am not sure why we went with the 76 jets as they are larger than recommended in the Recipe. The parts came from you.

Compression is good, all cylinders at 160 +/- 5 psi.

To be fair most of the driving done so far has been dawdling around town although there have been some highway miles that didn't seem to make much difference. I have driven the car about 1000 miles since getting it back on the road and overall it is running nicely, smooth with good power. 0-60 is mid to low 6 seconds and it passed California smog easily. Air fuel ratios bounce around a bit on my meter but are in the low 14s at idle, low 15s cruise and 12-13 WOT.

Thanks Cliff

Jim H:
 One more item...initial timing is at 9 degrees

77cruiser:
I think it could use more timing. What is the total WO vac adv?

Jim H:

<< I think it could use more timing. What is the total WO vac adv?>>

Thanks Jim, yes I think you are right. I do want to add more vacuum advance but I have to solve the idle problem before I can do that. The MSD 8428 kit provides 24 degrees mechanical advance so that plus the 9 initial gives me 33 degrees. I could add one more degree as California smog rules allow +/- 2 degrees from the factory setting of 8. I would prefer to keep the car legal if I can, that's less I have to undo come smog time and I already will have to swap out the electric choke and put the hot air back in to pass visual.

I have a thread from a few days ago on the idle, since then as I mentioned it is better since I tweaked the secondary linkage. It's down to around 900 now, I suppose I could try going to the next position on the limiter plate and see what happens. That would add 8-11 degrees. I think some guys get away with 15 initial and 15 vacuum, not an option for me.

 

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