Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Iffy idle, low vacuum problems....

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KJMason:
Will do Cliff.  I was surprised at the cam choice myself even though I know little about them.  Got any recommendations for a good replacement for street use that'll still give me good vacuum for power brakes while taking advantage of what parts are already there?  Any tips on the idle air bleed screw on top?

Cliff Ruggles:
On that carb the screw is main air, not idle air, so leave it fully seated (richest position) for initial testing.

A very good cam for that application at 10.5 to 11 to 1 compression is the Crower 60919 cam.  I would install Rhoad's lifers on it, but it will make over 500hp/550tq with decent idle quality and strong/broad torque curve.

We built and dyno'd a 455 with 87cc E-heads (unported) and that cam, and it made 505hp, 551tq and pushed a 3900lbs Firebird to 11.50's at 118mph in full street trim......Cliff

KJMason:
Cliff, enjoyed our conversation last week, hope your trip went well and your new Harley is as nice as you expected. 

As you suggested, I did a compression check and came up with 220lbs,  pretty much exactly what you said to expect with the small cam.  The good side is that my rings/valves/head gaskets are in great shape but the down side is that I guess that confirms that I have the small E Performer Plus cam. I don't suppose that tells you anything about what the cam timing is though, does it?

I also ended up R&R my original distributor with one from Summit as my timing had been wandering a bit and I found the lower bushing was completely shot and the distributor shaft badly galled.  Also replaced the plugs and wires.  Plugs looked to be in the right heat range but the mixture looks just a little bit rich with a bit of black soot on the base.

The new distributor has helped the idle a bit and the timing is rock solid but vacuum is still low of course. I'm still getting the timing and advance where I need it (still haven't road tested things yet) but given the continued poor idle it sure seems to me I must have a vacuum leak somewhere.  Before I replaced the distributor I tried both the carb cleaner and propane tests looking for a leak with no success and I'm thinking that the wandering timing may have masked the engine response to the cleaner/propane so I need to look again.

BTW, I did some looking into the 60919 cam/Rhoads lifters you recommended and that's what I'll eventually do as well as looking to replace my current intake and doing a drop base mod to the air cleaner but none of that'll happen for a while so I need to get the current combo working as well as I can.

Also, a last question but I've seen several places where people have claimed the stock power brakes should work down to about 12"-13" of vacuum but mine (stock booster/master/disk/drum combo) needs more like 15"  Should 12-13" really be enough for GOOD performance (seems doubtful) or is 15" more normal?  I'm considering replacing the whole assembly primarily to improve performance but also cosmetics.  I'm just really looking to prioritize my changes to get the car more drivable.

Cliff Ruggles:
The engine is doomed with that cam in it, and it will never run correctly.  The intake valve is just closing too soon, nand not nearly enough overlap for the CID and compression ratio.  That cam is a great choice for a 400cid engine build with 8 to 1 compression, but will never yield desirable results in a 455 build over 10 to 1 compression.

I'd start with a cam swap, and things will get a LOT better from there on out......Cliff

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