Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

Pontiac 400 - Idle bypass and Secondary rod hanger questions

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DieselPower:
OK,

Got back to working on this car.  Haven't touched it since my last post.  Installed a new AC Delco PCV valve and did nothing else.  Engine started right up (40* or so in garage) and went to a fast idle speed of 2000 rpm.  I had previously had this set to 1400 rpm, so I knew something had changed.  Readjusted fast idle and let it warm up.  Was able to dial the throttle back quite a bit.  Now the mixture screws do something with the best setting about 1.5 turns out.  It still stalls if I have idle speed in park set to 800 rpm.  Vacuum is about 14" still.  Set timing to ported vacuum and changed base timing all the way from 12* to 36* just to see the effect.  Vacuum keeps on increasing all the way to 36*.  Previously, I had about 28* with manifold vacuum. 

My questions now:

1)  Is it realistic to have this thing idle in park at 800 rpm and not have it stall when in gear and turning the steering wheel?

2)  Should I hook back up to manifold vacuum to get timing at about 28* with base timing of 12* (I have a vacuum cannister that is fully actuated at 12" of vacuum.

Thanks a ton guys!

Cliff Ruggles:
My book describes timing engines using manifold and ported vacuum to the advance, and how that deal really works.

In any and all cases you have to give the engine the timing it wants/needs at idle to make things happy, same as fuel delivery.

Using MVA brings in some problems in some applications as the advance can may not fully employ, or stay employed when a load is placed on the engine.

Light distributor springs can also make idle tuning next to impossible.  Make sure that the timing is rock steady at idle speed, and not moving around some, especially when a slight load is placed on the engine......Cliff

DieselPower:
Thanks again guys for all of your help.  I think I am done tuning for now.  Maybe I will go with a slightly smaller cam sometime in the future, possibly a Summit 2801.

For now, engine idle in neutral at about 950 rpm and in gear about 650-700 rpm (stock converter, listed as 1700-1900 rpm stall).  I ended up putting a "B28" vacuum canister on the distributor as a "B20" would not fully actuate in gear.

I now have total timing at 36* by 3000 rpm with base timing + manifold vacuum timing at 28*.  This engine definitely likes as much timing as it can get at idle and since the vacuum can fully actuates at 8" of vacuum, it is always actuated at idle.

Part throttle, cruise, and WOT are all awesome.  This car has only 2.56 gears and 29" tall rear tires but is still able to easily spin the tires easily even with limited slip diff.  I am probably going to put shorter tires on it in the future or maybe even a lower ratio to get a little more out of the car, but for now, it is a great highway cruiser.

Thanks again guys!

Cliff Ruggles:
Good news!  Good results are good results no matter where you end up with these things. 

I've never owned an engine that ran worth two squirts of duck poop with 28 degrees initial timing in it, but if that's what it takes to make your engine happy it's a good thing in my book......Cliff

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