Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

Mods on a 7041262 for a RAIV 455 engine. Are they OK?

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MattK2:
I modified a 7042262 to the "3rd recipe" for my motor, and it worked great when I first got it going last fall, but it dripped.  Ended up having a micro crack that would open when hot.

I sent my carb out to be serviced, he confirmed the crack, and found a donor 7041262 body and air horn.  It was a 11 day turnaround with shipping.  This "newer" carb has slightly different guts than the one I built.

My engine is a 455, 0.030" over, RAIV cam (adv.4*), 9.3 CR, 6X-8 heads.  400 hp/ 500 ft-lbs

The first carb: jets 74, rods 37, tubes 38<-------cracked carb
the second carb: jets 77, rods 43, tubes 36 <---------current setup.

It idles at about 13" vacuum, cruises at about 19"

Total timing is 37*, initial 15*, vac advance 15+*, curve is very generic and being addressed.

I'm still experimenting between ported and manifold vacuum signal to the vac adv. can.  At the moment I'm using manifold. 

Idle is poor when cold, seems like a choke issue, better when hot.

Restart is weak when hot, better when cold or warm.

At a 20 mph roll, if I drop the hammer in 1st, the tires break hard and it goes like hell, so that's good.

Cliff Ruggles:
77 main jets are HUGE in one of those carburetors.  I'd go back to 73's or at most 74's with 42 or 43 primary rods.

Idle tubes will need to be .038" for the RAIV cam at that compression ratio...

MattK2:
A 73/43 combo. OK. I need to purchase some jets and tubes.

Any thoughts on why a hot start seems overloaded with a weak vacuum signal?  That’s my assessment of it.  It starts soon enough, but doesn’t come alive like you would expect from a hot engine.  No quick pop off. I could set the idle up to 900-1000 and it’d start better but then it could develop runon at shut down.

And, it would be great to get the idle around 700 and not be so rich. I lean out the mix screws and it’s not helping much. The. I start messing with vac advance signal to help. Going in circles.

Cliff Ruggles:
Check to see if there is enough vacuum at start-up to fully employ the vacuum advance.

In many cases to effectively use MVA you'll need a VA that fully applies much lower or all of the timing may not be in at start-up or even at idle speed.....

MattK2:
Soon I’ll be swapping dist. Current one has a long curve. Generic.  Going to try 1000-3000 range.  Letting the builder decide on the rate.

Swapping jets and idle tubes once they arrive. Going to measure everything when it’s apart.

Given that carbs were spec’d to specific engines, does it make sense to modify a carb similar to a 69-70 RAIV spec’d carb. those carbs are around. Rare, but those specs are out there, right?  It’d be a good starting point.  Small tweaks from there.

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