Bad Leak from Baseplate Gasket

[rwberinger4x4]

Hey All,

I recently purchased a new (rebuilt) quadrajet from a reputable builder for my 283 with Edelbrock SP2P manifold.  This Quadrajet, Serial# 17058222 bolted right up and ran great for about the last 100 miles, but this weekend, the truck it's installed in would barely hold an idle, stumbling badly down around 450RPM, instead of the 700ish I had it set to. 

Covering the air inlet in the top of the carb smoothed out the idle immediately, so I knew I was looking for a vacuum leak.  Investigating with Carb Cleaner showed a big change in idle when spraying around the base gasket, where the carb meets the intake manifold.  The gasket used was supplied with the carburetor by the rebuilder.  It's one of the 1/4" thick, open-plenum gaskets with nylon reinforcing rings around the bolt holes. 

The throttle shafts on this carb should already be bushed, from the rebuilder, so I don't think thats the issue. 

Could the throttle plate have warped this quickly?  I was careful to only torque the bolts to 12-15 ft. lbs. and it doesn't seem like they've come loose.  Are manifold gasket failures common?  Could I have just gotten unlucky? 

A question for Cliff: I had ordered a rebuild kit for my old Buick Qjet I was trying to revive previously.  You provided both a thick "open plenum" gasket as well as a thin, 4-hole gasket.  I'm sure there was a method behind your madness, and I never had that setup leak at the manifold.  Should I be running a similar 4-hole gasket with this new carb (ID 17058222)?

[429bbf]

this may be a dumb question . did you match the gasket to the carb and intake before you installed it?ive seen where the gasket doesn't hardly seal on the carb on various setups .it seals for a little while and then sucks a vacuum trail past the gasket. fwiw

[Cliff Ruggles]

Some Edelbrock manifolds will leak at the front with certain q-jet carb to intake gaskets.  They will NOT work with the thick-open gasket with the cut-out in the front, you must use the solid version of that gasket...we sell them here.....Cliff

[rwberinger4x4]

this may be a dumb question . did you match the gasket to the carb and intake before you installed it?ive seen where the gasket doesn't hardly seal on the carb on various setups .it seals for a little while and then sucks a vacuum trail past the gasket. fwiw

To be honest, I'm not entirely sure.  I actually purchased this particular quad from Sean Murphy Inductions.  Sean provided the base gasket with the carb he sent.  He asked all the pertinent questions (what type of intake, etc.) before sending it so I made the assumption he sent me the correct gasket.  However, looking at Cliff's response, he got me thinking...I'll follow up more after I quote him...

[rwberinger4x4]

Some Edelbrock manifolds will leak at the front with certain q-jet carb to intake gaskets.  They will NOT work with the thick-open gasket with the cut-out in the front, you must use the solid version of that gasket...we sell them here.....Cliff

Cliff, I think you may be on to something.  I guess my question is - why?  I'll try to upload some picture of my manifold and carburetor.  Seems like there is plenty of meat up front on the Edelbrock to create a seal.  The other thing that is weird is that it DID seal (for about 100 miles).  I loosened up the carb bolts yesterday and re-tightened them, and it seal back up again...

[rwberinger4x4]

Cliff - If you think this could be the problem (or if I'm running an entirely wrong gasket) Maybe I can order a care package from you.  The idle speed screw is jammed on this carb, and like an idiot I stripped it.  Luckily it stripped at about a 700-750 RPM idle, but I should probably correct it. 

[Cliff Ruggles]

In all the years and tens of thousands of q-jets I've worked with never once have I seen a stripped out idle speed screw.  I've had a few that were seized up there, but with some heat and penetrating oil they always came out fine.

Are you running PCV on that engine?  I noticed a makeshift plug on the PCV line on the carburetor.

That gasket should seal fine on that intake.....Cliff

[rwberinger4x4]

In all the years and tens of thousands of q-jets I've worked with never once have I seen a stripped out idle speed screw.  I've had a few that were seized up there, but with some heat and penetrating oil they always came out fine.

Are you running PCV on that engine?  I noticed a makeshift plug on the PCV line on the carburetor.

That gasket should seal fine on that intake.....Cliff

Hey Cliff - No PCV - but I need to add one.  The engine spews blowby out the breathers, currently.  The whole driveline is being pulled out of the truck later this summer for an overhaul.  It has been running one breather on each valve cover since I bought it.  I'm sure crankcase pressure is high.

As for the idle screw - yeah it blows my mind, especially because the screw WILL turn, about 2-2.5 turns in either direction.  however, it won't back all the way out, and it won't go more than about halfway in.  It's almost like it was "staked" to prevent it from going beyond that, but I haven't pulled the engine yet to look at the screw threads. 
Nonetheless - is this something you sell?  I haven't been able to find someone who will just sell an idle mixture screw.  Otherwise, I'll go core hunting. 

Lastly, for the base gasket - if this looks like the correct gasket for the application, any suggestion on getting a better seal?  Is it a matter of decking the intake to ensure it's level?  The carb base doesn't appear to be warped and the throttle shafts are already bushed.

[429bbf]

as far as the idle screw goes try screw it in as for as possible, take a cutoff wheel and cut it  off and you should be able to get it out.tap the hole and it should be good . if you can't find one give me your address and ill send one to you. hth

[Cliff Ruggles]

Idle speed screw or idle mixture screw?

We sell both, and every carb to intake gasket made for a q-jet.....Cliff