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Help! Carb Problems/ Hot Slot Manifold

J Koehler

Active member
Joined
Jan 27, 2008
Messages
28
Location
New Jersey
Corvette
1969 Conv & 2001 Conv both are yellow cars
I have 69 with a 350/350 HP. The motor has just been rebuilt and I am having a problems with slight missing problems. I have done the following

1. Reset the timing to 8 BTD Center
2. Readjusted the lifters to 1 turn after snug
3. set the dwell to 30 degrees
4. rechecked the firing order
5. plugs, wires, cap, coil, points are new
6. there is 5-10 inches of vacume at an idle(OK??) 30 inches at higher RPMS

I think I have tracked down the problem to the Carb. The Carb by numbers is from a 1973 engine. In 68 through 70 they had a Hot Slot in the Manifold that helped warm up the carb with exhaust gases. I reinstalled the 73 carb when I rebuilt it with a 69 gasket at the manifold.

My question is, will the 73 carb by pass the exhaust gases to the intake? Is this why the engine runs poorly?

Any Sugestions Thanks
 
Joined
Jan 1, 2002
Messages
7,246
Location
Washington, Michigan
Corvette
'67 Marina Blue Convertible
Two issues:

1. 5"-10" of vacuum at idle is WAY low - you have a significant vacuum leak somewhere; you should show 12"-15" Hg. vacuum at idle.

2. In addition to the carb-to-manifold gasket, you also need the stainless steel baffle that goes between the gasket and the carburetor that protects the carb base from direct impingement of the hot exhaust gases in the "hot-slot".

This design resulted in a huge safety recall, as the heat from the "hot-slot" caused the lead plugs in the bottom of the Q-Jet float bowl to fall out, resulting in engine fires. I'd recommend that you plug the holes at the end of the "hot-slot" to stop the flow of hot gases. Sometimes 7/16" freeze plugs work, or you can tap the two holes and use allen-head pipe plugs.

HotSlotPlugs3.jpg


HotSlotPipePlug.jpg


:beer
 

J Koehler

Active member
Joined
Jan 27, 2008
Messages
28
Location
New Jersey
Corvette
1969 Conv & 2001 Conv both are yellow cars
The holes that I plug are in the manifold hot slot?
 
Joined
Jan 1, 2002
Messages
7,246
Location
Washington, Michigan
Corvette
'67 Marina Blue Convertible
The holes that I plug are in the manifold hot slot?

Yup, just like it shows in the photos I posted. That won't interfere with operation of the choke, which is heated by the main crossover passage below the manifold plenum.

:beer
 

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