7029207 (1686)

[Michael9040]

I rebuilt this carb about 18 months ago but didn't put fuel in it until the first start up which was last Saturday.  Overnight the fuel level in the bowl dropped dramatically, yet I see no signs of the leaking well plugs (which I thought were OK by this production anyway.)  Upon shut off, I see vapors coming from the primary side so I suspected the float level.  After removing the carb, I find a high build up of black soot along the carb heating groove and also where the primary well plugs are.  Total run time was 23 minutes and it doesn't like to idle.  So, what is the likely cause of this rich condition?

[Cliff Ruggles]

Sounds like you may be using an early intake with the exhaust channel in the front?....Cliff

[Michael9040]

It is a correct '67 427 intake, but I did utilize the metal block off plates...........we don't need carb heat in S FL!

[Cliff Ruggles]

I don't think a week goes by in the shop that we don't get a call about the early intakes with the heat crossover passage. 

I recomend blocking off the small holes at each end of the channel, to keep the hot exhaust gasses away from the carburetor.  The correct gaskets still have to be used, or there will be a BIG vacuum leak on the drivers side of the carb at the "channel".

An even better fix is to fill that end of the channel with nickle cast iron weld, and machine the flange flat.  Then the later gaskets can be used.

Another less intrusive option is to make a thicker plate the mirror image of the factory thin steel shim.  Use the correct gasket under it, then any gasket that you want on top of it.....Cliff

[Michael9040]

Cliff, thanks for the replies.  So then, you evidently think that the problem is boiling fuel so I will work on that.  But you don't think it likely that there are any bowl leaks?  I am going to lower the float level as it is not a race car.

[Cliff Ruggles]

I don't recomend running a low float level.  This changes the metering of the carburetor at every point.  Run the correct float level, pressure test the main casting to make sure the bottom plugs are not leaking, and eliminate the hot exhaust gasses under the carburetor. 

Making a slightly thicker steel plate/correct gasket to seal off the channel, then run the later style thick gasket on the plate as an insulator.  This is the easiest and best set-up/repair that I know of for the early intakes......Cliff

[Michael9040]

Thanks again, Cliff.  So you are wanting the steel gasket on the manifold with the thick gasket over it (under carb)?  Since this is the reverse of the normal setup I just want to make sure.  I have read about tapping out the transfer holes and capping with 1/4" pipe plugs (someone even used 7/16" freeze plugs).  These methods would be a lot more practical for me than removing the manifold and having the channel filled and machined.

[von]

This sounds redneckish but I did this years ago on both my Chevys, one BB and one SB and both are holding up just fine. I wadded up alum foil into a ball slightly larger than the hole diameter and stuffed down into both holes in the intake about 1/2" to the top. Then put JB Weld on top of the foil to the carb gasket surface. After the epoxy cured a couple hours I trimmed it off flush with a razor blade. Then I just used a std gasket between intake and carb. Worked for me.

[Cliff Ruggles]

Block the heat supply holes on either end of the channel.  It's best to remove the intake and tap them for plugs, but tapered plugs can be driven into the holes without removing the intake.  I've made many of them from brass or aluminum bar stock.

Install the correct stock gasket.

Make a THICKER steel plate same size/shape as the original.  In only needs to be from a peice of flat aluminum (easier to work with) or steel plate, 1/8" thick is PLENTY.

Install the later thick gasket as used from 1970 and up for most Chevy applications. 

You may have to make a longer choke rod, or bend the stock one to compensate for the higher carburetor height, but this is the best/easiest repair that I know of for those set-ups.....Cliff

[Michael9040]

OK......I plugged the holes in the manifold and adjusted the float (it was way too high).  That seemed to have cured all the problems.  But now I find that I have no vacuum at the port for the distributor.  I have 20in if I take a reading elsewhere on the manifold.  I assumed that I had a leak at the carb, but I can't find it.  What have I done wrong now?

[73 Z28]

I'd remove the carb and flip it upside down, then lay the base gasket over the carb and carefully inspect to make sure that the gasket is not blocking off the port (hole in baseplate) that allows vacuum to the distributor hook up location. If it is, you can simply drill a hole in the base gasket to uncover the blocked port and your good to go.

Paul

[Cliff Ruggles]

The distributor port on the 207 carburetor is ported vacuum.  The source is not covered up by the base gasket as it is high in the drivers side primary bore above the throttle plate.  It should show full vacuum right off idle, but nothing at idle.....Cliff

[73 Z28]

OK......I plugged the holes in the manifold and adjusted the float (it was way too high).  That seemed to have cured all the problems.  But now I find that I have no vacuum at the port for the distributor.  I have 20in if I take a reading elsewhere on the manifold.  I assumed that I had a leak at the carb, but I can't find it.  What have I done wrong now?

Disregard my last post in this thread, I misread your post thinking that you were using a manifold vacuum port to your distrib instead of a ported vacuum source. Cliff is absolutly correct.

Paul