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I got an Offy! Now I got problems...
https://slantsix.org/forum/viewtopic.php?t=17189		 Page 1 of 1
Author:  Reed [ Sat Apr 22, 2006 10:34 pm ]
Post subject:  I got an Offy! Now I got problems...
I purchased a used Offenhauser intake and it arrived in the mail yesterday:

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On the upside, it looks like this intake has never been installed. on the downside it was missing the carb plate. So I decided to make my own using a one inch carb spacer and a Mr. Gasket #1933 carb adapter:

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It was actually pretty easy. All I had to do was carefully measure the spacing of the four holes in the intake and drill them out in the spacer:

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Using the long studs from the spaced kit I was able to bolt the whole thing together:

Image

So now I just spent about five hours removing my home-made two barrel intake from my van and installing the Offy and the "adapter stack" setup. I am now running a stock 225 1986 spec engine with an Offy intake, one inch four-hole carb spacer, and a stock 1979 slant six BBD.

The adapter stack caused several problems. First, the automatic choke rod is about an inch too short (imagine that!); second, the kickdown lnkage needs to be fiddled with to work right; lastly, and most importantly, the engine will not idle below 1100 RPM. THis is what concerns me.

The idle speed screw is not touching the stop, the throttle blades are closing fully, the timing is set at the factory 16 BTDC setting, the curb idle mixture screws are turned out under two turns, I am pulling 18 inches of vacuum, but the engine just won't idle any lower than 1100 RPM.

Is this normal with an Offy intake? If not, what should I look for?

Another interesting discovery: the runners on the Offy intake are actually smaller than the runners on a stock one barrel intake. I eyeballed the two side by side before I installed the Offy and then got out the dial caliper and took some measurements:

Offy intake- 1.04 inches wide, 1.3 inches tall, 1.46 inches diagonal

Stock one barrel intake: 1.07 inches wide, 1.53 inches tall, 1.57 inches diagonal.
Author:  DusterIdiot [ Sun Apr 23, 2006 8:49 am ]
Post subject:  THat don't look good...
I see a couple of spots on the adaptor that are begging for the label
"Vaccuum Leak"....During the idle period did you spray the whole thing down with some carb cleaner to see if your idle changes?

18" seems a little low on a 'stock' cam.


-D.Idiot
Author:  Patrick Devlin [ Sun Apr 23, 2006 8:50 am ]
Post subject: 
Any time I do an intake swap, I'm really careful to check for vacuum leaks. To me, you high idle sounds like it could be a vacuum leak (though when I've usually had vacuum leaks, the engine wouldn't run with a lot of throttle).
Author:  Reed [ Sun Apr 23, 2006 9:04 am ]
Post subject: 
No I didn't check for vacuum leaks yet. But I have been thinking about it and I may just break down and order the Offy carb plate. That would fix all my linkage problems as well as eliminate some potential vacuum leak sources.

The engine runs fine and doesn't feel like there is a vacuum leak, but who knows. I've got two spacer/adapters bolted together so it is entirely possible that something is leaking somewhere...
Author:  Dennis Weaver [ Sun Apr 23, 2006 9:40 am ]
Post subject: 
Yes, vacuum leak.

All the "carb plate" is for the Offenhauser is really an adapter to go from a Carter WCFB (seriously old timey four-barrel) to an AFB/holley. I think the various carb plates sold by Clifford for their own intake will fit as well, but never have actually tried it.

D/W

P. S. - I suggest removing (cutting) the 4-hole "cloverleaf" from the intake if you're going to adapt to a two-barrel.
Author:  REDNECKMOBILE [ Sun Apr 23, 2006 11:03 am ]
Post subject: 
I believe I see a possible vacuum leak area; it is located between the manifold and the lower plate. It is were the intake is cast with a U shaped notch on the side that faces the motor possibly leaving a unsealed gap.
Author:  Reed [ Sun Apr 23, 2006 11:06 am ]
Post subject: 
Wellll, I want to keep the"cloverleaf" because someday I want to run a four barrel carb. I have an old 400 CFM Carter AFB that would fit nicely on the Offy. Hmmm. Maybe someday is today.... 8)
Author:  70valiant [ Sun Apr 23, 2006 1:04 pm ]
Post subject: 
Dont loose that train of thought Reed. 4-Barrel good :D
Author:  Reed [ Sun Apr 23, 2006 1:44 pm ]
Post subject: 
Quote:
I believe I see a possible vacuum leak area; it is located between the manifold and the lower plate. It is were the intake is cast with a U shaped notch on the side that faces the motor possibly leaving a unsealed gap.
You nailed it! This is why I need to keep the cloverleaf: to have a surface for the gasket to seal to.

Anyway, I solved the problem. Turns out it wasn't a vacuum leak. It was part of the throttle on the carb hanging up on part of the Mr. Gasket adapter. I ground down the adapter and all is well. I fixed my kickdown issue with a bolt and nut screwed into the kickdown linkage (too difficult to explain, but a really simple fix). I still am drawing only 17 inches of vacuum (I think I lost an inch because I am now idling at 800 instead of 1100) but I attribute that to the engine having 145,000 hard miles on it.

Now everything works except I still have a small exhaust leak and no choke. I don't mind the no choke because it is getting warm now and I don't really need one. By the time it gets cold again I hope to be running a Holley 2305 or that AFB, both of which have electronic chokes.

I had to run a tiny little aftermarket air cleaner to clear the doghouse, and there is no way this setup would work on a car without a hole in the hood, but it seems to be working good on the van. It feels like it has more mid-range power and if nothing else sounds great (but that may just be the exhuaust leak). For anyone else, I suggest just buying the Offy plate. It would have cost me $50 with shipping, so I used stuff I had laying around the garage instead.

Now to check the gas mileage.... :wink:
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