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 Post subject: Holley 1920 carb notes
PostPosted: Fri Oct 15, 2004 6:32 am 
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Joined: Tue Jul 27, 2004 9:27 am
Posts: 824
Location: Pittsburgh, PA
Car Model*:
Not all 1 bbl carbs are alike and it appears that the manifold are different as well. I'm sure this isn't news to most of you, but maybe someone else hasn't realized it yet.

Well, a few days ago the light went on! My PCV port wasn't doing ANYTHING!!! The incorrect mounting gasket and manifold without a hole had rendered the PCV system completely non-functional. I've known this for a while. So what???? (I thought) If the PCV was mearly a pollution control, I could surely live without it until I figure out why my engine is running so rich.

The problem is that chrysler knew that a predictable volume of air would be flowing through the PCV system. They designed the flow controls to work with that in mind. Without that flow, the idle adjustment can't be set correctly. (ever!!!!!!!!!!!!!!!!!)

All that was require was a small notch in the carb mounting gasket to allow vacuum to the pcv port. A new PCV valve provided more steady flow of air. Total cost $2.48.

NOW I CAN ADJUST MY IDLE FUEL MIXTURE. I must have wasted hundreds of gallons of gas over the last year :cry: The black crud spilling out my tailpipe was unburnt fuel. :shock:

Well, it doesn't smoke any more!! :D I'm sure I'll need to readjust my choke and idle speed and mixture a few more times to get it perfect, but this is the biggest single economy improvement I've made. I can't wait to see how much my gas mileage improves. (I stopped checking after clocking only 14 mpg on a long highway trip, 12 around town)

I feel pretty dumb for not figuring this all out before, but instead of pretending like it never happened, I'll share it with you and hopefuly help someone else.

This origionally seemed to be related to the lean burn conversion or converting to a 1920 from a 1945 carb.

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 Post subject:
PostPosted: Fri Oct 15, 2004 8:04 am 
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Joined: Sat Oct 12, 2002 11:22 am
Posts: 3555
Location: Sonoma, Calif.
Car Model*: Many Darts and a Dacuda
Good work getting the PCV system working again.
The PCV system does a lot for any engine so be sure to keep the valve and passageways clean, it is a good idea to replace the valve every 50,00 miles because the sealing seat can get worn.
The PCV system not only lets additional air into the intake for the proper A/F mixture but it also controls crankcase pressure. If pressure is trapped in the crankcase it can cause oil leaks and poor ring sealing.

As for the 1 bbl intakes, there are a bunch of different designs.
Many different foundries casted this item for Mopar over the years so there an a lot of variations. One big change made to the later cast iron intakes was the increase in the "heat spot", done to promote better fuel vaporization and resulting fuel distribution in the manifold. These intakes also have special "bumps" on the floor of the plentum to help direct the mixture and even-out the distribution into all the runners.
DD
http://www.slantsix.org/parts/list/engi ... otspot.jpg


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 Post subject: Perfect Example
PostPosted: Fri Oct 15, 2004 9:06 am 
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Joined: Tue Jul 27, 2004 9:27 am
Posts: 824
Location: Pittsburgh, PA
Car Model*:
That pic shows it perfectly! The big hole where the carb mounts has a little hole to the top right of it. This little hole is not drilled out on some manifolds. This minor detail makes a big difference in the operation of a holley 1920 and possibly others. Luckily, it's really easy to fix, if you know what to look for.

Any day now, I'll have it running like new again. :wink:

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