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Discussion Starter · #1 ·
If you put a carb on an engine that has too high of a CFM rating for that engine(example: put a 500 cfm on a stock 258) can you compensate for this by restricting the air flow into the carb. Such as making the hole in the air breather smaller. Is this possible or are there other facters that I haven't considered? I am assuming that a 500 and 390 CFM carb can be made to use the same amount of gas.

87 wrangler

 

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You absolutely CAN NOT do what you suggest.
If you do, you will interfere with the main well and idle well air bleeds, and possibly the float bowl vent. All resulting in screwed up fuel mixtures.
You will interfere with the primary boosters and discharge nozzles.
You will also kill all air flow characteristics of the upper Venturi throats.
It will be a wonder if the vehicle even runs after what you suggest, and will never have the proper fuel mixtures.

THIS IS A REALLY BAD IDEA!

If a tree falls in the forrest, and there is no woman around to hear it, is the man still wrong?
 

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Discussion Starter · #3 ·
Thanks for a very good explanation.


87 wrangler

 
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I have a holly 600 ddb on my 79 with a 304 and i am telling you thatif you put a 500 on a 258 you are going to have major overkill. My little 304 with that big of a carb has a hard time. i should have gone with a 500 or even less, so what i am saying is you need to stick to the smaller stuff

she thinks all my trucks are sexy!!!!
 

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Hey, where were you LAST week when I needed Quantifiable data!!!

small carbs damnit...the biggest of AMC motors( 401) with a very hopeful VE cant consume more than 550 cfm at 5500 RPM!!!

OzarkJeep
NW Arkansas
 

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What Team Rush said (well kinda) was..........
With what you suggested was wire your choke shut and see how it does.
NOT GOOD.
Aaron I'll try and translate when I can for a small fee of course./wwwthreads_images/icons/wink.gif

Wider is better but taller is cooler!
 

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Had a 750 holley on my 79 F250 with a 400M. Was too much, wouldn't idle well, and blew a lot of black smoke. Went down to a 600, and it idles and runs way better.

Pete

88YJ,4"susp,33"BFGMT,9kwinch,homemade swingout,258,999,4.10,weber32/36,GMHEI,one moonguy/wwwthreads_images/icons/smile.gif
 
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Muddog, Don't do this! If you think of a hose with water going through it, a smaller hose will have the same amount of water traveling at a higher velocity. This higher velocity is the "energy" your carb uses to operate effectively. Venturies use this mechanism to deliver the fuel into the airstream and mix it correctly. A low velocity (larger bore venturi) will not operate your as efficiently. Ken

http://members.home.net/nosweat/
 

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Discussion Starter · #9 ·
I picked up a motorcraft 2100 carb today- I did get the smaller cfm carb. Looks pretty simple compared to the one on the jeep now. Looks like all there is a fuel inlet and the vacume to the distributer to hook up. There is an inlet coming off of the choke assembly-do I need to hook this to something or can I leave it the way it is? Also where are the numbers at-I need to get a kit for it and I don't know what year it came off of(has to be early 70's)? I haven't got it all cleaned up yet-so I may have missed them.

87 wrangler

 

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I think the inlet off the choke housing is for a hot air tube that brings in hot air from the manifold and heats the choke spring and makes it open. You will need this.

Loose nut behind the wheel
Another right-wing conservative.....
Born and raised in Jeep-Town
 
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