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Author Topic:   Carb Set up?
Kromulous
Dirt Forum Champ
Total posts: 796
posted June 13, 2005 09:15 AM  
We have a newer style Holley 4150, 750 CFM Alcohol carburetor. I can get more info if needed, i dont work on the engine much.

Anyway it has the extended jets, and 4 corner idle adjust if that helps. Also it has 1 to 1 linkage on it.

I need to ask what power valves do we need to run on the front, and rear. As well as Jet sizes. Need jetting recommondations for summer time, hot & humid conditons, as well as better cooler air, maybe a range. I need to buy a few is what i am after, and want to get the right range jets.

Engine is a 365 cu in, roller cam 256 & 260 @.050 and about .650 lift. 6" rod, and .150 domes, its 13.5 to 1 compression. 215CC Dart pro 1's unported, with big step tube headers.

First time out the carb was junk, fell on its face. Couldnt get it to "get up on the pipes", so we think it needs rebuilt and gone thru. Its been sitting all winter, and we bought it used, no idea if he ran fuel lube or not.

Any guidance would be appreciated.

Thanks, Krom.

KPLugnut
Dirt Forum Champ
Total posts: 1019
posted June 13, 2005 09:51 AM  
Sounds like it's more a case of needing a rebuild, for starters.

KP

Kromulous
Dirt Forum Champ
Total posts: 796
posted June 13, 2005 10:06 AM  
Thats the plan KP, gonna order the stuff i need today, any suggestions on jet sizes or power valve sizes?

Kromulous
Dirt Forum Champ
Total posts: 796
posted June 13, 2005 04:11 PM  
Should the front power valve be converted over to one of the 50cc deals?


sixwillwin
Dirt Freak

Total posts: 493
posted June 14, 2005 06:37 AM  
I think you mean accelerator(sp?) pump.....

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KPLugnut
Dirt Forum Champ
Total posts: 1019
posted June 14, 2005 06:48 AM  
We use 50cc pumps both front and rear on our alky carbs. Some other builders use one 50 and one 30cc pump, but they are different animals altogether in both throttle geometry, fuel metering, etc, so it's comparing apples to oranges there.
And nobody every complained (yet) about one of our alky 4bbls being sluggish or that it had a hesitation...quite the opposite, in fact...
:-)

As for a jetting recommendation, it's impossible to get you close without knowing everything about the carb, it's metering blocks and your air quality (temp, humidity, altitude, etc).

KP

Kromulous
Dirt Forum Champ
Total posts: 796
posted June 14, 2005 07:15 AM  
Well, i'll be honest i dont know anything about these carburetors. So yes i did mean accelorator pumps.

Anyway, i went to the shop last night, and the Carb we have has the dual 50cc pumps. Now i gotta figure out if it has the bigger jets or the smaller ones.

I read somewhere that some carbs thats been converted to alcohol use a smaller number jet than ones that came from the factory for alcohol, i believe they start in the 130's numbers and the others are in the 90's numericly.

Now i know which pumps to buy, and just trying to figure out the jets so i can buy an assortment of them to tune the carb.

I believe we had a fuel pressure issue as well, i re-adjusted the bypass so it climbs to 10 pounds at full throttle. It was depressurizing at mid throttle. We just switched to alcohol this year, and its a steep learning curve.

Thanks for the info so far, sorry for the dumb questions, Krom.

[This message has been edited by Kromulous (edited June 14, 2005).]

[This message has been edited by Kromulous (edited June 14, 2005).]

[This message has been edited by Kromulous (edited June 14, 2005).]

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