Technical Carburetor adjustment

Hi guys, i got a new carb for my 57 chevy and have been having problems with adjusting it. It is a demon 650 road demon. I was wondering if when adjusting the floats should i level the carburetor? Also should the engine be running when adjusting the floats? Thanks guys

 

Demon isn't considered the norm on this forum. However, just follow this acceptable carb and apply to yours.

 

Just out of idle curiosity (pun not intended), how big is your engine (ci wise) and what modifications have been done to it?

 

it is a 283 and not sure exactly what cam is in it but it is not stuck but nothing radical either

 

The car should be on level ground and running when setting the floats, nice that it has built in clear sight windows but still have a rag and fire extinguisher handy just in case.

 

Level yes. If mechanical fuel pump use the left over pressure just after shut down when working alone. That way the fuel doesn't keep running out and out and out while trying to find time to shut the engine off. Electric, just turn the key to on position with someone else in the driver's seat to say STOP! if need be.

 

I think your carburetor is too big. For example, a 1967 Corvette 427/390 had a 590 CFM carburetor. "CarbKing" on here (who is a expert on this sort of thing) says that the most important factor in carburetion is selecting the proper size. You need a 390 or 450 for that engine.

 

No, don't "level" the carburetor..!
But, the "car" should be sitting on level ground, engine warm and running (idle, out of gear).

Mike

 

I agree with tubman bigger is not better in the case of carbs.

 

I bet what Carbking actually said was the most important adjustment is selecting the correct size in terms of CFM or venturi size.

The deal with float adjustment that I see, whether it's a lawnmower or anything else, let's say the float height is listed at 15/32nds or whatever. That's the bench setting, or dry float height, but it's just to get in the ballpark. It isn't set in stone. Holley really hit one out of the park with their adjust on the fly mechanism and the weep hole.

What you're really looking for is the wet fuel height in the bowl. Get in the manual and find out what that is. Set the float height on level ground wherever it needs to be higher or lower to achieve this. If the average fuel height is too low or too high it changes everything in terms of idle mixture settings, fuel starvation at high speed, even jetting, flooding etc. If you install a new fuel pump, it's wise to check it again.

 

Yea, missed that.
Unless it's a fire breathing 283 with 3.90 or lower gears and a manual trans., it should be more like a 500 or 550cfm carburetor for the best overall results.

Mike

 

unless you have an electric pump you adjust the floats with the engine running. The car should be at rest as in the way it sits when it is being driven. Adjust the floats so the fuel just dribbles out of the site hole or just comes up to it.

Idle mix is a little harder, unless you have a feel for it snag a vacuum gauge and hook it to non ported vacuum. Now begin working back and forth with your screw driver, you will have to adjust the idle a time or two probably. You are aiming for max vacuum at idle; on your 283 if it is not wore slap out probably in the 14-18" range.