General Category > Quadrajet Carb Talk and Tips

Lean condition at idle only

(1/3) > >>

jberenyi:
On a Rochester 4MV, what other things can you do to richen the idle circuit other than drill out the idle tube restrictors and downflow restrictors?  I verified the diameters of both and the idle tube is .040 and the downflow is .055.  I can cup the air horn at rough idle and it will smooth out nicely so it needs more fuel at idle but I'm afraid to open the listed restrictors based on what I have read other people using.  Seems like mine maybe maxed out.  Mixture screws are at 8 turns.  What I also fear is that even if I get it to smooth out with more fuel in the idle circuit I won't be able to get the idle lowered to an acceptable level like 700-750 rpm.  The latter statement I have yet to prove though...just a fear. 

Cliff Ruggles:
What is the carburetor part number?

What is the application, engine, type, CID, compression ratio, camshaft, etc?

What has been done to the carburetor up to this point?

What distributor, what has been done to it, initial timing, etc?....

jberenyi:
Application: Stock street use

Engine: 350 chevy

Type: Stock other than bored .030 years ago

CID: 350

Compression: 150 psi all cylinders with 8-10 cranks

Compression ratio: 9:1

Camshaft: L48 stock camshaft Intake: 195 Duration @ .050" , Lift .390" Exhaust: 202 Duration @ .050" , Lift .410" Lobe Separation 112

Carburetor: 7044213 built correctly by you. Only thing done is verify size of idle tube restrictors and downflow restrictors which are .040 and .055 respectively.  Jets are 74, prim metering rods are 44. CH sec rods. I haven't checked the diameter of the idle bypass air ports yet.

Distributor: rebuilt by you.

Timing: 36-degree advance just before 3000 rpm

Cliff Ruggles:
What is the initial timing set at?

How much vacuum is it making at 700-750rpms?

jberenyi:
I believe initial timing is 12 and the vacuum at 750 is about 10-12.  But when I cup the airhorn it rises up to 15-16.

Navigation

[0] Message Index

[#] Next page