Replaced my stock 3" exhaust & risers with an aftermarket (but basically stock) 4" system, including exhaust hose (no mufflers now or prior). Also changed spark plugs to RapidFire's (#1). I made no other changes to any component.

Now, motor idles fast (1000 rpm vs. 850 rpm).

Must I adjust the carburetor and/or the timing due to these changes? Carburetor is Holley 750cfm double-pumper (3310).

Thanks in advance,

D. Ocean
Pompano Beach, FLA

no timing changes.
Will need to adjust idle stop screw and possible readjust your throttle cables to make sure it goes against the stop.

OK...that I can handle, but how did the idle-stop screw and throttle cable get out-of-whack? I was careful to leave everything intact, other than the manifolds/risers.

???

D. Ocean
Pompano Beach, FLA

I think you must have been running a little rich. With the changes you made you just leaned the motor out a little and it needed it therefore the gain in RPM's....I think it'sas simple as that. Just reset your idle air screws to get the highest vaccumn at idle and you should be good to go. I don't think you need to touch the timing at all. But always good to double check and make sure.

BH

I would check with your manufacturer of the exhaust and see if they recommend changing the jets, you do not want to run a lean motor.

I would run her for a day and pull a plug and check to see if she is running lean.

Yeah definitley check the plugs...You don't want to run too lean.....Should have mentioned that As long as they look good then just adjust your idle-air screws to get the highest vaccumn at idle....

BH