Idle setting and overall performance
Thread Starter
Team Owner
Joined: Nov 2004
Posts: 20,708
Likes: 25
From: Sorrento Italy
Idle setting and overall performance
What is, if any, the correlation beetwin the idle setting on a big demon carb with the overall general performance through the whole rpms range?
Thread Starter
Team Owner
Joined: Nov 2004
Posts: 20,708
Likes: 25
From: Sorrento Italy
badly need an answer to this iussue, i suspect that the guy who's been messing with my mighty demon to set the idle some way would have harmed the general performance of the engine through the whole rev range...The idle is set now, but i 'feel' the car is running somehow lean on higer rpms...tell me i'm death wrong so i can go peacefully to bed
Tech Contributor
Joined: Aug 1999
Posts: 14,373
Likes: 6,370
From: At my Bar drinking and wrenching in Lafayette Colorado
It depends on what you mean by "idle setting." If you mean idle speed setting, this has no effect at all on anything other than idle speed. If you mean the mixture the screws, the mixture screws affect idle mixture and transition fuel mixture. Since fuel is discharged through the idle circuit and transition circuit during all modes of carb operation, messing up the mixture screws will affect all modes of operation.
Why don't you just readjust them and set them up right..?
Why don't you just readjust them and set them up right..?
Burning Brakes
Joined: Dec 2003
Posts: 1,004
Likes: 7
From: Adelaide South Australia
Hi Lars,
I have a similar issue getting my new turnkey crate engine running right....
Ignition timing and carb jetting/tuning was performed by builder prior to shipping out to Australia.
I had some issues chasing missfire/surge at idle and just off idle.
Have worked my way through the issues....
Replaced a cracked HEI dizzy cap (must have broken during installation)
I had issues with plug wires shorting (arcing) to pipes due to insuffiicient clearance - temporary fix with heat insulated boots
And then I found a vacuum leak in my accesories line was causing erratic behaviour. I've blocked off the accesories port and motor now revs cleanly once it is going, but the transition from idle to the primary main circuit is causing grief.... stall, surge or occasional backfire just as throttle is depressed (lightly)
I tried to set the idle mixture (Edelbrock 800cfm AVS carb) but it is very difficult to get a discernible change in rpm. I guess it could be due to the cam specs....
What is the best procedure to setup idle mixture in a longer duration/higher lift cam engine?
Cam specs are 242/240@ 0.050 with 0.594 lift with 112* LSA.
I wouldn't have thought this was too radical, but if you have any suggestions on how I can overcome my off idle woes, I'm all ears
regards
tom
I have a similar issue getting my new turnkey crate engine running right....
Ignition timing and carb jetting/tuning was performed by builder prior to shipping out to Australia.
I had some issues chasing missfire/surge at idle and just off idle.
Have worked my way through the issues....
Replaced a cracked HEI dizzy cap (must have broken during installation)
I had issues with plug wires shorting (arcing) to pipes due to insuffiicient clearance - temporary fix with heat insulated boots
And then I found a vacuum leak in my accesories line was causing erratic behaviour. I've blocked off the accesories port and motor now revs cleanly once it is going, but the transition from idle to the primary main circuit is causing grief.... stall, surge or occasional backfire just as throttle is depressed (lightly)
I tried to set the idle mixture (Edelbrock 800cfm AVS carb) but it is very difficult to get a discernible change in rpm. I guess it could be due to the cam specs....
What is the best procedure to setup idle mixture in a longer duration/higher lift cam engine?
Cam specs are 242/240@ 0.050 with 0.594 lift with 112* LSA.
I wouldn't have thought this was too radical, but if you have any suggestions on how I can overcome my off idle woes, I'm all ears
regards
tom
