1992 454. Port engine runs rough at idle. Otherwise runs fine. Starboard is fine. Both use same fuel tank. Rebuilt carb. New cap / rotor. New plugs. New fuel filter. The only thing we haven't changed is the spark plug wires. 1000 hours on motors. Any ideas????
Crusader Engine Trouble
- Thread starter MarkMuck
- Start date
Did you do the work noted above trying to correct this miss, or did it develop after? New parts, like Cap/Rotor, can be defective. So can Plugs. If it runs rough at idle but not above that, my first suggestion would be Vacuum Leak. Loose Carb, Wrong Gasket, failing Intake Gasket... Does Carb sit directly on Manifold, or is there a piece in between? If there IS, then what about the Gasket below that Piece?
WD-40 is combustible, but not like carb cleaner and other sprays. I've heard of spraying WD-40 around possible leak sources. Miss will change if the WD "finds" a leak.
Look, too, for broken/cracked Vacuum Hose or some Vacuum Device.
WD-40 is combustible, but not like carb cleaner and other sprays. I've heard of spraying WD-40 around possible leak sources. Miss will change if the WD "finds" a leak.
Look, too, for broken/cracked Vacuum Hose or some Vacuum Device.
Have you checked timing?
A carb/manifold vacuum gauge test can reveal a lot of clues such as rich or lean carb idle mix and so many other things, and is best method of really optimizing vacuum when adjusting the idle mix screws for smooth idle at lowest throttle opening.
A carb/manifold vacuum gauge test can reveal a lot of clues such as rich or lean carb idle mix and so many other things, and is best method of really optimizing vacuum when adjusting the idle mix screws for smooth idle at lowest throttle opening.
If you're sure it's running fine above idle, it sounds like it could be an adjustment of the low speed air screws on the carb. These are the two little screws low and on the front of the carb. These screws adjust the fuel to air ratio at very low RPM. There are 1, 2 and sometimes 3 pin size holes in the carb throat that line up with the butterfly of the primary throttle bore. They work by the air rushing by the edge of the butterfly and the wall of the primary bore and sucking fuel/air. They either allow more air or more fuel mixture depending on manufacturer.
As soon as the throttle is opened slightly, it stops the venturi effect on the little pin holes and no longer pulls fuel.
Any of these should tell how the adjustments are made.
https://www.google.com/search?q=adj....12160j0j7&sourceid=chrome&es_sm=122&ie=UTF-8
As soon as the throttle is opened slightly, it stops the venturi effect on the little pin holes and no longer pulls fuel.
Any of these should tell how the adjustments are made.
https://www.google.com/search?q=adj....12160j0j7&sourceid=chrome&es_sm=122&ie=UTF-8