Hi All,

I'm trying to find the source of of my rough idl on my '99 F4. 11k miles. I have an intake leak somewhere. Here's what I've done:
1. Rebuilt all carbs (did not remove from the shaft though)
2. New rubber hoses for carb balancing that go from the cyl head to the airbox
3. New intake boots
4. I've reseated the carbs after the engine was warm. I loosened the clamps, rocked the carbs back and forth and looked carefully to see that everything was properly seated before tightening down.

As this video shows, spraying starting fluid between the carbs causes engine RPM to rise. It's most notable between carbs 1 and 2 and 2 and 3. At a loss here and really want that elusive smooth idle!

Any help would be greatly appreciated!

Thanks!
Bob

 

If you were in my garage, I would use a smoke machine and find the exact spot in minutes. Know of any mechanics that have one?

Otherwise, try using the straw on the can to get a more pinpointed spray.

 

Is it common at all for there to be a leak between the shaft connecting the carb butterflies and carb bodies?

Good tip on the smoke machine! I don't know anyone locally that has one. I was thinking I could build one like the one below and pump smoke into the carb balancing hose of each cylinder (while given cylinder is at TDC).

 

i think you ate getting residual vapours from the starting fluid in through the air intakes, try a more concentrated spray , more direct.