question for the tuning guru's

[simonrc]

My idle speed screw is set so i have a 1-1.5 gap in the carb,.

My questions are

Why do I need to apply trim to start the car?
Why do I need to keep some trim to keep the car running? even though the wheels still spin whilst off the ground.

thanks as always

Simon

 

[MotoGod]

Sounds like your low speed needle may be a little on the rich side. I would lean it out @ 2-3 hours and see what it does then. Your idle may go up, so you will need to back down your idle gap a little bit to keep it more normal.

The trim is required because your air/fuel mixture is too rich. Too much fuel to burn, not enough air to burn it....or too much air...not enough fuel. Either way is considered rich.

Typically, the idle gap will be between .5 and 1.5mm or so depending on the engine and it's purpose. Race engines tend to be closer to the .5-.75mm gap area do to having a more race oriented tune on them.

You also did not mention how the car was running? Do you have a good smoke trail? How does it sound? What temp is it running at idle and after a high speed pass? Is it bogging anywhere? Does it have a good launch from a dead stop?

All important questions. So to me it sounds like your LSN may be the culprit here, but I'm guessing from the info you provided. It sounds rich, but you might get the same results if it were lean....except it would be running hot if it were lean...and cool if it were rich.

Give us some more info....we'll help you out as best we can.

 

[Rolex]

Good post, Moto.
Using the trim to start the car is sometimes required. Using trim to keep it running is not.
When it's warmed up, you need to reset the idle with the trim knob all the way down and the brakes fully applied.
It will usually require some adjustment to the LSN at the same time.