Engine revs take time to fall to tickover
Posted: Sat Jul 17, 2021 8:50 am
Hi
I'm having some trouble to get the 250 Road to respond correctly to a closed throttle.
The bikes starts easily, pulls away great, revs out and when moving all seems well.
It's when I shut the throttle that there's a problem, the revs don't die immediately, but take 5-10 seconds to drop to tickover.
Everything suggests an air leak somewhere, but there's no leak between the carb and the head.
To eliminate other causes I have tried both mechanical and electronic ignitions, set with a degree disk and verified with a strobe.
Checked the valve timing with a degree disk, and the timings are within 5 degrees of published spec.
I have tried two brand new carbs (Amal and Mikuni).
Cables are good and the throttle snaps shut when released.
Everything I've read about this problem said air leak.
In desparation, I removed the carb and clamped a piece of inner tube (with the valve in it) over the inlet, and pressurised it. the pressure fell from 30 to 0 psi in about 10-15 secs.
After a bit of investigation, I found that the air was escaping through the inlet valve guide.
Am I clutching at straws here thinking this might be the source of an air leak?
I'm having some trouble to get the 250 Road to respond correctly to a closed throttle.
The bikes starts easily, pulls away great, revs out and when moving all seems well.
It's when I shut the throttle that there's a problem, the revs don't die immediately, but take 5-10 seconds to drop to tickover.
Everything suggests an air leak somewhere, but there's no leak between the carb and the head.
To eliminate other causes I have tried both mechanical and electronic ignitions, set with a degree disk and verified with a strobe.
Checked the valve timing with a degree disk, and the timings are within 5 degrees of published spec.
I have tried two brand new carbs (Amal and Mikuni).
Cables are good and the throttle snaps shut when released.
Everything I've read about this problem said air leak.
In desparation, I removed the carb and clamped a piece of inner tube (with the valve in it) over the inlet, and pressurised it. the pressure fell from 30 to 0 psi in about 10-15 secs.
After a bit of investigation, I found that the air was escaping through the inlet valve guide.
Am I clutching at straws here thinking this might be the source of an air leak?