After landing today I noticed RPM's won't drop below 950, I have an optical tach and it confirms high idle.
With a flashlight I looked up through the cowl flaps to see if the throttle was hitting the stop on the carb, hard to see but I'm pretty sure it is.
Any ideas what else could cause a high idle?

Terry wrote:After landing today I noticed RPM's won't drop below 950, I have an optical tach and it confirms high idle.
With a flashlight I looked up through the cowl flaps to see if the throttle was hitting the stop on the carb, hard to see but I'm pretty sure it is.
Any ideas what else could cause a high idle?

Make sure mixture is going full rich. I had the opposite happen last week wouldn't idle, then it mysteriously went back to normal.

G'Day

You might have a vacuum leak somewhere in the induction system.

Check your rpm rise when you pull the mixture to cut-off. No rise might indicate an intake leak as mentioned. Then pull cowl & verify the throttle IS hitting stops.

Bottom line: get it fixed ASAP--it can sure screw up a landing not being able to pull the throttle off all the way.

Cary

Had the same problem. Found a bad intake gasket. Problem solved cheap and easy. Franklin 220

Thanks for all the advice, after pulling the cowl it was an easy find. Intake clamp.

Which clamp was this in relation to the induction system, after the filter I presume?
And that was responsible for perhaps a 300-400 RPM increase compared to normal idle?
Interesting.

Battson wrote:Which clamp was this in relation to the induction system, after the filter I presume?
And that was responsible for perhaps a 300-400 RPM increase compared to normal idle?
Interesting.

Yep, after the filter, it was the intake manifold hose between cyl 3 and 5. I'm not an A&P, but the hoses I have taken off always seemed to be almost glued on so I had my doubts that this was the problem. I started it before I installed the cowling and it idled fine. I haven't flown it yet or let it get to operating temp.