Engine running rich.

Mac · Post by **Mac** » Tue Sep 19, 2006 23:32

Hello all,

I have a question for the group regarding my engine but first here is some information.

It is an o235C1B with a 42" pitch prop. The engine only turns at 2000 rpm static. When I lean the mixture it will go to 2300 static rpm.

We pulled the brand new (rebuilt) carb (3 hours on it), tore it down and everything looked correct, the float was adjusted properly etc. The carb was installed under Lycoming service bulletin 1212 (accellerator pump).

We pulled the aircleaner off and only raised the rpm by 100 and it still ran rich without leaning.

Checked the primer and it appeared to be working, not leaking. Tomorrow I will disconnect the primer to isolate it and do another static test.

If isolating the primer fails to correct the problem does anyone have any suggestions as to where to trouble shoot next?

Thanks in advance,
Scott

Nathan K. Hammond · Post by **Nathan K. Hammond** » Tue Sep 19, 2006 23:45

You might verify the carb jets are correct. Although that means taking the carb back off.

nkh

gusc · Post by **gusc** » Wed Sep 20, 2006 01:21

I agree with Nathan. Once the throttle plate is wide open the main/power jet controls mixture.

If you are in hot/humid conditions or at high elevation then your carb is performing normally. If not you can use the mixture control to lean it to proper operation. We don't have that luxury with our A65s!

I would use the mixture to lean for max takeoff power/rpm. Also use it during taxi. Just be sure to make it a bit rich for cooling during climb. Carbs are designed to provide over rich mixture during wide open throttle, the extra fuel helps cool the engine during climb.

Paul Agaliotis · Post by **Paul Agaliotis** » Wed Sep 20, 2006 02:15

Mac,
I had a problem like this and it ended up being a cracked muffler. It let the exhaust in via the carb heat box.
Paul

Mac · Post by **Mac** » Wed Sep 20, 2006 19:32

Today I disconnected the primer, then capped off the primer line to keep air from entering the cylinders. I had a 200 rpm increase and it sounded much smoother. I tried to lean it with the mixture control at 2200 rpm and it had very little rpm increase. I think I have found the gremlin.

Thank you all for the help and ideas.

Scott

Nathan K. Hammond · Post by **Nathan K. Hammond** » Wed Sep 20, 2006 21:07

Good detective work Scott.
nkh