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Engine won’t idle

Future RV 9 Flyer

Active Member
I have a problem with my 9A.Engine is a Lycoming Io-320 with Airflow Performance FM 150 and dual P-mags timed 2 Teeth past TDC.3.8 hours on the engine burning 91 octane non ethanol auto gas.First 2 hours the engine ran fine but now it doesn’t want to idle smoothly.Erratic idle at 700 rpm and if I advance the throttle to about 900-1000 rpm it drops 100 rpm every 3-4seconds.Full throttle it runs strong.Static full throttle rpm is 2200 rpm.Exhaust pipes are black on the inside.Seems to me it is running too rich at idle.I turned the idle adjustment link 2 flats to shorten it but it didn’t seem to make much difference.Did I just not lean enough?Do I have an induction leak?Any ideas out there why my engine wont idle smoothly?Thanks. Dave
 
I agree with sailvi767 - leaning is good advice. You might also get some hints if you upload your engine data to Savvyaviation.com.

When you say the "first two hours", are you in the test flight phase?

What kind of prop? Static full power RPM of 2200 sounds low unless you have a fixed pitch cruise prop, indicating that the engine is not making full power.

I'd also check the plugs - perhaps you have fouled one or more. I assume you are using auto plugs - they are really cheap (Rockauto), I'd buy a bunch and then swap them out if you suspect an issue.

Also, some pmags were shipped with plug wires that were not correctly terminated - that would be something to check as well.
 
Thanks for the reply Mickey.Yes I’m in test flight.Prop is a Cato 3 blade cruise prop.Plugs are NGK 3691.I’ll take a look at the plugs today.
 
Dave,

Does it run the same on both mags? If yes then your problem is probably fuel related. Have you called AFP? Have you checked all the filters in the system, including the entry filter to the servo? How many rpm does the engine gain as you lean it out at idle/1000rpm/minimum rpm it will run smoothly? Max gain should be 50rpm, otherwise you are running too rich. If the servo was set up to run on 100LL what difference does running on 91 auto gas make? BTW 2 teeth past TDC is a lot! Assuming a 149 tooth ring gear that's nearly 5 degrees, 2 or 3 degrees would be more normal for a light prop, but probably isn't a factor in this discussion.

Pete
 
Hi Glenn,We are in central WI with temps in the upper 20s so don’t think fuel boiling would be a problem.Going to head to the airport this morning and change plugs and manually lean and see how that works.
 
Hi Pete,main filter before boost pump is clean and I’ll check the fuel servo filter today.I’ll retime the p-mags also. Mag check during run up shows both mags working.I’ll also watch Egts today also.Thanks for the suggestions everyone.
 
rough idle diagnosis should always start with confirming proper idle mixture setting. Sounds like this has never been done, so best to start there. "Turning 2 flats in" is NOT the correct procedure for getting an optimum idle mixture. FYI, the engines from the factories rarely have the idle mixture set correctly; usually filthy rich. This is on the installer. Many posts here on correct procedure. I prefer the lowest MAP method.

Larry
 
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rough idle diagnosis should always start with confirming proper idle mixture setting. Sounds like this has never been done, so best to start there. "Turning 2 flats in" is NOT the correct procedure for getting an optimum idle mixture. FYI, the engines from the factories rarely have the idle mixture set correctly; usually filthy rich. This is on the installer. Many posts here on correct procedure. I prefer the lowest MAP method.

Larry

+1
The new Lycoming IO-360-M1B arrived with a way rich idle mixture setting, so I much that I had to bring the mixture lever way aft to get it to idle on first start.

As a side note, I just replace the stock Precision system on this engine with AFP FM-150 system. On first start that too had an idle mixture setting way rich (like Don discusses in his install manual).

On both it took just a few minutes to make the adjustment. Some thoughts on this:
- While it is possible to do the adjustment with the engine running I find there is no practical reason to do such a risky process.
- The engine should be warm, but for the initial setting it makes little difference as it will be way rich to start.
- I look for a 10-40 RPM rise just before the engine stops when moving the mixture to cutout.
- I tend to do this around 900 RPM or so.

Normal operations I have the mixture well lean during taxi anyway - as in adding throttle the engine will baulk a little.

Treat you engine well, always run 10-20 degrees LOP in cruise and you will be happy.

This photo is my exhaust pipes at 260 hours.
Carl
A5-FD0212-F271-4-C43-B68-F-2-D97-FB65-C307.jpg
 
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