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Erratic idle

F

Future RV 9 Flyer

Active Member
I have a problem with my Lycoming engine in my 9A.Engine is an IO-320 with Airflow Performance injection and dual P-mags timed 2 teeth past tdc.I’m running 91 octane non-ethanol auto gas.First 2 hours the engine ran and idled fine but now the idle is very erratic and wants to die if throttle is pulled back too much.The exhaust pipes are black on the inside which makes me think it’s running too rich.I tried leaning the idle mixture by adjusting the linkage 2 flats but it doesn’t seem to make much difference.Am I on the right track here or is it something else? Thanks. Dave
 
Poor idle after 2 hrs. of run time

I'd also make a check of all intake system connection points just to be sure something didn't vibrate loose (after the first couple hrs.), and create an intake leak and resultant rough idle.

Doug Lomheim
RV-3A sold
RV-9A / 13B FWF
 
When I was first setting the idle mixture on my IO-360 I didn't let the engine warm up enough. After correcting that error I followed the Lycoming engine manual.

When the idling speed has been stabilized, move the cockpit mixture control lever with a smooth, steady pull toward the Idle Cut-Off position and observe the tachometer for any change during the leaning process. Caution must be exercised to return the mixture control to the Full Rich position before the RPM can drop to a point where the engine cuts out. An increase of more than 50 RPM while leaning out indicates an excessively rich idle mixture. An immediate decrease in RPM (if not preceded by a momentary increase) indicates the idle mixture is too lean.

Unfortunately some trial and error.
 
Future RV 9 Flyer said:
I have a problem with my Lycoming engine in my 9A.Engine is an IO-320 with Airflow Performance injection and dual P-mags timed 2 teeth past tdc.I’m running 91 octane non-ethanol auto gas.First 2 hours the engine ran and idled fine but now the idle is very erratic and wants to die if throttle is pulled back too much.The exhaust pipes are black on the inside which makes me think it’s running too rich.I tried leaning the idle mixture by adjusting the linkage 2 flats but it doesn’t seem to make much difference.Am I on the right track here or is it something else? Thanks. Dave
Click to expand...

Are you running the engine at full rich? If so, you are most likely loading it up as evidenced by your black exhaust pipes. All the RV's with the 320's I have seen will not run right when the mixture is set at full rich. Another thought is your timing. I also have dual Pmags and I don't recall setting the timing like you mentioned. george
 
The black in the exhaust; is black because the auto fuel contains no tetraethyl lead (this is not a indication of it being too rich; like it would be if using 100LL).

Do the mixture pull, with a warm engine, at 800RPM: if you get less than 50RPM increase; you need to enrich the mixture. If more than 70 lean the mixture.

Changing the mixture is accomplished by turning the wheel at the center of the linkage between the 2 arms. This linkage is on the side opposite of where the throttle cable attaches. There is an arrow and an "L" to tell you which way to turn for leaner (go opposite if you need richer).

Another place to look would be an induction leak. If you have a leak on a fuel injected engine it will generally increase the Idle RPM.
 
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BoydBirchler said:
The black in the exhaust; is black because the auto fuel contains no tetraethyl lead (this is not a indication of it being too rich; like it would be if using 100LL).

Do the mixture pull, with a warm engine, at 800RPM: if you get less than 50RPM increase; you need to enrich the mixture. If more than 70 lean the mixture.

Changing the mixture is accomplished by turning the wheel at the center of the linkage between the 2 arms. This linkage is on the side opposite of where the throttle cable attaches. There is an arrow and an "L" to tell you which way to turn for leaner (go opposite if you need richer).

Another place to look would be an induction leak. If you have a leak on a fuel injected engine it will generally increase the Idle RPM.
Click to expand...

I don't believe the type of fuel has any bearing on the color of the exhaust pipes. Unburned fuel does though. An induction leak on any engine will run lean, no matter if it is injected or not. Induction leaks have ruined many cylinders over the years with high CHT in aircraft that didn't have the instrumentation that most of the RV's have.
 
I'm assuming you have your issues resolved, if not I would have and A&P look at it.
 
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