O320 rough idle

[hcccs]

After being away for more than a month I've returned to my misfiring O320. Today a friend helped me spraying start spray on the intake flanges and hoses to detect any air leaks. We couldn't find any. I ran the engine for 15 minutes and noticed lower temps on cylinder 1. If it is misfiring all the time that would explain the lower temps so what is the next step? I don't know - plugs are new but sooty, ignition wires are new so what else is there to choose from? Any ideas are most welcome!
CHT: 87/116/129/137, EGT: 359/519/475/479

[10builder]

Originally Posted by snopercod

I have an O-290-D2 which is pretty much like an O-320 only with an MA-3SPA carb. Mine will idle down to 500 RPM with a wood prop. Looking at the Marvel Schebler troubleshooting guide for rough idle, induction leaks and primer leaks are two of the top suspects. Also, that hole in the carb barrel above the Throttle Fly is (I think) the "Primary Idle Delivery". This is the one controlled by the big Idle Adjusting knob mentioned earlier. Just under the Fly are the Secondary and Third Idle Delivery holes. There are lots of good diagrams here: http://www.insightavionics.com/pdf%2...b%20Manual.pdf

Thanks for attaching that link! I am experiencing a slight, momentary hesitation during acceleration and this guide indicates that my accelerator pump linkage is misadjusted. Perfect timing!

[E. D. Eliot]

I'd check the new ignition wires and their end connectors. Sometimes, new electrical components that come from the factory are bad. Easy ohm check just tp be sure. Start with the ht wires on number one cylinder. Good hunting!

[SPB W10]

Your engine data shows very low oil temperature and low cylinder head temps. So we submit the following from the Lycoming O-320 Operators Manual.
Idle Speed and Mixture Adjustment.
(1) Start the engine and warm up in the usual manner until oil and cylinder head temperatures are normal.
(2) Check magnetos. If the mag-drop is normal, proceed with idle adjustment.
(the following adjustments are fine adjustments of 1/4 to 1/2 turns, and may have to be repeated)
(3) Set throttle stop screw so that the engine idles at the airframe manufacturer recommended idling RPM. If the RPM changes appreciably after making idle mixture adjustment during the succeeding steps, readjust the idle speed to the desired RPM.
(4) 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.
If step (4) indicates that the idle adjustment is too rich or too lean, turn the idle mixture
adjustment in direction required for correction, and check this new position by repeating the
above procedure. Make additional adjustments as necessary until a check results in a momentary
pick-up of approximately 50 RPM. Each time the adjustment is changed, the engine should be run
up to 2000 RPM to clean the engine before proceeding with the RPM check. Make final adjustment of the idle speed adjustment to obtain the desired idling RPM with closed throttle.
The above method aims at a setting that will obtain maximum RPM with minimum manifold pressure.
In case the setting does not remain stable, check the idle linkage; any looseness in this linkage
would cause erratic idling. In all cases, allowance should be made for the effect of weather
conditions and field altitude upon idling adjustment.

Let us know your results.
Steven

[Lycosaurus]

Originally Posted by hcccs

My o-320 gives me a MAP of about 11 at 800 rpm. Yours is showing MAP of almost 15, which I suspect would indicate an intake leak. I would be inclined to check that area again, including any connections such as the MAP hose connections, carb/bracket/sump gaskets.

I had repetitive leaky intake gaskets, but solved that with an o-ring kit from one of our VAF posters/advertisers,Ross from SDS. http://www.vansairforce.com/communit...d.php?t=161030

About 1 year and 100 hours with the SDS o-rings. Works well so far.

[hcccs]

Originally Posted by RV8JD

There is a chance that the exhaust valve may be sticking in Cylinder #1. I could not find any reference in this thread to a compression check being done (maybe I missed it), which would help diagnose a sticky valve.

Good luck!

(BTW, it looks like you didn't have the Alternator online during this engine run, with a "Batt Volts" indication of only 12.1V)

I'll do a compression test to make sure. As for the alternator I'll remove it and have it checked. It was given to me and I don't know the condiction.

[hcccs]

Originally Posted by Lycosaurus

My o-320 gives me a MAP of about 11 at 800 rpm. Yours is showing MAP of almost 15, which I suspect would indicate an intake leak. I would be inclined to check that area again, including any connections such as the MAP hose connections, carb/bracket/sump gaskets.

I had repetitive leaky intake gaskets, but solved that with an o-ring kit from one of our VAF posters/advertisers,Ross from SDS. http://www.vansairforce.com/communit...d.php?t=161030

About 1 year and 100 hours with the SDS o-rings. Works well so far.

So, it comes down to a leak after all. I'll check all intake tubes and carb/oil pan gaskets and seal with some Permatex Blue RTV to make sure. That would be OK, or what do you think?

[Lycosaurus]

Originally Posted by hcccs

So, it comes down to a leak after all. I'll check all intake tubes and carb/oil pan gaskets and seal with some Permatex Blue RTV to make sure. That would be OK, or what do you think?

Didn't catch how many hours/years on the engine.

I have not used RTV, and I don't think it is recommended for fuel systems. I have used Hylomar Universal Blue as a gasket dressing, and that really helps when it comes time to change gaskets. It helps prevent the gasket material from sticking to the parts. There may be other materials that others have had some success with.

Changing the intake gaskets is cheap and not too much time or effort.

[hcccs]

Originally Posted by Lycosaurus

Didn't catch how many hours/years on the engine.

I have not used RTV, and I don't think it is recommended for fuel systems. I have used Hylomar Universal Blue as a gasket dressing, and that really helps when it comes time to change gaskets. It helps prevent the gasket material from sticking to the parts. There may be other materials that others have had some success with.

Changing the intake gaskets is cheap and not too much time or effort.

The engine has 4000 hours and new Millennium cylinder were install 700 hours ago.

[snopercod]

Hans: Did you find the problem?