I need some opinions on what to look for or how to rule out certain factors.
Engine is O-540 J series.
Here is whats happening: the engine is becoming increasingly more difficult to start, seems like it needs more prime, more cranking time. Battery and starter are both fine.
On take off, the RPM's are really slow to come up to redline, 2400, with MP in the green arc. Only above 25" or about 30 seconds will the prop redline. The prop cycles normally during run up and the prop control works fine in flight.

In flight I see fuel flow fluctuations/spikes higher and corresponding EGT changes. Flow increases about 1 GPH for just a second and EGT's drop across all cylinders, as one would expect them to do with more fuel. Then things stabilize for a while. It's getting harder to lean properly, either too rich or too lean when compared to normal. More carb heat and higher RPM usually results in smoother running. I usually cruise 20" MP or just off WOT if I can't make 20" at altitude and 2200 RPM with 40-50 deg F carb heat. Now it seems like it runs better with 2300 or 2400 RPM and around 60 deg F carb heat. All other engine parameters appear normal on the JPI and the factory gauges.

I have checked for induction leaks but couldn't see anything obvious. Fuel sumps clean. Checked the JPI FF transducer and it's fine. Replaced air filter and the air box seems clear. Mags are good. Plugs have been cleaned but were fouling up more than usual.
Anyone have any ideas? I can't see how the prop governor would tie into the other issue.
In Patagonia right now with not a whole lot of options until I get to bigger airport in a few days.
Thanks folks, your thoughts are much appreciated.

Oil fouling (wet black soot), Over Rich fouling (dry black soot), or Lead fouling (gray oval-shaped deposits)?

Is the fouling the same on all cylinders?

Just one row of plugs or both?

It's probably going to be an ignition issue, possibly bad coils in the mags or possibility of a valve trying to stick. Check your ignition system first starting with timing, then plugs, leads, and if that doesn't solve it I would have the mags checked out. If you think it could be a valve sticking issue there are some oil additives that can fix that without taking anything apart.

It's probably not likely that both mags would fail at the same time, have you tried doing a ground run on each individual mag? also curious if you happen to have a 6 place egt monitor installed, it could help identify what cylinder, or cylinders are acting up if that's the issue.

Bdiazair wrote:It's probably not likely that both mags would fail at the same time, have you tried doing a ground run on each individual mag? also curious if you happen to have a 6 place egt monitor installed, it could help identify what cylinder, or cylinders are acting up if that's the issue.

Just because the coils are going bad doesn't mean the mags will fail. When the coils heat up the they will cause a slight vibration in the engine but the mags will still work. They will still pass a mag check on the ground or at least that's been my experience on 2 different planes with bad coils. An engine monitor will show a dead cylinder or indications of a sticking valve.

C185D wrote:

Bdiazair wrote:It's probably not likely that both mags would fail at the same time, have you tried doing a ground run on each individual mag? also curious if you happen to have a 6 place egt monitor installed, it could help identify what cylinder, or cylinders are acting up if that's the issue.

Just because the coils are going bad doesn't mean the mags will fail. When the coils heat up the they will cause a slight vibration in the engine but the mags will still work. They will still pass a mag check on the ground or at least that's been my experience on 2 different planes with bad coils. An engine monitor will show a dead cylinder or indications of a sticking valve.

Why would an ignition problem cause spikes in fuel flow?

It sounds like the carb is gummed up with gunk to me. You would want to ask someone knowledgeable on carbs, but worth asking I would say.

C185D wrote:

Bdiazair wrote:It's probably not likely that both mags would fail at the same time, have you tried doing a ground run on each individual mag? also curious if you happen to have a 6 place egt monitor installed, it could help identify what cylinder, or cylinders are acting up if that's the issue.

Just because the coils are going bad doesn't mean the mags will fail. When the coils heat up the they will cause a slight vibration in the engine but the mags will still work. They will still pass a mag check on the ground or at least that's been my experience on 2 different planes with bad coils. An engine monitor will show a dead cylinder or indications of a sticking valve.

My experience with a coil that develops a leak after it warms up is it will tend to pop or sound like a backfire. Either way, if it doesn't give any indication after it is run up on the ground, fly it and do a mag check in the air (maybe stay over the ap in case the engine decides to quit)

My initial response was directed towards the possibility of it being an ignition problem which could be easily diagnosed or eliminated as a possible cause by running one mag or the other. If there was a sticking valve, that could have been chased down using a 6 place egt. He said he checked for induction leaks (they typically make airplanes hard to start) so that would possibly lead to a fuel delivery issue. If the fuel strainer/screen is clean, known good fuel going Into the tanks, i would start leaning towards the carb as being an issue. Does it shut down clean in idle cutoff? Is the butter fly valve loose in the throat of the carb? Good linkage going to mixture adjustment?

I'm with Battson, sounds like a possible carb issue to me.

x3 on the Carb. I've had lots of weird problems before... and Carb's are magic that I don't fully understand. But a good Carb OH will work wonders in lots of cases!

gunny

Carb issue makes sense to me too.. but the carbs I'm far more familiar with are a lot different from yours.

Any updates Paul? Bummed to see your having issues so far from home... hope your making progress!