912UL runs hot?

[turboturner]

Hi gents;
Sorry for tardy reply. I have to be honest (& you've probably figured it out) but I'm a "buy & fly" owner, not a builder. I'm still learning how to fix these issues & really appreciate your feedback.

Av8r: plugs are a nice brown on one cyl but powdery black (soot covered) on the other cyl of the same side! How can that be? They're both fed by the same carb. Altitude: 1200' MSL (lake altitude) to +/-5000 MSL is my range of alt ops.

Jim (avid): I'll run that s.plug check from a higher RPM shut-down - good tip. I gather that if they're brownish from a high RPM shut down, then it doesn't matter that it runs rich at idle?

BigJohn (& Dave S, kmach): I've discovered that the EGT probe is installed too close to the exhaust port: at +/- 55mm vs the recommended 70mm. Knowing that helps explain the higher readings. I hesitate to move it though because the probe is in a hole drilled in the exhaust pipe. Could I plug that hole with a metal screw? Ref the EGT in a full pwr climb, typically when I reduce the RPM in a full pwr climb, the EGT also increases. I'll try it for a 300RPM reduction to get a more accurate reading. Not sure about main jet size. I gather that the card needle position fixes that? The plug soot tells me that I'm not running too lean, but that's at idle...

JimS: I get to max RPM no problem, but not beyond. I think my prop pitch is close to where it should be, but I appreciate your explanation.

Thank you all again for your comments. Please feel free to comment further based on my answers above.

[Av8r3400]

Plug color: I really like the idea of the minimal idle to check plug color. I may try that myself. Remember these carbs are mostly running on the idle circuit until 3000 rpm.

I've seen the same issue with a black set of plugs on the front cylinder with the rear cylinder on the same side looking near fine. That does not mean that carb isn't running rich. (Sooty or black plugs indicate rich running.)

I would not recommend plugging the hole in the exhaust with a screw. Find someone with the proper tig welding experience and have it welded shut when you are ready.

[turboturner]

Just a follow up on some "tests".
EGT temp increases 60 deg F on a full pwr climb when the RPM is reduced by 300. I gather that is normal & desirable.

Plugs on cyl 1 & 3 are fine. Plugs on 2 were black (sooty) & 4 was light tan. I leaned the mixture on the left carb (feeds cyl 2&4) 1/4 turn & the plugs on cyl 2 were still sooty but the ones on cyl 4 were white! That baffles me. Can anyone explain why & help me correct it?

Knowing now that the EGT probe is closer to the exhaust than it should be re-assures me that its readings are on the high side (all other eng parameters normal). Next step is to connect a CHT probe & confirm that its the readings are within 15-20 of the coolant temp.

Thank you all for your feedback.
Carl

[Danzer1]

Given your current dilemma - I would want to know the cht and egt on each cylinder.

Is sooty #2 wet or dry?

Greg

[turboturner]

Good point Greg - check each cyl individually. I'll do that later in June when I return. Ref your question: dry powdery soot on the tip & electrode of # 2 but wet threads on that plug (?), dry white plug on # 4.

[Danzer1]

On #2 can you tell if the wet thread is oil, fuel or coolant? May not be a carb problem - could be rings on #2. Or if the carb is set to rich, you could have excess fuel in #2 and #4 could be lean for a different issue - maybe valves. Is it dropping any fluid levels at all? Are you sure you have consistent, strong spark at all cylinders. How may hours since cylinder inspection? Could be due for a look see - spark, valves, cylinders, rings! If your cht's and egt's are vastly different between 2 & 4, you likely need to look inside.

Greg

[turboturner]

smart questions Greg. Fluid levels are steady & the latest compression checks (over a year old) were good (130 on # 2 & 132 on # 4). When I "leaned" out the left carb ( 1 1/4 turn open vs 1 1/2) the plugs on # 4 responded immediately - they were white after one hop, but the "wetness" on the plugs in # 2 was gone (still covered in black soot). So it seems that # 2 is getting more petrol than it needs but the "metering" screw at the carb is doing its job. As you suggested earlier I'll connect a CHT on each cyl, in turn, & get their readings. I suspect # 2 to run cooler than 4. It'll be interesting to see by what difference, and then decide the next course... Could this all be because of a weak coil? I'll be comparing the resistance of all four too.

Thnx again.
Carl

[Danzer1]

Doubtful it would be a coil (but possible), more likely could be plug wires though - I'd check the resistance on each while you're doing it. The temps will tell you a lot - so you know where to head. I'm also assuming all 4 plugs are identical and properly gapped?

Greg