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WOT miss when HOT

Fltnut

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My RV12 with the 912ULS will not run smooth at WOT or get T/O power after it's HOT.

Last flight everything was fine until I left the power up at altitude to see what I could get for RPM in level flight. It started to run rough at 5400 RPM. After returning to the field I as unable to get more than 4400 RPM. The problem is always after the engine is hot.

Don't waste your time with suggestions to trouble shoot only because we've been through everything at least twice. But please, if you have had or know someone who has had the problem of not running at full power after the engine gets HOT, I'd love to hear what fixed it.

Ron
 
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Do you have any data stored to the SD card on fuel pressure etc you could share ?

When I Faa’s going through the fly off period I had an engine stumble and difficulty with hot running at high rpm. I took my carbs off and cleaned multiple times nothing changed. I did a fuel flow test with the floats removed and found one carb flowed considerably more fuel than the other. I took the carb apart blew compressed air repeatedly due the inlet channel. Eventually a very small piece of wood splinter came out. Problem resolved in my case
 
I haven't downloaded any data from the Garmin yet. Might run that today if I get the time.

Thanks for the explanation of what you found on yours. I've been through everything and read every post about rough engines. Your response is exactly what I'm looking for as I start going through everything again.
 
The problem has been fixed thanks to Roger Lee. I'm sure a lot of you know Roger or have seen his post on multiple forums. Well, he's come through again.

After talking for almost an hour on Friday and not coming up with an answer Roger said, "one more thing, check the choke shaft for a punch mark tell me which way it's facing". I did (after I found the small punch mark) and the 2/4 carburetor choke was assembled wrong. Punch mark 180 degrees out. After the 5 min. it took to remove the linkage, turn the shaft and put the linkage back on, I ran the engine and it seemed to be fixed. Saturday I put the cowl back on and went flying. Everything was as it should be. Today I flew again and did everything I could do to make it screw up, including sitting on the ramp for 15 min. after flying, to let everything get hotter. I did another T/O and then a touch and go and then declared the problem fixed.

There a lot of questions: how long has it been that way? There doesn't appear to be any reason the previous owner would have been into the choke in the 150 hrs. that he had it. Why did it the wait 30+ hrs. that I flew it? How did it run as good as it did? I am not knowing!

Thanks Roger
 
So take pictures of the choke, the dot and the lever installed properly, and post it up here, on how it should look, so we all know what to look for when reassembling the choke lever on the shaft.
 
Not trying to explain how the "choke" works 'cause I don't know how it works, but here is how the index mark on the choke shaft has to point toward the air pipe on the choke housing (3).

This would be the left carb:
i-ssWpB7g-M.png


This shows the index mark correct on the right side carb:
i-bSP6wTB-L.png


If the index mark on one choke is pointed 180 degrees away from the air pipe then you will know it. The engine will be very difficult to start on the chokes. With only one choke working correctly, a cold engine will try to start on only half the cylinders and the gear box will bang back and forth loudly and unhappily.
 
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