attempted first runup to 4000 rpm

I have a 912uls. while doing the first full run up to 4000 rpm and checking the ignition when I ran on B engine run rough dropping 1000 rpm seemed to run fine on both and a 300 drop on running on A.
I shut down and pulled the plugs. Cylinder 1 and 2 had both plugs fouled.
Cylinder 2 and 3 plugs were fine.
I'm in the process of putting new plugs and try again.Does anyone have any thoughts on what would cause this?
Alan
N603NH awaiting first flight

I would think the plugs could cause this. Will be interested to here results after replacement.

Heavy floats in the carburetor can cause those problems. Pull the float bowls and weight them, replace if necessary. You might want to look into the Marvel schnebler.https://msacarbs.com/product/rotax-bing-blue-epoxy-float-ms80-430/

supposedly this engine has the floats that aren't a problem
Alan

Fouled plugs

It is normal tendency for the front plugs on the 912ULS to become fouled after extended idling.
Make sure to reduce richness after starting the engine and progressively pull it back to keep the engine running smoothly while it warms up. First 2 minutes after start at 2200 RPM and then increase to 2500 RPM until in the green (60 degrees centigrade).

PaulvS said:

It is normal tendency for the front plugs on the 912ULS to become fouled after extended idling.
Make sure to reduce richness after starting the engine and progressively pull it back to keep the engine running smoothly while it warms up. First 2 minutes after start at 2200 RPM and then increase to 2500 RPM until in the green (60 degrees centigrade).

Click to expand...

no mixture control on 912uls

rich for starting

My 912ULS has got an enrichment circuit for starting, otherwise it will not start...
It's not a mixture control as found on Lycoming. But once the engine has started, if it is left unnecesssarily rich then it will foul the plugs and misfire during runup and fail to maintain RPM, as you are experiencing. I would check this first, rather than think that there is something wrong with the engine or floats etc.

troubleshooting with Dean at Lockwood ports to a trigger coil.
Unfortunately to get to it have to pull the engine out.
Alan
N603NH RV-12
1hr on the hobbs

I will tell you I chased a similar problem last year with excessive RPM drop on the "A" channel ("B" off). I checked everything with the ignition systems, logically, including swapping in known good ignition modules. After extensive conventional ignition system troubleshooting, and against conventional thinking, it was suggested by several that my issue could be carburetor related, and they were right. I wish I could tell you exactly what the problem was, I can't. My carbs were due 5 year service. I sent them to Lockwood for overhaul and asked for teardown report - I didn't get one. But when I reinstalled the carbs after the 5 year service, the engine ran fine and has been running great since. TT when this all began at was about 160 hrs, and I've put about 30 hrs on it since.

was able to pull the engine forward about 8 inches and tilt it a bit
involved allot of disconnecting
found an excessive gap on 2 trigger coils and regapped this time using brass feeler gauges.
hope to get it back together and run shortly
Alan
N603NH Rv-12
1.0 hr

yes that corrected the problem. 200 rpm drop now
Alan

amekler said:

yes that corrected the problem. 200 rpm drop now
Alan

Click to expand...

I usually see 80, maybe 90 rpm drop between the 2 ignition systems at run up at 4000 rpm.

I agree with the 80/90 drop.
Stan