Gearbox chirp while burping?

Quick update, found several references in the Forum regarding gearbox chirping after an OH, mine had an OH about 100 hours ago.  I've checked the mag plug and will continue to monitor but appears something I'll have to live with as long as nothing changes.

Mag drop is noticeable at 2500 RPM and at 4000 had 600 RPM on A. Pulled choke and got ~100 RPM rise, mag drop was not noticeably different; early forum thread say probably ignition (not carb) if no measurable difference with or without choke.  Swapped 6 pin connectors, drop stayed with A.  Installed new plugs and set to lower end of gap range as OAT is in the 20 F, no change in mag drop; all ignition boots appear tight & clean.  thoughts?

Appreciate the help, bob

Bob, check the idle speed jets on both sides (see item#6 on carbueretor diagram https://lockwood.aero/parts/four-stroke-parts/912-s-914/rotax-912-s-914-carburetor-parts-914.html?___SID=U) for blockage looking thru it end to end. Even if you see light thru it it does not mean its clean, makes sure it is clean as new. I keep an extra set in my tool box just for this problem. It sounds like a mixture problem especially if you use car gas. Also i had an intermittent chirp when my engine was new, it eventaully stopped happening.

all the carbs I've cleaned have a known number drill bit to help clean the varnish out, do you know the jet size of the idle circuit?

appreciate the help

bob

The idle jets aren't in play at 4K rpm so that 600 rpm loss isn't due to a clogged jet. Start with the most common and cheap diagnostic procedure. Don't just throw money at it. You can unscrew the plug rubber boots and trim the wire back 3/8" to get fresh wire then apply a dab of dielectric grease on the wire tip and screw the boot ALL the way back on. When it's fully on it will stop turning. This is a quick and easy check to help rule out a bad wire and boot connection. 

DO NOT put a drill bit in any of the jets or carb orifices or you'll most like be paying the Piper.

If you need to clean an idle jet out get a 6" piece of 16-18 gauge wire. Strip the insulation back about 4"-5". Then unwind one strand and slide that through the idle jet to help rod out any dried debris. Then follow that with spray carb cleaner and then follow that with high pressure air.

Many that have used drill bits have had to replace their jets. Idle jets can become clogged at times when planes are left to sit for months.

Or use an ultra sonic cleaner with carb cleaner. Like Roger said don't use anything that can even scratch them. Sometimes your problem can be caused by a stack up of minor issues. like a combination of ignition and fuel air mixture problems.