I have a new plane - a supersporster with a new 61 fx (~15 flights so far). When I get her into the air, the engine makes a crackling, sort-of-popping kind of noise. It sounds bad. Even one of my flying buddies who only flies electric says the engine does not sound right. As far as the mixture goes (the high speed needle that is), it seems to be okay - I set the mixture before each flight (~12,000 rpm). She idles good and does not cut out during flight. The engine sounds fine on the ground.

Why does my engine make this strange popping noise? Is it preignition? Maybe the wrong plug? I wish I could record the noise and play for you here as it is a very "popping" crackling noise.

Any help is appreciated!

Thanks,
Boots

I've never heard of this problem with the size of engine your refereing to here. BUT in the half A engine world when you hear that sort of sound is usually means your over compressed for the % of nitro that your running. We add a head shim to increase the deck height to solve this, but like I say I've never heard of this with a .60 size engine. What % nitro fuel are you using? Is this something new with this engine? Have you removed a head shim/gasket?

First of all, I wouldn't set the mixture before each flight. Once it is set it should remain fine unless you have a significant weather change. Even then, only a slight adjustent will be necessary.

Adjust it for maximum RPM on the ground then richen it a few clicks until you see a 300-500 RPM drop. This will insure that it doesn't lean out and get hot in the air.

Try flying with a richer mixture and see what you get it may be to lean.</p>

what plug are you running? maybe you have too hot of a plug </p>

I am an automotive technician for 39 years and in an auto engine......the crackling or popping sound means pre-ignition knock or the fuel mixture is detonating in the combustion chamber instead of a normal combustion. Like suggested already, the mixture could be too lean once the engine/propeller combo unloads(speeds up) in flight. Flight rpm is higher than ground rpm due to the unloading of the propeller once in flight.....resulting in leaning out of the fuel mixture.........resulting in detonating(crackling/popping) sound because the leaning out of the mixture is conducive to detonation in the combustion chamber. If this detonating continues it could blow a hole in your piston or wreck your engine. Try richening your ground rpm by reducing your peak ground rpm by 500 rpm by richening the high speed mixture screw.
larry

She's definitely too lean. What prop are you using?

crackling means too lean...as said above......tune to max RPM then richen a 1/4 of a turn as it will lean in the air....you want to see a smoke trail...not as much as a 4 stroke...but against a blue sky a slight trail....good flyin

I was having a similar problem with my 1.20 two stroke. It was either too rich to run right, or was making the crackling noise. I disassembled my carb and cleaned it very well with alcohol and T-pins and reassembled, problems seems to be solved.

I think a 'dirty' carb (even though the engine is still new?) was preventing proper fuel flow, compensated for a richer setting - so it was either too rich or too lean, never just right.

Just a thought...

I've had this happen on a OS 91 FX, practically the same motor as the 61. tried different glow plugs, shims under head, lighter prop.

The only thing that solved the condition was going from 15% nitro down to 10%.