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Reduction belt slipping?


paraflyer
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Yesterday I went off to my regular starting place. I started my engine F 200 in trike configuration. The engine started well and run good , but when I applied full power i noticed considarable less thrust than normal and a slight change from normal in the engine noise. At first i was sure the belt was slipping , but i think it is good tensioned so i was a bit suprised. Howewer when i looked at my RPM gauge it show a considarable and sudden drop in rpm at full speed from about 6500RPM (max RPM on this engine used to be and should be 7900RPM) when i apply more power the RPM on the tachometer show a drop to about 4000RPM, but the engine does not sound at all like dropping in RPM it just makes a slightly different noise and has not full thrust. The RPM gauge as you know is picking up the rews from the spark plug. How do I explain slipping of the reduction belt if RPM drops instead of increasing? Could this be a ignition problem? The engine runs wery well on idle and in mid range and starts good. Of course all the settings on the carburator is checked out H and L. Please help anyone?

Milan.

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You can lose power if the threaded bit on your plug where the lead attaches (assuming so equipped) is loosening and arcing internally.

This can appear as dropped rpm since it interrupts your tach induction readout feed.

Right up until the lead falls off the plug and kamikazes into the prop celebrating it's freedom.

Or:

Your coil is on it's way out, needs regrounding or circuit checked

Your tank vent line is plugged and starving engine tho unlikely to cause symptoms listed

Your silencer is plugged or plugging up

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You can lose power if the threaded bit on your plug where the lead attaches (assuming so equipped) is loosening and arcing internally.

This can appear as dropped rpm since it interrupts your tach induction readout feed.

Right up until the lead falls off the plug and kamikazes into the prop celebrating it's freedom.

Or:

Your coil is on it's way out, needs regrounding or circuit checked

Your tank vent line is plugged and starving engine tho unlikely to cause symptoms listed

Your silencer is plugged or plugging up

Today I tightened the reduction belt and also used some belt spray on it. Started up the engine and at least from the ground test it seemed like the engine has got back its thrust and the engine sounds normal. Howewer the tachometer RPM climbes up to approx 6000 rpm and then starts dropping even though i increase throttle and engine revs up more. The tachometer drops to about 4500 RPM at full throttle. I replased the tacho with another tacho and gess what the tacho nr 2 works normal and show 7850 RPM at full throttle. So I still have to do a flight test to be sure that all the thrust is back and maybe the conclusion could be two faults at the same time the tension of the reduction belt and a faulty tacho?

Milan.

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Your old tachometer served it's purpose, even in a questionable condition.

Always trust your ears once you have the proper running sound trained into them.

If you got some slack out of the belt tensioner and the sound is back where you expect it, pretty good odds that your new tach is reporting correctly and your thrust is back.

I recall smelling belt when a pilot took off before, perhaps someone smelled yours.

You cannot always hear a squeal, but there's always evidence if it's slipping.

Glad you got it sorted.

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