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What's it trying to tell me ?

8 posts in this topic

Posted

I've been chasing a rough idling (2000-3000 rpm) on this 912 for a year.  It will run fine above 3000 and idle OK around 1800 but between its got a very annoying miss.  It also has a high mag. drop (around 150 rpm.)  I've done all the usual things, sync'ed the carbs (over and over) had the carbs rebuilt, by myself and two separate professional companies, replace the plugs, plug wires and leads etc. checked for manifold leaks etc.,etc. Nothing had any effect, nada zip.....  The only thing I've found that has made any change is to turn the idle mixture screws almost all the way in.  The manual and all the experts say turn them out 21/2 turns and leave them, but mine have to be about only 3/4 of a turn out or its rough as a cob between 2000 & 3000 rpm.  I'm thinking something is screwy in the idle circuit because it runs smooth above 3000.  But what else to try? Any ideas ?

Thanks

EG       

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Posted

I don't know if your 2 1/2 turns out is a typo but the manual states 1 1/2 turns but if it wants to be at 3/4 to run properly that is where I would run it.

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Posted

hummm, is says 21/2 turns, must be typo.  Any idea on the mag. drop ?  This is my third 912 and the other two were less than 75 rpm, this one is more like 150-200.  About the same on either ing. box.

Thanks

EG

 

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Posted

That is well within spec, @ 4000rpm it must not exceed 300 rpm and 115 max difference between the two.

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Posted

Tried a different brand or type of plug? I'm not a 912 guy but my 582 really likes the iridium plugs. 

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Posted

I had the same issue a while back with my old 912UL powered Kitfox.

It was carbs.  I had them apart so many times I lost count but they finally worked and the problem went away.  I believe I had one of the enrichener valves reversed.  The other issue is this vibration eventually damaged the gearbox.  I wound up rebuilding the box completely.

How many hours on the engine?  Is it a UL or ULS?

Did it just start doing the vibration suddenly or gradually over time?

Has the gearbox ever been re-shimmed or serviced?

What prop do you have?

What do you have your plugs gapped at?  These are not very hot ignitions.  I keep mine at .022 - .024".

Stay with the NGK plugs.  DCPR7E for the 80 and DCPR8E for the 100.  I run the 8Es in my low compression Zipper motor.

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Posted

Has the prop been used on another engine? Any chance that it's out of balance as well? I realize you're getting a mag drop below what you want but just trying to throw other ideas at you as well. 

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Posted

Gearbox has been rebuilt. Prop is a new IVO three blade. Adjusted the idle mixture screws to 3/4 out and it is definatly better but still some roughness around 2500 rpm. Thing is I can slightly pull on the choke(enricher) knob on and it will run very smooth at 2500. However when I push up the throttle to 2500 it's rough.  I'm thinking the problem is it's too lean at idle but I can't figure out why. I've checked for induction leaks, replaced the rubber carb mounts etc.  sprayed starter fluid around but nothing turned up.  Errrrrrrrrr

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