Ignition Runup check issue

[Roscoe]

Hi all. Recently had a 200 rpm rev drop & rough running at exactly 2600 rpm during Runup.

 

Smooth at 2000 and full power .

 

Plugs all ok.

 

Seems intermittent but why rough at that specific rpm?

 

Would appreciate comments thanks

 

Roscoe

 

 

[AVOCET]

check under dissy caps ,

 

check mag gaps ,

 

sucking air in intake some ware ,

 

worst case , loose fly wheel .

 

plugs may look good might be worth changing them & try a new set

 

mike

 

 

[deadstick]

As AVOCET sugggests, check the rotors and dizzy caps, rotors should be glued solid to prevent them rocking on the shaft at certain engine harmonics.

 

 

[Roscoe]

Thanks Guys, as usual quick and clear response. Really appreciate your help.

 

Am shortly Posting another issue re fuel stains on Wing Root,

 

Cheers Roscoe

 

 

[planedriver]

Partially blocked fuel filter, perhaps?

 

Change it anyway, then try again.

 

You say ok at full power, but is it only for a short burst, or will it maintain full power without hesitation?

 

 

[Roscoe]

Ignition check smooth at full power and 2000RPM on both switches.

 

Problem is only at 2600 RPM on RH ignition.

 

 

[Roscoe]

And only on Runup pre flight

 

 

[brucechurch]

Look for coil wire short on engine mount happened to me space wires out from engine mount

 

 

[Roscoe]

Thanks Bruce

 

 

[jetboy]

At 2600 the carb would be delivering the leanest mixture. Simple diagnostic test is to operate carb heat to see if that helps by richening the mixture. Pulling the choke has the opposite effect, after a brief period of adding fuel it adds some air, leaning the mix. If any of this makes a difference, there is the mixture distribution ratio to individual cylinders, which may need trimming by rotating the carb, putting in a flow straightener - or finding an intake runner leak.

 

The symptoms described seem more likely ignition related

 

 

[planedriver]

Ignition check smooth at full power and 2000RPM on both switches.Problem is only at 2600 RPM on RH ignition.

That rules out filter as likely fault.

 

As Bruce has said,keep ignition wires away from engine.

 

Another slim posibility is a weak spring in the switch itself, causing the contact to bounce a little under certain vibration harmonics. Plus check that all ignition electrical connections are clean and tight.

 

 

[AVOCET]

when you find the fault let us know

 

mike

 

 

[brucechurch]

Did you find problem

 

 

[Roscoe]

Did you find problem

Changed Coil on LH side which seems to have solved problem but only flown once since because now i have a Radio issue which i am working on!

Hopefully Coil was the culprit with the engine issue but will keep eyeon it.

 

Thanks Bruce

 

 

[planedriver]

[Hopefully Coil was the culprit with the engine issue but will keep eyeon it.

 

We'll keep our fingers crossed for you.

 

Let us know how it goes. Always interesting know.