Jab stutters

[bushpilot]

Hi All,

 

My J160 has done 170 hours and twice recently has ran a bit rough for about 5 seconds at idle, after running for at least 3 - 4 minutes after start-up. Crack the throttle and it clears.

 

2 opinions I have been given by locals with Jabs:

 

1. The hydraulic lifter are the cause - holding a valve open for too long. Suggested that larger oil bleed holes is one fix - and is standard on latest lifters.

 

2. Sticking valves caused by the 'dryness' of Avgas. Suggested fix is small amount of 2-stroke oil in each tank fill! (Sounds a bit radical to me..)

 

Anyone had any experience with the issue or a view on these suggestions?

 

Cheers,

 

Chris

 

 

[Modest Pilot]

I'd also check the fuel bowl is clean, it's suprising what gets passed the fuel filter. One aircraft at the field had enough white stuff (fuel tank sealer?)in the bowl to block the start curcuit.

 

 

[bushpilot]

The stutters have been after carby heat application in run-up; and only in past 2 weeks, so warm weather. Carby bowl was clean at last service - 20 hours ago, but will check. Thanks.

 

 

[geoffreywh]

whomsoever told you about "dryness" of AVGAS needs to be totally ignored if you know what's good for you. What a crock....

 

 

[Yenn]

Carby ice can form even at high ambient heat. The cooling comes from the evaporative cooling as the fuel vapourizes.

 

I had a couple of instances of the engine stopping while taxying. The bottom of the bowl had a couple of very small dark lines which wiped off easily, but the idle jet had a very small build up of dark, hard material, which took quite a bit of cleaning.

 

 

[Ultralights]

my first thoughts are carby ice, with high humidity, it can occur at temps up to and over 30 deg C!