Throttle idle

[Guest Fred Bear]

Anyone else ever flown a Jab or know of one that when you pull the throttle back to idle then back a little more it cuts out (engine)? Only one Jab I have flown has done this and I wonder if there is any others out there and what causes it? It does not seem like a normal thing. On the ground, fine. Different story maybe on final.

 

 

[BigPete]

Hi Darren - doesn't happen to my J160c - I would have thought that it shouldn't happen on final, as the air tends to keep the motor ticking over, unless to slow an approach is used - if you get my drift.

 

regards

 

 

[Guest Fred Bear]

Pete,

 

It is when you keep pulling it back more than idle. For some reason I did it on the ground the other week and she stopped. A quick push of start and it fired up again. It has done it on final to someone too so unusual as you mention. If you know it's there it's ok but if not it could potentially get you by surprise. Cause thoughts??

 

 

[Captain]

Darren

 

Having recently set mine up, it sounds like bad adjustment of the stops to me.

 

The J throttle cable is soldered into ferrules (right word??) both ends so that it is actually a bit of a push/pull system.

 

There is a stop on the carby where there is a screw adjustment, and that sets the idle revs, plus there is a stop on the throttle linkages that limits the pressure that can be applied to the carby stop.

 

On the panel mounted throttles those latter stops are circular collars that are grub screwed onto both final linkages either side of the panel.

 

If those are not set correctly you can continue to pull or push hard on the cable, which then can pull/push hard onto the carby stops/adjustment screw and exceed a little where it should be.

 

As with all carby throttle settings in bikes, cars, karts etc, the stops in the throttle linkage system should be set so that you are not reefing the begeezus out of the end travel of the throttle/butterfly, or you will get lower than proper revs and maybe overstress or break the end off the cable.

 

I hope that helps ................................... and that I am right about the problem in your case.

 

Regards Geoff

 

 

[Guest Fred Bear]

Sounds as though you are right Geoff. I have seen the screw (stop) at the idle point and as you say they are probably wrong. That would seem like a simple adjustment. Will have a word to someone... Thanks for the input Geoff

 

 

[facthunter]

Unreliable Idle.

 

An idle check is part of the taxi- pretake -off check items. Probably hasn't been emphasised for a while . If the engine stalls when the throttle is pulled to idle the aircraft is UNSERVICEABLE. The idle stop adjustment on the butterfly shaft should determine the idle speed. If the length of the throttle cable becomes the determinant of the idle speed by default then it is setup wrong. N..

 

 

[Guest Fred Bear]

Nev, point taken and as a pilot I always do an idle check. No exceptions to this rule. I need to emphasise that this is when it is pulled back real hard to just past the idle point as in you put maybe 5kg of pressure on the throttle. You would not normally do this in an idle check. I did it because there was water half way down the strip and I wanted to make sure I would come to a complete stop before that point.

 

 

[Guest J430]

Ahhhh Darren,

 

I bet you are the type that pushes the mouse button harder to make a point, or push the volume button on your TV remote to make it go quieter quicker....hehehehehe

 

We humans are a funny lot!

 

Cheers

 

J;)

 

 

[Guest Fred Bear]

;) You are right though. Accelerator to the floor on the car sometimes too (and it's a manual)

 

 

[Ross]

Hi Darren

 

It occurs to me that it could also indicate that an engine has lost some performance and that a normal idle setting is not enough throttle (power) to keep the motor turning over, not necessarily so in your case but a possibility or a bit of both.

 

I think Jabs are supposed to be set to idle at about 800 RPM but some people set them a bit higher to get smoother engine running which could make the choke not effective and could hide the engine stall that would or possibly occur as the engine performance drops off due to normal or otherwise wear and tear.

 

Regards

 

 

[Yenn]

I fly with a Jab engine and had 2 stoppages at Old Station this June. The cause was throttle setting too slow although at the time I suspected carby ice. I upped the rpm. to 950 and no further problems. The fault was not evident on the ground pre takeoff but occurred when I slowed down on base and again on final. I restarted after the first stoppage but didn't bother to restart again until I was down to taxi speed.

 

 

[blueshed]

Mixture

 

This may also be possibly caused by the idle mixture being, either a little rich or a little lean.

 

This can possibly be affected by the difference in air density of the day, possibly due to winter verses summer or the in crease in altitude. Say you have flown from Bankstown to Orange or vise versa. Nearlly a 3000' change in altitude.

 

Cheers Guy