Inconsistant idle

[deetes]

Now that the Wedge is running again I find that I can't get a repeatable idle speed. If I blip the throttle it settles to one speed. Blip again and it slows right down. All the linkages are free and lubed. Only one return spring on the linkage. Difficult to set things up if it's all over the shop.

[350zwelgje]

On my flapper had something like that but not too bad: main issue was I couldn't get it to rev a bit more, the idle rev adjustment did nothing and CO-adjustment for MOT was very difficult.
Tip that helped me was to completely unscrew the CO-adjuster, clean it, put it back and check if there is an improvement. And he presto, everything back to adjustable/normal.

Rob

[honestjohntoo]

Even for a single plenum the basics are all here.

http://www.vintagemodelairplane.com/pages/Download...

[rev-erend]

Have you just added megasquirt.

Does this control the stepper motor ?

You might want to remove the stepper motor wires to see if this is causing the issue.. (clamp the pipe to stepper) ..

I would also check the throttle spindle is not worn - try to move it up and down with the engine ticking over and see if the tick over changes.

[Nacnud]

Sounds exactly like a problem I fixed last year - been plaguing me for years but had got so bad I HAD to do something.
Clean, Free, Lubed, etc - not the problem....

Was looked at by the garage who advised a replacement plenum - kerching, so I thought I'd have a closer look myself!!!!

I found two faults, both lying in the complex connection between the throttle cable end and the Plenum wall.

1) Slightly loose nut around the throttle plenum shaft gave a lot of play in the link. Could see the play by noting shaft position where it enters the plenum and look for differences between gently closing throttle and slamming the throttle shut. Tightened nut and all play was removed.

2) The return spring had gone soft with old age (the one around the plenum shaft, not the two main springs). I wound another turn on the spring, a bit fiddly but does the business.

I'm pretty sure either tweak would have fixed the problem on it's own, but doing both of them mean the idle revs are now spot on every time.

[deetes]

rev-erend said:

Have you just added megasquirt.

Does this control the stepper motor ?

You might want to remove the stepper motor wires to see if this is causing the issue.. (clamp the pipe to stepper) ..

I would also check the throttle spindle is not worn - try to move it up and down with the engine ticking over and see if the tick over changes.

Rev,

It was a flapper before conversion to Megasquirt, so no stepper motor.

Thanks for the suggestions and to eveyone else too.

[rev-erend]

Hope you get to the bottom of it !