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MG MGA - Strange idle

I posted this a few days ago on the Magnette board. Any thoughts?

I have an ongoing issue with my idle as it is too high (typically about 1200 rpm although it does vary a bit and maybe as low as 900).

This morning, I found that the idle had dropped to about 400 and sometimes the engine would cut out if I didn't rev the engine. The only change was the weather - first frost of the season.

I did find that turning off the heater fan improved things.

Then as I approached the car park it got better and returned to normal.

Has anyone else exp rienced anything similar, and should I worry about it?


cheers

dan
Dan Smithers

Carburetter icing? Goes away as soon as things warm up a bit?
D Sjostrom

Hi Dan. It's interesting that the problem improves when you turn off the heater fan. Im wondering if the blower motor is defective and drawing too much current, which then robbed power from the coil, dropping the idle speed?
Just a thought, and it doesnt explain the previously excessive idle speed. Please let us know what you discover. Cheers, Glenn
Glenn

No, not a warming up issue. The temperature guage was reading normal before this appeared and after it went away.

It has happened a couple of times since but not every time.

dan
Dan Smithers

Oil in the dashpots too heavy?
Paul Hanley

Dan

You are not one of those people who pulls out the choke and hangs a handbag on it?!!!!

Steve
Steve Gyles

Dan

I have just remembered some of the symptons of my recent ignition/poor MPG saga.

Might be a slightly sticky (fouling) piston. Check that they both bottom-out with a solid clunk. (The Magnette is twin carb?)

I had a badly sticking front piston. RPM varied much the same as yours. It idled generally at 850 RPM (the RPM I set it up at). However, this turned out to be with the piston slightly stuck. When the situation got worse the idle could be as high as 1200. When I discovered the problem and reset the piston and cover, the idle instantly dropped to 400 ish.

Steve
Steve Gyles

Steve, no I don't hang my handbag on it. If I did that the engine would stop (if you remember my comment on your no-choke issue).
I was begining to think that taking the carbs apart and cleaning them might help. I was planning to leave that until after I installed my 1800 engine though.

I did recently top up the dashpots (with SU damper oil) so I hope it's not that.
Dan Smithers

I hate to state the common obvious throttle shaft wear, but it seems to be the first thing to look at.
Tom

This thread was discussed between 14/11/2006 and 17/11/2006

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