Stuck Throttle Speed On 4K

[Tham]

When test revving my KE70's 4K at idle the other
day, the idle speed suddenly shot up on its own
to some 3,000 to 4,000 rpm, and stayed there.

Shutting down the engine and starting again
caused the same thing to be repeated.

First, we thought it was a jammed throttle cable,
which looked alright. Then we looked at the linkage
at the carburettor, which also appeared to have
returned fully to its normal idle stop position.

After some tinkering around the linkage area and
spraying some WD40 there, plus spraying lots of
carb cleaner into the throat, the idle speed returned
to normal.

I wonder what might have caused this ? It happened
a couple of times with my older carb too. Both carbs
are stock and replacement Japanese Aisans.

One guy told me the problem could be inside the carb
itself, where the secondary jet's metering is controlled
by some pin or needle, which can get stuck occasionally ?


On an offnote, China seems to be producing quite a
few replacement OEM carbs these days. Not sure of
their reliability. Here's one. The part number is identical
to the present replacement Aisan which is on my 4K now.

http://hzocean.en.alibaba.com/produc...100_13170.html

[oldcorollas]

do you have a vac operated secondary?
was it stuck open?

[lexsmaz]

I agree, sounds like the secondary throttle butterfly got stuck open a bit, which will cause it to rev like that .. especially if spraying caused it to come good ...

[Tham]

The throttle secondary is linkage-operated.

It didn't appear to be stuck open, but maybe
I didn't notice it at that time. The primary linkage
had closed fully down to its idle stop position.

There was a counterweight on the right side of
the secondary linkage, not sure if that could have
been the culprit.

[lexsmaz]

It would not be open very much .. But thats what the symptons are, primary throttle at closed, stop position yet car still reving ...