Uneven Idle Speed

[A1an]

Idle Air Control Valve

[jeffstevens763@g]

Originally Posted by Callum B

Thanks diver.....i think im the only guy in the world that has one of these....getting another "iac" valve is gonna be tricky!!......whatever an iac valve is??....intake air c..c...colostomy??.... sorry....im not fully outboard techy!!


.

your tohatsu wont have an IAC valve i'm doing at mercury 3.3 up at the moment i notice there's no fuel filter in line ive not stripped it yet but a suspect some form of filter in the fuel on/off valve which on yours might be restricting flow if yours is the same. mine is an early engine though, i would change the plug though ive just had a chainsaw with a bad plug doing the same thing thought it was a fuel problem.
hope that helps

[Callum B]

Thanks Jeff.

Ive just been googling and youtubing possible causes for the presenting symptoms.

I haven't changed the spark plug, as it starts on the button,....but i will try that to exclude it......other possibilities include engine timing, and incorrect oil, which i will investigate.....not sure how to check the timing, so i will leave that to last!!

There is no fuel filter in line, before the carb., unless its in the tank??..... ive had the tank off, with the fuel valve in line and get good fuel flow.

I too had an issue with a chain saw, ....cleaning the fuel pump in an ultrasonic tank got it running sweet.

I'll have another go at it today......That will maybe get me out of painting the fence!!

[jeffstevens763@g]

float chamber set correct valve not sticking, no hose splits etc, tank air screw ok, new fuel, head gasket ok.

[Callum B]

So....the saga continues......

New spark plug....no difference.
No obvious adjustment on the carb float.
All pipes and cables appear ok
New fuel
Air vent ok

Couldnt see if the float needle valve was sticky....but it all seemed free enough. It doesnt seem to flood, so im doubtful its the float chamber valve.

Head gasket ok , i think.....no emulsion in the oil , very little oil deposit in the wheelie bin, and no oil or water visibly leaking.

The revs wander about a bit on tick over, eventually resulting in a stall,.....a tiny tickle up, on the tick over, and it revs too high on tick over. I had something similar years ago, but it was the carb that was loose, drawing excess air,....an easy fix!!

It can only be fuel / air mix from the carb i think...... ive ordered an ultrasonic cleaner to give the carb the once over... we will see what that brings!!

Painting the fence would have been less mysterious....

[Davie]

Originally Posted by Callum B

So....the saga continues......

New spark plug....no difference.
No obvious adjustment on the carb float.
All pipes and cables appear ok
New fuel
Air vent ok

Couldnt see if the float needle valve was sticky....but it all seemed free enough. It doesnt seem to flood, so im doubtful its the float chamber valve.

Head gasket ok , i think.....no emulsion in the oil , very little oil deposit in the wheelie bin, and no oil or water visibly leaking.

The revs wander about a bit on tick over, eventually resulting in a stall,.....a tiny tickle up, on the tick over, and it revs too high on tick over. I had something similar years ago, but it was the carb that was loose, drawing excess air,....an easy fix!!

It can only be fuel / air mix from the carb i think...... ive ordered an ultrasonic cleaner to give the carb the once over... we will see what that brings!!

Painting the fence would have been less mysterious....

Have you drilled out the tamper proof plug in the top of the carb?