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1997 115HP Johnson V4 intermittent fast idle

P

PrincP

New member
Hi,
My 1997 115HP Johnson V4 fitted with carburetors and opto ignition has an intermittent fast idle problem.
This motor generally runs well however on occasion the idle increases to 2000rpm while in neutral for no apparent reason.No alarms are present on the LED and warning horn system.
This generally occurs after a period of running when pulled back to neutral but also on restart of the engine.
The engine operates in water temp of approximately 20 degrees Celcius.
I am aware of the engines SLOW condition (rpm limited to 2500) however this is associated with high engine temp.The engine also has a quickstart function however this is meant to operate to a max rev count of 1250rpm for 5 seconds.

Any ideas ?No WAGs please.

cheers PP:cool:
 
You may have fuel leaking into the cylinders. Might be from flooding carbs, might even be from a leakage in the vapor pump on top of the chamber.
Another option is leakage from the primer solenoid system.
It may even be a soon to be failure of the power pack that partly activates the 'quick start' function. The power pack reacts to the 'opening' of the beam( optical sensor) and not the closing as in normal running.
 
Thanks Haffiman37,

The fast idle continues for several minutes before returning to normal.Are there any tests on the power pact that can be performed ?.

How does the vapour pump work and can I test this ?.

cheers PP:cool:
 
As for vapour pump, pull off the pulse hose and see if any fuel in the hose. If fuel - change the pump. From your description it sound like the engine keeps on burning off 'excess' fuel. It might perhaps be time for a carb clean and re-build. If so, change the float valves at least. Even check with running engine that primer solenoid does not leak in the 2 small lines out of the solenoid.
 
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