AQ 171C Running on after turning off the ignition

[Dr Michael R. Taylor]

I own a Carver Montego wuth twin AQ 171C engines, both of the same age and both were decoked 18 months ago. One has now developed an annoying habit of 'running on' when the ignition is turned off. I had an idea there was an anti 'running on' device fitted to these engines - possibly an automatic fuel cutoff solenoid, but I cannot find any reference in any of my maintenance books. Can anyone confirm whether such a device is fitted and what could have gone wrong with it? Thanks.

 

[Don S]

Re: AQ 171C Running on after turning off the ignition

No, there are no fuel cutoff solenoids like cars had.<br />Check your idle rpm, too high will be a cause.<br />Also the timing, spark plug type and heat range.<br />Also make sure you let it idle for a minute or 2 after a hard run before shutting off.

 

[Bondo]

Re: AQ 171C Running on after turning off the ignition

both were decoked 18 months ago.

That's a Long Time, if they are running at all Rich......<br />As stated by Don, If it wasn't doing this Before,<br />It's No Doubt time for a Complete Tune-Up........

 

[Dr Michael R. Taylor]

Re: AQ 171C Running on after turning off the ignition

I will check regarding rich running. Plugs are the right type, electronic timing so not much I can do there. I started the engine last Saturday and ran it for 10 minutes at about 1500 to 2500 RPM and then reduced it to idle for about 1 minute ut it still ran on a fair amount. I wonder if I should rebuild the carbs if the tune up does not work?

 

[Bondo]

Re: AQ 171C Running on after turning off the ignition

That's the path that I would follow.........

 

[Dunaruna]

Re: AQ 171C Running on after turning off the ignition

Originally posted by Michael Montego:<br /> electronic timing so not much I can do there.

Its got electronic ignition, timing is ajustable.<br /><br />Aldo

 

[Dr Michael R. Taylor]

Re: AQ 171C Running on after turning off the ignition

Aldo - I agree re electronic ignition but timing is also electronic. Advance and retard is pre programmed into the electronic ignition module (approx 60 pre programmed settings) with a sensor picking up pulses from the flywheel to initiate the spark. Have I missed something?

 

[mcginleyc]

Re: AQ 171C Running on after turning off the ignition

This is not a fuel problem. If you have a manual you will need the wiring diagram page. Look at the ignition circuit. There should be a resistor in your engines ignition that limits voltage. When this resistor is blown it will allow the ignition to "backfeed" the ignition coil and continue to run after the key switch is turned off. Use a multimeter on the ohms setting and test that resister. I will bet this is your problem. Good luck and post back with results.

 

[Don S]

Re: AQ 171C Running on after turning off the ignition

mcginleyc, are you looking at a standard 4 cylinder ignition system with a ballast resistor. If it fails, there will not be any ignition voltage to the coil except in the start mode. No way will it keep running. If it was shorted it would just add extra voltage to the points and burn them up quicker.<br />Besides that he has an occasional "Run on" problem as in "Dieseling" when he tries to shut it off.<br />His 171 is even more complicated because it's the Renix electronic ignition, and doesn't even have a ballast resistor.

 

[Dr Michael R. Taylor]

Re: AQ 171C Running on after turning off the ignition

I ran both engines for 12 years before decoking and even then the heads were not that bad and I never had the run on problem. I find it hard to believe that it has coked up in 18 months. I have used the boat in exactly the same way - 2 hour trips along the south coast of the UK or 6 hour trips to France. I have recently changed the exhaust manifolds on both engines so maybe this particular engine is now running richer because the exhaust gases are leaving the head more efficiently. This is the only thing that I can think of but it does sound a little far fetched.

 

[Don S]

Re: AQ 171C Running on after turning off the ignition

You still have a distributor Michael, and an adjustment to set the basic timeing to 10 degrees BTDC. <br />You might also check the toothed belt on the front of the engine. If it's worn out and the tooth of the belt is narrower than the gap between them, and will affect the timing.