Mis-fire on aq170c

[mallers]

I have a problem with a late 70's triple carb AQ170C which I wonder if anyone else has encountered.
I have replaced the fuel pump with an electric facet one, all the fuel lines,cleaned the carbs, checked the tank for debris, changed all the plugs, leads, coil, distributer cap,points,rota arm and condenser.

The boat runs fine for about 40 minutes and then starts to mis-fire. The problem gets worse over the next 30 minutes until the boat eventually packs up.

When it's cooled down again I get the same scenario.

I suspect it may be a compression problem at proper working temperature, as I'm pretty sure it's not a petrol issue.
Anyone else experienced anything similar?

Thanks for all thoughts, I'm pulling my hair out.

 

[doadonut12]

Re: Mis-fire on aq170c

vent for the fuel tank good? can you run the boat until it act up and shut it off and pull the plugs and get a read on the plugs?

 

[captmello]

Re: Mis-fire on aq170c

Check the temp of the coil when it starts to misfire. Your coil may be wired without a resistor causing it to overheat. I agree with the previous poster on the fuel tank vent. Next time it misfires loosen the gas cap an see if sucks air in and runs better.

 

[mallers]

Re: Mis-fire on aq170c

Thanks chaps. The breather tube is fine but the coil maybe getting hot.It's brand new from a marine volvo dealer so It should be the correct one.
Anyone else had valve seats wear and cause this problem? A couple of car mechanics are saying this could be the problem

 

[captmello]

Re: Mis-fire on aq170c

There is most likely a resistor wire to regulate the voltage to the coil. While running, the voltage should be around 9v at the + terminal.
I don't see the correlation between the valve seats and your issue, but you could always do a compression test and see where things are. If you find low compression, a leakdown test could tell you if it is a valve or ring problem.