mariner 60hp late 80's flat spot

[jebbie_uk]

Hi been reading alot of posts cant find one that answers my problem hope someone can help me out with a flat spot i have with late 80's mariner 60hp 3cyl 2 stroke.
engine works fine starts and idles spot on but when throttle is opened up to about mid throttle then she starts to die but not compleatly, engine will throttle past this flat spot with no probs and runs ok at wot. Checked all fuel related items squeezing fuel bulb while running dosnt help at all, seems to me to be electronic. Ime thinking i may need to be under the flywheel but not sure what to look for once ive removed it. Hope someone has come across this before and can help me out.
Many many thanks

Jeff P

 

[CharlieB]

Re: mariner 60hp late 80's flat spot

Try testing the ignition using your timing light. Verify spark on each cyl while the motor is at the troubled RPM. If you have an intermittent spark then speed up the motor and retest.

If you see a difference on one cyl then you may need to verify the trigger wiring is damaged by DVA testing with the engine OFF and moving the trigger wires to prove the failure before ordering any NONE RETURNABLE electrical parts.

 

[jebbie_uk]

Re: mariner 60hp late 80's flat spot

Thanks charlie for the info
Forgot to mention the flat spot only shows its self under load so will check for intermitent spark while on trailer on slipway at weekend.
Am i right in thinking the trigger has something to do with ignition adv

Thanks Jeff

 

[CharlieB]

Re: mariner 60hp late 80's flat spot

Correct, linked to the throttle arm the triggers rotate below the flywheel to advance the timing as throttle increases.

A broken trigger wire caused by repeated flexing of the wires can happen, because the voltage/current are so small the butted ends may still carry enough to fire the ignition at some points and fail at others.

You can test this in the yard with the spark plugs removed using a remote starter button and advancing the throttle, watching for spark to fail on any cyl.

Saves a trip to the ramp.

If spark tests fine then you move on to the fuel system.

If is possible that you may have a slightly dirty carb and that it is time to clean them.