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mariner 60hp late 80's flat spot

J

jebbie_uk

New member
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
 
Without some background it's difficult to point to an exact cause.

Did this just start "out of the blue" or it happened after being stored or started after some other maintenance was done on it.

In general an ignition problem would not cause this kind of issue.

It sounds alot more like a synchronization problem (timing) or a fuel issue.

If any work had been done on it, it is possible that the linkage (that advances the trigger) could have got knocked or fiddled with - a delay in advancing the timing could explain the "dead zone".

If it consistently "dies" at the same rpm range at mid throttle then it is unlikely that is a clog in the carb - there is no jet, air or fuel, on these carbs that contribute simply in that range.

Likewise, the ignition only has high and low speed coils. If the high speed coils were toasted then after 2000 rpms or so you would have poor performance "period" - they wouldn't correct themself once it got over a (hump) in the rpm band....
 
The problem was there after buying the motor of ebay so dont have no history unfortunatly.

Also it does happen at the same rev point each time, some one suggested to connect a timeing light to each plug in turn to see if it looses spark when problem accurs, it only happens under load by the way, revs fine.

So i plan to try that at the weekend and i will also check the timeing linkages as well.

Is it likely to be anything under the flywheel was thinking of aquiring a puller to have a look but if faults unlikely to be there i wont bother.

Thanks for the help
Jeff
 
Yes, the timing light will definately confirm or deny an ignition problem.

At this point you shouldn't need to pull the flywheel.

Even if a timing light indicates an ignition problem, all components can be tested with the flywheel in place - so removal would only be necessary to replace a toasted part.

I have seen (what I call) "phantom" trigger issues where for one reason or other the trigger just fails to send it's pulse, normally to a single cylinder, and it usually tests fine in both resistance and DVA tests, but that is rare.

At this point I would make sure that the timing linkage isn't sticking - take the hood off, without the motor running, and just advance the throttle and watch what the link is doing - it should move smoothly back and forth - it's possible it's "catching" as you advance the throttle.

If it looks ok, try the timing light (use a buddy on board and run with the hood off) - test each cylinder in turn.

If both look ok, then it's back to the fuel system...
 
Thanks Galamb for your help

The timeing mechanism operates smoothly, probably nothing but the only thing ive noticed is if you take in to account the full movement of the mech at idle the mech is advanced by a third allready then moves smoothly to max at WOT.

We are takeing the boat out 2morra but cant get hold of a timeing light is there any other way i can check for spark at the plugs while under way.

Thanks
Jeff
 
The timing light is the easiest way for the most part.

There are (testers) out there that connect in series (wire connects at the coil on an extension that still allows the plug wire to connect). These hook up to all coils at the same time and display the all the results at a little box (I believe a company named Stevens built these in years gone by and there are newer designs out there).

But that isn't a (tool) that most places have around anymore (everything is "plugged in" to a computer now).

So unless you have an "old time" shop that will lend you one, the timing light is the way to go - even though it's a bit of pain to stop and switch the pick-up to the next cylinder as you work through things...
 
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