Ok Lets see if yall have any idears motor problem

[Hawk_308]

Ok I havnt had a chance to go out any this year on the pontoon untill today and the same issue came up that I have been tinkering with since I got the boat 2 years ago . 87 4 cylinder mariner 75 hp, Get to the lake and it cranks normal for a mercury , it powers on up and out and a crusin we ago , we ride about a hour up the lake and swim for about a hour it is a little harder to start and it stumbles a little bit pulling out pull back the throttle and try accelerating again and it runs up fine this time . We ride back up the lake and cruise around a bit and stop again for about 45 minutes to talk , a bit hard to start again and stumbles a bit on acceleration . We ride 5 minutes to the boat ramp where I cut it off to unload the family and its hard to crank and will not idle . I thought originally that I was have fuel issues but after eliminating that I leaning to a heat soak issue with the stator , coils or switch panel . I should have ruled out all fuel issues by now , Ive rebuilt the fuel pump , Both carbs twice and pulled the tank cleaned and dried also checked the gas pickup tubes all new fuel lines on and outside the engine and new primer ball line .

Thinking back on it, it seems the problem is always after a stop after running the motor a bit , I have in the past got to engine to crank with starting fluid but it with only run lower mid range RPMS it will die if I run any where out of the 2500-3500 range . So my only real guess is heat soak causing reduced spark .

[teecro]

Going to say that I've seen similar heat soak issues with motorcycles and we always asked the owners to start trouble shooting with a fresh set of plugs, check the connection or replace the spark plug boots as well as the high voltage wires and finally the coils. You may or may not be able to replace the wires as some wires are built right into the coils.

[rancherlee]

I'd say your on the right track also, its fairly common on older cars when the coil packs get old to loose spark strength when heat soaked. I'd pull a plug or two and check the spark while it heated up just to verify. Usually Stators will just Die, I really haven't seen them effected by heat soak.

[Hawk_308]

Thanks yall
I left it hooked to the truck so Im going to see if I can get it in the water this week one evening to test it . Ignition parts are a little pricey to be throwing at the motor especially since I plan on replacing it with a new four stroke in the next year or two . Ill check the ohms on the coils before getting the motor warm then run it a while let it set then see if there is a variation on any and also bring my spark tester out . Oh by the way just a note for the forum here if some one searches and finds this thread later the ohms on the older mariner/mercurys is 0.2-1.0 ohms input 800-1100 output and of course Ill post what I find.

[teecro]

Just keep in mind that when checking coils the primary side (low voltage) which is where your going to find the 0.2 to 1.0 ohm readings and the issue you might run into is unless you've got a fairly quality multi-meter ohm readings under 2.0 ohm are sketchy at best as just the resistance in the multi-meter leads can add up to 1.0 ohm or better and you must account for that in your readings....

[Hawk_308]

Thanks , my cheapest multimeter is over 200 bucks and I verify they are close to spec monthly . I do a lot o electronics work in my field .

[pond tuuunes]

I think I would look into compressin issues. When its cool, compression will be enough for it to start, and stay running. But trying to start it warm, the compression may be lower and not enough to fire the motor. Thats why it will start on starting fluid, but not enough compresion to run. Just a thought . JT

[Hawk_308]

I was getting 118 to 126 on each cylinder last year when I checked it. But I might also try a leak down test.

[pond tuuunes]

Is it a 2 stroke? Are you holding throttle wide open while your checking compression?

[Hawk_308]

Is it a 2 stroke? Are you holding throttle wide open while your checking compression?

Honestly I cant remember that was almost 2 years ago.

I checked the coils this morning and the number 4 was a bit off from the rest cold but with in spec at 811 the rest were 940- 952 so after running the motor and checking it again the number 4 had dropped to 535 ohms so its bad . Ordered a new one that will be in tomorrow and I can try it out again.

[Cowracer]

You absolutely sure it ain't a fuel problem? Sounds like you are losing prime and not getting enough fuel. Next time when you stop, give the fuel bulb a couple quick squeezes. see if it is hard and firm, and see if the motor starts easier.

Tim

[Hawk_308]

You absolutely sure it ain't a fuel problem? Sounds like you are losing prime and not getting enough fuel. Next time when you stop, give the fuel bulb a couple quick squeezes. see if it is hard and firm, and see if the motor starts easier.

Tim

I wish it was that easy , it will start on ether but will only run mid rpm range when it acts up . I can get home do nothing to it and go back to the lake to test it with out the family and it runs great for a while .

[Hawk_308]

Put a new coil on it and tried it out today .
Its alot better now it cranks easier cold and hot but its still not where it should be . It seems to load up after cranking it hot and letting idle so Im going to play with the carbs a little and see if its just a tuning issue

[kryptonite]

I had a mariner (only a 25hp) that was acting similar to what you describe. It ended up being the gasket between the carb and the reed valves. It was rotted out in the middle of the gasket.