Loose Spark #2 when warmed up

[fbriggs]

Have been having on going issues with this 82 25hp tiller steer johnson. No spark after 2-3min of run time. #1 sparks all the time. Let sit 5min and both have spark but #2 drops after min or less. Feel something is breaking down once warms up normally sign of weak coil, bad / loose connection, plug wires, of something in stator. Stator test good along with trigger, installed 2 new coils same problem, swapped coils problem stays with #2. Thinking power pack but can anyone tell me what determines when spark is delivered to each cylinder. Have had flywheel off and can only test stator using wires and ohm meter. My stator is style that is completely enclosed in plastic so can not determine if there are two triggers one for each cylinder, or 2 coils one for each cylinder, or does the power pack distribute spark differently to each cylinder?? I was told if I never loose spark to #1 cylinder than stator has to be good. Can any one explain to me how this engine determines when to distribute spark to each cylinder. On 2cycle snowmobiles power packs can break down and you can loose spark to only one cyl, not sure about this engine? Any help would be appreciated. Did install new power pack and in a barrel runs good for 10min or so, so guess I will be taking out to lake to see what happen in real time. Still would like some one to explain to me the delivery of spark to each cyl.
Thanks Fred

 

[oldboat1]

think I would make sure the lower plug isn't stripped/cross threaded -- can be torqued down properly. Make sure the spring clip in the boot is assembled correctly, and contacts both the plug and the wire properly.

Test the lower with an open gap spark tester -- somewhere around a half inch spark (would measure both top and bottom).

Do a drop cylinder test -- pull off the boots one at a time while running, and see what the effects are, if any.

Do a compression check and record the numbers (need baseline numbers, if nothing else).

Power pack can affect one or both, and heat can create issues as you suspect -- but look for simple stuff first.

 

[boobie]

As a guess I would say it has a bad power pack. JMO

 

[fbriggs]

All the above have been checked and rechecked every thing is with in factory specs when tested with equipment. Of course problem being that by the time I get out and start my resistance test every thing checks out perfectly. That is why this has been such a head ache, I hate just throwing parts at this but really that is what I have had to do. My big question it seems that no body can answer is what in the electrical system tells the spark when to fire for each cylinder. Like I stated in previous post, my stator is completely surrounded by plastic so I can not even tell what is underneath all that plastic can not see individual components like most breakdown pics show. All part pics I have seen either show individual components or the one piece enclosed stator?
Like I stated I installed a new power pack and have run motor in bucket of water in driveway for 10-15 mins at high idle and in gear as fast as I could in a bucket and never lost a cylinder, so next step is the lake. Wish me luck.
Thanks again hope someone on here can explain the firing order and what components are used to fire plugs at correct time.

 

[racerone]

??-----There is one sensor coil under the flywheel.---There are 2 magnets on the flywheel.-----There is a switch in the powerpack that flips back and forth to direct a voltage pulse to the correct coil.

 

[boobie]

Good Luck :clap2:

 

[fbriggs]

Sorry have not gotten back t any one lately about my problem, have been gone for past 2 weeks, I did install a new power pack and will be taking the boat out later today for a test run. Sounds like this almost has to be the problem since there is only one sensor that sends signal to pack and pack is suppose to switch back and forth to tell which cylinder to fire and when by the two magnets in flywheel which are all good. Will let everyone know the out come.

 

[scout-j-m]

Good luck! I have had a powerpack do the same for me and a new one fixed it.

 

[fbriggs]

Well took boat out on the water this weekend ran perfectly, so yes it was the power pack that was loosing spark too number two cylinder after a few minutes of run time. Thanks for all the help

 

[oldboat1]

all good! :thumb: