MisfireBandit
New member
1997 Mariner 100hp 2 stroke 2+2.
Going to be long winded so I get everything. Just bought boat. Previous owner was in 90s and hasn't used it much, but took it out few months back and said it ran ok. Under cowling it looks almost new. Never seen salt. Only thing changed recently was the starter.
I'm getting a misfire. Hard to notice at any speed other than 3/4 throttle and above. You can feel it shudder about every other second. Pretty easy to start, idles seemingly fine. Transition point is a little rough. Does feel like it misses a little at low RPM when you put it under load. Once warm, you can breath on the key and it will start and idle fine. It might be missing at idle, but I can't tell.
Fuel line on boat replaced. Ran on separate tank and same issue. So has to be something on engine. Changed fuel filter. Did the 1 gallon of gas/seafoam method, same thing. Changed plugs (noticed top one was looking fouled) Same issue. Checked spark with cheap inline, and every cylinder the same and consistent (orange not bright blue spark). Then checked by using a screw driver and holding about 1/2-1" from metal. All clicking and arcing. Bought a used CDM off eBay. Put it on cylinder 1, same issue. Checked plugs after about 10 min running, and cylinder 3 plug looked a little fouled. Took cylinder 3 CDM off, and put on the one I took off Cylinder 1, same thing. Then did cylinder 2 and 4. Boat is still acting the same. Guess I could have bought a bad CDM, but hard to tell.
Inspection of CDMs, there is a slight small crack on the shiny soft/rubber side on a few, not sure if that means anything. When running on ear muffs or at idle, I can push down the accelerator pump and nothing really happens. Again, not sure if that is normal.
Boat performance: 17ft boat, Runs 30-32 with throttle slammed. At 3/4 throttle it runs about 30. Should run high 30s given the 100hp with comparison to other similar boats. Planes pretty easy once the shuddering from flooring it stops (2-3 seconds). Once I plane out, I can really feel the misfire kicking, causing slight jerks while cruising. It will do it non-stop for 10 miles and maintain speed. RPM gauge doesn't work, but doubt it's hitting limiter. Prop is 13x21.
One other thing of note, when cleaning the fuel system. The fuel in the fuel/water separator was blue. Also noticed that when I unhooked the fuel line from engine, blue colored fuel came out. At first I thought maybe previous owner dumped a bunch of fuel stabilizer in it, but when it came out the engine fuel connection, that was after running a good bit of straight ethanol free gas. Almost like 2stroke oil is backing down the lines, if that's even possible?? Could have been residual stabilizer though, I don't know.
Thoughts on what to check next? It's tough for me to diagnose b/c on ears it runs fine. I have to put in water and run to get any sort of feedback. I don't mind testing every single item on the ignition system with guidance/instructions.
My next step is to buy new fuel pump rebuild kit, new accelerator pump rebuild kit, and if I have to 4 new CDMs. I just want to use the dang boat, but I'm kind of over changing parts, launching boat, making it 100ft from ramp and having to return home with same issue.
Going to be long winded so I get everything. Just bought boat. Previous owner was in 90s and hasn't used it much, but took it out few months back and said it ran ok. Under cowling it looks almost new. Never seen salt. Only thing changed recently was the starter.
I'm getting a misfire. Hard to notice at any speed other than 3/4 throttle and above. You can feel it shudder about every other second. Pretty easy to start, idles seemingly fine. Transition point is a little rough. Does feel like it misses a little at low RPM when you put it under load. Once warm, you can breath on the key and it will start and idle fine. It might be missing at idle, but I can't tell.
Fuel line on boat replaced. Ran on separate tank and same issue. So has to be something on engine. Changed fuel filter. Did the 1 gallon of gas/seafoam method, same thing. Changed plugs (noticed top one was looking fouled) Same issue. Checked spark with cheap inline, and every cylinder the same and consistent (orange not bright blue spark). Then checked by using a screw driver and holding about 1/2-1" from metal. All clicking and arcing. Bought a used CDM off eBay. Put it on cylinder 1, same issue. Checked plugs after about 10 min running, and cylinder 3 plug looked a little fouled. Took cylinder 3 CDM off, and put on the one I took off Cylinder 1, same thing. Then did cylinder 2 and 4. Boat is still acting the same. Guess I could have bought a bad CDM, but hard to tell.
Inspection of CDMs, there is a slight small crack on the shiny soft/rubber side on a few, not sure if that means anything. When running on ear muffs or at idle, I can push down the accelerator pump and nothing really happens. Again, not sure if that is normal.
Boat performance: 17ft boat, Runs 30-32 with throttle slammed. At 3/4 throttle it runs about 30. Should run high 30s given the 100hp with comparison to other similar boats. Planes pretty easy once the shuddering from flooring it stops (2-3 seconds). Once I plane out, I can really feel the misfire kicking, causing slight jerks while cruising. It will do it non-stop for 10 miles and maintain speed. RPM gauge doesn't work, but doubt it's hitting limiter. Prop is 13x21.
One other thing of note, when cleaning the fuel system. The fuel in the fuel/water separator was blue. Also noticed that when I unhooked the fuel line from engine, blue colored fuel came out. At first I thought maybe previous owner dumped a bunch of fuel stabilizer in it, but when it came out the engine fuel connection, that was after running a good bit of straight ethanol free gas. Almost like 2stroke oil is backing down the lines, if that's even possible?? Could have been residual stabilizer though, I don't know.
Thoughts on what to check next? It's tough for me to diagnose b/c on ears it runs fine. I have to put in water and run to get any sort of feedback. I don't mind testing every single item on the ignition system with guidance/instructions.
My next step is to buy new fuel pump rebuild kit, new accelerator pump rebuild kit, and if I have to 4 new CDMs. I just want to use the dang boat, but I'm kind of over changing parts, launching boat, making it 100ft from ramp and having to return home with same issue.
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