125 force cant get past 2500 rpms at WOT

[trevorrr1]

I'm going to try to make this as detailed as possible, so beginning of summer i bought 18ft bayliner cobra with 125 force 1988. i posted on these forums after buying it about the same issue im having now, not being able to get over 2500rpms. ended up getting a whole new powerhead and doing a full swap because the #2 piston blew up while trying to troubleshoot this issue, block was in rough shape due to previous owner not running right fuel mixture come to find out but regardless. So far these are all things ive looked at/replaced im completely lost at where to go from here.

1.replaced powerhead has roughly 140 comp on all cyl
2.replaced all igniton coils because they were arcing all over the block (thought this was 100 percent the problem) issue remained
3.used timing light adjusted the timing because it actually was quite off guessing probably happened during powerhead swap.
4.hooked up inline fuel filter between fuel pump and carbs to rule out fuel starvation under load. fuel filter stayed completley full while testing on the water.
5.made marks on prop to rule out spun prop
6.taken apart carb twice for total clean also put them through ultrasonic cleaner

So on muffs the engine runs amazing, starts up in 2 seconds. revs fine in driveway. the plugs look light brown after checking them after being on the water with the boat troubleshooting. The motor shakes/misses it seems when it is at WOT it shoots right up to 2500rpms and then thats it nothing more goes about 11mph max. this is the exact same issue before doing the powerhead swap so nothing i did with the swap changed anything. at this point i can only imagine it being a few things. power packs, stator, or triggers one of those failing under load? i just dont know how i would even go about figuring out which of those it could be. any input would be much appreciated. this has been very frustrating just want to enjoy my first boat before the summers up lol.

 

[Aquaholic90]

I fought a very similar issue on my 150 for 3 years. Only happened hot but it ended up being the switchbox. I replaced everything else before that. My advice to you is something I didn’t listen about and that is go get a multimeter and dva adapter and test power to and from your coils, trigger, cdi box. I threw 1000 in parts at mine cause I was too dumb to spend the 20$ on an adapter off amazon. That being said IF it’s a spark issue I would guess trigger or switchbox. If it’s fuel your carb jets might be clogged

 

[trevorrr1]

Yeah I did see people suggest getting one of those when reading other posts with similar issues, kinda just overlooked that. I’m gonna order one see what I can find out with it, since I have an extra trigger and Cdi box hopefully it ends up being one of them.

 

[jerryjerry05]

Timing? how did you set the timing?
You said: ."used timing light adjusted the timing because it actually was quite off"
Just swapping from one motor to another shouldn't move the timing much, if at all??
Do the static timing described above in the first 4 posts.

If the trigger works up to 2500 I doubt there's a problem.

outbooardignitiondotcom has test procedures.

 

[trevorrr1]

I’m not sure why the timing was off or where it got misadjusted but was retarded by at least 8 degrees, i adjusted seems to sound and run better especially at idle but still the same issue.

 

[The Force power]

Sounds to me like..........she's not running on all Cylinders.
While running in idle;unplug one cable at the time to check for RPM-drop----No drop-no fire
Check fuel-pump/hoses/vent on tank

 

[jerryjerry05]

What prop? Size?
Has the lower unit been changed from a 85hp?

 

[The Force power]

What prop? Size?
Has the lower unit been changed from a 85hp?

Good question! and that is why YOU ARE the expert!

 

[trevorrr1]

unless the previous owner put a 85 lower unit on it i believe it to be a 125 L/U. i read on the forums to put a clear inline fuel filter between the fuel line from fuel pump to carbs & if it stays full under load then you know its not a fuel starvation issue. so i ruled all that out after that. a DVA adapter from amazon is coming in the mail should be here next tuesday or wednesday.

i did do the pull the plug test and they all made an noticeable rpm drop besides cylinder 2 the rpm drop was very minimal but it does change slightly in tone when pulling it on and off. i believe they're all firing fine at an idle but when WOT maybe its losing spark from something in the ignition system?

 

[jerryjerry05]

#2 from the top?
Or #2 from the bottom?
From the bottom, that cyl. runs the fuel pump, check the diaphragm.

Do all plugs burn the same?

Take the carb off and check the reeds and make sure they are not broken
or missing pieces? A slight gap in them is OK>

Get a spark checker, check all cyl. have good spark?

You can test the stator with just an analog meter.

 

[trevorrr1]

Cylinder 2 from the top is the one with minimal rpm change at idle. But I checked the fuel pump diaphragm, used dva adapter to check stator the stator tested good but had burn marks on it so I just put a new one in still same exact issue.. tested triggers also they are fine.

Really having a hard time understanding how to test the CDI boxes though.. if the problem is only happening under load then the issue will probably only show its self on the cdi boxes when it’s under load?

All the plugs are burning the same, I’ve checked spark on all the cylinders, reeds look good. I really think something is dropping cylinders once I accelerate. It’s almost like it’s in a limp mode or something. Even after the power head swap and all the trouble shooting the problem has remained the exact same. Any ideas at this point would be much appreciated!

 

[Redbarron%%]

Check the actual output to the plugs, running. If you use an induction timing light on each plug wire to see if it flashes then you are at least firing current to the plug or the light would not detect it.
Also check the book for the firing sequence and use the timing light to make sure that they are actually firing in the correct order.
I think that the order is 1 - 3 - 2- 4, but I may easily be wrong. That means that the #1 fires close to TDC, #3 at 90*, # 2 at 180* and #4 at 270*.
are the two blocks electrically the same? the new one has exactly the same wiring as the old one? If you go a lot newer you could have a CDM trigger and flywheel and they are not compatible with the CDI boxes.

 

[trevorrr1]

I used the timing light to adjust the timing so I know the timing is correct, and the block was identical to the previous one I think it was the exact same year block. Maybe I’ll hook my Timing light up on every cylinder make sure it’s flashing. The main problem is it idles perfect and even revs up fine on muffs, as soon as it gets in the water is when it gives me issues.

1/4 throttle the motor will shake pretty decent amount almost like a backfire and WOT the motor doesn’t shake anymore, it just sits at 2500 rpms without an increase

 

[The Force power]

I used the timing light to adjust the timing so I know the timing is correct, and the block was identical to the previous one I think it was the exact same year block. Maybe I’ll hook my Timing light up on every cylinder make sure it’s flashing. The main problem is it idles perfect and even revs up fine on muffs, as soon as it gets in the water is when it gives me issues.

1/4 throttle the motor will shake pretty decent amount almost like a backfire and WOT the motor doesn’t shake anymore, it just sits at 2500 rpms without an increase

The problem is.......it's not running on all four
They will "idle perfect" even revs up fine on muffs" BUT they're NOT running on all Cylinders

Have you checked the Spark jump with a tester ( that Jerry suggested)
Have you looked into why #2 has minimal drop in RPM's