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Merc Classic 50 Misfires At Upper RPM's

F

Far2hip

New member
I have a Mercury Classic 50, 45hp 4cyl 2-stroke, serial# 0C133460 attached to my 1964 14' Arkansas Traveler that I recently rescued from the woods and did a superficial restoration. Very cool little boat! I replaced the old frozen Evenrude Lark III with this Merc and the motor runs and pulls super strong with one constant issue. At the upper range of RPM's it will bog down a bit and feed back a bit of a fluttering sensation that will persist if I don't back down to feel out the"sweet spot" to prevent this from occurring. I got the prop situation dialed to the level capable with this issue and have zeroed in on the Spitfire 4-blade 10.6"x 12"p that pulls this thing out of the water and on plane like a monster within about 6 seconds, rockets to 25mph on the GPS, and then hits this wall of fluttering that pins me there at 25 and I have to back off the throttle to get to the sweet spot again. The RPM's at that wall is around 4800 and the recommended range for this motor is 5000-5500. When it back off and get to that sweet spot then push the throttle to go up to WOT, it feels like a bogging affect and then begins to start with the fluttering effect again. If I force a quick blow out of the prop it will jump quickly into that range with no load so it is an "under a load" issue. When I installed 3 blade 16 pitch during my prop testing, the boat went to 29 mph at the same RPM wall which makes sense given the added pitch.

Can any of you point to where this issue may arise from and explain the reasoning why it would occur from what may be suggested as a possible resolution of the issue?? I can feel this thing wanting to go and it is smooth and strong on the hole-shot. Can feel it in the seat of the pants with 2 big guys on board and 12 gallons of fuel. But I would love to have that 25mph be my cruise and see 30 for that smooth water upper speed range with this thing if I could. Any help would be great and I can do the work myself with some sound advice! :)

Thank you VERY kindly!!!
 
Nothing?? I see most of this stuff here gets answered quickly. Should or does the rectifier play any sort of a role in the upper RPM range?
 
Most of the guys on here are in the USA so may be starting the day job.But I think the first thing you could try is back the idle screw out a 1/4 turn see if that helps the bogging.You could also be over propped,borrow a 15P that should lift it to 5000RPM's.
No the rectifier doesn't play a role in the upper RPM's but the stator does,high speed winding,however if you are making 4800 I don't think that is a concern.
 
You need to do a WOT plug check. (I assume your motor does NOT have gapless plugs?)

If you are not familiar with this procedure, let me know.

Jeff
 
Thanks for the replies. I found my issues I am pretty sure and over the next couple days I should have it fixed. When I did an ohms test on the stator, the values should have been for blue and blue/white wires between 5200 to 5800. I was reading consistently at around 1900 to 2000. WAY off! On the red and red/whites, they should be between 56 to 72 and those where around 50 each time. Rectifier was off on one pole as well so it's a combination of issues related to each other. Can't wait to feel what kind of boat I have under the seat of my pants when THIS gets sorted out!! This thing pulls super strong out of the hole and up on to plane already so it'll probably feel like a different boat!! I will report my results for sure!
 
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