Old boat, New captain - Could use some advice

[Captain Fishfry]

Good afternoon everyone...

I could use a bit of advice for a boat restoration project I've been working on. This is my 1st boat, so do your best to bear with me. My problem is that from what I have read, and my manual states that my engine should be operating in the 4800-5500 rpm range. Right now, I'm barely at 4000, and that is with myself, and a buddy. By myself, 4200. Here are some specs:

1981 Bass Tracker III 16'
40hp Mercury 2-Stroke, 2 cyl (#6053214)
10 1/4 x 13 prop, aluminum (mercury)

When I got the boat, it did not run well, which is to say, it didn't at all. This is what I've done so far:

New gaskets throughout, (carb, header, fuel pump, exhaust manifold etc. etc.)
Complete carb rebuild, I didn't just clean it, I actually replaced every part in it. (jets, needle and seat, float, everything. Fuel screw at 2 turns out)
New spark plugs
Complete fuel pump rebuild
replaced in-line filter under the hood
new 7.5 gallon fuel tank, with new hoses and primer bulb
new throttle and shift cables, properly adjusted per my manual
new water pump and impeller
compression test at 114 on both cylinders, although, one cylinder seems to take a few extra strokes to get there (???)

The engine fires right up, and it has a nice smooth operation when on the water, but 15 years of riding dirt bikes tells me that it's lugging a bit. I don't know much about the electronics or timing of the thing, but I do know that in order to get into the manuals rpm range I would need to back down to at LEAST a 9 pitch prop, more than likely an 8. That seems a bit drastic to me, what do you guys think? I would like to know if there is something I should look at before I start throwing money at props...

Thank you for any and all help

 

[QC]

Re: Old boat, New captain - Could use some advice

Can you verify your top speed for us? This will help with a reality check. GPS preferred. Thanks and welcome aboard!

 

[Captain Fishfry]

Re: Old boat, New captain - Could use some advice

Yes sir, thank you! It is right around 15-19 mph depending on water/wind conditions. It does take a little bit to get there, but it does it, haha

 

[steelespike]

Re: Old boat, New captain - Could use some advice

At 15 to 19 is it planing? Does it respond to a little choke when at speed? Don't know if the stator rotates on that year but does it rotate as it should and it should pick up the carb linkage as it advances."link & sync" Are you sure both cylinders are firing as they should?
Do the plugs look the same.Have you tried grounding one plug wire at a time to see if it on one cylinder?
Be sure to ground the plug wire you unhook to avoid damage to the ignition.
"fuel screw" I believe is the idle mixture and should be adjusted in gear at idle boat unrestrained.

 

[QC]

Re: Old boat, New captain - Could use some advice

Hard to see her not planing at 15 - 19, but maybe. Speed and slip etc not too out of whack there. Seems slow, but would be nice to have speed from a similar rig. Could be motor, could be data, I guess could be prop. Hard to tell at this point. is it 4200 and 19 mph with just you and smooth water?

 

[Captain Fishfry]

Re: Old boat, New captain - Could use some advice

Yes sir, it does plane. A little slow to get there but it does, for sure. Choke will bog the engine out, and both plugs look good, light tan, but they are new. I've put a spark tester on both plugs, and its showing me a spark on both. It's one of those cheap kind with the light bulb in-line. Regarding the stator, I have no idea. I would assume so because of the spark and what-not, but I'm not experienced enough to even deal with that...

 

[1080tommy1]

Re: Old boat, New captain - Could use some advice

I have a 16' modified v and a Yamaha 40hp and run an aluminum 12 pitch now and am underpropped slightly and will be going to a 13 pitch SS. Seems like something else is wrong because I would think that a 13 pitch, that would be ok for this motor. I will tell you I had a 9 pitch on the motor when I first got it and this was a disaster. I think you would be really underpropped with a 9 pitch and rpms would be extremely high at wot and fuel economy would be horrible. Mine was almost a gallon per mile with the 9 pitch. Good luck and sounds like mechanically you did a great job relplacing and rebuilding. Make sure that cylinder that takes a few extra turns to get compression is not the problem.

 

[Captain Fishfry]

Re: Old boat, New captain - Could use some advice

Thanks Tommy, I completely understand what you're getting at, the only thing about that that sticks out in my mind is that lugging a 2-stroke generally isn't too good for it. Although I'd hate to get sucked into a realm where 5 gallons of gas gets me to one side of a lake...

 

[1080tommy1]

Re: Old boat, New captain - Could use some advice

True, I was really under propped with that 9 pitch and my rpms were way high and I could tell just by the sound. I got the 3X10 5/8X12 mostly from advice received on this site and thought that would be a good starting point to get it right. I would think a 13 would be ok for a 40hp but you are certainly right about lugging the motor. Not good and will most likely damage the motor prematurely. I would definitely make sure there is nothing wrong with the one cylinder because that will affect performance. That is where I would go but for that the engine is running smooth. I would think if you had a cylinder not firing, there would be a rough run or no idle condition. Hope you get her right and I will post my results of the SS 13 pitch this weekend. I would think we should be similar in prop because my WOT range is also similar to yours. Mine is 4500-5500.

 

[Captain Fishfry]

Re: Old boat, New captain - Could use some advice

Very interesting. I'm going to look into engine issues a little further. I'll make sure my timing is set right, and do my best to check voltages where I can. Thank you for the help, I mainly wanted a point of reference before I started throwing props on there and you've done that. I will post back when I can about fixes etc. that could hopefully help the next guy.

 

[Captain Fishfry]

Re: Old boat, New captain - Could use some advice

Hey guys, I have another piece of this puzzle, let me know what you think. I'm doing a lot of reading/research on this, and I'm finding some things out. One thing is that when I had the RPM's at idle set between 700-800, it always seemed to die when I'd put it in gear. So one of my relatives who has had boats quite a while said it's no problem, and he adjusted the idle rpm's up to 900-1100 at idle. From what I'm reading, that is no bueno at all... This is starting to seem like it needs to be moved into the engine related topics forum...

 

[CharlieB]

Re: Old boat, New captain - Could use some advice

Just like your chain saw and weed-wacker, a two stroke idle mixture must be overly rich to provide the additional fuel for crisp acceleration.

The motor MUST BE in the water and at idle in Forward gear, adjust idle mixture to 'Best' idle speed, then add almost an additional 1/8 turn fatter.

Test acceleration/holeshot, ANY lean miss, cough, hesitation, in the slightest is a sign the motor needs even more idle mixture. Open the idle mixture just the blade width of the screwdriver slot then repeat acceleration/holeshot test.

Repeat to perfection.

Additional load such as loaded coolers, another passenger, etc., can create a need for additional idle fuel.

Verify WOT timing and that timing lever moves freely with throttle all the way to max timing.

The flashbulb type spark testers are worthless for an outboard, you need a real adjustable gap tester set to 7/16 inch.

Once holeshot acceleration is dialed in, test WOT RPM and speed, if RPM is still not within specs weigh the boat, check for water-logged insulation/floatation foam as a heavy boat may not allow the motor to get to top speed.

 

[Captain Fishfry]

Re: Old boat, New captain - Could use some advice

Yes sir...