1959 Lark 35 not reaching full RPM, sometimes???

[59 Sea Coaster]

Ok worked in a couple hours of "free time" yesterday! Replaced the fuel pump diaphragm and vacuum line. Both looked ok but what the heck easy to replace! Hit the water with the same results, bummer! Ran at that 15-16mph range for a while and bang starts running great hits 23mph and cruising nicely until I ran out of gas a minute later! Switch to the other tank and got going again up to 15mph. I started playing around and made a fairly hard turn and it cavitated and hit full RPM I straightened her out and it was still at full rpm but cavitating, back off the throttle a bit she hooked up and took off!!!! I ran around for quite a while varying throttle and running from 17 - 24 mph nicely, rather enjoyable actually. If I let her fall below 16mph she would not come back up to speed without that sharp turn. I tilted the engine up to the highest notch making it easier to cavitate and recover my speed it does run slightly louder at full speed assuming the exhaust is slightly out of the water.

I am convinced that I have been chasing the wrong issue! I took the prop off today but no markings as to what pitch it is. Parts look up show two possibilities one is NLA 10 3/4 x 13 the other is available and 10 3/4 x 11 . I also noticed some lower unit gear oil leaking out the water intake, presumable a upper shaft seal seems to be a one way leak as not much water in the gear oil. Parts ordered.

I am going to try and upload a video/audio shot with my phone during this process.

Thanks for everyone's suggestions and I will update this next time I get on the water with the 11 pitch prop.

https://www.youtube.com/watch?v=15uASlHUeHM

 

[59 Sea Coaster]

A little rough but not bad, right?

 

[59 Sea Coaster]

A little rough but not bad, right?

 

[59 Sea Coaster]

10 3/8" x 13 1/4 is the pitch!

 

[pro-crastinator]

Not bad at all.

 

[59 Sea Coaster]

Ok got some time this weekend and tried the 11 pitch prop. It was interesting, engine still fluttered but at a lower speed 12MPH which make sense. However it would get to full RPM and speed every time without forcing the engine with cavitating. I did this several times, dead stop full throttle - 12MPH flutter for a few seconds then bang she takes off to about 22 MPH. She would cruise along nicely at 15mph running smooth and able to accelerate to full speed at will. Idles perfectly, pulls hard from 12MPH to 22MPH and sounds strong at full RPM.

Now we decided to sit and watch the sun set while playing some cribbage (I was getting my butt kicked!). Sat for maybe 20-30 minutes. Restarted the engine and headed for shore, could not get past the flutter and 12MPH to save my soul! Could not force the engine to cavitate and pull full RPM, guessing because of the slower speed it was too far in the water yet at 12MPH but at 15 is was not?

I am beginning to suspect something in the drive that is causing the "drag" and I say this because of how she acted after sitting in the water for a while. Remember I mentioned there was drive oil coming out the water intake area? Another note of possible interest, this is not the original flywheel. It got damaged during removal to replace the coils, points and condensers. The timing seems to be on but cannot verify without removing the flywheel again.

The sage continues and my time is running out for the season!

 

[59 Sea Coaster]

OK still trying to work thru this issue! Time has been hard to find to spend and quantity of it on this issue. Here is what I have done that seems to make a difference. I replaced the seal below the water pump as there was gear lube making its way into the water pump. First time out she ran better? The hesitation (flutter) was maybe a couple seconds but it would get right past it on its own. We went and had lunch on a sandbar after about a 20 cruise, 4 people in the boat, lunch and blankets certainly the largest payload to date. Cruised along at 3/4 throttle 17 mph or so beautifully! After sitting for 45 minutes and eating lunch we decided to hit another sandbar down river. Motor started just fine but was stuck at that flutter again? We only went a few minutes down river and parked again. I decided to tilt the motor out of the water while we sat as that seemed to be a common issue after sitting for a while. We were there maybe 1/2 hour. Dropped the motor in the water, started her up and headed off with no issues? Ran 20 odd minutes to a local ice cream joint parked (left motor in the water) for maybe 15 minutes. Jumped in for the ride home and she ran perfect again! Except for that little one or two second flutter getting past 12-13 mph.

We went out a couple nights later for a sunset cruise and it ran well initially but then was getting hung up and fluttering for a long time again. I let Vickie drive for a bit and I tried some carb adjustments with no change. I reached over (not sure why) and pulled the shifter (at the motor) forward and it moved a far distance, boat took off! Tried that again with similar results, adjusted the cable to get more forward pull but the results seemed inconsistent? Cable appears to me at max adjustment. We ran out of daylight and put her away. I will be looking into this further and see if there is or is not and relation between the shifter and my running issue.

I will update as the saga continues!

 

[racerone]

The shift interlock could certainly prevent full throttle in forward.---Best to look at it all carefully.