Unrealistic expectations for 71 20hp johnson?

[Bman2895]

The boat is a 73 crosby 14ft sea sled. Originally I had it powered by if I recall correctly a 69 25hp Evinrude. It pushed the boat well. Didn't feel "sluggish" even when loaded down 2 people and gear. I dont recall the top speed, but it was decent I was happy with it.

Fast forward after getting rid of the boat then getting it back i no longer had the 25hp. Put on the 58 15hp johnson. Definitely not as good, but too be expected. It did fight to plane out, but would it with weight forward.

Recently picked up a 71 20hp johnson. I was expecting for it to feel and preform much more like the old 25hp. However it feels closer to the 15hp. Its better dont get me wrong. It'll plane two people. and even with one person and all the weight in the back it will still plane out, but it just doesn't feel quite right power wise. It reaches a top end that id expect. But it just feels sluggish getting on plane. I expected more pep off the line. Am I expecting too much from it thinking it should preform closer to the 25hp than the 15hp? One contributing factor is the person who had it for a period of time before I got it back either used the crappy spray on or roll on bed liner on the hull and im sure thats hurting performance.

The 20hp has a clean carb. Good spark. And by the way it sounds its running good. Just feels alot more sluggish than I thought.

 

[Crosbyman]

don't know about the 20hp capabilities but Crosby boats were great ! here is a Cruisette good for 90hp ...Sold it it years ago and now rotting in the guy's yard ...sniff sniff

guess where my avatar came from !

visit fiberglassics.com library

Crosby - Classic Boat Library

www.fiberglassics.com

 

[jimmbo]

The 25 hp of that Era, while it had the same displacement as the 20 of that Era there were some differences. They used the same Block, though with different Pistons to alter the Port Timing. The different Pistons resulted in less Compression. A different Head was used in the 25 to restore the compression, the Carb, Manifold, and Reed System were different, and so was the Crankshaft(better Balanced). All the differences resulted in the 25hp having a Powerband that was 1000rpm higher than the 20hp.

Now about your 20hp. Any Compression Numbers? Are the Points set correctly, that can affect Timing? Is the Timing advancing fully? Is the Carb opening fully?
What Prop is on it?
Bed Liner on the Hull? Hmmm.... I wonder if that was/is to conceal a leak or two on the Hull? If it is not smooth, there will be additional Drag, which will not only affect Top Speed, but also Acceleration

Pics Please

 

[saltchuckmatt]

don't know about the 20hp capabilities but Crosby boats were great ! here is a Cruisette good for 90hp ...Sold it it years ago and now rotting in the guy's yard ...sniff sniff

guess where my avatar came from !

visit fiberglassics.com library

Crosby - Classic Boat Library

www.fiberglassics.com

I bet she was a lot of fun with many fond memories!

 

[Crosbyman]

Only had it a few years like a lot of things I should have kept it. Pushed it with a Merc 50 with surprising results. Came with 2 bunks, toilet (overboard !!) wash basin with overhead water tank... ( the owner who sold it to me is the one who had good memories... ! I think he married one passenger

 

[Bman2895]

The 25 hp of that Era, while it had the same displacement as the 20 of that Era there were some differences. They used the same Block, though with different Pistons to alter the Port Timing. The different Pistons resulted in less Compression. A different Head was used in the 25 to restore the compression, the Carb, Manifold, and Reed System were different, and so was the Crankshaft(better Balanced). All the differences resulted in the 25hp having a Powerband that was 1000rpm higher than the 20hp.

Now about your 20hp. Any Compression Numbers? Are the Points set correctly, that can affect Timing? Is the Timing advancing fully? Is the Carb opening fully?
What Prop is on it?
Bed Liner on the Hull? Hmmm.... I wonder if that was/is to conceal a leak or two on the Hull? If it is not smooth, there will be additional Drag, which will not only affect Top Speed, but also Acceleration

Pics Please

Ill have to get some today after work. The engine is more or less an unknown. Bought it cheap with complaints of a running issue. Took it out and it stumbled and hated to idle well, but seemed okay top end. Went through the carb and it was fairly clean. I know it acts like the fuel pump isnt working at times, but it pumps fuel when tested so I assume its an issue with my hose connections. It now idles fine and takes thottle well it just doesnt have much punch. And it is running on both cylinders.

I need to pick up another Compression tester. I usually go off feel and so far i haven't picked a bum engine yet. Atleast not due to Compression. But I do suspect maybe an issue with timing as it runs good but just revs slow. The throttle is just isn't as snappy as I'd expect.

 

[jimmbo]

What pitch is the Prop?

 

[racerone]

Remove bypass covers ( 4 screws each ) look at pistons / rings.