Sea King 5hp high RPM issue

[chuckm51]

Some of you may have seen my previous posts, discussing my progress rehabbing a '63 Sea King 2 cylinder 5hp.
To date, I have replaced all the ignition parts (points, condensers, coils, plug wires, plugs). Thanks to NAPA!
Dismantled and cleaned the carb, blowing out all the holes.
Drained and resealed the lower unit.
In my test tank ( a large wheeled trash can) I tuned it up and was happy to find it actually reacted to slight adjustments to the low and high speed knobs.
In the test tank, with prop on, it ran really well, with the rpms up very nicely.
So I took it out to the lake and installed on my 13 ft aluminum fishing boat.
On the water the engine will not rev up anywhere near its potential. In neutral it revs fine, just like in the tank, but when underway it seems like its only running about half speed.
It idles great, runs and accelerates smoothly from idle to wide open throttle, it just doesn't want to run at higher rpms.
Don't have a tach to check it.
Would this be a link and sync issue?
Or too aggressive a prop pitch? (It's a 2 blade prop and likely the original)
Or too heavy a boat?
I put my Eska 5hp 1 cylinder (3 blade prop) on the boat and it ran wide open with no issues other than noisy and vibration.
Any thoughts would be appreciated.
Thanks for a great forum!

 

[Tom @ Buzzard Bluff]

Re: Sea King 5hp high RPM issue

Some of you may have seen my previous posts, discussing my progress rehabbing a '63 Sea King 2 cylinder 5hp.
To date, I have replaced all the ignition parts (points, condensers, coils, plug wires, plugs). Thanks to NAPA!
Dismantled and cleaned the carb, blowing out all the holes.
Drained and resealed the lower unit.
In my test tank ( a large wheeled trash can) I tuned it up and was happy to find it actually reacted to slight adjustments to the low and high speed knobs.
In the test tank, with prop on, it ran really well, with the rpms up very nicely.
So I took it out to the lake and installed on my 13 ft aluminum fishing boat.
On the water the engine will not rev up anywhere near its potential. In neutral it revs fine, just like in the tank, but when underway it seems like its only running about half speed.
It idles great, runs and accelerates smoothly from idle to wide open throttle, it just doesn't want to run at higher rpms.
Don't have a tach to check it.
Would this be a link and sync issue?
Or too aggressive a prop pitch? (It's a 2 blade prop and likely the original)
Or too heavy a boat?
I put my Eska 5hp 1 cylinder (3 blade prop) on the boat and it ran wide open with no issues other than noisy and vibration.
Any thoughts would be appreciated.
Thanks for a great forum!

Start with the simplest possibilities---is it running on only one cylinder?

Have you re-adjusted the carb after putting it on the boat? If not you must do so. Carb adjustment in a test tank are just a preliminary----fining them down must be done on the water.

 

[chuckm51]

Re: Sea King 5hp high RPM issue

I did fiddle with the low and high adjustments on the boat; the optimal point is pretty obvious as it will stumble if the high is moved too far either way. Likewise the low adjustment affects low idle.
I hope to go out and get the motor today and will check the plugs for operation on both, but by its smoothness running I think they are both firing.
And it slow idles like a dream. I don't think it would do that if one cylinder was not firing. It really runs smooth and quiet...just no guts it seems.
It's a pretty solid, 1950 aluminum boat. All riveted. Pretty heavy. No leaks.

 

[F_R]

Re: Sea King 5hp high RPM issue

I will almost guarantee it is running on one cylinder. That is the classic symptom--half power or less, idles good, etc. They will run amazingly well one one cylinder, just no get up and go.

Remove and ground one spark plug wire and see how it runs. Then do the same with the other one. Betcha it will make no difference with one grounded, but won't run at all with the other one grounded---that is the good one.

 

[steelespike]

Re: Sea King 5hp high RPM issue

I'm with him^.