1966 40hp performance and prop question

[chrisroberts916]

I have a 1966 40 HP on a 1957 Lone Star Skylark that I just put on the water. The motor starts, idles and runs great. Yesturday I took it out for the first time to a local lake that is no wake except for certain area at certain times so I cruised around for an hour and when I finally got to open her up to my amazment the GPS read 8 MPH! I was dumbfounded. I made 4 or 5 laps and reached 9mph once but I think the wind was to our backs. The Skylark is a small fiberglass runabout about 400lbs with me, my brother and the dog being another 400lbs I tought we'd move a little better.

The prop on it is a Michigan PJ 30 A atleast thats what stamped on the hub. Can anyone tell me what pitch this prop is?

I didn't have a tach so I don't know the RPMS but the motor sounded good at WOT, we just wasn't moving fast.

Am I just expecting to much or should this motor push this boat enough to atleast make pulling my kid on a tube fun?

 

[oldcatamount]

Re: 1966 40hp performance and prop question

That ol' 40 shoulda blown yer hat off, even with yer brother in there. It's possible that you have a "spun" prop, meaning the bond is broken between prop and prop shaft. I can't tell you if you have the correct prop or not but I'm sure that someone else will shortly.

 

[boatingfanatic123]

Re: 1966 40hp performance and prop question

hey Thread i have an old 16.5 1966 glaspar boat with a deep hull i got a 1966 40 hp super sea horse jhonson motor that is not in top condition and it can reach up to 18 mph with out the planning fins on motor so u definetaly have a problem
i'm not very knowlegeable at any of this but i did manage to replace the cradle in the motor. if any1 can give me some advise on wiring diagram from battery, solenoid, switch, starter i would really appreciate it.

 

[Rick-va3rzs]

Re: 1966 40hp performance and prop question

I would say prop is pun also

I have a 40hp on a 14 foot runabout and can pull my kids with no probs ...

also check the sheer pin when I got mine some one had put a steel roll pin in there insted of the brass one .. it did cause me a little problem untill I put the right pin in !



Good luck

 

[chrisroberts916]

Re: 1966 40hp performance and prop question

I did pull the prop off and the sheer pin was in and good. Could it be a fuel problem even thou it runs smoothly from idle to WOT. I checked linkage ond the carb is opening fully.

 

[JB]

Re: 1966 40hp performance and prop question

hey Thread i have an old 16.5 1966 glaspar boat with a deep hull i got a 1966 40 hp super sea horse jhonson motor that is not in top condition and it can reach up to 18 mph with out the planning fins on motor so u definetaly have a problem
i'm not very knowlegeable at any of this but i did manage to replace the cradle in the motor. if any1 can give me some advise on wiring diagram from battery, solenoid, switch, starter i would really appreciate it.

Not good manners to hijack someone else's thread, Fanatic. Start a new thread of your own.

 

[samo_ott]

Re: 1966 40hp performance and prop question

While it could be a spun hub there are other things it could be also.

Is this a new to you engine? If not when and how did this start? If it is new to you then you have some basics to do. First start off and take the compression readings for a baseline. Next ensure you are getting good strong spark on both cylinders.

 

[chrisroberts916]

Re: 1966 40hp performance and prop question

New to me engine, I have ran it in a tank. Compression check was 100 in each cyl. Replaced the impeller and changed gear oil. The engine runs great, starts right up without choke.
I'm wondering if the fuel pump could cause it?

Can anyone recommend or tell what prop they run or if the number on mine (PJ 30 Michigan) tells you anything.

When you say spun hub do you mean something differnt from the sheer pin?

 

[samo_ott]

Re: 1966 40hp performance and prop question

A simple search came up with this info on your prop:

http://www.shipstore.com/SS/HTML/mwc/mwc012022.html

It appears to be fine for your engine.

A spun prop is different from a bust shear pin. It means the rubber hub has separated form the prop itself and will not fully turn under load. To test it, remove the prop and draw a line on the inside across the hub and prop. Then replace the prop, run the engine, then remove the prop and check the line. If it does not line up anymore, it has spun. It can be fixed at a prop shop or buy a new/used prop.

Also, an engine can seemingly run fine at idle on one cylinder. I would do a load test (unplug one spark plug wire at a time when it is at a fast idle) and see if the engine speed drops evenly. Use insulated pliers or a good clean rag to do this or you will get zapped. Running one one cylinder will produce the speeds and results you have mentioned so you should check this.

Also, 100 psi is a tad low for a bigger engine but still fully adequate.

Unlikly it is the fuel pump. It is obviously working. It's rare that it will deliver fuel at low speed and not high speed.

Oh and btw, I have a aluminum '59 Lone Star Malibu.

 

[boobie]

Re: 1966 40hp performance and prop question

I agree with Samo, make sure it is running on both cylinders by doing the cyl drop test he suggested.

 

[F_R]

Re: 1966 40hp performance and prop question

A spun prop causing that much speed loss would be obvious. The motor would race and you wouldn't go anywhere. Like spinning your wheels on the ice, if you live in ice country. You never indicated that it is racing out of control. So.o.o.o, all bets are on the table that it is running on one cylinder. Yes, they will run very well on one, just no power.

EDIT: I just noticed you are in Medina. You know about spinning wheels on ice. I used to ride my bicycle to Medina when I was a kid.

 

[chrisroberts916]

Re: 1966 40hp performance and prop question

"So.o.o.o, all bets are on the table that it is running on one cylinder. Yes, they will run very well on one, just no power."

I would've never believed that it would run so good on one cylinder. I had a chance to check it today and the top plug was not firing. I pulled it apart to see the coils and everything looks rather new and very clean. What should I check first? Should I switch the coil from #2 to #1 and see if it's the coil or is there an easier way?

Thanks for all the help so far!

 

[samo_ott]

Re: 1966 40hp performance and prop question

I would first unhook the two black cutoff wires coming from under the flywheel. To make sure neither are being grounded somewhere as these are the cutoff wires. Have you cleaned and gapped both points yet? That's also a good easy start.

 

[Chinewalker]

Re: 1966 40hp performance and prop question

Clean and gap the points to .020".

 

[chrisroberts916]

Re: 1966 40hp performance and prop question

Thanks for all the replys. Today after work I got to take a closer look and found the two black wires and found one was rubbed thru. I pulled it away from the block and got "shocked" I mean spark. I believe I found the problem and will be water testing it tommarrow after work on Springfield lake. Hope I can make a wake this time.

 

[chrisroberts916]

Re: 1966 40hp performance and prop question

I got her up to 29 mph and I think I'll get a little more out of her with a little more time in the water. Friday afternoon is the next test and tune!

 

[samo_ott]

Re: 1966 40hp performance and prop question

Yep. Those two black cutoff wires can get ya.

That's a fine looking old boat 29mph is not bad at all. The boat looks like it could be a bit heavy.