1974 Johnson Seahorse 6 hp wonbt plane Please help

"I just bought a 1974 Johnson

"I just bought a 1974 Johnson Seahorse 6 hp model 6r74.
I have it on an 11' aluminum starcraft v-hull.
I really expected to get alot more speed out of this motor when I opened it up. Instead I can't even get it to plane.
Even if I put a couple of cinder blocks in the bow and ride solo, i can't get it to plane. Pretty disapointed with it. It almost feels like it has a governor on it, but it doesn't.

I was thinking of putting an aluminum prop on it. I went to a mechanic and i guess they make a 3 blade prop. Right now it has a 2 blade plastic prop (8" x 7 1/4"). Will a new prop really change things much? I am hoping that it will.

I still think that I should be getting more speed out of this motor even with the stock prop on it.

I am thinking of bringing it to a mechanic and have it looked over from top to bottom with hopes of a solution, but I am not sure. Don't want to spend anymore money than i absolutely have to.

Any advice would be great.

Thanks

Edzo"

You need to confirm whether it

You need to confirm whether it is running on both cylinders.It has dual ignition ( one for each cylinder ) and can be running on just one.

Thanks

I'll do that. I

Thanks

I'll do that. I didn't even realize that it could be running on just one.
That would definitely cause a horsepower problem.

Shouldn't you be able to hear some abnormalities in the sound of the engine if it was running on only one cylinder?

Although the rpm's don't seem to rev as high as they should when the throttle is fully open.

"These things run remarkably w

"These things run remarkably well on one cylinder although since I have had the effect on more than one occasion, I find I can see a slight vibration increase when it occurs. The more obvious symtom is the loss of power.

Just run the motor on idle at first and pull one plug boot at a time. If the engine doesn't stall out when running on one cylinder at a time, then both cylinders must be operational. If it does stall when you pull a boot, it is the other cylinder that is not operational. Good luck a report back."

Thanks DOug

I'll try th

Thanks DOug

I'll try that out. Totally makes sense. I hope that is the problem and I hope it's only a bad plug. The motor does vibrate a bit.

I'll report back on that. Won't be until after this weekend though when I head down to the cottage on Cape Cod.

Thanks

"It sounds like a good solutio

"It sounds like a good solution to check the cylinders to see if you are running on both. As far as the propeller issue is concerned, The stock factory propeller do deflect or bend a lot more causing less thrust than the metal do, so switching to a metal prop would make a slight difference but probably not a whole lot with a 6 hp engine. Three blades compared to two will also make a slight difference. The dual blade are better for slow trolling as they don't push as much water. If you are not trolling and only use the motor to get you on and off the lake then a triple metal prop will serve you best."

"Thanks

I checked the motor

"Thanks

I checked the motor to see if it was running on both cylinders and it is. I was hoping that it wasn't and that would explain the lack of horsepower.

I will replace the prop with an aluminum 3 blade.
SHould I change to a different pitch?
Right now the pitch on the plastic prop is 7 1/4"

I am not expecting a huge difference, but anything helps.

I am just really surprized that on an 11' aluminum with just me in it, it won't plane. I had a 1973 evinrude 4 hp on this boat years back and it would plane. Not fast, but it would.

I'll also replace the plugs.

Don't know what else to do.

Thanks"

"Edzo,

I'm with you. Th

"Edzo,

I'm with you. That motor should plane that boat. My 4 and 5.5 hp both plane a Sears 12 alum vee hull which weighs about 150 lbs. I would be doing everything you have planned.

Joe Reeves and Graham Lamb wisely stress starting with the basics and systematically addressing them. Therefore, I would make sure that the compression is good, the spark is good color (blue) and strong(bridging 1/4 gap in a tester), the points are set properly, the plugs are of the right kind (Did the previous owner use the right plugs? Wrong plugs can really mess things up.) and are displaying good color (light gray or brown), that the carb is clean with needle valves set correctly, and that the engine is running at proper temperature. Like you, I suspect something is wrong somewhere.

Blessings!

Jim"

Thanks for the support Jim.
I

Thanks for the support Jim.
I was starting to think that I was just expecting too much out of a 6 hp.
I saw a video on youtube of 75 evinrude 9.9 and that motor was planing that boat like crazy.

The 6 hp is only 3.9 hp short of that.
WHat I plan on doing is:
-Replacing the plugs
-Replacing the prop with a 3 blade aluminum
-Then I'll take it to the shop and have them run it through the appropriate compression and spark tests.

I have no idea how much they'll charge me.

Thanks for the post Jim