6 hp johnson

[biedAss001]

i have a 6 hp johnson(1967 model)on a 19 ft grumman aluminum canoe with transom for outboard.canoe is pretty light but it reaches a peak speed of 6 mph according to my gps.seems to be running good and prop looks good but i thought it should go faster than that.just want some opinions on what approximate speed you guys think it should go.i may have to get a bigger motor if thats all i can det out of that 6.thanks,Jay

 

[tashasdaddy]

Re: 6 hp johnson

how deep is the motor to the bottom of the transom. the flat plate above the prop should be in line with the bottom of the boat, or just slightly higher.

 

[wbeaton]

Re: 6 hp johnson

I would think it should go much faster. My 50's 7.5hp pushes a 12' aluminium boat at about 20 mph. They are probably about the same weight.

Like tashasdaddy, I'd suspect you have it too deep off the transom. Are you sure the motor is running properly? Do you have enough compression or spark in both cylinders? Is it running too rich?

 

[biedAss001]

Re: 6 hp johnson

i thought it was running fine but i did notice that when i crank it it revs very high but after i get it idled down and in gear and back to top speed it doesnt sound like it even revs up half as much.the flat plate is exactly even with bottom of boat.didnt check compression but has new plugs,wires,coils and points.got me confused but hopefully someone can help.thanks for posts guys.Jay

 

[tashasdaddy]

Re: 6 hp johnson

start the engine, with insulated pliers, pull and plug wire off, it should keep running on 1 cylinder, but drop rpm, replace then do the other. it it only runs on 1 clylinder, check compression and spark. be sure the foot is submerged in water .when starting

 

[biedAss001]

Re: 6 hp johnson

ok thanks i will try it and post my findings

 

[DHPMARINE]

Re: 6 hp johnson

Is there a HP rating on the canoe? If not the Grumman site probably can show you a similar model,and ratings.

My thoughts are a square back 19 foot aluminum canoe is probably rated for at least 15 HP,if not 20HP.Your 6HP is rated at the crankshaft and looses a lot going thru the lower unit.And it's 40 years old.

I think you're doing OK.

DHP

DHP

 

[wbeaton]

Re: 6 hp johnson

Could be you are missing spark under compression or you have a loss of compression in the motor. Since you installed new plug wires it couldn't hurt to double check that they are making a good connection with the coil and boot.

DHPMARINE raises a good point, but it still sounds to me like something mechanical. Especially if you are not getting full RPM's. Did you clean the carb when you rebuilt the ignition?

 

[biedAss001]

Re: 6 hp johnson

i had a guy rebuild the carb but suspect something might be wrong because it will only crank with throttle wide open.canoe is rated for 4 hp but can handle alot more i think.i will go over the ignition system and check compression to make sure but if its in the carb im in trouble because i know nothing about them.will be a couple days before i can check it out and post findings.thanks everyone for responses,Jay

 

[steelespike]

Re: 6 hp johnson

I suspect your motor may be running on one cylinder.If you do the plug wire test it will tell you if it is running on both cylinders.
A canoe is not designed to plane and your 6 is pretty much a waste of power.The canoe is very easy to push up to about 6 to 8 mph.but is difficult to plane And won't be happy if you get it on plane.If you run it at about 6 mph it will go very efficiently.If the transom is 18 or 20 inches wide it may plane but it isn't likely to be its most efficient speed.

 

[biedAss001]

Re: 6 hp johnson

well,i tried pulling the plug wires off one at a time and it was still running.it got alot of rpm's in neutral but i know when i was at the river and in gear it sounded like it was only going about half that fast,maybe thats normal for it not to get as much rpm's in gear.and then spike's probably right about a canoe not planing too because mine has a narrow transom.i looked at all the ignition system and dont see any obvious way i could be losing spark.i dont have a compression tester to check that with.i wish i had a small flat boat i could try it out on.Thanks again guys,Jay

 

[LORDY611]

Re: 6 hp johnson

WAAY back in the day I had an 8' hydroplane with my 1960 5-1/2 Johnson on it. I had to lean forward and push down on the bow to get it to plane. It might have reached 20 mph, but who knows. I had the bright idea that a lighter boat would go faster so my dad and me helping built an 8' pram (smililar to a john boat, but short, and wooden ). It was defintely lighter, but narrower than the hydro, and as a result drew more than the hydro and went slower. I think, as previous replies, that the canoe is too narrow to plane and just plows thru the water, narrow as it is, and the 6 HP just moves it at the best rate the hull will allow. Hey--it's a canoe...

 

[steelespike]

Re: 6 hp johnson

There is a slim chance that as you advance the throttle lever one of the plug wires may be rubbing and shorting out but usually a plug dropping out is pretty obvious.
I think if you run at a speed just below where the stern starts to squat you will have the most efficient speed probably about 6 to 8 mph.It may even run faster with 2 people as it will resist squating better with some weight in the bow.If you have to run alone a tiller extension will help.