1970 6hp Johnson Seahorse

[gvegas88]

Ok, I have been cruising this forum for long enough! am looking for some even more technical support than I have already found. I'm just a college kid who likes to tinker with anything I can get my hands on, no detailed knowledge or work experience, other than spending all my free time on the water. I basically rebuilt a Sears Gamefisher but in the end, time ran out, project failed, but I learned alot.

To the chase, I just aquired a 1970 Johnson Seahorse yesterday and look forward to putting it on my 13ft duck hunting boat. The owner said it was rarely used by her aunt (freshwater only) and then it sat in a barn for 10 years and then 3 years ago she paid a mechanic $300-400 bucks to get it running and then it sat in her warehouse eversince.

I began my tinkering early this moring and found much new hardware, fuel pump and revamped carb. A part of the throttle system was siezed up and I eventually "fixed it" but I also need a new throttle handle because the old one it rotted and slips everyonce in a while. It has great looking sparks and lower unit oil. I took off the cylinder cover and broke the seal on the headgasket (should I replace before running? I've got some silicone greese to put on it) just to check out the cylinders and water cooling area. The cylinders looked great to me, and the rest had minimal flaking that I somewhat wiped off. There was some sand in the water jacket and I tried to blow most of it out. I have not checked the impeller but I plan on finding it tommorow and ordering another when I order the new head gasket. I have already ordered the owners manual and plan on fueling with 40:1 ratio of 87 octane gas and what oil? I also drained the leftover fuel in the lines and have not come close to starting it, what should I look out for before I get it running? Thanks, Tyler

 

[wbeaton]

Re: 1970 6hp Johnson Seahorse

Take a look at the coils and make sure they are not cracked or chalky. Since its a 1970 they should be ok, but you really should clean the points and check the gap anyway (.020). A compression test can't hurt, but if you feel good compression then it probably has enough to run.

Replace the head gasket, spray some oil in the cylinders to lube everything up and then try to start it. If it runs then replace the impeller and enjoy the motor. If not then rebuild the carb and try again.

I'd also run it at 50:1, but 40:1 is fine.

 

[samo_ott]

Re: 1970 6hp Johnson Seahorse

I'd try the old head gasket and see what compression you got. You might save the cost of a new one. Also, the 1970's are all 50:1 ratio. More oil wont hurt it though. And I use fully synthetic oil tcw3.

 

[wbeaton]

Re: 1970 6hp Johnson Seahorse

Head gasket is under $10 and available at your dealer. I wouldn't cheap out on that one. JMO

 

[samo_ott]

Re: 1970 6hp Johnson Seahorse

What? they're that cheap? I was sure I paid over $30 for my 5.5 hp head gasket... huh...

 

[wbeaton]

Re: 1970 6hp Johnson Seahorse

I've got one in my shop I mistakenly bought for a 7.5 hp. List price is $5.80 US for the OMC and $5.20 US for the Sierra. Surprisingly, I see its only $4.55 CDN at an online place I go to in Canada.

 

[iwombat]

Re: 1970 6hp Johnson Seahorse

As previously stated, don't reuse the head gasket. They also go on dry (unless the shop manual contradicts me on that). You'll want to really check out those coils. My guess is they got replaced as part of that $300 job at the shop.

 

[gvegas88]

Re: 1970 6hp Johnson Seahorse

Thanks, I will keep those things in mind. About the head gasket, How can I get one shipped to my house, and possibly a water jacket gasket as well?

Thanks, Tyler

 

[rick_l]

Re: 1970 6hp Johnson Seahorse

If you found sand in it, I would replace the impeller. I was always told, if you run the motor in sandy areas its good to replace the impeller every year otherwise every two years.

 

[gvegas88]

Re: 1970 6hp Johnson Seahorse

I have just ordered a head gasket and impeller. I cannot find a gasket for the water jacket, any ideas? I tested the compression this afternoon and both cylinders read exactly 70lbs. That reading was taken with the old gaskets, but how much pressure do I need? I heard that it takes 90 lbs for a good explosion.

Thanks, tyler

 

[iwombat]

Re: 1970 6hp Johnson Seahorse

With a pull start motor, I'd say a reading of 70psi is pretty solidly passable. A reading where you'd care to measure actual values requires 300rpm at least. Pretty tough to get from a rope-pull. There's also a big variance in gauges. If it's even its good. Let your motor tell you when it's all worn out, not a gauge.

 

[gvegas88]

Re: 1970 6hp Johnson Seahorse

LEAN vs RICH
There is a knob that turns from lean to rich, I am familiar with the difference between the two but not their relatipnship with running my motor. Where should it be set/adjusted and when?

Thanks for all the help so far, Tyler

 

[iwombat]

Re: 1970 6hp Johnson Seahorse

That particular knob is the adjustment for your idle mixture. A key concept here is that you can pull that knob totally off (pull straight out) and push it back on with the pointer centered at any time. With that in mind . . .

1) pull the knob off.
2) with the cowling off screw the mixture needle (what the knob went on) in (clockwise) until it is just seated (won't go any more). Don't force it tight, just gently until you can feel it shoulder out.
3) Back out the adjustment screw 1.5 turns.
4) Put knob back on - centered.
5) Put cowling back on.
6) Start motor.
---
7) Throttle down as far as you can while the motor stays running.
8) Let it run for a few minutes.
9) Slowly turn the knob in.
10) Turn until the motor seems to run the fastest.
Repeat at step 7 until you have reached the best idle.

11) back the knob out 1/4 turn.
12) remove and recenter the knob.

 

[gvegas88]

Re: 1970 6hp Johnson Seahorse

Thanks for the help, I ran the motor yesterday for a while on the local lake, it runs great and planes my little boat out. The only problem is that the grip for the throttle is broken so I had to order one and it makes it difficult to know where to start the motor throttle wise. I still haven't recieved the new head gasket but I got my impeller today. It looks way too big compared to the one that was on my 7.5 gamefisher. Oh well, How do I get the lower unit off? I removed the 4 bolts and the screw in the shifting shaft, but it still won't fall out, any ideas?

 

[iwombat]

Re: 1970 6hp Johnson Seahorse

Probably stuck on the drive shaft. Put the 4 bolts back in about half way, then tug on the rope start a few times. That's usually enough to get it to shake loose. The other possibility is someone didn't put the o-ring on the driveshaft and you've got a rusted driveshaft. Let's not go there yet.

 

[gvegas88]

Re: 1970 6hp Johnson Seahorse

Yeah somehow everything seems to fall into place when I listen to you guys. I got to the shaft and it had a few rust pits but not much of anything and I greased most of those things up. I got to the impeller and it looked great so I just left it in and now I have a spare. I'm still waitin for my head gasket but it runs now just fine as far as I know, I will ckeck everything out again when I replace the gasket. hopefully the cylinders are too disgusting. Thanks for all the help so far.

Tyler