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Johnson 30 Javelin question

timguy

timguy

Silver Medal Contributor
Hi. Is there any truth that the Johnson Javelin's of the late 50s actually produced a little more horsepower than advertised. I'm about to restore my 1956 30 horsepower and ship out to the West Coast. The buyer is curious how it will push his old 52 Screenshot_20230731-133449.pngJohnson 16 ft wooden runabout which has also been completely restored. Thanks again, Tim
 
Great, thanks Racer. Can I modify to produce 35 hp? Or even 33? I have a boatload of "Big Twins" around here.
 
Slap a 35hp powerhead on it. 25, 30, 33 hp are all 2-7/8" bore. 35hp is 3-1/16" bore. You might be able to tell the difference. But probably not.
 
it always seemed like my older omc motors of the 50s was a little faster than later motors of the same hp but maybe im just biased
 
Thanks, Gator. Yes the older motors really seem to pull stronger. Brupp, a contributor on this forum, lives near me in Virginia MN. He restored a 1932 7.5 horsepower and on the same boat as his modern 15 horse is only 5 Screenshot_20230802-091210.pngmiles per hour slower.
 
I have compression of 128 and 121 on the 1956 Javelin. Does that sound okay? You really can't pull it over with the rope....? Do you think its got carbon build up. My gauge has been certified too. Also, I assume its a 6 volt starter, can I use a large 12 volt solenoid, not those little compacts like found on the newer 28 hp. Then spin with 12 volt? I did the compression testing with a 12 volt and the starter never even got warm. Tested each cylinder three times. Motor has been sitting for 30 years. Buyer wants to eliminate the external solenoid box. I will provide a second wire off the other set of points to allow a "proper" way to stop the motor. Stupid idea to use the choke to stop, eh? Thanks, TimScreenshot_20230804-235300~3.png
 
The 35 horsepower 1957 that I just shipped out showed 109/101 compression. That of course has decompressor valves in the head when rope starting. Easy for me to rope start. I really dont think even DwScreenshot_20230805-102946.pnguane Johnson could rope start this Javelin.
 
I used to rope start a 1966 Johnson 100 HP V-4.--------These 30 hp motors are hard to start on a stand when there is no steering hooked up I think.
 
Yup, you got something there. Im trying to pull it in the test tank. The rope is higher than when in the boat. Its better for the shoulders when pulling up at an angle.
 
yep they take some grit to rope one over the electrical connector on my lark gives me issues it has 130 top and bottom ive rope started it a few times the decompressor stuff is missing i plan on finding those parts cus it would seem to take some wear and tear off the recoil mechanism dont wanna brake that stuff getting harder to find everyday it seems. and dont quote me but i believe 57 was the first year for 12 volt on that engine
 
Yes, I think your right. Got a few Larks here. What parts are broke, I probably have what you need. Is it safe to spin the 6 volt starters with a 12 volt? The motor will pop off immediately every time. What's your experience Racer, Gator, Joe, anybody with hands on experience?
 
someone took all the decomp stuff off long ago im not sure why they would do that but it is what it is. i was gonna see if the starter bracket was the same for the 6 volt motors and the 12 volt motors but apparently the schematics are not available for the 6 volt years you may be able to bolt a 12v starter in place of the 6v unit if the brackets are the same. if you run a 6v motor on 12v you should be fine. in Ohm’s Law, Current is Directly Proportional to the Voltage if resistance stays the same. the windings may run a little hotter but i doubt it will hurt it as long as you dont crank it for more than a 8 or 10 seconds im not sure what size but you could use a large resistor inline with the starter just like they used to do with 6v coils on 12v systems and drop the extra current if a 12v starter cant be fit on that motor

ohms law .jpg
 
Excellent. Send a picture of the top of the motor and cyl head. Ill see what I have, if you want to fix it. They DO make a lot nicer on the recoil too when you get stuck with a low battery and forced to crank by hand.
 
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