1979 Johnson stinger 75 hp / surging, misfireing, not reach top speed

jgriner

Petty Officer 2nd Class
Joined
Jul 22, 2010
Messages
146
ive got a johnson stinger that when i got wot, it surges, misfires, and will not reach top speed.

sunday when i took it out its top speed going out on the lake was right at 16 mph according to my phone gps. comeing back in its top speed was 19 mph, it would pause at 16 for a while then surge to 19 and hold it.

wednesday its top speed going out again was 16 but come back in was only 14 at times it would surge down to only 11mph

I would think that this 20ft pontoon boat should get about 30 mpg on a 75hp

details details details from day one.

i got this boat 3 weeks ago, the old man who had it before me could not get it running right so he missed with stuff. he had the timming way off and the the idle turned way up.
we bought a generic book on the net, it said to set the timming to 18? - 20?

I also put new spark plugs in the boat.
Checked the compression 147-150 psi on all 3 cylinders


I took it to the lake it would only go about 1/4 trottle and it would bog down and it not gain any more speed.
took it home and checked the carbs the high speed jets were clogged, I pushed it out with air. took it back to the lake and she ran good, top speed, probably about 30 mph

took it to the lake the next weekend and at about 3/4 throttle she starts missfireing ,and surging again

ive taken the carbs off 3 more times now and all jets are open and clear, replaced many hoses, ive replaced the tanks, main fuel line and pump, cleaned the fuel pump screen.

ive talked to a local tech and he said shoot starter fluid in the carbs if it bogs down then the carb is getting plenty of fuel, if it takes off then its not getting enought.
when we did that test the 1st carb would bog the engine a little bit. 2nd carb killed the engine every time. and the 3 carb would bog it down quit a bit.

one more tab bit of info.
on wednesday when i took it out, it started at the ramp and ran good to the rock quarry, i turned it off and went swimming, after bout an hour got back in and tried to leave, it would not start the battery would turn the motor over but not fast enough(the battery had always struggled to turn over the motor), i had someone jump me, thats when going back was only 14mph

yesterday i bought the biggest battery wallmart had, I also put new spark plugs in it and tested it at the river on the trailer still same problems.

thanks guys for all the help :)
 

Chinewalker

Fleet Admiral
Joined
Aug 19, 2001
Messages
8,902
Re: 1979 Johnson stinger 75 hp

Re: 1979 Johnson stinger 75 hp

Not a battery problem. Check the cables for cracks, chafing, etc. Check all connections. If still no better, then it's probably the starter itself. If you pull the base off and check the brushes, I'll bet they're worn down to nubs. New brush kit is less than $25.00.

As for the running issue, sounds like one carb is leaning out a bit. Due for a thorough cleaning and rebuild. And STOP using starter fluid! It is terrible for 2-strokes. If you really want to use that method for testing things, use a squirt bottle with pre-mix. Starter fluid will rinse oil from internal parts and can also attract moisture.

As for your top speed, I doubt you'll see 30mph on a toon with that motor. That's pretty fast. Tunes are very inefficient at speed. I think you could do a tad better than high teens, but not much... Also, make sure your motor is propped for a heavy load. Top RPM should be in the 5500-6000 RPM range. Anything less is lugging it - akin to driving uphill, towing a trailer, in fifth gear.
 

jgriner

Petty Officer 2nd Class
Joined
Jul 22, 2010
Messages
146
Re: 1979 Johnson stinger 75 hp

Re: 1979 Johnson stinger 75 hp

thanks Chinewalker
I belive that the engine has been rebuilt recently, with that i think the carbs got rebuilt also. You can tell that the carbs has been scrubbed clean with a wire brush.

If we are to assume that the carbs are good what would be next?

Some one told us that it could be the high speed stator, if it was going out would it cause the engine to miss? how bout the battery not charging up making me have to jump start it after running at wot for bout 20 mins?

is there a way to test the stator?

thanks john
 

oldstinkytoe55

Recruit
Joined
Aug 16, 2011
Messages
3
Re: 1979 Johnson stinger 75 hp

Re: 1979 Johnson stinger 75 hp

this is Aug 16 2011 i am posting here so maybe my info will help. my 75 stinger a 1978 vintage runs great but has a problem with the carbs. problem is sometimes i do not get fuel to all 3 carbs or just one carb will get fuel. .I have found that the needle valves in the carbs stick. I really haven't put much time into researching this and it is a problem. It is an easy fix but requires removal of the carb and the fuel bowl. If any one has a positive fix i would like to know what it is. Also fuel delivery seems to work off of the middle carb so i have an idea to deliver fuel to each carb like you would with a car 3 carb set up. i see no reason why this wouldn't work just haven't tried it yet. Its an easy fix just need to reroute the fuel lines. This is an old thread so my post is new. Still looking for why the needle valves stick and what to do about it. anyone got any answers email me at oldstinkytoe55@yahoo.com as i doubt many folks read this post. Thank You.
 

Haffiman

Commander
Joined
Dec 17, 2009
Messages
2,454
Re: 1979 Johnson stinger 75 hp / surging, misfireing, not reach top speed

Do you have the newer type needles with a clip-spring attached to the floats, or just the old plain 'gravity' ones?
 

oldstinkytoe55

Recruit
Joined
Aug 16, 2011
Messages
3
Re: 1979 Johnson stinger 75 hp / surging, misfireing, not reach top speed

the old gravity ones. i would like to get the spring ones as most engines today use those do you have a kit no # and were to find thank you stinkytoe55
 

oldstinkytoe55

Recruit
Joined
Aug 16, 2011
Messages
3
Re: 1979 Johnson stinger 75 hp / surging, misfireing, not reach top speed

I thank you for your help. I will look for the newer spring type and also will dabble in a 3 carb feed bypassing the stock feed system. If it works ok were good to go. Just tired of raising the motor going to the lake and only one carb has gas. Funny! After all these older engines are not exactly rocket science but they are temperamental. TLC is the key. Thanks again.
 

Haffiman

Commander
Joined
Dec 17, 2009
Messages
2,454
Re: 1979 Johnson stinger 75 hp / surging, misfireing, not reach top speed

You can just buy the new needle kits or the whole carb kits. At least the OEM have the clip springs.
The same valve needles goes to most of the engines.
 
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