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Johnson 35 hp 1979

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majkmajk

New member
Hello,

I'm a novice regarding motors and I'm struggling hard and in need of help.
It's a regarding a friends motor and I think it's a 1979 but might be a 1977 or 1978, not sure that matters, either way a late 70s Johnson 35hp.

The motor is bought 2nd hand so it's not like it's been running great for years and then all of a sudden something happened, not sure what the previous owner did and did not. It was running fine making 24 knots which I think is reasonably considering the boat which is about 5m / 1.7m or something like that.
I saw that the hose clamp from the tank was leaking so I replaced and tighten it and after that it wasn't running as well as it was before.
I have replaced all the fuel lines, spark plugs, cleaned carb and new carbkit as well as replaced the fuel pump as well as connected the tank directly to pump instead of quick connect to ensure it's not some leakage there but it's still making about 16 knots or so and, it runs great up until half throttle after that it barely gains speed.
Another johnson ~1979 25hp makes about 21-22 knots with the same fuel lines and tank on the same boat...

Cowl on or off does not seem to matter, the lean/rich mixture screw does not help, I've tried playing around with the linkage but did not matter much either.. mostly just made it run worse until I went to default. Pulling the choke while running made it run better so it seems to be fuel related but what am I missing?

All troubleshooting has been done in the water, not muffs.

Thanks.
 
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Comp around 100, not sure if it was 95 or 115 but around 100 so I think to my knowledge it should be ok on that regard, dont have the motor on hand right now.
 
Hi majkmajk,
Newbie on the site as well.
Couple tips you can try that won't cost $;

*Check the fit of the fuel filter cover. If it's crooked, it can't seal well. Speaking from experience :)

*On the fuel tank hose clamp you replaced; disconnect the hose and trim an inch or more off the end of the hose. Reassemble. This allows a 'new'
bite for the fitting into the hose.
Cheap and easy. Fire it up and try it.
Hope it helps, let me know what you find!
Patrick from North Central Idaho.

.
 
Water pump impeller replaced ?---Post the actual compression values here.----You installed a factory fuel pump and carburetor kit?----Or something else ?
 
There is no fuel filter. I did cut off the end of the hose when I replaced the clamp, the 25hp johnson ran multiple times without problems on the same tank and hose(with quick connect connection).
As I said I connected the fueltank to the fuelpump directly(with bulb) and it still didn't run, I previously saw a small leak in fuel drip in the quick connect(might be called something else.. thats what I call it..) on the motor side which is why I did that but it did not help.

Yes impeller replaced, I don't know the exact comp values as I mentioned.. I don't have the motor at hand, he has had it at my cabin all summer but now it's not summer any longer unfortunately and he has brought it home but the comp was not bad when last measured.
I have opened up and cleaned the canals as thermostat as well and the thermostat has been tested that it opens up under hot water.

Motor is peeing good but it just runs like crap on higher than 50% throttle
 
Also saw someone experiencing similar issues with a different type of motor but not running great on WOT that suggested spraying starting gas into the motor without the cowl on to figure out a leak, I tried that.. it did not make a difference.
 
Also worth mentioning I guess is that I did not do all things at once, the impeller got replaced in the start before it ran bad then it started running bad due to other circumstances, I cleaned carb, ran like crap still, hoses were bent, old and damaged so I replaced all hoses, ran like crap, carbreplacement kit, ran like crap, replaced fuelpump, still crap. I've tried pumping the bulb while running but it made no difference, pulling the choke managed to get it to full throttle/speed. I've opened the carb and trying to clean the carb and adjust the float MANY times but without success.

As I said earlier I tried to adjust the linkage arm(timing?) not sure whats it called and it did not help, I should have looked into the carb though to ensure it was horisontal on full throttle.. I did not but my adjustments did not help.

No matter what way I tried it, it did not run good.
 
There is indeed a screen inside the fuel pump. Remove the center screw & plastic cover.

Did you ever check for spark on both cylinders? YES/NO
 
Not sure what you mean with screen inside the fuel pump, I said there is no fuel filter, the fuel pump has been replaced. Yes, spark on both cylinders. I have opened the carb 4 times because I thought there might be something wrong with float as well as sprayed it thoroughly, maybe I need to soak it?
 
A factory fuel pump has a " filter screen " on it.----All you need to keep fuel pump and carburetor screen.-----Maybe it is not a carburetor issue.-----Simple trouble shooting finds the real issue.-----Does spark jump a gap of 3/8" ( 1 cm ) on both leads , yes or no?----Run with a timing light , one cylinder at a time and see how spark behaves.
 
Ok well I thought you were referring to a separate fuel filter like I have on my own motor. I opened up the old fuel pump and saw the screen, it was not bad but I had already ordered one so I replaced it. I don't have the motor on hand so looking for suggestions to look into next spring, I don't know how to run a timing light as of now but I will look into it if you think that might be the issue. But could the timing be bad if it ran great when it had a fuel leak on the the tank hose which I fixed and then started running badly? In my mind that sounds unlikely but it's behaving like it's struggling for fuel and the leak should mean it would get less fuel I would guess.. I'm just out of my depth on this one I think..
 
Checked the flywheel key?-----Rem,ember advice is based on your description.-----I can not see , hear or touch your motor.----Likely an easy fix if it was on my workbench.
 
Not sure what the flywheel key does, care to elaborate? I mean.. does not take much to be a better mechanic than me so sure, it might be easy for you.
 
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