Johnson outboard

[Lostboy2]

have a older 70 hp Johnson starts right up runs great at home with a hose have done when I get it to the lake and I put it in gear it's like it's running out of gas and dies it appears to have plenty of gas and good fresh gas to boot firing on all cylinders just don't have a lot of money but would really love to get it running right

[Onmygame]

One thing to check is if water is circulating properly.

If the impeller has failed, the motor will bog down once it gets warm, and will act the way you've described.

Just make sure there is a stream of water coming out somewhere along the back of the shaft.

This is likely only one of several possibilities to rule out, others will be along I'm sure with more of them for you.

The best of luck.

onmygame

[SalmonAddict]

like onmygame stated, theres several possibilities. Just slowly rule them out one by one.

next i would check the carburetor. when was the last clean or rebuild? you might have a stuck float to where it won't allow anymore gas in when you apply gas.

[Hunter757]

When you run it at home do you have the cowl on or off? Have someone squeeze your primer bulb when your on the lake running and see what happens.

[Lostboy2]

Yeah water is circulating just great did clean the carburetors out but did not rebuild them when it's on the hose at home it starts up immediately and idles up just fine when it's in the water it'll go into gear but when you give it gas it dies the compression is great the spark looks good nothing is more frustrating than being in the middle of the potholes and not be able to throttle up

[Lostboy2]

Yep tried pumping the ball goes into gear and idles but as soon as you at throttle it's like it's flooding out or the gas is going away

[Amx]

Maybe there is a clogged passageway, or jet, in one or more carbs. Might be from varnish or ethanol residue.

How long was the motor setting?

Have you sprayed carb cleaner down inside the carb's venturi? Aiming at any and all openings? And take off the fuel lines and spray inside those passages.

[Hunter757]

With the engine NOT running have someone move your throttle to full and back and watch the choke plate and make sure its opening up completely. Check your fuel line for holes, make sure the primer bulb is correct direction and fuel filter if you have one inline.

Does your primer bulb stay hard after you pump it for some time without the motor running? Check your linkage to the carb and make sure everything is connected and moving with the throttle. Posting some picture of the carb area and fuel lines and connectors might help us see something your missing.

[Hunter757]

Also try running the motor on the lake without the hood on. Sometimes when a motor has an exhaust leak it will run great on the hose but when in water the exhaust fills the hood up and the engine can't breath. If with the hood off it runs great you found your issue.

[Lostboy2]

Yes I have tried running it with the cowling off have a new fuel line on from the tank to the outboard hooked it up and tried my Kicker motor tank to it new fuel filter new fuel pump all hoses and filters ran the right Direction I did pull the Jets and they look shiny and clean I would think if it was a float or something it would do it all the time but it seems to only affect when under a load hands is why I was worried about compression once it catches and goes it runs great till the next time you stop then it's back to Feathering the throttle to get it to catch again it would be the weekend before I could get any pictures of it thanks

[Larry3215]

Its a back pressure issue. When its in the water, the exhaust cant exit as easily because the prop is under a couple of feet of water. On the hose, there is no back pressure.

That kind of thing almost always comes back to the carb or possibly the reed valves or it could be electrical/spark. If any of those are week or off, extra back pressure makes it worse.

Get yourself a spark gap tester or make one. The spark needs to eb able to jump a pretty large gap - I forget exactly - it will be in your manual - but its in the neighborhood of 1/2" to 3/4". A week coil will jump the gap on a plug but not go as far as it should under stress.

Lots f other things to test/adjust but you need the service manual to get the details.

It could be a timing issue too - get the manual and do the linkage adjustment routine - thats very important on those older engines.

[Larry3215]

By the way, its common to have bad coils on those engines. Luckily they arent that expensive. The spark gap tester will tell you if one is bad.

Also, the original OEM manual is much better than any of the unofficial brands like Haines, etc. Finding one is the trick. Check Ebay or Amazon or Google it.

[Larry3215]

Its been several years since we got rid of our old Johnson 70, so I keep remembering things.......

Back to the back pressure - when you adjust the carb idle mixture and idle speed, its best to do it with the lower unit in a tub/barrel rather than on the hose. That way you have close to the correct back pressure. Other wise, you will need to re-adjust those things after you are on the water.

I used to use a large metal garbage can. We installed a drain in the bottom of the can just for fiddling with the engine to make it easier.

[Hunter757]

I think Larry is on the money, get the book and check youtube to learn how to make a spark gap checker for an outboard very easy to do. How many carbs are on this motor?

[Hunter757]

How fast is your idle? You say it idles great how long will it run idling in your driveway and does it die at all when just letting it idle? Have you looked at your fuel pump?

[TrackerPro16]

First things first. Tune up. New plugs may be all it needs. Make sure it does not have points. If there are, replace and adjust them as well. As was stated, running in a 'no load' situation is not anything like running in the water. My experience with people's two stroke problems is probably 80% spark plugs and or improper fuel/oil mixture.
I live by SeaTac Intl Airport if you are close by I have a large plastic barrel I use for running large and small outboards I would loan you.

[AJ's Dad]

2 summers ago I had this problem with my 200HP Yamaha. It's a 1996 motor but the symptoms were the same. It would run well on the hose, and it would idle nicely at the lake. When I tried to get up on plane and run, it would hesitate, and eventually would not even get up on plane. I took it to a local marine facility and they looked it over. I thought I was going to have to have all three carbs cleaned, but they checked it and told me that was not my problem. The motor needed to be de carbed. Remove the excess built up carbon in the cylinders. To do this you remove the spark plugs, liberally (no political pun intended) spray seafoam into the cylinders, and let it set over night. add a whole can of regular seafoam to 5 gallons of gas and go run the motor at a pretty hard pace. The sprayed in seafoam breaks up the carbon in the cylinders, then when you run it hard on the water, it blows the carbon out the exhaust. Putting in new plugs prior to doing this helps, as well as after your done. Also, you can run the motor on the hose prior to spraying the seafoam in the cylinders. You can spray the seafoam into the intake while the motor is running. Spray until the motor almost dies, then let it run till it runs normal. Doing this two or three times can help clean out the carbs. After I did these two things, my boat ran like brand new again.

Good luck

[Bodofish]

Many older OB's have a manual as well as centrifugal timing advance. So they have a manual that rolls with the throttle that's normally a sort of big ring around / underish the fly wheel. Make sure it moves with the throttle. And check in the distributor for the other advance, just like in an old car. Any water and or salt can do a job on them. Opening the throttle with out advancing the timing = bog and die. Idle all day until you hit the gas. SeaFoam can work wonders too, if you spray it straight in the plug holes, make sure to spin it with starter before you put the plugs back in and fire it. Pools can be tough on plugs and if it's on the compression stroke, it can bend the conn rods or crank.

[Lostboy2]

Thank you everyone for the great ideas hoping to work on it this weekend I have came up with a barrel thank you tracker I live in startup SeaTac would have been a little far to go for one going to try the things that have been suggested the ones that I have it already done this motor has ran like a dream for years I guess if none of these other things work I'll have to attempt carburetor rebuild not sure why that has me a little scared I guess it's just getting all the adjustments back right and all the carbs in sync and if I get it all messed up you really hear me crying on here LOL

[Hunter757]

So from what I understand you have owned this motor for a few years? No issues before now. Do you run regular pump gas or non ethanol fuel in it? How big is your fuel tank? This almost sounds like fuel was left in the carb bowls over the winter and the fuel had dried up and tarnished them up, if that is the case you will have to remove them and take them apart and clean them up.

If your using pump gas you might have water in your tank and old fuel is no good for old motors. If you have a smaller tank dump the fuel into your something else and get yourself some fresh non ethanol fuel put your mix in and go from there. The seafoam in a small tank and run your motor for an hour on it just might get your carbs cleaned out if you left old fuel in them over the winter. Good luck keep us posted were here to help!!