Old Johnson 100 Hp problems/questions.

[A. Sharp]

Hey, I recently bought a boat with a 100 horse 1972 Johnson. It is a 4 cylinder 2-stroke engine. It runs fairly well immediately after starting, but once it warms up it randomly bogs, skips, or even dies at all ranges of throttle. It is considerably worse however at lower RPMs. Also, when I took it out for the fist time the other day, it had no power under load. At full throttle I was traveling at a blistering 10 Mph. The guy I bought it from says the carbs were recently rebuilt and they do look quite clean on the inside, so I'm pretty sure it's not that the carbs are dirty. I did notice that all of the low speed needles were screwed in all the way, which seems wrong but I'm not sure how to adjust them. I thought that the problems might lie in the spark plugs/ignition system, so I pulled the spark plugs and took them to several auto parts stores looking for replacements. Unfortunately, no one around here had any of the old school Champion UL77V plugs, so I was wondering if I could replace them with a better, more modern plug? Anyway, this is my first boat and I still have tons to learn, so the problem could be something really obvious.

Any suggestions would be great, thanks!!

 

[Daviet]

Re: Old Johnson 100 Hp problems/questions.

Welcome to the forum.
First do a compression test and check the spark with an air gap tester, the spark should jump a 7/16" gap and be bright blue.
If the above is in working order, I would suspect that you still have a fuel delivery problem. The engine break down I looked at did not have adjustable low speed needles, what is your model number.
I think the UL77V surface gap plugs were replaced with L77JC4 plugs with a center electrode, much better plug.

 

[A. Sharp]

Re: Old Johnson 100 Hp problems/questions.

The model number is 100ESL72R. I will hopefully run to the auto parts store to get the air gap tester, compression tester, and spark plugs within a few days.
As for the needles I referred to, I'm pretty sure that they are low speed needles because there are arrows labeled "low speed adjustment" pointing to access holes directly over them.
Also upon inspecting the needles, it appeared that fuel had been leaking out of a few of them, so could the needle gaskets or the needles be worn?

Thanks for the input!!

 

[Daviet]

Re: Old Johnson 100 Hp problems/questions.

Your engine does not have adjustable low speed needles, unless someone has swapped carbs.
#40 is the idle orifice, it's non adjustable. #42 is a plug.
:: iShopMarine.com ::

 

[jimmbo]

Re: Old Johnson 100 Hp problems/questions.

I believe it was 1973 when they did the fixed low speed jet. 1972 still had the adjustable low speed needles.

 

[emdsapmgr]

Re: Old Johnson 100 Hp problems/questions.

The 1971 engine was the last with the adjustable idle needles. They are fixed on the 72 100 hp. Check for spark on all 4 plugwires. Possible that when the engine warms up, that it's not firing on all 4 cyls. Weak ignition components tend to work when the engine is cold, then may not work well once the engine heats up to normal operating temps. An inductive timing light will show the firing patterns on each plugwire when it's fully warmed up. When my 72 100 hp warmed up, it just quit. Turned out the timing sensor was bad. Yours does not exhibit that failure mode, but you get the idea. If you are not working from a factory service manual, check out this website for ignition troubleshooting info for your engine: cdielectronics.com Only run the factory-recommended plugs.

 

[jimmbo]

Re: Old Johnson 100 Hp problems/questions.

I stand corrected.

 

[A. Sharp]

Re: Old Johnson 100 Hp problems/questions.

Thanks for the help guys.

Another question: how much water should come out of the two ejection holes at the back of the engine? There are little drops and steam that come out, but nothing very substantial. I did some reading and people said that this is perhaps typical for older engines, but I wanted to make sure.
I hope to get some pictures up pretty soon, so you guys can see the carb. and what not.

 

[Daviet]

Re: Old Johnson 100 Hp problems/questions.

If you are running it on a hose, you woun't get much out of the exhaust ports.

 

[emdsapmgr]

Re: Old Johnson 100 Hp problems/questions.

You will get a little exhaust out for the first minute. When the thermostat opens, you will get a little light water mist mixed with exhasut. That's a good sign that the stat opened-entirely normal.

 

[RoyDH]

I have a 1966 100 hp Johnson outboard. Doesn't idle well and only goes about 18mph.

 

[nwcove]

I have a 1966 100 hp Johnson outboard. Doesn't idle well and only goes about 18mph.

welcome to iboats Roy!! you should have a look at the forum rules regarding posting in old threads tho. start a new thread on your motor issues and im sure you will get some great help.

 

[emdsapmgr]

Point of clarification. If your engine has the idle adjustment needles, it is likely the engine is actually a 1971 model. That being said, that unit has the old points and condenser ignition system. So, you need to evaluate the ignition system using 1971 ignition troubleshooting information, not 1972. This website should have some useful troubleshooting information that is helpful: cdielectronics.com