70HP Johson loses power intermittently

[imported_mnmike]

I just got a used boat and 70 HP Johnson. owner said it was winterized 2 years in a row. Motor is very clean. When run in a tub it took a minute or two to fire then it ran great, pumps water great. On the water, it ran for 15 minutes and then lost a bunch of power, tried different tank, fuel line, lowest plug was not hot like 1 and 2, finally found a coil pin plug (lowest cyl) almost out of the connector, pushed in and boat ran great for 1.5 tanks. then again power loss. Messed with connector again and got a few more good laps but then power loss. Could this be a coil issue? Power pack issue? Carbs looked very clean in the bowl. Float needle perhaps? I would appreciate any ideas.

Thanks,

 

[imported_mnmike]

Re: 70HP Johson loses power intermittently

I forgot to add, this is an 1981 I am told. Model J70ELCIH. I also tried to pump the bulb when no power, no go, choke, no help either. Could the float be sticking and when I tilt the engine, I am disloding the needle, I did have the bowls off and they were very clean, no crud in the bowl at all.

 

[papasage]

Re: 70HP Johson loses power intermittently

may have a coin breaking down . do a spark test on it. and a compression test to.i have a 1974 did that . after it coold down it would run goo for a few minutes . changed a coil that had a crack in it then ran good all the time

 

[imported_mnmike]

Re: 70HP Johson loses power intermittently

Thank you for the reply, I looked at the coils, #2 has a crack in the clear portion on the top of the coil. I cannot feel it, but I can see it from the top. I had all 3 plugs aout and all have excellent spark, also, all could read .4 ohms each, when set on the 200 ohm scale.

 

[tashasdaddy]

Re: 70HP Johson loses power intermittently

if you have or can borrow or buy an induction timing light. take it for a spin, when it starts acting up clip on each plug wire and activate light, watch for a miss. this will give you.a direction. if you find one missing you can exchange one coil with another, not the spark plug but move the complete coils, if the problem follows the coil, you found your problem. if it doesn't follow the coil, it's probably the power pack going out. no change with the choke or pumping the bulbs point to electrical. good luck , post your results, and welcome to iboats.

 

[imported_mnmike]

Re: 70HP Johson loses power intermittently

Yet another puzzle, does this have a temperature switch? I see a lead that goes to the block, the engine certainly does not seem overheated.

 

[jim_in_day]

Re: 70HP Johson loses power intermittently

yes, it has a temp sensor. brown wire comes out of the head. That is a switch that sounds an alarm in your control box (if everything is hooked up) will not be the cause of your intermittent power lose. Follow Tashasdaddy's advise, and you will discover exactly what your problem is.

 

[imported_mnmike]

Re: 70HP Johson loses power intermittently

Thanks for the advise, I like the timing light test, I did check the temp sensor, I do have a buzzer so no overheat going on.....The power pack is the box right behinde the coils? Are they expensive?

 

[Walker]

Re: 70HP Johson loses power intermittently

Clean the coil ground on all 3 coils, especially the bottom one.

 

[rickdb1boat]

Re: 70HP Johson loses power intermittently

There are places you can get a CDI pack for about $65.00 + shipping....But first things first. If you were loosing sparks on all 3, then we would look at the pack as one of the causes. But do the tests above and it will narrow it down....Personally, I think you've narrowed it down to a coil problem already. I'd focus in that area...

 

[imported_mnmike]

Re: 70HP Johson loses power intermittently

Thank you all for the input, I will go the timing light route for now. I will post again when I know more. I suspect the coil with the dark line inside across the top, (possible crack?) may be my culprit.

Thanks,

Mike

 

[imported_mnmike]

Re: 70HP Johson loses power intermittently

Hi Again,

I replaced the lowest coil with a new one and also 3 new plugs, I ran the boat for about 40 minutes at all different speeds, and no problems, (other than a bit boggy out of the hole) A marine mech, told me to run a bit of Seafoam in the gas to clean any minor carb gook out. Anyone see anything wrong with that?

 

[tashasdaddy]

Re: 70HP Johson loses power intermittently

you can try the seafoam in the gas, doubt any change, is usually one of two things, dirty carb or linc n sinc. you need the manual to do the linc n sinc, it's lengthy is directions, but simple to do. it put the timing in sinc with the carbs, so both advance at the same time. if you rebuild the carbs, you will need to do it anyway, and besure to use a rebuild kit, don't just clean it and put i back together. another thing that will help the preformance is, doing a decarb with Seafoam Deep Creep. it cleans all the old crud and carbon build up out of the innards, most people are amazed at the results. the nieghbors will hate you because it gets a bit smokey. good luck, keep us posted, glad it's running.