1979 Johnson 70 hp

[Dkg57]

having trouble on water when it is on wot the motor starts to bog down I have cleaned carbs replaced all fuel lines ,replaced the entire fuel line and primer bulb, also coulld the plugs be making it do this? Ran well Sun morning then started doing same thing as weekend before. pulled plugs out when i got in Sun morning soaked with fuel could this be the problem? Been about 3yrs since they were replaced.

 

[jtexas]

Re: 1979 Johnson 70 hp

Does it start and idle ok?
What condition are the plugs in, apart from being wet? Any carbon deposits?
When you cleaned the carbs, did you soak 'em overnight & install new carb kits?
Get a spark tester and look for a strong blue spark across a 1/2" gap.
I have the same motor, the plugs in it right now (champion QL77JC4) are about 3 yrs old, the tops of the center electrodes are getting uneven but otherwise they look great.

 

[tashasdaddy]

Re: 1979 Johnson 70 hp

did you remove and clean the high speed jets, and the float needle seat.

 

[Dkg57]

Re: 1979 Johnson 70 hp

hard to start then it idles ok and runs fine then when i shut it off its hard to start after it gets warmed up I had the carbs rebuilt last year. tried pumping the primer bulb and holding choke halfway closed and still doing same thing checked spark and it is ok on the wire side. The primer bulb is hard after priming it. The plugs are black oily looking

 

[jtexas]

Re: 1979 Johnson 70 hp

Let's review: hard to start cold, idles fine, accelerates fine, bogs down while running at WOT, hard to start warm - anything else?

How long have you had it and has it been this way since you got it?
Did it sit idle for a long time (like, over the winter, or longer)?
Done any other work on it?

Normal for plugs to have a light coating of oil right after idling for awhile. Did you check the gap? (should be .030)

"checked spark and it is ok" - if that means anything other than you got a strong blue spark across a 1/2" gap on all three holes, then you haven't ruled out an ignition problem.

Cold start: pump primer until firm, lift hi-idle lever to full up position, push key in and turn it to start, hold it in until engine starts, then back off the hi-idle lever much as possible without the engine dying, if it starts to die, bump the choke.

If you did the spark test as described, then:
Replace spark plugs.
Do a compression test and report the numbers here.
Make sure the fuel tank vent is open.
If the gas is more than a couple months old, replace it.

Tashasdad, when did you make 'supreme mariner'? I must have missed it....my hat's off to you!!

 

[Dkg57]

Re: 1979 Johnson 70 hp

The plugs did the trick thanks for your help.

 

[jtexas]

Re: 1979 Johnson 70 hp

Thanks for reporting back - soon as I leave the office I'm going straight to autozone for a set of plugs - no sense tempting fate!

 

[Dkg57]

Re: 1979 Johnson 70 hp

I went with the denso plugs instead of the champion plug they wrere able to cross reference the champion so i got them

 

[jtexas]

Re: 1979 Johnson 70 hp

I went with the denso plugs instead of the champion plug they wrere able to cross reference the champion so i got them

had to go to three different stores, but got the champions, won't put nothing else in my engine.

 

[Forsaken]

Re: 1979 Johnson 70 hp

hi, i am having the exact same problem, as seen here!... my motor is a 1975 70hp evinrude though... im glad i came across this thread, im on my way to advance...lol.

my symptoms:

hard to start cold, idles fine, accelerates good, then starts bogging at WOT. but i can tap the choke switch when at wot and it runs great for a split second...

 

[bigbob_FTW]

Re: 1979 Johnson 70 hp

I went with the denso plugs instead of the champion plug they wrere able to cross reference the champion so i got them

I highly recommend going back to the champion plugs. Others just seem to give OMC motors fits. Also, if you troll a lot, run at low speeds a lot, you can increase the gap to .040 to help reduce carbon buildup.

 

[Lodgepole]

Re: 1979 Johnson 70 hp

Forsaken; If a quick flip of the choke switch helps the bog momentarily, then you have a fuel problem. Could be dirty carbs, fuel pump, fuel line air leak, or dirty fuel filter. Or of course, tank vent closed.

 

[Dkg57]

Re: 1979 Johnson 70 hp

Forsaken my boat did the same thing about 2 years ago had to have carbs rebuilt and it fixed the problem.

 

[Dkg57]

Re: 1979 Johnson 70 hp

I am going to run the denso plugs for awhile they are doing great been out 4 times since changing the plugs no problems yet. But if I do start having problems with the denso plugs I will go back to the champion plugs.Thanks for your advice.I Pulled the plugs out today and no carbon buildup on them yet Ill keep an eye on them and let you know how they do.

 

[my70johnson]

Re: 1979 Johnson 70 hp

Mine is a 77, does anyone know if there is a kill switch or safety switch that would prevent starting if something isn't in line somewhere? Can I go around it or can I find it easily?

 

[jtexas]

Re: 1979 Johnson 70 hp

Mine is a 77, does anyone know if there is a kill switch or safety switch that would prevent starting if something isn't in line somewhere? Can I go around it or can I find it easily?

welcome to iboats - let's continue discussing your motor in the thread you started - be a little less confusing...........................