70HP Johnson 1976 not firing on all cylinders??????? any help much appreciated

[jasonbbo]

OK just bought a nice little fishing boat and on the back theres a 1976 Johnson 70HP. first day we hit the water its only running on one cylinder i had a good look around it but couldn't fix it there and then so took the boat out of the water, day 2 i took all the carbs off and gave them a clean and replaced the spark plugs and dropped her into the water and presto fixed!! had a great day but it all goes down hill from here. the next time i take her out after 10 min it just drops a cylinder?? i Finley get it back to the harbor with my trusty 5HP 4 stroke, to cut a long story short its never worked properly since.. some times it starts on 1 or 2 cylinders other times it wont start at all! it seem the bottom cylinder works on and off, after cleaning every wire connection i could see on the outboard and cleaning out the carbs again it seems the top and middle cylinders are working fine but the bottom one is coming on and off.... theres a good spark also i think i if it was a blocked carb it just wouldn't work right?? iv tested this by starting the engine on just one cylinder she will start on the top one and middle one, and every now and again on the bottom one, the same goes if I'm reving the engine , if i pull the top spark plug lead out it still runs then the middle one again its hit or miss that the engine will keep running or choke on the bottom cylinder ?? any bit of advice on this matter would be great

 

[HighTrim]

Re: 70HP Johnson 1976 not firing on all cylinders??????? any help much appreciated

You need to get an adjustable spark gap tester. They are under 10 bucks at any auto type store. Set it to 7/16". The spark should jump this gap with a bright blue ZAP!! If it doesnt, it is time to troubleshoot further. Start by swapping the coil from one of the cylinders that is sparking well. If the problem follows the coil, replace the coil. If not, let us know and we will troubleshoot further.

If the spark is intermittent, best bet would be to get an inductive timing light, and watch the spark, one cylinder at a time while running to see if it is running or cutting out.

 

[jasonbbo]

Re: 70HP Johnson 1976 not firing on all cylinders??????? any help much appreciated

dose any one else have any ideas?

 

[Joshua Nichols]

Re: 70HP Johnson 1976 not firing on all cylinders??????? any help much appreciated

Okay your post is a little confusing for me... So I will just tell my story and hope it helps... I had a ol 65hp Johnson.. Kinda the same thing... It would do weird stuff.. This cylinder would fire then that cylinder.. Sometimes they all worked perfect.. I moved coils around to check for a bad coil.. Seemed like it always fired on the top.. I ran the engine like that for awhile cause if I could get it to run it would run pretty good.. Finally it gave up.. Left me on the water.. Got her home.. Fooled with it.. Got it going again... Well soon after that it died.. After testing this that and the other... Checked all the grounds.. Took the ground off the power pack.. Tested the trigger.. After every coil I had worked... I broke down and bought a new power pack from a company who handles CDI products.... 0581713 POWER PACK 3 is the Johnson number... Any how I read that the CDI units was a pretty good product, better and cheaper than OEM.. Was like $120ish... I hooked up the new unit.. Hooked the battery up.. Bam fired up.. Took the ol girl to the lake and it even ran better than it did before... Not to say that this is for-sure your problem, but it seems to be the weak point of the system... Could be the rectifier could be the timer base..Get ya a spark tester... I like the inline one ..... As far a fuel related stuff.. I had nasty carb fun too.. The way I found my faulty carb was to use carb cleaner.. Get a friend let them drive.. Throw down the hammer.. While the engine is missing.. Hit each carb with carb cleaner.. When you hit the one that has the plugged up jet.. Hold on cause the boat will take off.. That's your problem carb.(Dont do it too much the cleaner washes away the lube oil). You have to remove and clean that little ORIFICE PLUG.. That thing will give you grief.. #35 GOOD LUCK

 

[jasonbbo]

Re: 70HP Johnson 1976 not firing on all cylinders??????? any help much appreciated

Okay your post is a little confusing for me... So I will just tell my story and hope it helps... I had a ol 65hp Johnson.. Kinda the same thing... It would do weird stuff.. This cylinder would fire then that cylinder.. Sometimes they all worked perfect.. I moved coils around to check for a bad coil.. Seemed like it always fired on the top.. I ran the engine like that for awhile cause if I could get it to run it would run pretty good.. Finally it gave up.. Left me on the water.. Got her home.. Fooled with it.. Got it going again... Well soon after that it died.. After testing this that and the other... Checked all the grounds.. Took the ground off the power pack.. Tested the trigger.. After every coil I had worked... I broke down and bought a new power pack from a company who handles CDI products.... 0581713 POWER PACK 3 is the Johnson number... Any how I read that the CDI units was a pretty good product, better and cheaper than OEM.. Was like $120ish... I hooked up the new unit.. Hooked the battery up.. Bam fired up.. Took the ol girl to the lake and it even ran better than it did before... Not to say that this is for-sure your problem, but it seems to be the weak point of the system... Could be the rectifier could be the timer base..Get ya a spark tester... I like the inline one ..... As far a fuel related stuff.. I had nasty carb fun too.. The way I found my faulty carb was to use carb cleaner.. Get a friend let them drive.. Throw down the hammer.. While the engine is missing.. Hit each carb with carb cleaner.. When you hit the one that has the plugged up jet.. Hold on cause the boat will take off.. That's your problem carb.(Dont do it too much the cleaner washes away the lube oil). You have to remove and clean that little ORIFICE PLUG.. That thing will give you grief.. #35 GOOD LUCK

thanks a mill, that sounds just like the problems im haven. oh i have an other Qs were on the carb can you adjuse the mix ? i cant find a screw anywere i think i mite try and get a new power pack is there away to test it? also how do you test the rectifier could or the timer base?

thanks for your help

 

[Joshua Nichols]

Re: 70HP Johnson 1976 not firing on all cylinders??????? any help much appreciated

There is no adjustment... Mine had a little needle valve screw that adjusted idle speed but that was it( where #26 is).... I remember you unplug the rectifier and if everything starts working... Thats the problem.. Easy huh... Now all the other goodies there is more to it.. The trigger timer base thing.. You test it with a meter and ofcourse I no long remember the numbers but I found some online info.. This wasn't the page I used.. I couldn't remember where it was, but it should work...http://www.ebasicpower.com/downloads/cditech/CDI-Troubleshooting_Guide-JOHNSON-EVINRUDE.pdf

When ya get her running.. Be sure to post your findings to help others out in the future.. Plus I would like to know

I hardly haunt this part of the forum.. Just so happened to see your post...

 

[cr2k]

Re: 70HP Johnson 1976 not firing on all cylinders??????? any help much appreciated

You really need compressed air and a small needle type orfice to blow all the crap out of those carbs. They have a lot of places where gunk can hide.