25 johnson wont run past idle

DougyB · May 5, 2012

1986 Johnson j25cdc outboard wont run. past low to mid idle, just cuts out.. brand. new gas., fuel lines., gas tank primer bulb fuel pump plugs and compression is 115 and 120, high speed jet was even replaced....holds a prime... any idea guys? I've tried everything I know how to do

oldcatamount · May 5, 2012

Re: 25 johnson wont run past idle

Have you check the spark yet? If you have an air gap tester, the spark should be strong and blue at 7/16". After you have had it running (at idle) check the plugs. They should appear nearly the same, so if one appears wet, so should the other. I'm thinking you may be dropping a cylinder which would allow it to idle but not excellerate.

DougyB · May 5, 2012

Re: 25 johnson wont run past idle

I have not done tha yet oldcat, but I removed one spark plug while engine was running, and then did the other, and the motor ran on each cylinder by itself and sounded the same... Does this eliminate the dropping of a cylinder?

oldcatamount · May 5, 2012

Re: 25 johnson wont run past idle

Yup, it's firing on both pistons alright. So why did you replace the high speed jet? Was the carb dirty?

DougyB · May 5, 2012

Re: 25 johnson wont run past idle

i thought it was... ended up being clean looking, had it rebuilt anyway... when it still did the same thing i figured replace the jet just to see what happens

DougyB · May 5, 2012

Re: 25 johnson wont run past idle

wow, I did the same test again (last one was a few weeks ago) and now if I remove the top spark plug the motor shuts down... yet the powerhead reads 115 on top and 120 on bottom, which are pretty good numbers. I just checked since i figured I'd do a rod check, rods were good.

This motor is confusing me, I'm not sure if this is an electrical problem now or a cylinder issue

oldcatamount · May 5, 2012

Re: 25 johnson wont run past idle

Try swapping the top coil with the bottom coil and see if the problem follows the coil. If it does, you have either a bad coil, coil wire, or connection.

DougyB · May 5, 2012

Re: 25 johnson wont run past idle

will do, ill be back on soon

DougyB · May 5, 2012

Re: 25 johnson wont run past idle

old cat when I try to switch the coils, all I get is a backfire, the engine will not start... I first just rerouted the spark plug wire, after that failed I put the wires back to their orignial coil, and took off the entire coil of each, and swapped coil positioning... both ways gave me a backfire

oldcatamount · May 5, 2012

Re: 25 johnson wont run past idle

Just change the coil positions. Leave the wires right where they are.

DougyB · May 5, 2012

Re: 25 johnson wont run past idle

oldcatamount · May 5, 2012

Re: 25 johnson wont run past idle

Top coil: unplug the plug wire and remove the coil completly from the motor.
Bottom coil: do the same thing as the top coil.
Now take the top coil and re-mount it where the bottom coil was. Re-connect the bottom coil wires to it.
Now take the bottom coil and re-mount it where the top coil was and re-connect the wires.
Do not swap any wire locations. If you do, that's where you get the backfire. All we are doing is "testing' the top coil with the bottom cylinder to see if the coil is bad or not.

DougyB · May 5, 2012

Re: 25 johnson wont run past idle

did everything oldcat, and it backfires. The only way I can get it to start is to move everything back to starting point, or swap coills and cross the plug wires. I left all wires with original location, it just wont turn over

DougyB · May 5, 2012

Re: 25 johnson wont run past idle

would i maybe be better off with one of these? to test it http://www.ebay.com/itm/Digital-LCD...089?pt=LH_DefaultDomain_2&hash=item27c6a6ce41

Beings I left this out, the first time this problem occured, I had been running WOT and the engine cut out. I started it back up and was able to idle but not accelerate, and it then died all together and wouldn't start up. When I got the boat home, it idled fine on muffs, but at the test lake it would again not accelerate above low rpm's. At this time is when I started doing the complete engine rebuild, except for electrical. When I first started I had done a running plug test, and it would run on either cylinder... now if I remove the top plug boot it dies right away. Still, the motor has the same problem.... wont accelerate past idle without dieing. It will idle pretty good. clean gas, fresh carb, whole nine yards. I will buy a spark tester tomorrow and give it a try, but I am open to any opinions

DougyB · May 5, 2012

Re: 25 johnson wont run past idle

anything?

DougyB · May 6, 2012

Re: 25 johnson wont run past idle

Ok guys, I went out today and bought a new spark gap tester and ohmmeter. I did my testing and wala!!!! the bottom plug wire is not jumping the gap, top one was the only jumper. The question I have now is, where do I go from here? What must I do to troubleshoot the exact problem now?

oldcatamount · May 6, 2012

Re: 25 johnson wont run past idle

DougyB, It looks like your diagnosis is over. You have found the problem. The bottom coil is bad. But, before you buy a new one, check the continuity of the bottom plug wire and the connections first. Who knows, the spark plug wire may be the culprit and that would save you some money!

DougyB · May 6, 2012

Re: 25 johnson wont run past idle

Is there any way it could be the powerpack? should I even open my digital ohmmeter and check? I'm just trying to make sure the problem isn't coming from the powerpack so that I don't buy a coil for no reason.

oldcatamount · May 6, 2012

Re: 25 johnson wont run past idle

I'm not sure how to check your powerpack but It makes sense to try anyway.

AlTn · May 6, 2012

Re: 25 johnson wont run past idle

mark your coils Top and Bottom..T,B..1,2...Upper, Lower, U,L...anything to distinguish the two...swap them < not the plugwires >...now which has no spark?..Top?..replace the coil..Bottom?..move on up the line to the powerpack..test procedure at cdielectronics.com/troubleshooting and you'll need a dva adapter for your MM...with the 2 cylinder CD Ignition the odds are it's the powerpack if you have spark to only 1 cylinder and both coils have proven to be good

25 johnson wont run past idle

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