1994 Johnson 150 good idle, weak spark.

[WRXSTi0487]

I recently bought a 95 Smokercraft deckboat which has a 94 Johnson 150 (J150ELARA) I bought the boat with the engine in non-working condition, salt water had entered the fuel system and cause the needles to corrode shut. I was told the engine had run fine before that. Now since then I have gone through and rebuilt all 6 carbs and found that the needles were in fact all corroded shut. I ran the carbs through ultrasonic cleaning and rebuilt using OEM carb kits setting the floats as called out in the manual.

I have run a compression test resulting in 105-110 on all 6 cylinders. Now after the carb rebuild (and removal of the tank from the boat for thorough cleaning) the engine fires right up with little effort and seems to idle very well both on the hose and when first put on the water. First water trial we leave the dock everything running fine I begin to put on some power and only slightly above idle it begins to bog down heavily and smoke heavily (running premix 50:1 previous owner disconnected VRO and removed tank) we continued to putt around at idle trying to let the engine warm up and see if it would ever make power but never would. Would occasionally spike to around 2500RPM before bogging back to 1500 or so. The engine occasionally dies when returning to idle from a throttled up position my assumption is from the fuel loaded cylinders at that point but continues to idle just fine. It was run on the water for about 30 minutes on a hot Florida day and nothing ever changed with how it ran from start-up to going back to the launch.

I have since tested the spark on all 6 cylinders with the CDI spark tester and found none of the 6 cylinders will jump a 7/16" gap. At. 3/8" gap the right bank will intermittently jump with a faint white spark. The gap must be further reduced for all 6 to fire. Testing with a timing light as a Tach I showed all 6 cylinders firing at idle and did not appear to want to go over 1500RPM once throttle is applied.

I currently do not have a DVA for my multi-meter but should have one soon. Does anyone have any input or advice on where to really start with this issue? I am currently thinking Powerpack or Stator as it seems uncommon that all 3 coils would fail. But also the power and ground wire to the battery seem to be in poor condition and I intend to replace them.

Thanks in advance for any help.

[Joe Reeves]

In cleaning the carburetors, did you remove and manually clean the six high speed jets that are located horizontally in the bottom center of the float chambers (way in back of the float chamber drain screw plugs... If not, do so as your explanation indicates a lean condition as fuel struggles to get past those jets. Maybe not your problem BUT that's the first place I'd look.

Carefully use a piece of single strand steel wire as solvent just doesn't do that job properly.

[WRXSTi0487]

I did not run anything through the jets, but did put the carbs through ultrasonic clean one at a time with a mild degreaser mix. I was considering taking the carbs back apart to do that but when I found the weak spark with the spark tester I was starting to think that may be my issue of it just doesn't have enough spark to handle the load once power is applied.

Also let me add I replaced the bowls as they were leaking, all fuel lines from the tank to the fuel pump have been replaced including the lines from the pump to the carbs. As well as a brand new fuel filter. I have tried bypassing the filter and everything with a kicker tank and the results are the same as using the main tank.

Trying to brainstorm everything that could be an issue at this point.

[Joe Reeves]

When testing the spark, the spark plugs must be removed in order to obtain the highest cranking speed possible. Were your spark plugs in or out?

You replaced all of the carburetor float bowls (float chambers)? Did you have new high speed jets or reuse the original jets? If the original, what did they look like?

[WRXSTi0487]

I think you may have just hit the point I was looking for. I didn't remove anything from the original float chamber or order a new jet to go in there. I just pulled the parts diagram and your referring to the Orfice behind the brass plug correct? If so that may be my problem as I doubt the new foot chamber came with it.

And on the spark test no I had the plugs in. So I will retest that when I get back over to the boat.

Luckily I kept everything that I removed and replaced so I will take a look at that when I get home as well. Would be nice if that's just what I missed.

[WRXSTi0487]

Okay so totally missed the high speed orificies when I replaced the float chambers. I have removed them from the old chambers and am currently running them in an ultrasonic clean cycle. They looked clear and free of debris but heck I have the cleaner so why not. Then I may run a pipe cleaner through and put them on and will post back when I'm able to test the engine with proper load.

[WRXSTi0487]

Wanted to report back and let everyone know that was in fact my issue. Just a show of what being tired and frustrated trying to get the engine to run right and not leak did. Took her out on the water today and all was well ran great. May be slightly under-propped but that's an issue for another day.

Thank you for your help because I was looking in the wrong direction the whole time.

[Joe Reeves]

The float chambers do not come with the high speed jets as the float chamber fits various hp models. Yeah, it's not good to work when overtired... been there a few times. Glad you're now up and running and back to being a happy boater.