Johnson 100 javelin low power

[Aardvark earthworks]

G'day there peoples,
Need some help with this brain bender please.
'79 100 v4 low power and slow to plane
pushing 16 ft carribean.
has been frustrating my efforts for a while now.
Suspected spark so began by installing new plugs and gave it a run, Top left hand plug (looking towards bow) is clean but wet,looks unused. The other 3 plugs all have nice tan insulators.
Next did a spark jump test that seemed ok (spark jumped at least 7/16"), but had a spare new coil so changed it anyway. Took it for a run, same problem.
Next step Compression test. All pots between 95 & 100 from memory.
Have yet to totally disassemble carbs but did remove and check all jets, they were all found to be clean and clear.
Strainer at fuel pump is clear, found an damaged o-ring at tank fitting possible air sucker, replaced that. Checked primer bulb, it's ok. Tank vent always open.Fresh fuel used.

After running in barrel last week noticed steam come from spark plug hole when I removed it, therefore thought the headgasket may be blown, so removed head.
Found a few small flaws in mating surface that I was not happy with ( possible or potential future problem), so surfaced head till removed, replaced gasket ,torqued to spec and sequence. Took it for a run, same problem. ( may have been a slight improvement but probably my imagination)

Where do I go from here ???
Powerpack ( bearing in mind that there is spark at that cyl)
OR
Carby ( bearing in mind that the plug is wet)

Also is it normal to be able to hear water draining from leg through plug hole when exhaust ports are open? ( hearing this influenced my head gasket theory until I heard the same gurgling from top plug hole on other side of engine upon inspection for curiosities sake).
Sorry this is long winded but you'se got to have all the facts jack ha ha.
Thanks for any ideas.

 

[Bifflefan]

Re: Johnson 100 javelin low power

The compression is a bit low. But probably OK.
Id redo the comp test, then timing and a link-n-sync.
After that it may just be a tired motor or the prop has to much pitch.
You may need to prop down a step or two to help the motor out.

 

[Aardvark earthworks]

Re: Johnson 100 javelin low power

Forgot to mention in my previous post today re low power/slow to plane,
while running out through no-wake zone to outer marker with engine running at low revs that it will "pick up" intermittantly like it's running on all 4 for a couple of seconds before dropping off again.
Definately sounds electrical to me.
Your thoughts please ?
Thanks again

 

[tashasdaddy]

Re: Johnson 100 javelin low power

check spark, compression, and could be dirty carbs. http://forums.iboats.com/showthread.php?t=299680

 

[emdsapmgr]

Re: Johnson 100 javelin low power

Sound like the top port cyl is misfiring. You are probably running on only 3 cyls most of the time. (wet plug) On the occasion that the plug does fire, you said you can feel a pickup in power for a while. You can see the misfires if you put an inductive timing light on each plugwire. That engine has two power packs-each feeds the spark plugs on one side of the engine. I'd swap the two packs and see if the miss on the port cyl moves to the other (starboard) side. If so, replace the bad power pack. The compression on that engine was in the 125 range when new. I'd run a can of OMC Engine Tuner through it a couple of times and see if the compression comes up any-I'll bet you will see an improvement.

 

[bkwapisz]

Re: Johnson 100 javelin low power

I had a similar problem on mine, along with a plethora of other issues. Had a nice spark jump on all 4 cylinders, ran with a miss and some surging, then just ran low. Got it back to the to the house and realized that I had a bad wire. Corroded at the plug terminal under the boot and when I removed the cowling it finally popped out. Whoops. Gonna make new wires and make sure they don't interfere with the cownling again.

Just another thing to check I guess....

 

[oldrudedude]

Re: Johnson 100 javelin low power

Which cylinder has the lowest compression and is it the one with the wet plug?

You write a good post. I enjoy reading it. Lots of information with a little humour.

 

[coolguy147]

Re: Johnson 100 javelin low power

after you fix the spark problem id do a decarb to maybe raise compression numbers

 

[Aardvark earthworks]

Re: Johnson 100 javelin low power

Thanks for all the gr8t replies everyone.I really appreciate your help, I've been scratching my head on this for a while & can't afford to lose any more hair ha ha
I'll try the powerpack swaperooni tomorrow arvo if I can finish my current job early enough.
Old rude dude the low comp cylinder may be the one with the wet plug from memory ( been a while since I did the comp test )
By the way mate, glad you like the post. Maybe I should have been a journo instead of a digger driver
I'll let you'se know how I go
Cheers

 

[Aardvark earthworks]

Re: Johnson 100 javelin low power

Well managed to swap the powerpacks over today and take the boat for a spin,
same problem
Pulled the plugs when I got home and I've still got the same clean one although there is some evidence of it having fired ( small brown spot right at the end of ground electrode)
Even though the plug looks wet, maybe its not getting wet enough eh?
I guess the next plan of attack is to pull the carbys off and give them a thorough going over
This is getting like a soap opera.
I'll let you know how the next episode finishs ha ha