Johnson 120HP

[knuuttila]

Just recently I,ve noticed my engine is only running on 3 cylinders. I,ve found out which one is not running and changed the sparkplug, put a new HT lead on it and still it is not running. There is a spark at the plug, and when I remove it, it,s wet, so I guess petrol is getting to it.<br />Can anyone suggest anything else to check?<br /><br />Rgs<br /><br />Brian

 

[promotec]

Re: Johnson 120HP

Hi Brian<br />The next logical move is to check the compression as this will give you an idea of any physical damage within the cylinder, check all 4 cylinders and youll get a comparison, chances are pretty good that the cylinder that wont run is going to be lots lower than the other three if not then it may serve to eliminate physical damage from the cylinder, also note the colour of each of the 4 spark plugs, post your results back on this thread and it will shorten the distance to understanding where your problem lies.<br /><br />Kind regards Chris

 

[tvpear12]

Re: Johnson 120HP

Fire,Fuel and compression are the 3 ingrediants,<br />you are missing one of these.<br /><br />plug colors are as stated.<br /><br />Black-rich<br />White-lean<br />Tan-just right

 

[knuuttila]

Re: Johnson 120HP

Thanks,<br /><br />looks like a compression test is next.<br /><br />Rgs<br /><br />Brian

 

[R.Johnson]

Re: Johnson 120HP

When you say you have fire at the plug! how stong? If it's just jumping the plug gap, thats not enough. It should jump about a 7/16 gap.

 

[Walker]

Re: Johnson 120HP

Might try running it at night to see if you have a spark leak on the bad cylinder. Just because its firing across the plug gap doesn't mean its firing inside the cylinder in the compressed atmosphere.

 

[knuuttila]

Re: Johnson 120HP

Dear Walker, you got it right.<br /><br />There was sparking along the whole body of the plug.<br /><br />It was a new one, but I replaced it with a good old one, put plenty of grease around it and problem solved. A new one on me.<br /><br />Cheers<br /><br />Brian