96Johnson 150 FastStrike Detonation?

[Josh Knapp]

I am working on a 1996 150. the problem lies at 2500 to 3500 RPM the motor sounds like its detonating. I have not had much time to look at it the other night I took it out to the water and it runs good just has that sound which is really annoying cause when you let off thge throttle you can really hear it(sounds like a rod knocking). but its been doing this for almost a year. and hasnt come apart yet. a few weeks after this started the regulator caught on fire when loading the boat on the trailer. the motor has run fine since it has been fixed, we put on a new stator, regulator, powerpack, and optical sensor. these are genuine Bombardier parts, not CDI or Rapair. I was just wondering if anyone knew a little more about these motors and could give me some insight as to whats making this noise.<br />thanks,<br />josh

 

[Dhadley]

Re: 96Johnson 150 FastStrike Detonation?

If you back off the throttle quickly on some 60 degree motors you may get a noise that sounds like a rod knocking. Its called "de-cell knock". We've taken several of these motors apart looking for the cause and/or damaged parts. Never found either.<br /><br />The "knock" can be worse on some and non existant on others. Spark plugs, fuel grade and fuel freshness are critical. Use Champion plugs only. The cooler the plug is the less the motor seems to be prone to this. Use 87 octane. Again, it may help if the owner is using something higher. Make sure its fresh. Fuel loses octane after 30 days or so.<br /><br />You can hit the primer to make the "knock" go away. We have experimented with richer mid range jets. It did have some (little) effect but that may be the "blubbering" you are hearing at 2500 to 3500 if someone has tried that.<br /><br />Obviously this is assumimng all the other adjustments are in order like timing and sinc & link.<br /><br />Let us know what plugs and fuel youre using.<br /><br />Good luck!

 

[Josh Knapp]

Re: 96Johnson 150 FastStrike Detonation?

sorry it took so long to get back to ya. I am running Champ L77JC4 plugs in the motor. as for fuel it is whatever the customer puts in. we added octane booster to the fuel and it did no good. still makes the same noise. and I dont have the boat again cause the customer took it to another tournament. i did the sinc & linc last year after I replaced all the ignition components other than the coils. it doesnt only happen when you let off the throttle you can be cruising at that RPM and hear it. we are not a johnson dealer so I have limited information on this motor, all I have is an old service manual on the motor. would the VRO possibly have something to do with this? we ordered one in and have it but never did put it on, due to the customer wanted the boat back just before we got it in. and last week was the first time he has brought it in since.just wanted to know if it may have something to do with it.. if you have any ideas let me know.<br /><br />thanks<br />josh