1988 Johnson V4 90 hp carb idle jetting

[rcrowell]

I've read several comments regarding service bulletins for plug gap changes, .040" to .030" (Dunk); and and that with "todays gas you have to rejet the carbs to not run lean"(Dhadley). I would like to know if any mechanics recommend opening the fixed idle jets from .034" to a larger size with a number drill (.040" or .045")?? <br />Also, would changing the plug gap from .040" to .030" significantly change the resultant ignition timing?<br />Is there a means to acquire all of the technical service bulletins for a particular engine? I purchased the factory manual and parts book from the dealer. <br />Thanks for all of the great info!<br />-Rich

 

[rcrowell]

Re: 1988 Johnson V4 90 hp carb idle jetting

bump

 

[Dhadley]

Re: 1988 Johnson V4 90 hp carb idle jetting

As the fuel changes its not unusual to have to fine tune a particular motor. X dimension and back pressure have a lot to do with it. Many times we see a certian motor that has a lean "sneeze" at idle and when all else is OK, rejetting is what cures it. Remember, motors are calibrated for the fuel thats available at the time they were produced. <br /><br />I have very rarely seen that going leaner on the idle jets as much as you are suggesting helps anything. If your motor is running that rich at idle we need to look at other things first. <br /><br />Yes, we also change the plug gap but its mainly for higher RPM's. Once you get above 7000 it starts to make a difference. <br /><br />I am not aware of any data base available that deals with particular engines on particular boats. Most of us deal with fine tuning as it comes up. <br /><br />One more thing about jets, I personally dont like to "drill" jets. I know in certian cases (high speed jets on high RPM motors) we have to ream them but I prefer to change them. That way the ID stays the same and could avoid confusion later. Especially if you have a couple hundred jets in your collection. Or if someone else works on the motor it can be very misleading. <br /><br />Good luck!

 

[rcrowell]

Re: 1988 Johnson V4 90 hp carb idle jetting

Dhadley,<br />Your comments are well taken, especially concerning the drilling vs. the i.d. on the jet. Thanks for the reply!<br />My rejetting experiences have always been on high speed jets, but have read some comments about fuel changes over years and curious if anyone has found performance "corrections" by rejetting the low speed jets. <br />I am also curious if one can get on a mailing/e-mail list to receive technical service bulletins that would have been published for particular engines after printing of the factory manuals. <br /> - Rich

 

[Dhadley]

Re: 1988 Johnson V4 90 hp carb idle jetting

We have corrected idle problems with rejetting the idle circuit many times. I am still curious why you want to go so much leaner on your idle jets. To be honest, thats pretty rare if the fuel delivery system is in otherwise correct order. What is it that your motor does or doesnt do that you are trying to change?<br /><br />As far as a technical exchange, it seems this board (and others like it) is a pretty good one. Here we can deal one on one with each boat/ motor combination as needed. To print something that covers your motor in every possible situation (on a bassboat, pontoon, barge -- transom mounted, jackplate mounted, bracket mounted -- commercial boat mounted in a well etc) would be massive and Im sure no one would read it all. Most everyone here tries to pass on as much good info as possible that pertains to your particular question. <br /><br />Let us know more about your problem.