Elevation Changes and Jetting Adjustments

[troy ballard]

I have a ’89 Johnson J175STLCB V6 with a jet pump. I use it at greatly varying elevations. Steelhead fishing in the late fall and winter at 1,800 feet; sturgeon fishing in the summer at 2,800 feet, and trout fishing in the summer and fall at 6,500 feet. The engine is set up for the lower elevations and works great at 1,800 and 2,800 feet(I don't notice any difference in performance). When I go to Henry’s Lake, Idaho several times a year I get severe plug fouling and extremely poor performance and fuel economy. Can I simply change a set of the jets up or down one or two steps without having to perform a complete readjustment of the engine? The balancing procedure is extremely difficult to perform since I do not have a lower unit and prop. The mechanic that tuned it last time did a good job but he said he just took a stab at it. In the carbs there is a set of two “High Speed Orifices No. 61C”, one “Orifice No. 36”, and two “Idle Air Bleeds No. 31 upper, No. 36 middle and lower”. Which orifices should I change, how much should I change them and what adjustments are necessary when I make the changes? Your advice would be greatly appreciated.

 

[clanton]

Re: Elevation Changes and Jetting Adjustments

Upper carb,<br />low speed 31M<br />Intermediate 41C<br />High speed 57C<br /><br />Middle/lower carb<br />Low speed 36M<br />Intermediate 41C<br />High speed 57C<br /> <br />Jets for 3000/6000 feet. Service bulletin 2217 dated Jan 1990.