Originally Posted by christian.hess
do you want me to show you the page where johnson SPECIFICALLY says this is so Im not arguing...I agree....the bes way is to change carb completely however on some engines, specifically the one I mentioned
the johnosn 9.9 and 15 series its simply carb jet size and manifold...NOT CARB
Like others have posted before and have experience in this(I restore motocrcyles too) you can absolutely depending on where adjust your jet sizes for performance where you need it(most carbs come jetted for sea level naturally) if you are in a lake up in tahoe it makes sense to do your due dilligence and rejet...
the correct jets however are almost NEVER installed in your carb, especially if you live in countries like the good ole use or europe where epa and other nuissances DICATATE what power and emmissions you can get from a certain engine especially when its sold commercially to major areas.
so i disagree...but thats ok...to disagree....
this also comes from experience in small engine rebuilding...on water and off
for example most carbs especially on motorcycles these days have specific kits called smog block off kits, evap removal kits or in some cases even pilot jet cap removal kits as some carbs are soooooooo EPA compliant that they wont even let the owner fine tune the slow jet for easy starting depending on your altitude and climate
lets not even go there...its very easy to get a little more oopmh from these simple engines...especially once you have propped right
here is another tidbit
saying the jets that come with all outboards are perfect makes no sense...especally since many dinghy outboards for example used at idle when they were designed to run at wot or 3/4 foul plugs up naturally, especially if 2 stroke and hence why most older outboards had nice rich lean knobs to fine tune your idle mixture
if yo were a diligent owner you did this every time you started and stopped the engine
not here to argue just offer my point of view...and experience
Not even close to being an expert on anything, but do have 30 years of experience with off road motorcycles, nine of them, two of which were 4 strokes. About 66 years experience with outboards, ten of them, two of which were 4 strokes. Changed a lot of jets, primarily because of altitude changes.
Last 2 stroke I had with an adjustable high speed jet was a 1959 50 HP 2 stroke Evinrude. Anyway, what I found, in general, was that the factory installed jetting or setting, was spot on at sea level.
My last 4 stroke motorcycle, a Honda 200, ran perfectly at sea level but loaded up at 6,000 feet. A lower restrictive exhaust system was the only thing that solved the problem, re-jetting helped a bit more.
I think that if there is something wrong with the OP's motor, the stock jetting would the last thing I would try changing. The 6HP 4 stroke Tohatsu I bought a year or so ago ran perfectly right out of the box, both at sea level and at 6,000 feet elevation. Don't know how many props the OP has tried but Pvan1's suggestions on props is where I would start.