I've got an '03 Predator that I just got done rebuilding. I've been working on engines for a few years now and have rebuilt many 2 stroke engines and 2-3 4 strokes so I definitely do not consider myself an expert. With that said, I have very little experience with mods. I typically rebuild my engines to stock specifications, with the only exception being that I will ocassionally bore the cylinder over a bit depending upon what is needed.

When I bought this predator, the engine needed a rebuild. The vehicle came with a Yoshimura exhaust from a crotch rocket. The guy that owned it before me, modified the pipes to except the muffler. It sounds wicked when its running so I kinda like it. the problem I'm having is I not sure I fully inderstand the impact of modifying the exhaust. I believe a less restrictive exhaust will effect the performance, but the only thing I can figure is that it must place less back-pressure on the exhaust valves and in turn, the combustion chamber, but I could be way off. I've completely overhauled the carbs and do know by looking at the jets, that the jets are stock. I suspect that it should have been rejetted when the exhaust was replaced. The reason I suspect this is that after riding the ATV for a minute or two, the engine wants to start screaming. To me that would indicate that the fuel/air mixture is not correct, it seems to be running lean, which I suspect may be connected to the less restrictive exhaust. Can anyone that is familiar with rejetting and mods lend some advice? This is outside my realm of experience. Also, I know I do not have any air leaks in the engine, I have done a leak-down test as well as a compression test and both are within tolerances.

Any advice would be appreciated.

-Always learning!