jonand 0 Posted June 30, 2008 Just thought I'd share a recent development regarding main jet sizes. I am running a QEP S16 / Mi16 hybrid engine with catcams, forged pistons, 12:1 compression, megasquirt management and R1 carbs on my grass racer. I had been suffering a high end misfire since fitting the engine, which seemed to be getting worse. So I had it on a rolling road session for a diagnostic analysis last week, and was suprised to learn that it was greatly overfuelling from 5000 ish - causing the misfire. I had fitted 185 jets initially, as the general consensus was 175 ish for a std Mi16. The RR session eventually concluded that 160 was right for my engine which still just started richening at 7000rpm (safety factor). I have now competed with this new jetting, and can certainly confirm that the misfire has gone and that the performance is MUCH better. It is also worth noting that float levels seem to play an important part to this scenario - as the (Yamaha) factory settings no longer apply due to the angle the carbs run at. As a footnote - the RR operator was most complimentory regarding the ignition setup, as he had never before had an engine running under load with such a rich mixture (lamda 0.62 from memory) Jon Share this post Link to post Share on other sites
