Q: Hi guys and I hope you all have a great holiday because I’ve enjoyed your site all year so keep up the good work in 2019, I’m sure you will?
Anyway back to my question. I own one of those Honda FMX 650 Supermoto fun bikes from around 2007, I believe. I’ve owned the bike for many years and it’s never given me any problems. However, it’s covered in a ‘thousand’ pipes surrounding the engine in the name of reducing emissions I suppose, and I like to take them all off.
I’ve been told this will increase power and living in Jo’burg, at altitude, it also needs a jetting change because the plug seems to run ‘black’? So is this correct and what sort of jet sizes should I be running to get a bit more power from this old 644cc single? The bike also runs the stock air box and exhaust (filter is clean), in case you’re wondering.
Thanks for your time and don’t get too ‘hammered’, which I’m sure you will.
A: We’ve taken all this emission pipe work garbage off before and on the dyno it makes no difference at all to improving power output. The only advantage there is it tends to save a few kilograms of weight. So we wouldn’t bother unless you desire a less cluttered engine to look at?
Regarding jet sizes we tend to drop the size by around 7 to 8% for our 1500m altitude. So take out the main jet and see what the size is, it will have it engraved/stamped on it, and drop accordingly. We also recommend some sort of less restrictive exhaust because the stock twin cans are also very restricted for emission control. They could also affect jetting so try to do that first and check the plug colour as this could lean the bike off considerably.
Hope that helps and thanks for the comments and have a superb holiday too.