BannedCR500Riders.com

Gettin worked over by this on an '01. Has a low RPM miss at 1/8 throttle, blowing back lots of premix into boot. Black plug, putting down too much carbon. No spooge. The miss fades away with increasing RPM. Can not cure w/ jetting - tried it all. The motor rips everywhere but has that little stumble when rolling on.

What it is: '01, EG port, Gnarly, turbinecore, stock cage w/ boyesen super stocks, 927 @ 36:1. 6000' elev. 42 pilot 168 main #6 slide & a variety of DGx needles.

What done so far: Jetting, crank seals, reeds, service silencer, check intake/filter setup, replace carb w/ new PWK, replace coil, inspect entire electrical. Since the motor had been modified some I sent it off for a reliable-type port job/head work so I knew what I had at least. No sign of any bottom end leak. Reeds/cage look perfect.

Not sure where to look next - reed spacer, different pipe, different reed block? All my bikes have had some blowback, but what I got here is too much. That & the 1/8 miss related? Too much black in the cylinder to live with as is. What m I missin?

I've never run into fuel blowing back before, maybe I'm lucky.
Just my thought here, but when I lived in Calgary at 3500 ft, people said to cut jetting back 10%. It's been a lot of years, but my main was maybe a 154 or 156, can't remember. I know the bike ran well and had good plug colour. Based on that, your main is maybe a little rich for that elevation, but at that throttle opening that's a little early for the main jet to have a huge effect.
Maybe Roostius will check in tomorrow morn, pick his brain.

vf reeds? they're the worst.

They all have reversion like this. The Ron McCord Pulse Injection system captures this reversion and re-introduces it into the intake charge, kinda supercharging.

Gorr and many other porting guys make everything to flow inward better, that just means it comes back as easy, its the reversion that needs to be addressed, my portwork is based on correcting this.

Quite possible it's in the porting, the motor had " trail port " listed when I got it - which I think is code for " I mightta ruined it ". So the cylinder is not ruled out - even though I thought EG gave it a clean bill of health. I'm thinking there's something else at work - always had a prob. since I've owned it.

I hear ya about a port job to fix the port job, if I sent it to you you'd be the 3rd guy in there. Wanna rule out everything else first though.