Does anyone know of a good guide for cr80rb with Mikuni carb jetting for various temps, altitude, and pressure for karting and c12 fuel?
I’ve found apps for moto, but they are for the stock carb, etc. Lots more for 125’s of course, but that does me no good. A simple chart would be fine with me.
Thanks in advance!
Honestly 80’s can be such a mixed bag I’m not sure a chart would help.
Best I can advise not knowing the exact build you have is find a baseline for your setup…
Run a higher octane racing fuel. For sure 98 MON or higher.
Acquire an air density gauge of some sort.
Start with a big main and work your way down.
@NSEWnoah might be able to give us an idea of what a “big ass jet” looks like in an 80. I can’t remeber.
Fuel is VP C12, so MON is 108 (before oil - honda racing at 32:1). Kart and engine were previously raced in California, prepared by Kartspeed Motorsport. Conditions yesterday at race time were:
Altitude: 750 ft
Temp: 85 F
Pressure: 30.17 Hg
For yesterday’s race I started practice with a 180 main, then went up to a 190 which had better lower end torque. Engine head temp shows 150 on the Mycron (but the laser gauge shows about 143), which is what I was initially trying to lower to about 125 with the jet change. No change with that though, so I will straighten some of the bent fins and add ducting to the radiator for next time.
I’ve never run head temp on a watercooled, but I can say that you’re shooting for 120-130F water temp for ideal performance, but you’re really looking at adjusting that with cooling system, vs jetting. Unless you’ve got too much ignition advance, then you will want to address that too.
I’d run closer to 24:1 oil ratio personally, anticipate going up in jet size to compensate for the leaning effect the extra oil will have.
Have you reached out to kartspeed at all?
@KartingIsLife I prefer the Keihin on my 80’s that I build, however I would think somewhere in the 220-280 range for mikuni mains?.. again depends on the build etc etc etc
I received a response from kartspeed saying that they no longer have any information on those and to ask a couple vendors about mixture settings.
Temperature, I worked over the radiator straightening some bent fins and will be using ducting for the upcoming race on Sunday. Should help with cooling significantly.
Water wetter will help bring the temps down some as well if you’re not using it already.
145-160 head temps are normal for water cooled engines running around 125 degrees of actual water temp. You will find the head temp goes they bigger “swings” over the lap that the water temp itself.
Thanks for that info. I was told that the head temp should be around 125, so that’s great to hear.