Jetting chart

[GMP]

The stock jetting on my 300 has been as good as you can ask for in moderate to high temps at 0-1000' with just a tweak of the air screw. Its been warm here in NJ and still is in the afternoon(over 60 today), but cold is due in this week and I have a race 10AM Sun. Figuring temps in the low 40s at the start. Being I have no time to test especially at the lower temps, I'll have to go by the AM Beta specs and hope for the best. Some sand, so I do not want to be lean. Any experience or comments?

[Enmerdeur]

No Beta specific experience (not yet at least) but I would go one step richer on the main and needle to start. Should not have to adjust your airscrew more than 1/4-1/2 turn to compensate on the idle circuit.

[GMP]

Thats exactly what I have done, thanks. I was just wondering if the AM Beta specs in their altitude/temp chart were actually tested or just extrapolated from the basline settings.

[Timber]

Where can I find the AM Beta jetting chart?

[GMP]

Here you go:

[dirtbird]

.... and for the 250 as well.

2013 250 RR Carb Settings.pdf

(55.34 KiB) Downloaded 778 times

However and for the really fast riders it is recommended to jet richer than that.

During the EWC race in Greece on past June (with temps close to 40deg C - that's more than 100F) and 1000-1500 feet altitude, the Beta teams (Factory and Boano) were running 38-40 pilot and 170 main, i.e. quite rich. KTM and Husa factory teams was using similar jetting and you could see the riders 'cleaning' their engines as they were coming form the connecting stages and before entering the special stages.

The reason was that during the SS, top riders were using WOT (actually only the one SS had big straights, the other two were a quite tightEnduro test and a very tight Extreme inside the town) as much as they could and the engines would overheat with normal jetting.

[GMP]

Well, here on US fuel by this 55yr old mortal, not the slightest hint of being lean. Its really spot on by all indications, so not much room to wiggle when it turns cooler. I also don't want to go too rich because I can't afford to wate fuel with that 2 gal tank. I put the N2ZW in at #3 with a 168 main, left the 35 pilot. I can run it around the field a bit in the AM before the race and adjust if needed. I also have the half clip variants(N8RJ, N8RW) for fine tuning as well as the NED/NEC series. Its very easy to access everything for jetting changes, no tank removal required.

[Timber]

Here you go:

Cool. Thank you. With california fuel I was never able to get supreme unleaded to run clean even with the 35 pilot. I checked the squish on mine at about .080" so I might have been able to use a lower octane fuel to get it to clean up. What are you using for fuel?

[GMP]

Pump 93 with 10% ethanol here in NJ. I treat with a healthy dose of Startron and let sit for a day or so before mixing oil and use. So far so good. This is the first bike I've had in awhile that I did not feel the urge to have the head cut ASAP, I know what you mean. I haven't even measured compression yet, which I should do.

[Hawkeye]

Glenn, I run 50/50 mix of BP 91 octane premium and Sunoco 260GT race gas that I get from my local stock car supplier.

Here's a link to Sunoco's website page on 260GT, it is 110 octane unleaded. http://www.racegas.com/fuel/20

I run this mix in my 300RR and all of my two stroke bikes (even the kids'), because of storage and carb varnishing issues (headaches) I've had in the past and also that my YZ250's motor was built for this 50/50 mix. I am really happy with how long I can leave this cocktail in a bike or in the can and not have any issues with clogged pilots or surging or pinging. Well worth the $7.50/gal for the 260GT in my time alone, not to mention performance. Forgot to mention that in my PM about jetting, as I imagine my motor is running cooler than those on pump fuel alone are under WOT or heavy loads.