All 2st Jetting Chat - Need Help? Post Your Questions Here

Can it gummed up even with VP C9 storage fuel wihich I use exclusively on my bikes? It does not contain ethanol.

Have just had delivered my pwk 38 AS (thank you motorhead) and have no idea on how to jet to my bike. I have a 2004 WR250 fitted with FMF gnarly exhaust with standard tail pipe and use 97 rom fuel at 50:1 mix and am in jolly old england so is at sea level or there abouts and cold!!!
Am looking for a basic set up then i can fine tune from their. Any help greatly recvieved.
Thank you in advance

Find out what jets/needle are in it and for starters and report back. Do you have any extra jets available yet?

Jetting , what is that says Lectron

Right I have no jets in the carb but do have what i think is a jd jet kit comprising of Blue, Red needle a 45, 42 main and 178, 180, 182, and 185 main. What would be a good starting point?

I think James will send some instructions along with the kit to get you started. Don't be afraid to experiment with changes. I had a JD kit in a KX I had and it ran really well.

The bike is fitted with a stock tmx so would i be able to check and use like for like jets that are fitted to that?

No the Mikuni jets are different. I would just put the carb on your bike and see how it runs...

Just got back from a trip away and really want to get this carb on. As it has no jets fitted what one would you recommend fitting to get started?

Those are really big main jets you have. I would start with the 45 pilot, 178 main, and blue needle with clip set on third position.

any thoughts on jetting a 99 360 wit a 38TM Mik and an FMF Gnarly?
I will be riding 3000' to 7000' mostly about 4000 -5500' and lot's of single track
also taking a 93 360 same set up, just they are ported a little different but guess same jetting?

How should I rejet for an elevation drop of approx -350 metres?
Without rejetting would this result in a leaner or richer condition - i'm guessing richer?

This would result in a leaner condition

Really, higher elevations have less air density than lower ones - at high elevations our engines are getting less air, so they need less fuel to maintain the proper air/fuel ratio?
What would I experience in terms of performance change if I rode descending through the entire elevation change without rejetting?
Also, how would going from a stock exhaust system to a less restrictive exhaust affect jetting?

If you drop elevation it will run leaner because it is set for the higher elevation with less dense air. You will be at a lower altitude with more dense air therefore you will need more fuel. That being said a 350 meter drop won't drastically effect it unless it was already set on the lean edge at the higher altitude.

Ok, nice - getting there!
And the prevailing logic is that 'breathier' pipes also tend towards leaner condition?

Yes, the engine is basically a pump. The easier it is for exhaust to get out,the more air it will draw in.This may require slightly richer jetting in some cases.

Any circumstances where a 'breathier' pipe would result in a richer condition, for example reduced back pressure?

How jetting relates to a pipe is way more complicated than wether it "breathes" or not. The topic of pipe design would need it's own thread. As far a jetting relates to a pipe change it's best to give your bike what it wants by riding it and adjusting the jetting until it runs it's best for you. You can look at other's feedback and post your feedback to help others.

If you really want to understand what pipe changes really do, here is a link to get you going. http://www.google.com/search?q=2 st...9GsegyAHSiYGwBg&ved=0CEkQsAQ&biw=1635&bih=941

Ok, thanks ..
one more thing ..
I have been reading that compared to an exhaust change, which is often little more than a placebo effect, a 'breathier' air filter will have significantly more effect on air/fuel mixture, again tending towards a leaner condition?