Input needed for jetting on an 86 250R with some modifications

[250rBeast]

I am about to add a few aftermarket performance parts to my completely stock 86 250R. This machine is nearly 100% stock save for the twist throttle, it is also a very low hour machine. I stopped by ESR last week on my way home from work and picked up a billet o-ringed exhaust flange as well as placed my order for their 310 powervalve cylinder. Now this weekend I plan on installing the ESR airbox eliminator k&n filter, the ATC5 pipe and silencer, along with the V-force reed valve system. Also going to install some NOS +3 Nasa wheel spacers and a NOS Nasa front fork stabilizer. My question is what type of changes should I expect to make as far as jetting is concerned. Right now it has the stock 145 jet, I went and purchased the 155, 160, and 165 jets. Also I picked up two pilot screws 45 and 48.
Please, only responses from experienced persons and not from people who think or speculate without actual knowledge of the subject matter.


Thanks for your time and Merry Christmas to everyone. Allan

[mike from long island]

i am not a master mechanic but i would think that the kit would include directions for putting the correct jets in. when i installed a set of t-5 pipes for a banshee they needed to know my zip code for the elevation and all. they sent three sets of jets with the pipes. i went with the middle set and have had to change it yet. your best bet might be to ask some one at ESR. good luck.

[Dammit!]

Every bike is going to be a little different but, to give you a place to start, I was running a 160 main in my R. At the time is had no airbox lid, K&N filter, FMF pipe, ported.

[deathman53]

unless you do only sand, don't use the airbox elimator, also, the 310 pv you might have problems with it fitting, and if you have a 85 plan in grinding the frame rail above the in a groove to make putting in the plug far far easier, you got a carb??? a 310 kit won't perfrom to its potential without a 38 a/s or 39 pwk, also you should have got a temperature gauge for the coolant, big bores can run hot. I would start at a 170 for a 310(really 295), if you are ditching the airbox, a 180. I use a 170 on my 310pv with a cr ingiton, 39 pwk, paul turner pipe and aluminuim airbox. I also use boysteen cr 250r reeds with a 1/2" spacer. you shold upgrade your reeds also, to a boysteen or v-force cage.

[250rBeast]

Thanks for the suggestions thus far. Now I do realize that come the PVL cylinder, I will encounter more major changes concerning jetting and tuning. For now all I am wanting to know is some jetting advice with all the other mods I mentioned, the airbox eliminator, ATC-5 and silencer, and V-force reed valve system. Eventually when I do install the PVL set-up, I plan on upgrading to either the ESR/Mikuni TMXX 41.5 carburetor or the Keihin 39 PWK. I probably will not run the PVL cylinder until I find a good extended swinger. Someone mentioned that I should run a water temperature guage, I already have the ESR billet water temp guage. I plan on riding mostly dunes with this bike with the occasional trail so the airbox eliminator is going on along with the outerwear cover. I'll submit some photographs of my bike later tonight. Thanks again for the advice. Allan

[Dammit!]

By the way, I have one of those airbox eliminators and it does not fit very well. They might fit fine on the quads but on my trike it looks like I'd need to cut one of the airbox mounts off the frame to make it work and even then I don't think it would fit right. If you haven't bought it yet, save your money. Hell I'll sell you mine if your dead set on having one. There's no performance gain versus just running without a lid.

[3Razors]

I say keep it stock and original. Unmolested 250r's look awesome and are worth alot more $$$. Clean original R's are tough to find!!