I posted this over on ADVrider but as their seems to be more traffic here I wanted to post my questions here.

I just finished having the 351 kit installed on my completely stock 250. Along with the 351 kit I also had

- BB's 34 mm pumper carb
- Barker full system exhaust from Bill made for the 351 kit
- SAS/smog stuff removed; Bill's block off plate installed
- stock snorkel replaced with KDX snorkel
- New timing chain, exhaust valves.

The difference is amazing and I love it (except for perhaps the increased noise.)

I have 2 issues though to get dialed in:
1. The header/piper is really hot. I burned a hole in my pants today and have never done that before. The pipe is thicker though/appears to hang out a bit farther with a smaller heat shield.
2. It coughs/hicups/sputters in the last 20% of the throttle. I used to ride on the freeway with the throttle just pegged; it was weak but smooth. Now the last little bit seems to hic up a bunch.

I'm guessing my jetting is a bit off? Any suggestions on which direction I should go?

Thanks!

Rick

 

Pull your plug and see what it looks like, sounds like you are running lean.

 

You might post the size of your main jet, I don't have your set-up but if you put it out there someone might chime in with their sizes. At wot the main jet is probably where to look first, maybe lean maybe rich, both will affect how clean it runs.

 

Also pull your airbox lid off and see if it's better or worse, better your rich worse your lean.

 

did you make all the changes at once?

 

Sounds lean for sure. I wouldn't run anymore until you go up a couple sizes on main jet. Might get expensive...



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Thanks for all the input guys! Embarassingly I don't even know my main jet size; I spoke with Bill Blue for a bit on the phone re: our weather here - riding conditions usually in the high 80's to mid 90's F temp with 70 -95% humidity and he said he'd try to set the carb up close.

I am a jetting virgin but I knew I'd have to get in there and dig some time.

Redpillar - yes I had all the changes done at the same time. It was almost intentional to try to "wow me".

I'll start with the plug as I know how to do that.

As far as performance I haven't done the test yet but I'm guessing it will accelerate 3X faster between 50 - 65 mph. I'm sure it's 5X faster in accelerating between 50 - 70 mph but that's because it used to take forever to climb from 65 - 70 mph. (And infinitely faster in accelerating ON THE LEVEL between 50 & 80 mph as it could not do 80 on the level before and can now.)

I mention those #'s as they are important to me when I am riding on our crazy freeways here. Unlike 1st world countries we have tractors/loaders etc on our nice freeways along with Ferarri's. Being able to pass a big, slow moving vehicle quickly is uber important to safety.

 

Don't be intimidated about working on the carb jetting. Many on here can give guidance.

If the bike is surging at high rpm under load (on the highway) there is a real chance you are lean enough to melt a piston.

The spark plug is probably going to be very white/clean looking.

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