Just curious which jet you guys run with stock header and slip-on muffler. I have heard from many sources that jetting specs from back then are rich on today's fuels. So with that in mind what size dynojet you are you guys running?

 

How high is up? Same question..... Your jetting requirements are going to be different depending on a number of factors, what brand of slip on, what type air filter, what altitude, etc. The only real way to tell is by old fashioned jetting, making runs and plug reading, or dyno testing.

 

Only about 700-900 feet. I don't consider differences between slip-on's to be big enough to justify jetting changes from one pipe to another. I am running stock filter

Seems that most people say the 126's are too much for just a slip-on

 

Seems some people would be wrong too, I got my 93 F2 with a K&N filter, D&D slip on and 135 jets, and it had an aggravating flat spot right at 4K, and always seemed to sound lean. Working at it little by little, jetting up, I also wound up cutting my down D&D a few inches, and I'm now running 150s, and the bike is stronger than it's ever been, 11.20s at 118 mph in the 1/4 mile, and 7.20s at 100 mph in the 1/8 mile.

 

Ever had a A/F sniff on your bike? Still using the stock needle? My guess would be your top end is very rich as you tuned the 4K range based on your main. 150 is a lot of jet for 150cc. Make when I had the Vance and Hinds full exhaust I had DJ 122's and had a AF sniff and it was crazy rich above 9K to the tune of 11.8:1 At that point I had some real tuning issues and limited dyno time. I put on a stock header and a cut down D&D pipe in hopes of easier tuning. As of right now I still have a very lean 4-8K range. I can fix it by lowering the needle, but then my 2-4K range is so pig rich it smells and doesn't run right under WOT. I have tried using Keihn jets and stock needles. I can up the jet size and the low, mid scream, but once I get to about 11K it starts to stumble as its too rich. So right now I am stuck with this un-tunable mid-range. I spent all last summer trying to fix with no great luck. About ready to break down and purchase two hours on the dyno.

 

I've been planning a dyno run, but my dyno guy has been smokin busy. I do most of my tuning by driving it every day and racing at least twice a month. I really don't think it's rich up top, it will pull way past redline. When it did have a surge or misfire at 10K~12K, more main jet fixed it. My low end isn't great, but it's still responsive, no flat spots, even from a 2K roll-on, it just doesn't scream till about 5K. When I last changed jets, it was pretty cold, and the exhaust changes I've made have probably leaned it out enough to compensate for the warmer weather we've had lately, and seems to have moved the powerband up a little as well. It used to pull hard from 4K, now it's 5K. Here's the exhaust:




I've shortened it even a little more since those pics. My header is 4 into 2 into 1, and I've shortened the 2 pipes going into the 2 into 1 by 2" as well, and cut 2 more inches off the slip on.

 

Looks like your pipe is a little shorter

What I have learned from dyno /w many quads, and bikes is your butt lies. lol Not to say your bike isn't running great as it may be. Perfect example. I have a Raptor 700r quad. I added an intake, and pipe. Ran great, good top end as compared to other raptors. Didn’t miss or sputter at all up top. Put it on the dyno and it wouldn't run past 6K because it was so pig rich. The dyno loads it more than on the road apparently.

Anyway now that I am back on the stock header I might try the way you went. Put the stock needles in and keep jetting up. My bike is +5 on the rear sprocket and when the mid is tuned correctly the bike is a wheelie machine. When its not it’s a dog no wheelies

 

The butt may lie, but the timeslips (ETs) don't, , the daily driving helps me keep smoothness and driveability good, and the ETS tell me if I'm making more power. Started out at 11.70s and poor driveability(BAD flat spot at 4K), now it goes 11.20s and it's much more user friendly and smooth driving. I'm -1 on the front sprocket, stock rear.

 

Does that exhaust have any packing in it?

Sounds like a straight pipe

 

Yep, still got the factory D&D fiberglass wrapped around the baffle/core, it's a lot shorter though,
I fired it up with the slip-on off of it, and I promise ya, it's a LOT louder with straight pipe,