To rejet up or to rejet down that is the question!
 

Oh the pain of it all, ok i recently bought an f2 1991 with a micron full system and movable clip position needles (not sure of make) i presume stock main jets (135) ive put a ramair filter on and changed the plugs, so here are the problems im still having:

1st gear pulls fine no probs, all other gears at low speeds at 2500k revs open throttle bogs down under load, past this pull hard all way to redline, at cruising speeds above 30mph seems to be hunting or hesitant up to 80mph then cruises fine ( not that i go that fast ;) ) there is a throttle pause when round country lanes giving it a bit, i can eliminate most of this pause by changing clip positions but it makes the bogging down worse, ive eliminated a lot of the bogging by replacing the standard air filter with the ramair, even tried with no filter for a short run ( i know, naughty naughty) this didnt cure the problem so i can only conclude the jets need altering or the coils are breaking down maybe. Carbs are syncd and air screws have been tried in various positions, tthey are now at 2.5 turns. The question is do i go up to 140 mains and if so would i need to change the pilot jets or do i go down to 130s.On the plus side I am now very very good at removing my carbs in under 2 minutes flat HaHa. Thanks for any info.

My eyes decieve me (or i was hungover) the mains are 138s so im going to try some stock 135s. Hopefully will cure all ails!

If you're pulling hard to redline after 2500, then your mains are not your problem - they don't take over fueling duties until around 7000 to 7500.

What you need to determine, is whether or not your pilot circuit is too lean, or too rich... am I right to assume that this ramair filter is a hi-flow type filter, like the K&N? If so, and you have a full race exhaust system, then your top end will possibly suffer when dropping back to 135 mains.

I'll give you a for instance, but bear in mind, even bikes of the same year/model, with nearly identical mods, have subtle differences, and of course, there is the atmospheric affects of elevation.

The Factory Pro jet kit supplied me with 138 mains, for hi-flow air filter, and slip-on, along with the aggressively tapered and adjustable jet needles.
I run a K&N filter, regularly cleaned and oiled, a race header with a shortened Yosh RS-3 CF muffler, and stock cams and timing - the 138 was insufficient, and the issue was that I was still very lean.
I ended up going to 142 mains, stayed on the middle needle clip position with the original shim, and 3 turns out at the pilot screws, and it runs like a scalded dog.

If you've got 138 mains, and everything above 2500 is fine, I wouldn't mess with that, but then again, you could experiment with 140's, and see if you get even more top-end power (roughly 7500 to redline).

The key is working from the top down - don't make multiple changes at one time - get your mains dialed in, then play with your mid-range (needles), then finish with your pilots.

Oh, I didn't mention - the pilot jets themselves are the original 38.

Good luck! :icon_beerchug:

Great info, thank you, I'm not to concerned with getting more power out of it I just would like the darn thing to run smoothly! The ramair is hi flow yes, yes the pilots are stock, maybe then its them also that need changing up too if I get bigger mains.

Well I went down to stock 135s moved my clip position to #2 set air screws to 3.5 n its sweet as a nut, I've lost a only few hp but nothing drastic, I'm happy :)

Wah wah wah wah!!!!!! I thought id sorted this, i took it for a proper blast a while back now and low and behold now above 7k it chugs and splutters and labourers to get to redline if it gets there at all, so i did some altering and messing about with the clip positions tried some new mains and got some bigger pilots, here are some of the results.

Clip pos #2. pilot #40 main #142. Pulls great all throttle positons 1st gear, 2nd gear ok to 7k splutters and coughs other gears fine to 7k sputters etc.

Clip pos #3 & 4 pilot #40 main #142. 2.5k wide open throttle splutters coughs to 3k then kicks in to 7k less splutter but still not ideal.

So obviously the aggresive taper of the needle is messing with my mind, should i go to #150 mains so i can stay on clip #2, would 150s help in the top end given the leanness i require in the low range, there is no more hestitation at cruising with the bigger pilots now but i just cant seem to strike the balance!!! The force is not with me!!!! :icon_no:

An afternoon spent on a dyno would be infinitely helpful to you. Seat of the pants feeling of fueling ratio is deceptively difficult.

Well i put the 150s in with the 40 pilots on clip pos 2 and its ten times better, no bogging down low range and pulls hard to redline 1st 2nd 3rd, 4th stutters a bit but then totally leans out, i could move up to clip pos 3 this would cure it but i know id get bogging low range, so up to 155s i go!!

Went up to 160s stayed on clip pos 2, this gave me the full range without any gremlins........however......normal razzing about is great it goes like s*#t off a shovel every gear to redline but when im motorway riding/cruising at about 7.5k+ all is well for about a mile or so then it feels like its being starved of fuel, if i go down to 6/7k it settles and all is well again till i rev back up then after a mile it does the same, can i assume having the much larger jets has imbalanced the fuel circuit and would an electronic fuel pump solve this. Any suggestions please otherwise im gona throw it off a cliff (not with me on it)!!!