PHPERFORMANCE

I Just Bought Another 98 Hawk And Im Porting The Heads,i Have Ordered A Factory Pro Jet Kit .does Anyone Have A Starting Point With The Jets.also How Much Can I Shave The Heads Saftley?

JamieDaugherty

I'll have to check my notes, but from memory I'm running the 4th needle setting (next to the richest) and 180F/182R mains. I'm also running the #50 pilot but I probably should have the #45 because it's only at 1-1.25 turns out. Mine has ported heads and 0.5mm overbore. It's also got Jardine full race (the special order ones) RT-One high mounts and a K&N. It runs neck-and-neck with an RC51 down the straights at Mid-Ohio.

Hawkrider

Nice! You should try the #48 pilot. That'd probably work best for you with that exhaust and the head work.

Do you get surging at very small throttle positions? If so that's an indication of lean mixture. The VTR (at least stock) is pretty sensitive to that.

JamieDaugherty

Actually I meant #48, somehow I typed 40. Yeah, I get some surging, but only at high-ish rpms, like trying to maintain speed in 3rd at 6000rpm. My understanding is that the pilots are no longer controlling the mixture at this point. That would make sense because my pilot mixture is rich. The needles are correct and the main jets are right. I'm not 100% sure why I get the surging, but the bike runs so good otherwise that I'm not going to mess with it.

PHPERFORMANCE

its not the same bike in the pic. its got devil high mounts on it if that makes a difference?i bought the spark advancer, a factory jet kit,the bmc race filter.instead of putting the spark adv. on ,can i just change the advance with the tps?did u cut some off the heads?i have pictures, just cant get them to attach.

Hawkrider

If you're surging at 6000 rpm you need to raise your needles a notch (lower the clip). That'll richen it up in the midrange and prevent lean surging.

Jamie, actually you wrote 45 and 50. You didn't mention 40. Now I'm confused.

PHPERFORMANCE

so you think i should start out at the 4th setting with the needles and a 48 pilot with180f/1802r.i dont have the heads done yet ,but once i get it running i can put it on the dyno at work and tweek from there.i also ordered sprockets 15f/43r.i got the bike for a good deal,the motor was hurt. i just want to see what i can get out of it without spending a ton of money.any other input you have would be very helpful.THANK YOU!!

JamieDaugherty

My surgining is a lean condition, but I'm sure that raising the needle would do more harm than good. I've tried that and it makes everything else (which is 99% of the time) really bad. I think it's my airbox intake mods I've done. At those speeds it's pushing extra air in and causing a lean condition. I'm not saying it's ram air, but the concept is the same. The surging only happens at high rpm's and small throttle openings. It happens so infrequently that I'm not too worried about it. I might try a larger main jet but I don't want to hurt full throttle power.

By the way, I've got an air/fuel gage and oxygen sensor on my bike so I have a good handle on what's it's doing.

mikstr

To rectify your lean surge, could you not just vent the carb fuel bowls into the airbox, that way the presurising in the airbox would makes its way into the fuel bowls thereby keeping everything in balance (in this caes richer). I know this practice is used on snowmobiles (mind you most have non-CV carbs) and works well.

cheers
Mikstr

PHPERFORMANCE

What Did YOU Do To Mod Your Air Box? Do You Have A Pic With Your Skinz Lower Cowl?

JamieDaugherty

Yeah, that was going to be something to try. For now it runs really good so I'll probably just keep it as-is for a while.

Basically what I did was to cut out the plastic cover just below the airbox inlet to allow the cold air a direct path from the high pressure area right above the front head. The old F3's used a similar setup with their ram-air systems. This might not sound like much, but I noticed a difference as soon as I did it. The surging started immediately too. It got much better once the jetting was sorted better, now it's just a nuisance I get once a week or so.