Jetting woes *headslap*

So I've been playing around with the jetting on my customized 94 vfr..... I have a K&N and a slipon exhaust. My first and only attempt so far was ordering a Sigma jet kit. Basically you write them with what mods you either have or are planning to run with the jet kit and they send you the appropriate sizes. Not foolproof obviously but it ended up being pretty close. The kit had #42 pilots all around, with 132.5 mains on the front cylinders and 130 on the rears. To balance this I was running with two extra needle shims per cylinder. Stock comes with one shim each needle (or at least mine did), so that would make a total of three shims per cylinder, This was paired with running with the snorkel off of the airbox, so I was utilizing the extra cfm's the proper way. Everything was 90% awesome. The noise the airbox makes is addicting and it pulled off the line like a vtwin. Smooth roar all the way to redline. Heres where it got tricky......I was having a problem that my local tuner shop told me was the bike running too rich. Basically the bike would be fine 85% of the time but then it would flood a bit and would run crappy for about 15 minutes until i burned off the extra fuel. This would happen at random and especially if i was really pushing the high rpms alot...it would just start running like terd. So after hearing what the shop guys said ive returned the jets back to stock and also the needles.....now the stock flat area mid rpm's is REALLY ANNOYING...and it didnt used to bother me that much...but now i know how hard the bike can pull when its opened up...so im only partially satisfied with the bike now and thats no good. Im feeling like I should have just popped one of the shims out per cylinder rather than knee jerking it back to stock...since the tuning was ALMOST perfect before...but I cant have a bike that randomly runs rich right when you want it solid. What to do!!:uncomfortableness: The kit actually came with 2 135 mains..in case i want to run 135's on front and 132.5's on back......but I'm not enough of an expert to know if my problem was too much fuel or too little air......i certianly dont want to pay the shop 400$ for a full carb tune...they dont blame me either...lol

Please experienced guys only....newb speculation about jetting wont help me at all...lol

 

I don't know off the top of my head what the stock set up is on a 94, what is stock pilot and main?

 

Mine is 40 pilots, and 125s. But I've heard of others being different

 

I have jetted more than my fair share of gen 1 and 2 and have been wanting to change the jetting on the 94 I bought for my friend as it could use it, I was thinking of going up one size on each jet and one shim on each needle with the snorkel in. That is the most I would try oot of the gate as a little is a lot when making changes to jetting and we have altitude changes to consider, 6-8 thousand foot change is normal for day ride . I would never use an after market needle unless it was an FCR carb, they just tend to be way to aggressive.

 

I was thinking since everything was so spot on except the richness, that maybe just going back to the same setup but dropping 1 shim might be the answer? I still don't quite get the airbox flow to jet size relationship. If the jets determine the air...why does the airbox opening matter?

 

The jets determine mixture at full throttle and the needles & shims control mixture at part throttle. So if it's too rich and fouling plugs running WFO, try smaller jets, but leave the shims and needles alone if the midrange was working well. On a lot of bikes, shims are all you need to wake them up. The manufacturer often jets them rich on top to save valves and pistons, and they don't need more gas except at low to mid throttle. As always, YMMV, your bike is different from mine, etc.

 

Yeah Ive had similar thoughts....maybe keeping the stock jets like now, keeping the snorkel in, and trying just one shim per needle this time...so basically stock with a bit extra gas to richen up the midrange flat spot that Honda put into the bike for sound reasons. I got really attached to that airbox roar though...lol. I put my quieter pipe back on because my non baffled 11 inch pipe was loud.....like track loud. With my "quieter pipe" on...basically the same pipe as the short but stainless and a few inches longer...the combo of the airbox roar and that was super nasty and tasteful at the same time.

 

Kind of funny Ive been riding it stock for a weekish now. When its 90+ degrees in atlanta it tends to run a bit lean with the stock jets but nothing too bad...as soon as it drops back into the 80's and below it really rolls smooth. Honestly I notice far more of a difference from going a tooth down on my drive sprocket than the jetting did. Im trying to decide if its worth even messing with anymore for theoretically 1-2hp. Some of the feeling could have been placebo affect from hearing the airbox opened and not actual horsepower. Food for though

 

I have two gen 3 bikes, both with stock needles and jets/pilots, un-molested air boxes except for removal of PAR junk. One bike has .02 shims under the needle, other does not. Stock jetting is 130 with pilots being 40 (I think.) Never saw 125 as mains though, both of these bikes have K&N filters too, with one having a slip-on. No seat of the pants feel differences mind you, plugs looked nice, as do the tips of the exhaust pipes (not too much black soot.) Bike withh the shims does do a higher top end, not as smooth as thea ones without, neither has been on the dyno and the one with the higher top speed has a bazillion miles on it. Just some food for thought.

I had a NT650 that I use to experiment with jetting on with different jets on the front cylinder compared to the rears. Used to run it without an air box lid too, it had a full right hand exit exhasut, loud obnoxious bike too. Bear in mind, it was a second hand bike that ran but not that great when I got it. Never could get it to run properly and left me with a bad taste in my mouth. Ended selling it thank jesus, and never missed it. My Ninja 500s would run circles around that pos btw. Anyway, good luck and like the "big-toe" sed aboove, a little is alot, usually you can go up 5% on mains, but thats with a full exhaust system etc. Cheers

 

Well everything I read says even with a dyno....the carbs have to come in and out multiple times to get a perfect tune. So...I'm gonna start first with pulling the carbs again and just doing shims.....1 shim to be specific per needle. This will at the minimum hopefully get rid of the flat midsection we experience with the stock jets. I will then probably remove the snorkel and see how it runs in the mid/top range with stocks jets and shimmed needles. If it runs amazing all the way through...great, I win. If it runs amazing up to the very top then fizzles out...then maybe i will go back in and drop some 128 mains in instead of 125 stocks. If the midrange is still a bit lean even with a shim then i know 2 shims and 128 mains might be the next step. Really if it works great but I have to keep the snorkel in, i may just decide to keep the snorkel in and screw it. There IS a limit to how many times im willing to take the carbs in and out..lol

 

Basic tuning requires that you start smaller than optimum and keep enlarging main jets a step (or two) at a time until your top speed (or dyno results) show no further improvement. You've gone too rich at that point, so need to try next step smaller main. Don't try tuning midrange (with shims) until you have best main jets dialed in FIRST. For correct F/R jet stagger, use plug colors to guide adjustment.