Hard breathing? Shearing noise? (more jetting questions)

I’ll make this short as possible. We’ve been doing some high-speed running (WOT-5th gear) recently and I’ve realized that my ’99 WR stops accelerating long before I hit the rev limiter. My riding buddies on 426s leave me in the dust when we open it up. I’ve found that if I “pop” the throttle, kind of “winding it up”, the bike will continue to accelerate under the same conditions. I’ve decided to do something about this because I know the power is there, it just needs to be unleashed.

The manual describes symptoms of rich jetting at full throttle as slow speed pickup, stops accelerating, and sooty plug. (I haven’t done a full throttle plug check, but my plug is usually a nice light brown color when I take it out. Of course, this doesn’t indicate anything about full throttle jetting conditions.) So I think I’ve been jetted too rich. I’ve been running a 175-178-180 main (bike came with a 180). I also have a 45 PJ, 60 SJ, 200 MAJ, 100 PAJ, and a DTM needle on the 4th clip. Altitude is less than 300 ft., and avg. temp has been around 75 F. I still have the stock header but I have an FMF Megamax II muffler with 8 discs. I'm running WR timing.

After all I’ve been reading by Taffy, Missile and others regarding how lean they have their jetting and how happy they are with it, I bought a couple of new jets last night to try them out. I got a 165 and 168 and put the 165 in just to see what it did. The bike ran great! I was very surprised to say the least. I expected it to sputter and feel like it was running out of gas. The manual describes symptoms of lean full throttle jetting as hard breathing, shearing noise, and whitish plug. I’d like to go even leaner to see how it runs but I don’t know what “hard breathing” is. I certainly didn’t notice a “shearing noise” when I rode it briefly last night. What I’d like to do is go just low enough on the main that it’s just a little lean, using the manual descriptions as a gross indicator of the jetting conditions. When I get close, then I’ll start looking at the plug. (We all know what a PITA it is to get to that damn plug.)

I think I’m on to something here (thanks mainly to Taffy who has convinced me that leaner is better) but I don’t want to burn up my engine. I’m also thinking about putting in a 42 PJ to see if I get better snap off the bottom. The bike has never been much of a wheelie machine and I think it should be.

Thanks for any comments on this (probably overdone) topic.

[ February 12, 2002: Message edited by: Rich in Orlando ]

Your Heading in the right direction there Bro....

You might think of backing the PAJ back down from 100 to 75 when you drop the PJ... It will make a world of difference.

Bonzai :)

Well I did some testing tonight and found some interesting results.

First, I have to admit that I've been messing with the timing recently and I had it wrong. A thread had been going around about what timing mark to use on the flywheel: the "H" or the "I". That was my dilemma. A few weeks ago, I checked my valve clearance and my timing. I thought I was off by one tooth on each cam because I could not get both punch marks to line up with the surface of the cylinder head. (In the past I wasn't sure if that should be checked with the cam chain tensioner on or off. I now know it should be checked with the tensioner doing its job.) So I referred to a Dirt Bike magazine article that instructs you to line it up with the "H". WRONG. The manual clearly states that it should align with the "I". The "H" (and I just realized this yesterday--when in doubt, read the instructions) is used to check the timing with a timing light, not to set the cam timing. To make a long story marginally shorter, I adjusted the cam timing properly and the bike rips. Enough said about that.

But back to jetting, I did the plug check thing. Run it WOT for a short distance, cut the engine with the throttle wide open, and coasted into my garage to look at the plug. With the 165 jet, the plug was a very light brown--not bad looking at all. But I wanted to see what it looked like with the stock 168 jet. It was a light brown, too. I'm keeping the 168 for now. After I did the timing change with the 168 it's like a whole different bike. The front end wants to come up very easily now. Tomorrow evening, I'm going to work on low end and mid-range.

The funny thing is that right now, my jetting is almost bone stock. Go figure.


I went to the #100 PAJ when I deoctopused based upon the instructions on Thumpertalk. Since that's an air jet, wouldn't going smaller richen the pilot circuit? I think that would kind of defeat the purpose of going to the #42 PJ. Your thoughts?

E Series Needle !

Taffy's APJ mod.

Get the main jet sorted first. Then work on the rest.

Make sure your PJ and PAJ ratio is 'correct'... they are linked according to Taffy who posted a chart in the thread 'Jetting Q's. Buy the Pilot Air Screw.

Buy JD's jetting guide for $19.95 and you will see exactly the effect on gas flow (rich/leanness) for all the changes you want to make.

Also...go the whole hog. If you like the sound of someones jetting / performance and their riding profile - year, exhaust, elev, temp etc matches your profile COPY THEIR JETTING. Chances are it'll be pretty darn close and if it still needs tweaking then you can work from something that is probably close to great. I made the mistake of following Taffy bit by bit instead of diving right in across the board. This whole thing works like rubiks cube. You change one part it has an effect elsewhere.

Also...interesting reading on gearing vs sprocket sizes vs jetting thing from yesterday from Taffy.

If you are going to do this search for "easy carb removal". There are a coupla tricks which make life easy when working on the carb.

Oh and one last thing....I think that doing a plug chop and reading/interpreting the results takes an expert. If you are an expert.... great...if not you may chase your own tail.

This is different than taking a measurement of the colour/state of you plug after a ride or two which is much easier to do.


really well done!

you should be very proud of what you've achieved. the next stage is to lower the needle after and during some roll on tests in fourth and fifth gear.

don't ask me where? as long as you try all kinds of throttle responses you'll find you've either improved it or you haven't.

it's all about response. getting the jetting down enough that it reacts.

the missile said it all about the PJ/PAJ relationship. get the screw!

read jetting Q's because it's when i get down to 42PJ that i start discussing the "relationship" of the two and maybe it'll come to you.


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