Just another update. I had to cancel the dyno for a couple of days. I was trying to get to the 100 mile mark and then change my oil before the dyno run. About 30 minutes into the ride, it started to seem a tiny bit off in the mid range. It also started popping a lot on decel. Thought I messed something up pretty bad. It turns out that my mega bomb is cracked at the weld going into the expansion chamber and was sucking a lot of air. Just removed the pipe and took it to a guy who rig welds a lot of snowmobile stuff. I'll have it back tomorrow or the next day. Then I'll be back on track.

 

Wow that sucks, i hope you get it fixed soon. Not the first i have heard of cracking megabombs, it seems like a widespread problem.

 

I got my pipe welded and got my package with my new jets!! I decided to go with the DJ148 with the clip on the first position (1N) and both washers on top. Just took it out for the first ride. I only went up my road and back a few times. Couldn't go far due to being a domesticated father type. The bike still kicks butt down low and low mid. There is a tiny low spot in the upper mid range, but the top end is way more powerful. it crackles a bit when i cut throttle at 10k but doesn't pop through the whole deceleration. Not sure, but i think that indicates a bit of richness right at the top with unburnt fuel getting ignited in the pipe when it goes back to a lean condition..... not sure. I think that I'm going to leave it in this configuration for the dyno run. It seems like a good middle ground for the power curve and the AFR chart. I can adjust accordingly from here without multiple dyno trips. I'll keep you guys posted and I'll try to shoot a video at the dyno.

 

No one knows what sounds will emanate from a well fueled 351 - but it will certainly be different.. Decel is fueled with the fuel screw and pilot jet. I think you are running a #38 pilot jet. For a 250, a good "ballpark" setting on its' fuel screw is 3 turns out. I know you have a drilled slide lift port. That is unfortunate. Lets see what the dyno says about your fueling to see about that "flat spot"..


DJ148/1N with stock spring and slide lift port is exactly where I would start dyno testing if I had your 351.. No one, certainly not me, knows what to expect from the dyno.. But, you certainly have a "dyno butt" report that is exactly what I expected - same or better low/mid with radical top end..

 

What KLXSTER said.
Also, if you have a slight hesitation in the upper mid-range, it might be the needle. Try 2N to richen it slightly.

 

Well craig, usually, when we use large main jets in a lidless performance modded KLX (to properly fuel the top end), a problem of momentary overfueling can occur just when the slide reaches "full open" (6k-7K rpm).. We have to try to control this transition as best we can with what we have available - top clip, stock spring, stock slide lift port - If his drilled lift port is allowing "full open" a little too quickly, he'll get a momentary "surge" of fueling too soon..

In the case of lidless performance tuning, the struggle is to keep the low-mid properly "leaner" while keeping the top end properly "richer".. There is a psychological barrier to using such radically different CVK setups (from the "norm") ... I had real trouble dealing with having to increase my main jet size so much during my dyno tuning - it just didn't seem right - but the results are incredible.

 

Is there some formula out there that would help to determine main jet size as elevation goes up?
Klxster, your testing all seems to revolve around sea level or thereabouts so is there a way to see how elevation change affects jet sizing?
Also, it seems many people here are trying to get the most power at or near redline. I rarely rev mine to that level and when I do it is for such a short time. I'm more interested in getting the most power from 3k to around 7k rpm. What difference in jetting/ settings should I look at?

 

You altitude adjust your jet size from instructions/calculations on either of my Dyno tuning threads.. The recipes have been verified to 5k ft with a re-calculated main jet..

I know of no one that is trying to get the most power at or near redline. What I think you are misunderstanding is that, once a lidless KLX is fueled properly, the power levels above 6K increase so dramatically that THAT is what is noticed more than the increases below.. Study all my dyno chart threads and you'll see that low-mid increases are also very significant - stock vs lidless etc etc..

 

And what difference would having the lid on but with no snorkel? That is how I keep mine.
Thanks for the explanation.

 

To answer the question about running at redline.... I'm not looking for redline power, I'm looking for as much power out of this bike as I can get. That includes power down low, in the middle, and up top. I know that everyone loves the bottom end power that this bike has, but there is a top end too. I have the SF version so riding low in the tach isn't always an option. Even if I had the S model, I'd want to be able to scream if need be. I have to say that if I paid all the money for the 351 kit and just did the standard and ran the dj132, I'd be angry at the loss in top end performance. I didn't spend all that money to go slow faster or do 2nd gear wheelies. I want all the power available to me. Even with a DJ140 there is a big flat spot from 6500 to redline. Now with the 148 the flat spot is very momentary and then it takes off and cranks the whole way to redline. I feel that I'm getting more for my money.


Does anyone know how much a new diaphragm costs and where to buy it? I think that klxster is right about the slide coming up too quickly. If that is the case, the stock slide hole will make this thing a linear beast.