Good jet info- and yes- I agree with you... the dynojet is a waiste of money. I'm completely happy with the kit- and it serves its purpose... but it wasn't until AFTER I had installed everything did I realize I could have bought the jets from an autoshop. - hey- you live and learn.

When I say my machine stops powering in 4th and 5th- I mean it accelerates... but MUCH MUCH slower than when in 1-3 gears. It doesn't PULL hard through the gear. I almost think i'm running rich- only because my remote control T-Maxx truck does the same thing when it's too rich. It can't get enough power to shift into second gear. But once I lean the high speed needle a 1/8 turn... it takes off like a bat out of hell.

I just need to keep looking for that sweet spot on the 400. So what do you think....? Is there an adjustment that I can do that doesn't effect my low end... and will lean out ONLY the high end?

-I love the 250ex- but my wife NEVER drives it. So unfortunately- I'm going to sell it. (Which is actually a good thing because I'm dumping all that money into my 400ex) I'm thinking about beefing up the suspension with the Elko shocks and longer a-arms. -possibly a 440 kit)

 

"Is there an adjustment that I can do that doesn't effect my low end... and will lean out ONLY the high end?"

I really don't think so, jetting remains the same from gear to gear (that's kinda what I think the "experts" are trying to say about jetting, "the engine doesn't care what gear you're in, just what position the throttle is in&quot. But I'm certainly not the end-all in jetting answers, maybe someone else has a solution (I've never discovered one, however - but then again, it really hasn't crossed my mind!).

I do know what you're talking about though. It's pretty normal for a quad (especially a four stroke stock engine) to loss acceleration power in the upper gears. As the gearing gets higher (like in 4th and 5th gear), the engine has to work harder.

Quick example: if you've ever ridden a bicycle with multiple gears, its certainly easier to pedal as fast as you can (rev limiter or redline for an engine) in 1st gear. Now put that bike in a high gear (10th for a ten speed bike, 18th or whatever for a mountain bike). You will find that no matter how hard you pedal, you will never be able to pedal like you did in 1st gear (i.e., its hard to reach the rev limiter or red line). Also, it takes longer (acceleration) to pedal as fast as you can in a high gear. And that is why your 400ex doesn't pull as hard in 4th and 5th gear.

By the way, you might want to test your jetting (especially main jet), as described above anyway (go up on mains until it skips). You shouldn't trust dynojet to give you accurate jetting specs. Like the above poster said, every machine is different. You might be surprised, you could be lean (you'll know if you're too rich, you can't miss it - see symtoms above).

Last (and this might relate to your RC truck), lean jetted machines make more power. Some people run them more lean than rich in order to get max power (lean jetting will produce more power).

You can get away with this more in a 4 stroke than a 2 stroke - as 4 strokes don't depend on their gas for oil. Even though, since gas is the main source of internal cooling (ever spill gas on your hand, it's cool/cold because of high evaporation), leaning out the jetting will cause the engine to run hotter. So even 4 stroke engines will get damaged with too lean of jetting. The hotter an engine gets, the more the metal inside it expands, causing clearances to shrink - thus, in the worst case, metal to metal contact. To make matters worse, the very thing protecting metal to metal contact - oil - will also thin as the heat increases.

So that's why people drop one more size down, even after the overly rich skipping stops - to get a bit more power.

An aside: I do it too now (drop one main size down after skipping stops), because when I rebuilt my 400ex to a 416 (10.8:1 compression), I noticed quite a bit of black soot on my piston top, indicating that the mixture was a little rich (I had piped/jetted it previously).

Back to topic: So, even after you jet it perfectly, you will still see an acceleration slowdown as you go through the gears.

After I modified my engine to create more power, it now pulls harder, even in the upper gears. That is probably what you're looking for.

By the way, I just got elka shocks all the way around - they are unbelievable compared to the stockers. If you want to make your quad feel even slower, get these. Why slower? Because all the bumps you currently feel will all but go away; therefore, all the speed related cues and indications you feel now won't be there. The only cue that's left? The ground below you seems to move by you faster (grin).

I gotta stop writing these novels.

ogre