Alternatives to the plug chop for reading jetting?

[Feanor]

Hi All!

Now that we're in the midst of the "green sticker only" season here in Ca, I've been doing some general maintenance and such on the KDX.

Although the bike runs well, I am still certain that it is on the overly rich side given the blackness of the plug when I pull it to check, the amount of exhaust smoke, and the crackle and slightly rough going at low RPM transition to mid RPM...

Its an 04 KDX-220R and the engine has the following mods:

1) Boyesen Rad Valve with power reeds
2) FMF Gnarly REV Pipe
3) FMF Q-Silencer
4) Snorkle off, airbox lid on, but unmodified
5) Needle clip in second position from top
6) air screw at 1 7/8 turns out

I'm still running the stock 145 main jet and 42 pilot...

My main dilemna is that I've never found a place where I can pin 4th or 5th gear for 30 seconds to do a proper plug chop :( I could have actually done it last time I was at Pismo Beach, but wasn't able to get around to it while there. Plus I _wanted_ to be running overly rich there because of the sand's high RPM and low speed effect.

My request for aide is twofold...

Is there a reasonable alternative to doing a 30 second pinned in 4th-5th gear plug chop for checking main jetting?

or...

Is there someone with the same or similar mods who has done testing and has a good handle on jet sizes for that setup at about sea level?

thanks in advance!

Feanor

 

[dirt bike dave]

http://www.eric-gorr.com/tech/carb1.html

This is an old article by Eric Gorr with lots of good info. Check out the jet by ride & feel section.

 

[john stu]

umm 30 seconds seems like an awfull long time to be wide open just for a plug chop .......

 

[Rhodester]

You could accomplish the same thing by riding very aggressively around some kind of track where you kept the throttle pinned nearly the whole time. Do a couple of laps and you'd have a pretty good plug chop substitute. The method that I've come to use is the 'seat of the pants' method. This, however, takes some pretty good experience at knowing what's going on inside of your engine by sound and feel. You also have to be meticulous in logging your results.

 

[Feanor]

umm 30 seconds seems like an awfull long time to be wide open just for a plug chop .......

From KDX only

Checking the Main Jet– Warm up the engine and go for a short ride letting the engine comes up to its normal operating temperature. Install a brand new plug that's been properly gapped. With the new plug installed aggressively accelerate through the gears until you reach 4th or 5th gear. For best results you should accelerate up a slight up hill section to place additional load on the engine. Continue to run the engine at WOT for 20 to 30 seconds longer if there is not fear the engine is running lean. If you suspect the engine is running lean 15 to 20 seconds to give you an indication. At the end of your full throttle run simultaneously push the kill button, chop the throttle and pull in the clutch. This procedure is often refereed to as a " plug chop". It is important to perform a plug chop exactly as described. If you allow the engine to run or leave the throttle open for even a few seconds after the plug chop the plug reading will be invalid. Now remove the spark plug and carefully look at its color.

 

[Feanor]

Thanks guys for all the great tips! especially the Eric Gorr sound and feel method...

I'll give that a shot as well as try doing aggressive laps around a track as fast as I can to get a good mainjet reading...

Thanks again!

Feanor

 

[pete fry]

I had a read of the ride and feel section and gave it a go.Brilliant it made jetting alot easier for me and the results were worth it.

 

[Green Hornet]

Feanor-If you have not removed the airbox lid, give it a go. I had mine drilled and then removed and I do feel and hear a difference in the engine. Let the girl breathhhhhh. More air in the engine, leaner motor