New KDX'er questions

[Hellbender]

Hello everyone,
I've been lurking here for a month or so and thought I would join in, looks like a good bunch of guys and gals.

Here's my history, I'm 45 years old, 185 lbs, 6'2" tall, lived, ate and breathed dirtbikes/mx (all 2 strokes) from age 10-20, have been out of bikes since then.

I bought a used '95 KDX200 a couple months ago to ride w/ my 12 yr.old boys. Rough old bike w/ a pro-circuit pipe on it, stock otherwise. Fouls a plug every 3-4 hours of riding. I fell in love with most of it, except the low end torque and hard seat.

I wanted a nicer bike, so I just bought a 2002 KDX220, stock except a FMF Gnarly pipe on it (Desert or Woods????, how to tell????) and UNI filter and some suspension work. It has never had any top end service, so I'm planning on a Wiesco piston and rings ASAP.

I will be riding VERY tight wooded trails with my boys, almost all 1st, 2nd, & occ. 3rd gear trails, lots of logs to pop over, lots of idling and semi-trials type stuff.

What I want out of this bike.....

Very good throttle response off idle (hopping over 4-10" logs).
Very Important---Ability to idle/putt around a lot w/o problems.

Here's the mods I'm planning (from lurking this site)...

New piston & rings, W/P bearing ASAP, clean KIPS
While apart, Boyenson reeds (2-stage type)
Torque ring from Freddette (?????)
Airbox mod
Proper jetting
A slightly hotter plug(????)
12/51 gearing
CEET taller seat

Questions....

Will retarding the timing a couple degrees help the low end?

Should I swap the bigger carb off the 200 and add an aftermarket divider plate ($25 bucks or so)?

Reed spacer?

Should I polish up the ports (not change, just polish) while I have the jug off???

Any suggestions (pros/cons) about what I'm planning?

Thanks for the help,
HB

PS, I have a full machine shop and experience with automotive/off-road speed/suspension stuff, I can handle about anything mechanical. I am also a Mech. engineer/designer by trade.

Thanks again.

 

[trailryder]

the pipe should be stamped somewhere. K-35 is the torque pipe and k-30 is the rev pipe.you can also have your carb bored with divider plate installed,cheaper than buying a 200 carb unless you can get on used.Good jetting will clean up your throttle responce throughout the entire rpm range.Lose the airbox cover. The torque ring doesn't "make" more power if I correct, it just moves the meat of the power band down a bout 200-300 rpm's..If your hopping logs I'd invest in the best skid plate you can get.I'm not sure polishing will help your motor....If I understand corectly the roughness of the ports help to "mix" the air/fuel mixure for more complete combustion.This may be something I remember from turning wrenches under the hood as a kid...I wouldn't retard the timing, it may give you mixed signals while turning the rest of your hop ups.From what has been said on this site in the past just installing better reeds are a better bang for the buck than a new reed cage.This is what I hear..Have fun and please post the mods you did and what you thought of them.....

 

[skipro3]

I'd like to add that you do just one mod at a time, get it adjusted, then move to the next mod. A flywheel weight will help with keeping the motor spinning at lower rpms too. If you are needing a hotter plug, then the jetting still isn't correct. Get the jetting set up right and the plug recommended will work right.
The tall seat foam is as hard as a 2X4. I know, I have one. But, it does help in getting my butt off the seat and standing on the pegs more. I recently bought a used seat so I could interchange between them. The stock seat is sure cloud soft, but after just one ride, I was sitting way too much and my reaction times were suffering. So back to the tall seat where I find that riding standing helps with the flickability and the effort to move from sitting to standing is much less.
The torque ring is mainly beneficial for the stock pipe. It increases the header length before the expansion chamber, thereby lowering the powerband rpm's.
Oh, and welcome to our little disfunctional family here at JustKDX!

 

[John Harris]

If you are only going to run at slow speeds as you have indicated, you will be happier with the smaller carb on the 220 as opposed to the larger one on the 200. The smaller carb will give you better mixing and vaporized mixture velocity at slower speeds (demand). You may have the ability and capability to bore one out, but I would never do that for much is at risk for little gain. If later you want to go to a bigger carb, sell the little one and buy a big one and you will be ahead. (Opinion based on experience) You will enjoy riding with your boys. Cheers John

 

[motorider200]

I'll add that a DFII reed cage helped throttle responce greatly and added some power. The DFII also has high and low tention settings to boost top end or low end.

 

[Hellbender]

Everyone, thanks for all the good tips!

trailryder---I'll look for some #'s on the pipe, thanks. I still have my KDX200 so I could just swap the carbs at no cost, IF it would be the right thing to do. I wonder if I would get the best of both worlds (33mm & 35mm) with the larger carb w/ the divider plate??? I wasn't sure if the torque ring worked with aftermarket pipes, you would think the "torque" pipe would already be designed for the lower RPM power. I have a skid I'm taking off the 200, but I need to weld on more side protection. I was thinking the same as you on the port roughness, but wasn't sure on a 2-stroke. I'll not mess w/ the timing now. The reeds seemed like a good $35 gamble.

skipro3--So you would wait on the new reeds during the rebuild???? Break it in, adjust everything, then do the airbox mod, and do it all again, add the reeds, do it all again, etc, etc? Seems it would be easiest to do all the mods, start with the jetting recco'd in this site, and go from there. Am I missing something? Who makes the flywheel weights? Would they slow down the throttle "snap" to lift the front tire at low/slow speeds?
I guess I will pass on the CEET foam if it's harder, it seems I always end up sitting on the rear part of the seat that only has 1/2" of pad (I'm tall). I may have to make my own. I won't be riding hard for another year or two (as my boys progress from thier Yamaha TTR125's) so I'll sit a lot, and I have a bad lower back so I need the "cush". I wondered if the ring would help w/ a torque pipe. Thanks for the advise and the welcome!

John Harris--The only reason I thought of the carb swapping is I have one now at no cost. Thought maybe the divider plate would make up the difference lost to the smaller carb. My boys and I have been having a blast, I just bought my wife an XR100R 2 weeks ago and she likes it, too!

motorider200--I will do a little research!

Thanks again!

 

[Tom L]

H: You're right about the flywheel weight. Skip it. It will slow the response and inhibit the ability to pop the front wheel up over logs. Some like the smoother control for hill climbing and such, but NOT for log hopping. Maybe go the other direction and take a little weight off of the flywheel for snappier response. Get the RB-Designs carb mod. He bores out the carb and installs the divider plate on the exit end. It improves low end response under 1/2 throttle and extends top end revving. Well worth the $165 IMO. While you're at it, send RB your head so he can increase the compression a bit for more snap (only $40). HAVE FUN!!!

 

[Tom L]

Oh yea! Go for the reed spacer, low tension carbon fiber reeds, BR8EIX spark plug (or any with a thinner electrode), 12/52 sprockets. The taller seat foam might be good if you drill a bunch of holes in the foam (obviously, remove the vinyl cover first!, then just staple it back on after drilling)

 

[the trail rider]

if i were you i would get the jetting set up , drill holes in the air box. if you have the woods pipe keep it . if you dont have it get one. change your gearing to 12/47 or 13/50. get some inexpensive boyessen power reeds. you should have a ton of low end power after these mods.

 

[KTM Mike]

Hell - you are clearly describing low rpm, lower speed needs for power. Dial in the jetting, dont mess with the carb.

I have two boys, and have spent MANY hours plonking along with them - you indeed will want it jetted spot on down low so you dont foul plugs. Give the boys some time though, and they may leave you in the dust! My kids can now ride a decent enjoyable pace for me (though I do blast on ahead occasionally!) My 12 year old is on a KDX already (he is a big kid for his age). Nice bike. He is already starting to eye my pumpkin though!

The 220 is known for great bottom end, weak top end. The carb mods or swaps with a 200's carb are aimed at improving top end, and unfortunately (from what I have read - no experience here!) does this at the expense of bottom end. Not what you want.

Just a wild guess, but I would bet the pipe you have on it is a rev pipe (again, typical 220 mod aimed at improving top end power). Given that, a reed spacer block, torque reeds, torque ring etc. may indeed be in order with that pipe. If it is a torque pipe. maybe not.

But, I would suggest getting a few hours in on the bike before you do anything! Get a better feel for what you need to change - maybe it is spot on as it is!

 

[kdx220freak]

well i can say from experence. Dont switch out your carbs. If you want low end keep your carb. I have a 2001 kdx220. I also have a kdx200 carb, the larger bore give better top end, but does take some from the bottom. (i can still flip the bike to easy). I would suggest getting new reeds or a reed cage, running differnt sprokets, and drill you airbox out.

 

[Green Hornet]

well i can say from experence. Dont switch out your carbs. If you want low end keep your carb. I have a 2001 kdx220. I also have a kdx200 carb, the larger bore give better top end, but does take some from the bottom. (i can still flip the bike to easy). I would suggest getting new reeds or a reed cage, running differnt sprokets, and drill you airbox out.

***NOT***
I have done the carb swap. From experience you will not notice the Low-End Change, but you will notice an increased upper response. Go with the RB Designs mod, if you are concerned about the low-end. The porting on the 22o in conjuction w/33mm carb is what gives the low-end characteristics. You could put a Torque or Rev Pipe on and that wakes the bike up more. Get rid of the stock reeds and go with boyseen or DF3. You could go with a head squish mod or cylinder porting. I would do the last two last. See how you like the bike with the earlier mentioned mods. Also get rid of the Air Box Lid and get your jetting on.
Well I see you have the FMF. You can change the gearing also, Larger in the rear for more low end. Forget about screwing with the timing. I have the FRP Torque Ring and I feel it does give a little down low, but thats me.

 

[oldturtle]

Steahly makes a removable flywheel weight for the KDX.
http://www.steahlyoffroad.com/index.html
I have used these weights on CR250 and KTM250 when needed to tame the abrubt hit for trail riding but I have never felt the need for more flywheel effect on any of several KDXs I have owned. But this is a popular mod when combined with pipe and reeds and probably carb work to get more top end without sacrificing bottom.
After reading all the advice above I think for your use I would rec'm doing only the top end and power valve work now. Then I would rec'm inspecting and lubing head bearings and swing arm/linkage bearings. Then have the suspension serviced with oil change and new seals and valved and sprung for your weight, riding conditions, and experience. I think this very important bearing and suspension work is too often overlooked in favor of looking for more performance in the motor.
Then just go ride and find out for yourself if you can use any more motor.

 

[Green Hornet]

True, suspension & a good set of tires. I had the front end done on mine and with the addition of good rubber it is one of the best mods. A flywheel weight to help tame the powerband? Then people should just leave the bike stock:)

 

[Rhodester]

ADVANCING the timing will increase bottom end snap at the expense of top end run out. RETARDING the timing has the opposite effect. A modified and properly jetted KDX has plenty of snap to the power...enough to quickly wear out a back tire, hence the flywheel weight (at least with the 200H). I'm glad I put one on.