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Yeah, I am not too big on trying to get two uses out of a head gasket.

pressure / vacuum would be great.

BTW, to any naysayers, the 220 piston that we pulled out was cracked in three places and one top end Rev from disaster.

Put me in the...replace the stock 220 piston ASAP crowd. I told my buddy about it before opening it up, and definitely got some justification. It was trashed, which made me think that was why it was running rough. Amazingly enough, the cylinder was clean. No gouges, nothing.

the saga continues. Not giving up yet. Got some work to do next week.

So, installed a 35 pilot jet and clip on position 2...now the air screw and idle screw actually do something. Any concerns with running it that lean on the pilot?

What is the temp when it is running? Hot as heck??

ANY KDX original piston is from spring 2005 or earlier. That means 15+ years old. 16+ for KDX220R. 27+ for an "E" model or KDX250. REPLACE THEM ALL!

That's what I'm concerned about running that lean. I guess the air screw would be the deciding factor. Less than 1 turn out probably need to go richer. The 40 and 42 both reacted the same. Idle adjustment and air screw had no affect.

Out of town now but I'll get back to it next week.

Try a 38 PJ? Every bike is slightly different, but 35 does seem a bit lean. AS and plug chops will tell the true story.

I have a RB carb w/ head mod. 42 pilot, needle CEK 3rd position, 152 main. I run in about 1000' - 2000 altitude.

Here is the piston that came out of it

That's what a grenade looks like just after the pin is pulled lol

Close only counts in horseshoes, hand grenades, and 220 pistons. ;)

We have 2 / 220's and it seems to be a nature of the beast , I hate it also and have helped it some with larger carb slide , ect.
Did you put the 220 carb on the 200 ?

The 220 porting leans towards much higher intake velocity than the 200 at lower rpms , the more you mod a 220 the worse it gets. That said , usually the jet numbers will be smaller with the same carb on a 220,,,, but i may be wrong

C George wrote: 03:25 am Sep 10 2020 The 220 porting leans towards much higher intake velocity than the 200 at lower rpms , the more you mod a 220 the worse it gets. That said , usually the jet numbers will be smaller with the same carb on a 220,,,, but i may be wrong

Stock jetting of 42/145 (220) and 48/160 (200)...what your saying makes sense. The carb size 33 vs 35 may be a player as well.

We did not try the 220 carb on the 200. We did the opposite and got the same results.

Chamfer the engine piston skirts

It is always best to start at the very bottom or easiest things first assume nothing when trouble shooting as often as not its a simple thing the spark plug caps are 5000 ohms i think and its when they go open is when they act up as your speaking of also you probably already know this many if us here do not use the marks on the kips valves as they can be a tooth off but the kips is not your problem

You mentioned that the floats were within spec. Myself and a lot of others (from what I've read here) set the floats to 18mm instead of 15. My 220 with a brand new carb was rich on the bottom even with a 35 pilot. I reset the floats to 18mm and that took me to a 40 pilot with a really responsive air screw set at 1.5 turns out. Off idle to 1/4 throttle is excellent. Mods are RB head, 35mm AS carb, VForce reeds, and rev pipe.

I've been having the same problem. Did you get the issue resolved and if so, what did it?

Did you check float level?
My 220 runs a 38 pilot and a 140-142 (depending on weather)
Acted the same way until I corrected it.
I ride 500 to 2000ft.ASL

bufftester wrote: 09:30 pm Sep 09 2020 That's what a grenade looks like just after the pin is pulled lol

INCOMING!!!
You were 1-2 kicks from the last kick for that piston.

I’m running a PWK35 air stricken on my 220, it has little stumble low to mid also.
My jetting
Main 152,
Slow jet 42
3rd clip, using the needle form the original 33mm 220 carb.
Air screw, 1.5.