Jetting

No bottom end...backfire...AS omly 3/4 of a turn...sounds like a leak between the carb and the cylinder. Check the condition of the intake boot. Could also be a bad seal at the pipe (check your o-rings) but my first guess would be the intake boot.

First things first, about your jetting compared to others here. Most jetting specs I've read are for a 200 and not the 220 like you have. The 200 has a larger carb and a more radicaly ported cylinder that requires a richer jetting. I have a 220 and use a 140 main and a 35 pilot with the stock needle at the lst clip (leanest) The only thing different between your bike and mine is that I have boyesen reeds and a fredette torque ring.
Second, to test for a vacuum leak. Start the bike and warm it up. Remove the air filter and squirt a little carberator cleaner down into the intake of the carb. If everything is tight, you just added more fuel without increasing the air, a rich mix that should stall the engine with a flood if you spray a lot. So just spray a little and listen for a drop in RPM or a stutter in the exhaust note. If, on the other hand you have a vacuum leak, such as a damaged intake manifold between the carb and cylinder, then the engine has just gotten an additional load of fuel with the carb spray and a source of air to mix it with via the leak. The engine will rev up. Here in California, we have to go through smog tests on cars and trucks. Most test failures are due to a vacuum leak through a hose that cracked and this simple test using a can of carb cleaner sprayed around hoses, intake manifolds, etc. identifies them quickly. The tester will charge an hour labor at $65 per and usually will just have to trim the end of a vacuum line that cracked with age then reinstall. I digress. Also, don't worry about going too lean. The engine will give plenty of warning before it is damaged. If it isn't knocking or pinging, or over heating, it isn't too lean. Just don't jump on it after a jetting change. Work your way up to full speeds and keep an ear open and a wet thumb testing the cylinder temperature. I hope these tips help.

Try just moving the needle clip down a notch. It made big difference in bottom end for me.

At the top of this forum is a stickied post:
'Every kdx rider should read...'

Go there (CDave's site). Bookmark it.

He has basic jetting info listed for step by step modifications.

It's a backfire? Not a 4-stroke (firing every other time) sound? I'd be surprised if it's a backfire.

Adjustment of the AS is via throttle response (all other things being ok..like no vacuum leaks). A quick twist of the throttle, say in 2nd gear from a slow roll should give instant response. There is a difference between a lean bog and a rich one....either of which can come from a misadjusted AS.

Originally posted by Woodbyrd
135-PSI Compression

Now here is the question: why is the bottom end so tame?

Click to expand...

Woodbyrd,
That is fairly low compression. Is the bike hard to start? How fresh (or not) is the top end?

The original question was in regard to jetting and bottom end effects.

Didn't intend to discount/overlook other obvious factors. Certainly there is a plethora of things that can hose bottom end response other than jetting.

Condition of the topend is certainly one of them. So are reeds and a failed/failing KIPS.

Originally posted by Woodbyrd
As far as compression being low, it's only 16-PSI below max and it is not hard to start. Is that bad?

Click to expand...

Not necessarily. Since you had already received jetting advice my point was that you should check that the mechanical condition of your bike is in good shape. Often times we’ll chase jetting problems that are induced by other factors. Low compression could be one factor, as could a PV that is stuck open as CC stated.

If you feel confident in the bike's mechanical condition I would follow Tom Ludolff's advice first. This will provide a quick indication of which way you need to go if it IS a jetting problem. If so, then follow the jetting guides mentioned.

Good Luck. :thumb:

'Often times we’ll chase jetting problems that are induced by other factors..'

yeah. what he said!

No offense meant....so don't take one. ;)

re: four stroking
A two stroke engine fires every piston TDC event. A four stroke engine fires every second or every other TDC event. It's not uncommon for a two stroke to 'four stroke' in some situations.......like choke cold starts. The blubbering exhaust note you hear on such a choked start is the two stroke engine firing every other time.

When at speed and not under load with the throttle backed off, you hear the same thing.