KDXRIDER.NET

New to me KDX. Been racing, tuning since the early 60's and this one has me stumped.

When I got the bike it would start cold without the choke, not a good sign but I thought "what the hey" just needs a smaller pilot, air screw adjust, filter clean etc, no big deal. Right. The only way to get it to run without slobbering all over the rev range is to shut off the fuel and wait for the carb to empty. Just before it dies, runs great. Play a tune on the fuel valve and it runs decent.

Here's what has been done:

Pulled the top end, piston is almost new and installed the right way.
Spark arrestor removed and cleaned.
Filter cleaned and lightly oiled.
40 pilot, stock needle in middle, 152 main, float level about 16 mm (tried lowering but no change), new needle and seat.
Reeds look OK, no chips.

What am I missing?

Its possible the `jet block` rubber gasket has perished...? this can give the symptoms you are experiencing....
You can replace it with a new one as they don't cost too much.......try `jets are us` for a replacement & let us know how you get on.

I was going to say the jet block gasket, too. I bet that's your problem.

mxoldtimer31 wrote:New to me KDX. Been racing, tuning since the early 60's and this one has me stumped.

When I got the bike it would start cold without the choke, not a good sign but I thought "what the hey" just needs a smaller pilot, air screw adjust, filter clean etc, no big deal. Right. The only way to get it to run without slobbering all over the rev range is to shut off the fuel and wait for the carb to empty. Just before it dies, runs great. Play a tune on the fuel valve and it runs decent.

Here's what has been done:

Pulled the top end, piston is almost new and installed the right way.
Spark arrestor removed and cleaned.
Filter cleaned and lightly oiled.
40 pilot, stock needle in middle, 152 main, float level about 16 mm (tried lowering but no change), new needle and seat.
Reeds look OK, no chips.

What am I missing?

hook a new line to your inlet and blow on it while opening/closing the float needle (with the float up/down).

the jet block has a gasket that is $10 from jets r us. it fails after a chemical dip, and floods the jetting with fuel.

150 is rich for summer, I'm finding 138- 140-ish is great with gnarly pipe and pro circuit, at 600-1500ft and 90f / 90% humidity:

Well now I don't feel so dumb. I assume the jet block is the fairly large chunk of aluminum secured by the torx screws. Mr. Keihn, you won the first round.

Thank you very much guys. Into the shop tomorrow to check this out.

Sigh.

Couldn't wait for tomorrow. Forgot to mention I have spare carb left over from our shifter cart days and it exhibits the same symptoms. Sooooooooooooooooo, pulled the jet block from both carbs and the gasket looks good. Still has the adhesive, no flat spots or cracks, soft and pliable.

Now what?

Could be the air inlet tract to the idle circuit is clogged. Spray it out with cleaner fluid.
Could be the rubber tip on the gas inlet float valve is cracked. A new valve is $36.50 from raonayers.com and its number is
16030-1057.
Could be the tract that the idle air/gas mixture flows out from is clogged.
Make sure there are no rats nests in the exhaust pipe at the beginning of the stinger also.

FWIW, I've had a jet block gasket look just fine and still leak.

Just so there is no confusion, this is the gasket in question:

Hmmmmmm, what adhesive would one use to install?

No adhesive. I put a TINY bit of grease on it to help it not get pinched when it's installed, but that's it. The gas will dissolve the grease (you can use Vaseline) and leave a nice seal.

Thank you from Edmonchuk. I have a spare, try it tonight.

Installed new gasket as instructed. No joy, still runs like a dog until carb is almost empty.

Sigh

mxoldtimer31 wrote: Play a tune on the fuel valve and it runs decent.

What does that mean? Are you tapping on the petcock or blowing into the vent tube on the tank?

Close the petcock until it starts to run decent then turn it on for 2 seconds, close, repeat. Hit the kill switch, remove carb, drain. Get about 5 cc fuel which means anything more than fuel in main jet cavity and it pukes all over itself. Anybody got a spare carb that works for sale????

Gotta be the float valve or float height. I had a spare carb until recently, but alas, it is gone. If you MUST buy a new one, may as well buy one already done up by Ron Black.

Check your float valve height. If you order a new carb bowl drain plug from Kawasaki you can even tap it and build your own level gauge.

Now that's a great idea. Just happen to have a spare. When my frustration level drops below throwing stuff around I will fab up one. Lets see, set float high, close valve, when runs good mark level, reset. Cool. Off for a ride on my KLR. On the trails. That will motivate me on the KDX.

If it's rich you'd want the float height set LOWER than it is.

mxoldtimer31 wrote:Now that's a great idea. Just happen to have a spare. When my frustration level drops below throwing stuff around I will fab up one. Lets see, set float high, close valve, when runs good mark level, reset. Cool. Off for a ride on my KLR. On the trails. That will motivate me on the KDX.

lol but ya, understood

klr's are awesome bikes, just like kdx's are awesome, just in different environments :D

OK 2 lessons relearned.

1. Check other threads before posting an issue. Found out my problem wasn't unique or new. Sorry about that.
2. Listen to the people who "been there" and are kind enough to share.

Got an old scummy carb from a 1990 that sat in a barn since 2000. Cleaned it up, bolted on and runs like a charm. Still a little rich on top but a 140 should fix that. Ordered some gaskets from Jetsrus, will rebuild a spare 4 vent I have around.

Stumbled across 2 complete KX 500 front fork assemblies in the same barn. Neat.