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KDX420 Almost Ready to Ride

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#1
Hey everyone,
It's been a long haul and quite a while since I posted on here last. I did a complete tear down and rebuild of my '81 KDX420 over the past year or so. Unfortunately, I get distracted with other things and had to put it aside for a while, but now I'm almost finished and need a bit of help with a carb problem.
I did a full rebuild on the carb and tried to make sure everything went back together the way it was supposed to, but I can't seem to get it to stop puking gas out of the bowl overflow vent. I set the float levels according to the specs in my clymer manual, but it just doesn't want to stop overflowing. Any thoughts or suggestions would be great.
I'm gonna try to include some pics of the ALMOST finished product.
 
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#2
Is the float and needle/seat in good shape? Are they new? Are you sure the float isn't sticking? If yes, then try adjusting the float level down just a bit more.

Make sure to post up some pics of that beast when you get the chance!
 
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#3
When I did the rebuild on the carb I only replaced the necessary gaskets and seals. I assumed everything would work as it had before I tore it apart. It was always a little tough to start cold, but always seemed to run fine after I got it going.
I have looked at the float valve assembly a few times assuming that maybe that's where the issue is, but is looks ok. The floats themselves appear ok also. Maybe my problem is just in the adjustment at the moment.
 
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#4
Just got back from the garage again. I took the carb apart, removed the float valve assembly and made sure it was clean and free of defects. It looked fine of course the proof is in the pudding, so I put the body of the carb on with the bowl off so that I could press on the float valve with my finger. I attached the fuel line and opened the flow. I was able to control the fuel flow through the float valve just fine, so I don't believe the float valve is at fault. Next I filled the fuel bowl by itself to make sure the floats were actually floating.....no problems there either.
I adjusted the tabs for the float contacts down a bit further and retried the whole thing again, but it's still puking out of the bowl vent.
The tabs on the float lever can be installed 2 different ways, which is what I thought I screwed up from the very beginning, but in the pic taken from my clymer manual, it clearly shows the tabs stepped upward towards the top of the carb (since the carb in the pic is upside down) which is exactly the way I installed mine. Is is possible that this info is incorrect? I have no reference to go by except the book. Any thoughts out there people? It would really help me out.
 

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#5
Nice bike, when you hold the carby upside down bowl off, are the floats prevented from going any further where they rest against the needle or are they hitting something else?
 
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#6
Can't tell. The floats on this 420 ride on posts inside the bowl and are independent of each other and the float lever. The only way to see if they would hit something would be to put the bowl back on the body of the carb and then of course it's impossible to see inside to see what they're doing.
 
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#7
Any suggestions?

Anybody out there got any thoughts or suggestions on this carb issue? I'm gonna head out to the garage and start adjusting the float lever until it stops leaking out the vent or I can't adjust it any further.
 
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#8
ok, I guess I found another major issue on this bike. The last person to use it was my brother a few years ago and after he returned it to me I never fired it up again, just assumed it was still working other than the brake and clutch levers he broke. Turns out the best I can get out of the engine is just shy of 50psi on a compression test. I don't know that much about 2 strokes but I'm pretty sure that's not good. The clymer manual makes mention of anything below 100psi being bad.
As for the carb, adjusted the float level to a point where it stopped leaking....at least I thought it had, came back about a half hour later and it was starting to drip out of the bowl vent again.....ARGH! This things driving me nuts.

Any suggestions on a plan of attack for the engine? Am I looking at a total rebuild here or are they prone to certain issues I should be looking for with low compression? Not sure how willing I am to keep dumping money into this thing.
 
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#9
Are you a member of the KDXrider.net forums? If not, join up. There is a lot of KDX owners there that are not members here and they might be able to help.
 
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#11
The other approach is to just get in the habit of turning off the petcock when you aren't riding. Even after 4 carb cleanings, its the only way to keep my son's KX-60 from hosing down the garage...
 
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#12
Sounds to me like the crank seals have failed. A common problem on two strokes when they haven't been used for a while.

Dave R
 
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#13
I really doubt the crank seals would affect compression to that extent. You really have to do a leak down test for leaking crank seals to become evident. If the cylinder/ring seal was still good, compression would still be testing out OK regardless of leaking crank seals. Looks like you'll be pulling the jug and checking the cylinder, piston, and rings.
 
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#14
KDX 450 -Two Stroke

Hello , Just taking the chance and hoping that someone will be able to give me advice.
Cant seem to find the correct crankseal for a KDX 450 1980 model .
Triple lip crankseal measurements are 62x38x10.5.
Everytime order crankseals it is not the same - Any idea why this model would be differrent or who I could contact.Thanks .
 

jaguar

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#15
if the float(s) have a pinhole leak then they get heavy with gasoline and don't work right.
take them off and feel to see if they are heavy.
the exception to this is when floats are made of that styrofoam like stuff.
 

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