Kdx problems! help needed

steveokdx · Sep 22, 2012

I'm having troubles with my '91 KDX 200.........

It seems to idle fine, but when i go to give it a bit of a rev it want to die out.

doesn't seem to running rich

What gives??????

arnego2 · Sep 22, 2012

how many hours you got on your topend? If not that the float needle level could need a readjustment. But with a worn top end chasing jetting is no good

DBragg · Sep 22, 2012

Have you performed any recent maintenance on the bike? If so, did it run properly before the maintenance? Some of the more silly common causes of bog are a rag in the intake or an improperly packed muffler... (dont ask me how i know :whoa::)

Do you know the condition on the top end and reeds? Inspect the reeds for chips, cracks, holes, etc. Get a compression reading on the cylinder. After the elimination of other possibilities, you may need to inspect the top end's internals.

What are your main and pilot jets? What needle are you running? What clip position on the needle? How do these jetting specs compare to the stock settings?

Have you modified the motor in any way? If so, describe.

I may have left something out, but this should get you going. Let us know what you find, and if you fix it along the way.

_JOE_ · Sep 22, 2012

Sounds like a clogged main jet. Some history would help. Has it been sitting for a while? How old is the fuel? Did this happen all of a sudden during a ride? Have you done anything maintenance wise?

mudpack · Sep 25, 2012

Well? You asked for advice, and got it.
Haven't heard from you, not even a thank you for those who took their time to give detailed answers.
Do them the courtesy.....?

You also might try something as simple as screwing in a fresh spark plug.....I've had fouled plugs do just what you describe.

steveokdx · Sep 29, 2012

I strenously apoligise! i couldn't find this post, it said it had moved but i couldn't find it, please forgive this newby!

I have an update................

I replaced the plug about 100klms ago, plug isn't oiling up, i purchased a new plug today just to be sure it wasnt the plug, it started with the choke on and i could ride it but i couldn't give it to much gas or it would want to die, but if i just fed the throttle on a little it was actually ridable but not running at its best. I pushed the choke plunger back in and it stalled and was unridable.

I took the plug out when i returned from the ride arund the block and it has a tan/brownish colour to it.

As for the condition of the engine itself, i bought the bike about 3 months ago, i have only done only about 300-400klms since i've owned it, i was told by the guy i bought it off the it had a full re-build just before he sold it to me, but of course thats what he said, maybe just to sell it? i can't be sure? As far as i know the engine is stock.

I did a service- plug, gear box oil, air filter and it ran fine up until i tryed to ride it to work and it broke down.

I appreiciate all the help that you guys have given!

Thanks in advance!

_JOE_ · Sep 29, 2012

I'd start with a good thorough carb cleaning, remove the jets and float and blow everything out with carb cleaner and compressed air. Make sure you get all the air passages and choke circuit. I've heard of lots of people accidentally leaving a rag in the air boot when servicing the filter. Go over it really well and make sure everything is properly connected, attached and adjusted. Let us know how you make out.

DBragg · Sep 30, 2012

As Joe stated above, give the carb a good cleaning is in order. At the very least remove the main and pilot jets and ensure they are clean. The pilot jet's orifice will just look like a speck of light when looking through it.. The main jet's orifice should look crisp and round. Squirt the main and pilot passages in the carb body with carb cleaner as well. Carb cleaner should spray into the venturi when sprayed into the hole were the pilot jet lives. The same goes for the main, and is pretty obvious when spraying that its a pretty direct shot.

Take your time and take care to ensure that the floats are set to approximately level when re-assembling the carb. Your cab may not be identical to the one pictured HERE but its going to be similar.

steveokdx · Oct 6, 2012

ALAS!!!!

I have found the problem!

I started to take the carby apart and as i pulled the slide out i relised that the needle didn't come with it, i thought to myself WTF???? looked in and noticed that the circlip had come off! simple fix, just crimped it back onto the needle and hey presto, i'm back to doing wheelstands!

However..............................

I have another question, i read in the service manual that the circlip goes on the 4th groove from the top, what happens if you put the circlip in any of the other grooves? does it run richer?

Thanks for all your help guys!!!

mudpack · Oct 6, 2012

The closer to the top groove you put the needle clip, the leaner it will run AT ABOUT 3/4 THROTTLE. Below approx. 1/2 - 3/4 throttle, the needle does not come into play (as you've found out)...and at WOT, the needle does not come into play.

A Mikuni-type carb has about seven different phases, each controlled by a different "circuit" that come into play as you open the throttle. These seven different "circuits" will overlap, but each can be changed independantly. They are:
1. air screw
2. pilot jet (aka slow jet)
3. slide cutaway
4. needle diffuser
5. needle
6. needle jet
7. main jet

There is an eighth "circuit", the air bleed, that is non-adjustable by the owner. One could also consider the float level to be in this group, and if you know what you are doing you can adjust this to make fine-tuning adjustments. But, most tuners simply set this to factory specs and forget about it. It's already complicated enough....

steveokdx · Oct 6, 2012

yeah thats what i figured. I only asked because i wasn't sure which groove the circlip come out of? but it runs very well, and i'm happy with it!

Thanks so very much guys! you were a big help! i appreicate it!!!!!

Kdx problems! help needed

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