Just got '94 KDX250, help

[alltat2ed]

Hey guys. whats's up? I'm new to this board but you guys seem to really know your stuff. I just picked up a 94 kdx250 for $400 and its not in too bad of shape, but i have to bump start it. . I drained all the fuel out, took off the carb and cleaned it really good, put in a new plug (br7es hotter than stock) and i filled it up with premium gas in 40:1 mix bellray synth. If i pour some gas in the jug it fires up on the first kick. So its a fuel problem right? ? The fuel line is not clogged. Any suggestions?

 

[dirt bike dave]

Cracked or warped reeds can make a two stroke nearly impossible to kick start cold. Inspect them closely.

Another common problem is low compression due to a worn out top end.

Make sure the fuel cap is breathing properly, too.

On my old KDX250, if I remember correctly, it wanted NO throttle on a cold start. Try these techniques: turn the gas on. lay the bike on its side for a good 10 seconds (this gets gas into all the circuits of the carb). Pick the bike up and kick it over slowly (with no throttle) two or three times to prime the cylinder. Find top dead center (kicking slowly you will feel the compression buidlng, as soon as that backs off, you have just gone past TDC). Return the kicker to the top of the stroke and kick as hard as you can (no throttle).

Congrats on finding the bike so cheap. With some attention to set up (especially to the forks and jetting), the KDX250 can run pretty good. One of the members has compiled lots of the '91 - '94 KDX250 tips into one page. Search for threads by blackduc748

 

[alltat2ed]

Thanks, bro. I'll try our tips. I've got new reeds on order already. I figured it can't hurt to replace them anyway. I'm hesitating on ordering the new piston and rings only because I've never done it before. I'm just getting into 2 strokes for the first time. I've always had 4strokes before this andthese are like a totally different animal.

 

[KIWI KDX]

hey mate, welcome to the KDX 250......beware!!!

the 250 is a grate bike,
I would also suggest piston and rings, as well as crank seals and main bearings while you are in there. i had the same problem u described with starting, had to crash start it or feed it fuel, with new crank seals it starts first kick every time!

2 strokes are so easy to work on, a rebuild is easier then routine maintanince on a 4 stroke

there is heaps of mods for ur bike, cut the silencer after the bend and move the end up. then u can loose the rear sub frame for the gaurd, a KX250 pipe gives more power and saves a heap of weight over the stock one. just a few.

and if u think it is an animal now, wait til u have a new top end in it!!!

 

[alltat2ed]

I just pulled the top end off. Top of the piston looks like burnt toast! I ordered wiseco piston kit today. The cylinder walls look real good except at the very top in front is a little scored. Is this ok or do need to have it bored out? I don't want to bore it out if I don't have to.

 

[alltat2ed]

Do I need to split the cases to replace the crank seals? I've never done this before. How hard is it?

 

[KIWI KDX]

some small scoring in the bore is fine as long as there is no chips or deep scratches,
you will need to split the case to do the seals.
by the sounds of it you may want to get a bike shop to do the them as u need to heat the main bearings to get them out to get to the seals. if i was u i would get a conrod kit and do that too, it will cost a bit more but after that u wont need to touch the engine for at least 50-60 hours!

its a good strong bike, and they are worth the effort!

 

[alltat2ed]

Thanks, that's what I was hoping to hear. Not that I want to get cheap, but I really don't want to put more than $600 or so into getting this thing going. This is going to be more of a back up bike after this year but I'd like it be reliable.
Do you know of anything I can soak the cylinder in to clean it up? There is quite a bit of carbon built up around the exhaust valves.

 

[dirt bike dave]

IMO, it's hard to justify spending big money for a bottom end rebuild on an old KDX250. With some attention to the jetting and fork setup, it's a decent bike, but it is old and does not have much resale value.

The excess carbon on the exhaust valves suggests either lots of miles or stock jetting, or both. Oven cleaner gets that stuff off, but is not good for soaking as it is very strong.

 

[alltat2ed]

Thanks for the input, i agree on the resale value. I'll try the oven cleaner.

 

[dirt bike dave]

Both my buddy and I had KDX250s. On both of ours, when the side KIPS valves were all the way open, the floor of the open valve was raised up a few mm above the cylinder's exhaust port. We took some of the material off the KIPS barrels with a dremel to make their openings flush.

BTW, for your rebuild, use a head gasket from an '88 KX250. It is thinner than your KDX gasket, and the extra compression will help power everywhere and still run fine with premium pump fuel.