Running problems over 4000

[Montanna]

Hello all,

I have a Honda XLX250R like a 1984 XR250R (Twin carbs). I've just done a top end rebuild on it, new rings, valve stem oil seals etc but it's now got a problem running. It'll run fine and pull properly, for a while then suddenly it won't rev over 4,000 rpm, often when I turn the engine off for a while it happens when I start it again. Below 4,000 it's fine, all runs propperly then as soon as it reaches 4,000 it stutters and pops. Then if I just it leave it for a while 5 - 10 mins it'll be fine again

I've given the carbs a good clean and replaced the plug and plug cap and it's still doing it. Ordered a fuel filter as it dosn't have one at the moment but I doubt that will help.

If anyone's got any ideas that would be great, Ant

[Kiffer_XR250R]

It's either your jetting or (God forbid) your ignition timing is off, most likely too far advanced. I seriously hope it isn't your timing.

Edited March 11, 2010 by Kiffer_XR250R
error

[damone]

What about a valve that after heated to running temps is out of spec?

[damone]

My buddy had smae year XL and after riding for a ways the debris in the tank would work it's way to the carb and plug the main jet. Let it stand and the debris would fall away and run fine again untilt he debris worked it's way back to the jet.

He cleaned and lined his tank and all was good.

[Kiffer_XR250R]

Just did a consult with my brother and dad, and both think it's either timing or your jets. Clean your carb again and check your timing.

When timing on a enigne is advanced too far, it affects higher revs because the engine is firing late, and the air/fuel mix is still burning on the exhaust stroke, cuasing the stuttering and popping you've been hearing.

[Montanna]

Hello, thanks for everyone's ideas,

Kiffer: I'm hoping that it's not the timing too, although I don't think it is because it runs fine through the full rev range when started from cold / when been left for 10mins and keeps running for different amounts of time. It's such an intermitant problem that I think it's more likly to be somthing else.

Damone: That's interesting about your mates XL, I'm gonna try cleaning the carbs again and see if that helps. Pretty sure it's not a valve out as I've checked the valve clearences when the engine was hot so shouldn't be a problem.

I'll give the carbs a clean and see what happens, I'll let you know!

[Wild Alaskan]

at least its not OVER 9000!!!!!

[Montanna]

Right, I've replaced the coil and fitted a fuel filter, so now I'm pretty sure it's got to be the CDI these are way too expensive for me so I've found a CDI from a CBX250. Big question is "will it work on my bike?". I don't see any reason why it shouldn't rev limit should be about the same and as for the advance curve if it's a little bit different that won't make a huge difference .... will it? Thanks in advance for any ideas! Anthony

[lbxr400]

If its the same motor it should be about the same rev limiter although i would think the cbx would be higher. If the specs for the boxes are close it should be fine. Or look for an aftermarket box.

[catuk]

Next time you have the head off, check for any cracks between the spark plug hole and valve seats. My 1985 XR250 was doing a similar thing.

[Montanna]

Hello again, I'm still havibg trouble with this damn bike! ?

The problem is getting worse it's every time I ride it now and I only get 100 yards down the road befor it starts. I've replaced the spark plug, plug cap, coil and HT lead, Just put a new CDI unit on it as the last one had a crack on it and i thought it might be that and I've cleaned the carbs and put a fuel filter on it.

What else could it be? I've had a quick check over the electrical connections and found a couple of dogy ones (now repaired) so now I've started suspecting the stator!?! does it sound like a stator problem though? not running over four thousand rpm? I supose I could ave damaged the wires when the engine was on the bench as it's only started since the rebuild.#

Please help? any sugestions welcome I just wanna ride it!

Anthony

[Montanna]

Right ... just stripped the cover off the wiring from the stator and found two bare bits of cable one was quite frayed so I crimped it then soldered it. Then I heat shrinked all the cables to re-insulate them. But it wasn't the problem ?

It still sounds like it's got a rev limiter at 4000 rpm .... Agahhhh! This is getting really iritating and expensive now what else could it be?!?!

[Kiffer_XR250R]

If it's getting worse over time it's gonna be something mechanical. Check your valves, and make sure they aren't sticking, especially the exhaust ones. If you can, do a compression test. What is your oil like? Is it dark? What color is your sprak plug?

[DarrellT]

Possibly valve float? Maybe one of the springs broke after install? Might be worth a looksee...

DT

[Montanna]

Hello all, the plot thickens, it's not a valve, they all went into the guides fine and I know I put it together properly. Also I used a spark viewing do-hicky today and you can really see the spark go inconsistant at 4 - 5,000 RPM so it's definatly electrical. Sooo what could it be? First idea would be the CDI but I've replaced that and the coil. Any ideas???

[DarrellT]

Try checking the wiring and the timing pick up under the flywheel cover. Might be loose and vibrating at higher rpm.

Darrell

[chicagojoe]

Did you ever figure out what this was? I have an 87 XL250R with the same problem

[Montanna]

Hello there, Sorry havn't been on here for ages! No still havn't sorted the bloody thing out. Haven't really had a chance to look at it in the last couple of months, currently trying to decide between paying for an auto electrician or buying another CDI off of ebay, but i'm not too sure! Also still got to check the pick up.

I will post up what it was when I find out! Ant

[Wild Alaskan]

you may want to try a new wiring harness or a hotwire to make sure its not something shorting once a certain voltage is reached

your bike has basically the same setup as this, so heres how to hot wire it, actually this is for the 400ex so your cdi is different i believe. hope this helps i had a similar problem

[wallrat]

I read further back that you adjusted your valves with the engine hot? Maybe not the problem but you're supposed to do that on a cold engine iirc.

Might see if you can get your hands on a multimeter and test the voltages. Still have your regulator and stator to narrow down.