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Odd Vibration in Pegs

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All,

My XR250L has had an odd vibration in the pegs ever since purchasing the bike. In that time, the engine has had a fresh top end performed, as well as a new chain & sprocket set, and other various maintenance items as necessary. Oddly, I had thought it might have been chain slap of some sort - it only occurs under load, and only in the higher gears... (Slightly in 4th, sometimes in 5th, fairly commonly in 6th.) Not a problem while cruising at a flat RPM, but when any load or steeper hills are approached, you can feel it...

By vibration, I mean.. Imagine if you were standing on a piece of metal, and somebody tapped the other end of this piece of metal with a hammer. I can feel jerks / vibrations through my feet in a random fashion - there is no pattern to them... just ...tick...ticktick.......tick..................tick...tick...ticktick... - all while the engine is under load.

Interestingly, there is no chain in engine pitch while this occurs, and no detectable loss of power. Bike runs great, otherwise... Plug looks good, and the bike should be properly jetted for my assortment of air filters and so on. Chain is properly adjusted with good tension.

I had thought it was perhaps a jetting issue with predetonation, but I don't quite thing that is the case... It did this prior to the rebuild, as well as after the rebuild, where a new Wiseco piston was installed along with a bored out top end, cam chain, and so on.

Any suggestions? I'm trying to take a week long trip here shortly, and I'd hate for this thing to break down. That said, I've put about 2500 miles on the bike since purchasing and rebuilding it - and that problem has been there since day one, oddly enough. It doesn't seem to be getting 'worse' per se, but I'd really like to figure out what is going on.

Thanks.

Edited by Yoshizuki

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Im not a expert but I had very similar vibration to me on my old dr400 and it turned out to be the rod bearing.

Dont want to freak you out or anything, but thats what mine was.

Hopefully somebody else will reply with better news.

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Appreciate the replies.

When I tore the engine down, I checked the connecting rod for any roughness or excessive play, but found neither; it rotated very smoothly, and only had a barely perceptible amount of play... fractions of a milimeter or so. Seemed great at the time. Crank bearings also didn't seem to be an issue. I was concerned that it could be something internal, but everything seemed to be pretty damned solid when I check it out around Thanksgiving. I rode the bike for about 900 miles prior to the rebuild, and have had it on the road for about 1600 post rebuild. Problem was there from day one, oddly enough.

One more perhaps interesting note/detail..... At higher RPMs, it seems to either go away, or perhaps no longer be detectable due to engine vibes. This only occurs when the engine is used in the lower to mid engine RPMs.

Will give the bike a good look-over today while I'm outside.. It is due for an oil change - it's first 'long' interval of 1000 miles since the rebuild. Oil was changed numerous times during break in, and again at 300 miles, so we'll see how it looks at this point.

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have you found out anything on your vibration?

Well... Yanked the plug again yesterday while changing the oil and adjusting the valves... Oil and filter looked great - no shavings. Plug gap was too small, however, and the plug color was much more grey / white than I'd like it to be.

Paying a bit more attention, it seems as if the vibration is only apparent after the bike has been running for 8-10 minutes. This makes me wonder... Could it be predetonation? It doesn't seem like the power changes or that there is any perceivable sound... It's just a vibration.

Thoughts?

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Some confirmations from tonight's commute home...

1) The bike runs better - seemingly stronger and smoother - right after first being started... No 'vibrations' are present in any of the gear, even during long pulls up hills.

2) As the bike warms up over the next 10 minutes, the vibrations begin to appear. Bike doesn't seem to be as strong when the engine is hot.

3) Pulled the plug... grey color, but thankfully not bone white.

So.. I'm a bit confused here. It has been generally taught to me that if a bike runs better once it is warmed up, it is too lean. Hotter air means less density and less air molecules per given volume of air, thuse enrichening the air/fuel ratio. Conversely, if a bike runs worse once it heats up, then perhaps it is 'rich.'

So, given the conditions... One could say that my bike is displaying rich conditions, given that it runs worse once it warms up. But the plug does not appear to be tan in color, and is more of a grey color.

Any ideas? Is it possible that the jetting isn't too far off, but that the engine runs into detonation problems once it warms up? I'd like to think that a transmission problem wouldn't have anything to do with heat in the parts, or warmup... A bad connecting rod bearing, for example, would be bad all the time, in any given gear, correct?

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I wouldnt think its the jetting unless you just bored it out , then you would want to go up a size or two.

I run mine rich, they set them too lean from factory. MY opinion . I would rather be a little rich and change a plug here and there, than have them too lean burning up my top end.

I dont like my plugs very white at all.

Im not sure about the air thing, because whee I live hotter air does not mean less dense.

Until the outside temp gets to about 90 degrees or so, I dont have any noticeable power loss. But when its real humid, 75-80 percent or so, that will make them run richer because of lack of oxygen.

All my bikes I run rich, and they run better after warmed up.

Pre detoniation problem would make it run hot, check the timing.

As far as bad rod bearing or wrist pin. NO. It wouldnt necessarily be bad all the time.When you first start it the oil is cold and thick, taking up any extra space in a bad bearing. As it gets hot and thin it would start knocking or ticking.

In a lower gear the enine does not work as hard as higher gears.

I might try a colder plug, check oil pump, oil lines, oil cooler. Ive also heard of people putting the filter in backwards somehow.

Also my 200,250, and 400r have internal oil screens as well as the filter.

Make sure you dont have a clogged one.

What type and weight oil you using?

Hope some info is helpful..

Hotter air where I live usually means more dense, but more humid too.

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I wouldnt think its the jetting unless you just bored it out , then you would want to go up a size or two.

I run mine rich, they set them too lean from factory. MY opinion . I would rather be a little rich and change a plug here and there, than have them too lean burning up my top end.

I dont like my plugs very white at all.

Im not sure about the air thing, because whee I live hotter air does not mean less dense.

Until the outside temp gets to about 90 degrees or so, I dont have any noticeable power loss. But when its real humid, 75-80 percent or so, that will make them run richer because of lack of oxygen.

All my bikes I run rich, and they run better after warmed up.

Pre detoniation problem would make it run hot, check the timing.

As far as bad rod bearing or wrist pin. NO. It wouldnt necessarily be bad all the time.When you first start it the oil is cold and thick, taking up any extra space in a bad bearing. As it gets hot and thin it would start knocking or ticking.

In a lower gear the enine does not work as hard as higher gears.

I might try a colder plug, check oil pump, oil lines, oil cooler. Ive also heard of people putting the filter in backwards somehow.

Also my 200,250, and 400r have internal oil screens as well as the filter.

Make sure you dont have a clogged one.

What type and weight oil you using?

Hope some info is helpful..

Hotter air where I live usually means more dense, but more humid too.

Response appreciated.

FWIW, I just rebuilt the engine last Fall, and the bike was finally on the road at Thanksgiving. Previous owner had left it very leanly jetted, and the piston and cylinder needed replaced. Everything else looked good at the time; connecting rod had minimal play, felt very smooth, and the camshaft / rocker arms were in great condition. I *did* swap in a Wiseco - she's now 266cc according to the specs, and the Wiseco also raised the compression a tiny bit to 10.5:1. I have been running premum (93) in the bike. Oil screen was checked and cleaned during the rebuild. Currently running Rotella 15W40 with a HiFlo 112 filter, *not* put in backwards. Already running a slightly colder plug in the XR... I'm using the one that the XR-R normally runs.

I'm going to try covering up the airbox for this morning's commute and see if that helps enrichen things a bit. If this thing is indeed lean, this cold winter air sure isn't helping. Will report back, though it sounds like I'm going to need to change the jetting a little no matter what I end up doing.

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I realized as I was running out the door this morning to mention that... When I rebuilt the engine, the cam chain was stretched and needed replaced. Tensioner was in good shape. Rebuild went fine, and the fresh cam chain had the tensioner block pushed all the way back out, as it should be... (rather than all the way in, when I first found it with the old chain.)

An update...

I covered up the airbox for this morning's commute by about 1/2. The bike ran much more rich and would want to bog when I gave it wide open throttle, but the knocking and vibrating had disappeared! I suspect that the bike was just borderline lean to the point of having some sort of knock under load in the higher gears.

This XR doesn't have the middle plastic cover / plate thing between the airbox cover and the actual side cover. Wasn't in there when it came from the previous owner, so I suspect that perhaps I'm getting a little leakage through the airbox cover, and that combined with the normal opening on the airbox was enough to push things over the edge.

I may look into finding one of those replacement covers, but in the meantime, I'm going to get a bigger pilot and main jet(s) in the mail. I was already 2-2.5 turns out on the carb adjustment screw (and that hadn't really helped the lean condition, so I suspect I'll have to go up to the #42 pilot jet. I hadn't expected I'd need it, as most reports show that the #40 is sufficient. (Currently running 40/128 with a somewhat opened XR250L exhaust, XR-R header, and a unifilter... Top of airbox has not been removed.)

Edited by Yoshizuki

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Another update.. Hopefully I can get some feedback prior to purchasing jets, if necessary.

I was just out in the garage playing with the idle screw. Pulled the plug prior to doing this, and had a much nicer tan coloration... I was quite happy to see that.

That said, looking at the various jetting setups for MANY XR250L posters, it seems that the #40 pilot jet is sufficient for the XR250L carb.

I followed the directions here (http://www.thumperta...ost__p__7033060) and it seems that 1.75-2 turns is necessary for me to get the nice slow idle that I need. Going out beyond that did nothing, aside from stalling out somewhere around 4-5 turns. The bike also stalled at about 1/4 turn from completely screwed in...

So... 2 turns. That's pretty darn typical, and pretty good from what I understand. And that test was actually done with NO tape over the airbox intake, for what it is worth. If that test says that my slot/pilot jet is sufficient, however, then why is it that when I cover up the airbox, I get better coloration of the plug and no more detonation / knocking / vibration?

Do I actually need to go up to a 42 jet to enrichen things across the board? Can you still have a pilot that requires only 2 turns for a good idle, but still isn't rich enough across the board? Or is there some other factor at play here, such as a decent idle, but too much air being pulled in at higher revs or more loading on the engine? Might I have some sort of other problem with my carb? (For what it is worth.. Carb has been cleaned... Jets were new as of a few months ago... Needle is stock, no washers.)

Thanks in advance for all of the responses... this has been quite the mess to sort out.

Edited by Yoshizuki

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