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RMX Mid-range Hesitation

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Ok, I have really cleaned up the bottom end (on my PWK36 fitted 98 RMX250), by dropping the pilot down to a 42, hot starting is now a doddle too!

So now bottom end is great, top end really flies but I have noticed on the last couple of rides (even before I changed pilot) it has a hesitation/deadspot just before coming on to powerband, usually while going up a slight hill or when loading up the motor, at getting towards WOT. On the flat ground there is no problem but it now really drags its heels up hills. :moon:

I have only noticed this the past couple of months (since it started getting really hot here), this is the first summer I have had this carb on the bike.

Sound like just a needle position or still rich mainjet issue, could it be the powervalve sticking??

It used to run great and never had this problem.

Edited by dirtynidge

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It could be the needle or the needle position, but I'd check the exhaust valve first. If it still hesitates try lowering the needle one clip (move the clip up) to make midrange mixture a little more lean.

Or, just run WFO all the time and you won't notice it. :moon:

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After another quick ride I can say it certainly hesitates even when opening at WOT.

Does this eliminate the needle or would this stll come into play??

I havent ever played with PV before, what can I check? I was planning a topend and good once over in the early new year.

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It's quite possible the valves are gummed up. You could check to see how easily they move by removing the cover on the right of the cylinder (behind the exhaust pipe.) Move the rod up and down, and see if there's any resistance. There should be very little.

If you have never cleaned the valves it's probably past time. They're easy to clean; the hardest part is getting the front cover off to remove them.

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The power valve is a real bitch to get to on them when the cylinder is still in the frame, as posted above pull the side cover off and and check that it all works smoothly if it is all ok then drop the needle one notch and give it a go(again as above).

If you find that the power valve is sticky you might want to pull the whole cyl off to get to it.

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You' re right, it is a bitch to get to but it all seems to be working ok. Will try dropping the needle down a clip next.

I have been wondering though, could the needle position cause some hesitation when cracking the throttle wide open??

From what I have read the needle doesn't come into play after 3/4 throttle. Up a long hill I can be holding it wide open and it never "clears its throat", even when wide open for a good while.

I have to knock it down and rev the guts out of it to get it into the powerband.

Needle pos or main jet, what do you reckon??

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I have only noticed this the past couple of months (since it started getting really hot here), this is the first summer I have had this carb on the bike.

Sound like just a needle position or still rich mainjet issue, could it be the powervalve sticking??

It used to run great and never had this problem.

When you say it used to run great, is that in reference to the old carb, or the PWK during the winter? Is the R1469m the stock RMX needle or the one that came in the PWK?

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Did you do a plug check? Is it ok? How about the float level? I would check that first. I would try the next size smaller main jet after that and do a plug check.

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I have been wondering though, could the needle position cause some hesitation when cracking the throttle wide open??

Most definitely. If the needle position is too high, or the needle itself is too rich, the wide-open transition will be too rich causing hesitation.

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It did run great in winter with the PWK and this jetting. I have dropped the main from a 180 to a 175 to try and resolve this issue but hasnt made any difference (except given a bit more top-end go)

I checked float level when I put the carb in 6 months ago and was perfect, I cant imagine it would change???

I did plug chops in July and posted results here: https://thumpertalk.com/forum/archive/index.php/t-754128.html

The 1469M is the stock needle from the PWK, the old PJ had a 1471.

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Most definitely. If the needle position is too high, or the needle itself is too rich, the wide-open transition will be too rich causing hesitation.

Good, it makes a bit of sense now. I was wondering why dropping the main down a size had no effect.

I will drop the needle a clip or two tonight and see what happens.

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Good, it makes a bit of sense now. I was wondering why dropping the main down a size had no effect.

I will drop the needle a clip or two tonight and see what happens.

It's best to move in small increments, 1 clip postion is plenty at this point. What letter or letters follow the R1471, was it an "m" also?

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If I remember right it was an 1471N which was in old carb, this was a leaner needle than the 1469M right?

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If I remember right it was an 1471N which was in old carb, this was a leaner needle than the 1469M right?

Thats correct. 175-180 main is about right and so is the 42 pilot.

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Yes in 2 ways. R14 = the taper, no difference there. 71 and 69 = the straight diameters, 71 is leaner (2.71mm vs 2.69mm). The letter designates the tapers location, "M" locates the taper 1/2 clip position (.45mm) closer to the top of the needle than "N", so "N" is 1/2 clip position leaner.

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Ok, now I have to apologise. I just dropped the needle a clip and it was a 1469H NOT a 1469M that was in there, it was also in the 2nd clip pos (not 3rd as I said), now is in 1st.

From what I can tell it is certainly quicker and more 'zingy' in the midrange, harder to keep front down, a slight bog off pilot but that will be an airscrew tweak.

I pulled plug out after 15 mins of screaming around neighbourhood and is a nice mocha/chocolate colour. I know for a fact that when I started riding today it was wet/black (as it always has been). Would it re-colour a wet black mess so quickly??

I have a lean paranoia but one clip pos surely cannot take it too far.

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Thats good news. You an RMX rider too Mick??

Yes mine is a 99, although i still have the PJ carb atm.

If you have a look on DBW there is a bit of info on there about the PWK on the RMX, but iirc most of the guys are using the blue JD needle.

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I have had a good look around on DBW but is mainly info re. PWK 38. A few of us on her have been playing around with PWK36 as KTM seem to be using them on all of their 2 strokes these days, not much jetting info around for these carbs on an RMX though!

I know there has been much debate on DBW on the use of this carb on an RMX.

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Yes in 2 ways. R14 = the taper, no difference there. 71 and 69 = the straight diameters, 71 is leaner (2.71mm vs 2.69mm). The letter designates the tapers location, "M" locates the taper 1/2 clip position (.45mm) closer to the top of the needle than "N", so "N" is 1/2 clip position leaner.

So now I know I have an 1469H In there, that would explain why it is on the top clip pos; this is a much richer needle than the 1469M I thought it was?

Basically, H is richer than M??

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