2008 MCX 270 stalling and lazy at low rpm

[DaveB]

I use stock plugs gapped to 18 thousands. Most use that on boosted Nytros.

Try a fresh set of spark plugs, X2 on what Northernboy said to use...
Sometimes we've seen partially smoked plugs, or plugs that sat over the season, mimick a rich condition because of an incomplete burn of the mixture... and look exactly like that.
You didn't perhaps change fuel brand?

I did actually. The previous owner ran 50/50 AV gas premium. I was told this machine will be fine with "good" premium....so I've been running 91 Shell Gold with Torco Accelerator to 94 octane.

 

[rxrider]

X3 on the 0.018 inch plug gap, that's what I set mine at.

 

[DaveB]

OK...new CR9E plugs at 18 thou....put back together (kinda missing my old two stroke sleds here, LOL)...she fired right up and idled at 1750 then up to 1950/2000 within 10 seconds and stays there. Easing into the throttle would not produce the burble I had before. Test drive tomorrow....wife has me heading out to a Christmas function and now I smell like gas in my good clothes, LOL.

 

[DaveB]

OK...I didn't even know this thing was supposed to have a high idle function when cold...it never even worked before. As mentioned above, fires up, goes to 1950 or so for a few minutes (warm garage) blip it and it idles fairly good at 1450 or so. Still loading up a bit, but I can't make it stutter at 2500 by juuuust cracking the throttle as before. Anyways...ditch-test: runs much better. Clutch is way off I believe. At 14 lbs (3000' elev) it snorts pretty good, but shiftout is 7900 or so. Seems to me we want it around 8500 to 8700?

Popped out a weight and the spring. Spring is black with two pink stripes. Weight has no numbers or markings, but weighs 95.0g. Helix is a Shockwave....adjustable from 42 to 58*....it is wound in 3/4 of the way, so probably about 51*. What next?

 

[rxrider]

Go down a few more degrees on the helix to say 48 and see what it does.

Personally I don't like tuning rpms adjusting the secondary. Secondary is for adjusting upshift/downshift caracteristics, primary is for adjust shift rpms, take off rpms.

I recommend buying a set of SuperTips adjustable clutch weights, 55 grams base weights. They're highly adjustable with the ability to load 42 grams on each weight arm.

Set the secondary at say 47 degrees with the spring at 60 degrees or 3+3.

Start tuning the clutch weights until you get close on the target shift rpm.

Set the helix at the desired angle for the upshift/downshift you like.

Fine tune your primary.

From a standstill when you hammer the throttle and to top speed the rpms should go to the shift rpms (where maks HP is, 8800 on the nytro, 10400 on the RX-1, 10700 on the Apex) the rpms should stay close to maks HP all the way to top speed.

Hope this helps.

Jan-O
rxrider

 

[DaveB]

Went to a Yammy blue/brown/blue primary spring and Dalton weights set to 78g, EPi pur secondary spring and a straight 47 helix. NEW SLED! She get's up and dances now. Just got back from a weekend in Revelstoke and it never missed a beat.

The only (maybe) issue is a harmonic or buzzing at zero load/slight decel at low speeds 5000rpm. Doesn't do it when you are under any load or clamping on 'er, but just toolin' around kinda downhill in and out of the throttle you can hear a buzzing rattle as the RPM passes through 5000 or so. Maybe I am being picky as it is obvious the Yammy clutch rattles and clanks like no other clutch I've ever heard...I'm told this is normal. I'm going to look into it this week...maybe a roller is toast or something...? I'm not even sure it's in the clutch...might be something else....but I never noticed it before.

 

[rxrider]

Cool Dave

Sometimes it's the track making the harmonic.

 

[DaveB]

Pretty sure the noise is under the hood and *probably* the clutch. We usually get track harmonics on the hard trail (not the deep powder) and it is a much throatier sound...this is a metallic buzz. I looked at the rollers tonight and they roll nice and appear fine. The pins that hold the rollers do move back and forth about a mm....this might cause a buzz at a certain RPM? I might try a tiny plastic washer behind the nut on each one to lessen the movement and see if the noise changes.

 

[rxrider]

Clutch rattle is common on the Yamaha clutch, more so on the 3 cyl engines due to harmonics, what you say. Yamaha had a shim kit to tighten up the plastic gliders in the 3 towers, don't know if the upgrade kit still exist. It did take off most of the rattle in my old RX-1.