I did see 101 mph on my MCM'd 250sf. 15x39 downhill at about 3% into a local tunnel, no vehicle draft used. Bike was a bit sketchy though. Slow and tight curves are much more fun and suitable for these bikes. Dragging pegs at 40-60 mph is what I like. Don't know how anyone can dislike the MCM effect. I would guess the bike was out of tune if stock cam timing feels better.

 

How do you define out of tune?

 

He just means that whatever is inside your CVK (or going on inside your CVK ) fails/falters when exposed to the increased throughput and vacuum of the MCM..

No biggy.. It's just seems that, along with the MCM, you'll have to get inside your CVK, analyze how it is set up, and likely make changes before you'll get all the "goodness"..


I told myself I wasn't gonna say the below comment, but, I lied..
A problem with "pulling from 3k rpm on moderate hills" is kinda weird - Attempting to ride and throttle from 3K rpm (outside of 1st gear) is well within the realm of "lugging the engine"/improper operation of the KLX250S.. Any cruising @ 3k would require a downshift for proper acceleration. Since I ( and likely, most) have never attempted to operate from 3000 rpm - outside of 1st gear - I/we may not know anything about the way the KLX250 performs in this odd situation...

I would not be surprised if this "operating from 3k rpm" is actually fueled significantly through the pilot system (and fuel screw) meaning that changes to your perceived throttle response and accels might be just a twist of the fuel screw away - in which case your assessment that it seems "starved for fuel" may be accurate ! Anyway, if you want to ever try the MCM again, I'm certainly willing to help you figure out your CVK setup and change it accordingly..

To sum up, while MCM makes lots more TRQ below 6500 rpm, if non-MCM feels better to you, when riding at 3K rpm, more power to ya ...

 

Thanks for that offer! However, I really like riding more than wrenching and only did the cam timing change because it is relatively simple to do. When it comes to fine tuning carbs, that is a little beyond my ambition and maybe my pay grade.

I probably shouldn't have quoted a specific rpm. Maybe it was at 3000rpm, maybe 3500 rpm, maybe 4000rpm. You look down and try to see where the tach is at, and of course by the time you look down, the tach is no longer where it was at when you started to feel the bog. It felt like when your pumper mechanism in a carburated car is shot when you try to accelerate, and I don't mean hard acceleration. And however "good" or "bad" my riding style is, the stock setup never gave me any problems, quite the contrary. I don't really believe my CVK was/is in a bad state tune, at least for the stock cam timing. The only issue that had concerned me in the past was 50mpg fuel consumption, but as I have mentioned before I have pulled the sparkplug more than once and the color has been a nice tan.

Happy New Year!

 

14/49... does slow it down a tad. I ran a 13/47 for a bit, ran pretty tight at 65 mph, but way better in rough stuff and no bogging in the Michigan sand. If I was mainly street with only easy back roads and no tough off road I'd be running the 15/39. Grows long legs, with the sacrifice of acceleration, but that's expected.

 

Loc Tite or just proper torque?

 

I have done a bit of reading on the subject of fastener failure modes and root causes and for some reason a new to me idea popped into my head as to the root cause of fastener loss of tension over time. Would anyone know of any studies or data regarding the variation of nut or bolt head contact force with the clamped surface vs. the angle about the fastener's axis? It is well known that vibration can result in tension loss in bolts but I am asking why. If a nut touches down on one small area due to thread pitch then the bolt will be bent into the complementary angle of the pitch angle as the nut is torqued down and there will be a variation in the bearing force from min to max at 180 degrees apart. At least that is how I am imagining it. If that is true then should the vibration induced force exceed the static friction grip at the point of minimum contact force it follows that a torque will be induced in the fastener. That has lead me to the idea of using washers with a hard and soft layer. The soft will yield and conform to the pitch angle regardless of angular position and the hard to support and spread the load to the clamped parts. This way the contact force at the nut will be uniform and eliminate a source of loosening torque. Physicists and engineers please comment as it applies to this thread or PM me as fastener issues are getting to be a subject of interest in recent years as I have occasion to give my opinion at work when bolts fail and even amongst my colleagues, including engineers, there appears to be ignorance on bolt failure. Here is an interesting web page.

 

That was part of the problem... I couldn't remember if I used Loc Tite... I only have the blue on the shelf, but couldn't actually remember using it... LOL

 

From the article:
In general terms, the key to preventing self loosening of fasteners is to ensure that:
1. There is sufficient clamp force present on the joint interface to prevent relative motion between the bolt head or nut and the joint.
2. The joint is designed to allow for the effects of embedding and stress relaxation.
3. Proven thread locking devices are specified. Specifically, thread locking compounds - such as "Loctite", flanged fasteners such as "Whizlok" or torque prevailing fasteners such as "Nyloc". In general, loose washers, of the plain or spring variety, are not generally advisable.

My thoughts on a softer side of a washer would be the possibility of compression allowing the tension on the bolt to relax, since it is more malleable, and would also have a lower level of sheer strength in material used. It is about fastener stretch due to torque holding the surface contact at a level where it should not slip. Engineers will design with that in mind. I would think that fasteners torqued to the correct setting should do the job, but a dab of thread lock compound would definitely add to the security and safety wire would virtually insure it. My thoughts based on some engineering education and experience, but not, by far, the final word. I'm thinking a metallurgist with engineering knowledge or help would have a definite conclusive answer.

 

Now you're making me nervous!