So yup. Had the cam timing right. Put the 132 main back in and runs good. Honestly I'm really starting to think there's some truth to an even bigger main working better even with this stock cam setup
Gonna ride for a couple of weeks like this. If I feel I'm wrong, I'll go back and do the cam mod again. I just needed to do this to see if some of my other issues were a result of the cam mod.

 

Well, your modded stock muffler and KDX snorkel are an unknown for main jet size other than following the pack.. Put on a DGR or FMF slipon, pull the lid, and your able to use my data.. And a DJ132 is not even close to what's needed.. Other members are running DJ136/5n near sea level on standard cam timings and loving it.. I'm thinking standard timings could produce higher HP numbers way up high in the RPM band - but only if the main jet feeds it an AFR in the mid to upper 12's.. (12.5 to 12.8 :1) Even with the MCM, my bike picked up around 2hp on top once I got close to correct on the main jet.. It's ashame to loose that much HP over a $2.00 part..

 

So I 'undid' the cam mod and rode for a couple of weeks....
Didn't like it! It wasn't as much fun. Honestly. Maybe just where the torque is. I prefer a little more down low and didn't like reving it out all the time.

Changed it back . I like the bike again.

Gonna try a couple of larger main jets but I'm close to having it right for me.

 

I don't understand.

The mod moves the torque curve lower. The MCM mod actually discourages reving it out as the bulk of the power comes on around 4.5 - 7k rpm. Where as stock you're generally not seeing that power until 5.5K and up.

You sure you did it right?

 

Pwjm, I think our dyslexia is kik'in in.. He said he didn't like having to rev the snot out of it - so he re-did the MCM..

While I don't have charts to compare pre and post MCM powerbands, I do believe the MCM is enhanced efficiency/performance over the entire usable RPM range 4k-9.5k.. Remember we are not advancing both cams (which obviously would move the power lower) - we are advancing the intake cam and retarding the exhaust cam - and that changes everything.

Lets see.. with MCM the power stroke lasts a little longer as the exhaust valve opens later.. The intake starts a little sooner on the intake stroke as the intake valve opens a little sooner.. As far as overlap, I don't know.. Woof says overlap is increased with MCM - the # of degrees at which both valves are open/unseated at the same time at the top of exhaust stroke/beginning of intake stroke.. This seems reasonable. And generally, increased overlap favors higher RPM volumetric efficiency.. This and seat-o-pants is why I think MCM is all-round enhancement..

 

Ever consider doing half the modification might have been daft?

The fact remains that by peak power the full modification brings both cams into line with where they should be for known proven ICE cam timing. My bike runs strong with it after jetting is in. Even with the jetting off a bit the power was there in the deep sand I encountered in Michigan last summer.

Right now I'm running extreme tall gear, for no particular reason, but it pulls the gear fairly well. I went to a 15/39 just because I wanted a taller road gear last fall. The engine pulls it, but having a 650, I'm a bit jaded on how strong it is - the 650 is just plain strong, the 250 mediocre... until single track...

Key point is that this is a reasoned out and well documented change, with dyno charting as well. The science of cam timing is taken into account. As I said before, I've seen the same reasoning applied to the 1986 Nighthawk S by the well known Joe Minton, back in 1989. Same thing - exhaust too advanced, intake too retarded, changing them (both) gained useable power over the entire range.

Doing half of something and expecting the same results simply does not make scientific or mechanical sense. Changing the flow only at the intake may not have been enough.

In addition, engineers are tuning this bike to get it through the EPA, possibly part of the reason for the 10,500 rpm redline since that is considered when testing. Might put the bike in a more optimum range based on number play. Clearly no knowledgeable engineer would jet the bike like it is for performance reasons and possibly the same is true with cam timing. They do it for other reasons as well.

I really do need to alter that gearing... maybe a 14/47 is the ticket.

 

You are missing the point entirely... It is not "moving the torque curve down". It is delivering more power from a lower rpm up through the power band to the peak. More torque nothing "moved". Sure we say the torque curve moved down, but that is only a relative term to a line on paper. The fact is more power where needed.

The power is fatter from lower up through the range - more power where you can actually use it best. That is the same thought process with a big bore, the larger displacement gives more power through the entire range. It isn't about high revs. In fact the stock engine shows true power peak at around 8600 rpm, I believe Marcelino ends up around 8200 or so. Key point - who is always up around 8600? Most ride in and around 4500-6000 rpm, so boosting torque (true power versus the calculated horsepower) is definitely good. More punch where you need it to pass a car or pull away.

Which brings up the point - the 10,500 rpm red line is pure wishful thinking if you think it is useable power up there nearly 2000 rpm above the actual factory claimed peak. It is all over-rev. I learned decades ago that most Japanese bike red lines are anywhere from 500-2000 rpm above the real horsepower peak. Find the horsepower claims for a bike and you will see that. My old Nighthawk S peaked around 9500, but the red line was 10,500. Reving there was a waste.

Marcelino's mod allows a rider to work with more power through the entire power range versus the stock set up, only losing a few hundred rpm at the very top. That allows a rider to not have to gear as low to get similar performance.

Look again at that higher torque curve through virtually all the power range and think of it as what it is - the ability to do more work, pull stronger. Now think about it... do you want less power at 4000 rpm? Less at 5000 rpm?, Less at 6000 rpm? Less at 7000 rpm? Do you want to have to rev your bike harder, slip the clutch more? Those are avoided when power is increased in the lower range. The cam mod and big bores deliver more mid range where it is useful.

 

Put my head down over the bars on a long level straight-away, nailed it, then chickened out at 91 mph indicated (A tire(s) started bouncing).. That's MCM + FMF + Dyno Tuned + stock sprockets for ya..

 

No not daft. I knew all along what I was doing. I also made it abundantly clear that I only ever did 1/2 the mod so that others can use the info as they see fit.

I did my own research and calculations and only did half the mod for the following reasons
* Most power gain is probably due to the higher effective compression ratio (the inlet valve closes earlier)
* Risky amounts of valve overlap might cause valve/valve or valve/piston clearance issues as the engine wears
* Didn't want to mess with the ACR
* I didn't trust M's power curves and calculated some of his angles might be slightly wrong

It's probably me that is wrong, but that's fine. Everyone else seems happy with the mod, so that's also fine.

BTW fuel consumption has reduced by about 10% for the 3 tanks of juice I used since undoing the 1/2 mod.

 

Again - half is not all. Run to the 50 with the football and it ain't a touchdown.

You dissed doing the mod because going HALF WAY didn't work for you as you wanted. What else is there to say? Do half don't get good results. Either go back and do it all to see if there is more or return to stock. You did the latter.

I did have one advantage when it came to the worthless KACR, I knew riders disabled them on their 650s - far tougher to turn over even with the KACR - so I knew the 250 would likely spin just fine without. So I disabled it and did the whole change.