I put the stiffer stock spring in this afternoon. I wanted to install the #40 jet, but the top of the phillips screw holding the throttle assembly to the carb was stripped and I couldn't get it out so I decided to just change the spring.

Initial impressions, well it seems to be stronger. The front tire will lift about a foot off the ground on the street when it couldn't before. I get a lot of wheel spin which I think prohibits a true power wheelie. I'm on the original tires (3500 miles) and they're dry and worn and I'm 130lbs so not much weight on the back tire. I also probably sit closer to the tank than most.

I still need to go to my usual riding spots to know for sure, but it does feel more tuned. snappier with quicker revs from low rpms to about 8000.

 

130lbs! Your experience (with the bike's performance) will be very different than mine (@230lbs), but it sounds like you got the increase expected.. The stock spring alleviates a small RPM range of overfueling (usually 5.5-6k rpm when you go WOT in 4th gear from 3.5k).. This overfueling is seen on a dyno test/chart but, IMO, depending on your riding style and your light weight, you may or may not have ever actually experienced it. However, it now seems conclusive that NON-MCM lidless running should be stock spring only...

Snappier with quicker revving 3k-7k is exactly what is expected..Congrats!

 

I'm running the 152K, 2152 kit needle with stock spring at 2N, #40 jet and 1 3/4 turns out, lidless, Q4 with stock header. I'm also running 13 & 50 tooth with a 110 chain as I only run this as a woods bike, with very limited street use. The gearing would make a difference as well

 

Mine is drilled. Haven't gotten
to test ride yet. 3 turns + seemed off @ 2N. I will adjust the fuel screw this time as well. Hopefully this weekend during our heat wave in middle TN...

 

13/50 ! That's the big difference with your wheelie test showing such crazy capability compared to those with stock 14/42..

It would be interesting to add a Megabomb header and a K158 main jet to your bike - the gearing would tend to maintain usable power below 6k, but the radical increases above 6k would create "race bike" like performance..

Alternatively, simply adding the MCM to your current setup would create a crazy "TRQ monster" - radical increases in power levels below 7K with same (or near same) power levels above..



I assume highway performance is limited due to the high RPM's "at speed" ?

 

Wow, @ 13/50 you must top out around 60mph and shift 4 times before you're through an intersection. However, I bet the woods are a blast! true dirtbike gearing.

 

60 mph equates to about 8,000rpm, but I'm only on country roads to get to the trails (I can get up to 70 but she's revving pretty good...50-55 is comfortable). Yes, more shifting, but I can select the gearing I want for any situation, plus shifting is fun.

As a note, my buddies KDX 250 can't keep up on the road as he maxes out at about 50mph. He's obviously has more power in the woods, but his 1st gear is almost unusable.....he's in 2nd the entire time I'm in 1st

I do mainly single track, technical trails. In the woods I can creep mine in 1st on tight trails and lift the front anytime to clear obstacles, or blast out a turn with the front wheel up. Second and third on a fire road is awesome....the front end just skips along along with the rooster tails one would expect.

This is no longer a street bike that is good on the trails. This is a full on woods bike that is ok on the street. Don't get me wrong, it's not a Husky but it does pretty darn good for what it started out as.

 

Kevin, Fud for Thot, with your gearing, if you setup the bike like mine (adding FMF Megabomb, FMF PowerCore 4, MCM, DJ144/1N) you'll have power you won't believe from 4k-10.5k RPM.. I can't even imagine my power levels magnified with 13/50 spraughkets !

What's important is that you still have several "next level performance increases" available for future enjoyment..

 

I assume the Q4 will have the same type of output as the Power Core 4. I'm a bit vervous of doing the MCM. I'm pretty good at puttering, but I've never gone "into" an engine. Also, without the MCM I've heard that the stock header is the way to go.

 

MCM is actually very simple now days. If you can pull the cam cover off the top of the Head, the cam chain tensioner, and the spark plug, you're "there".. Rotate till the cam gears' marks "line up", alter timing one cam at a time, pull the KACR spring off the KACR (it's on the end of the exhaust cam), button it up, and DONE!

The stock header makes more TRQ below 7k rpms, MCM or not, compared to a larger dia. full system..

The outlet on the PC4 is 1.5" , Q4 with standard tip is 1.4375" (1 7/16")... So probably very similar.. Q4 is waaay mo hush hush tho..