Like 50, Naraku Racing CDI, Need Advice on Improving Top Speed

[Vintage MX]

Hi folks,

I'm an old hand at tuning two stroke dirt bikes but this is my first scooter.  Sure would appreciate some good advice here.  These are the facts so far:

1. I have a 2012 Like 50 two stroke with 300 miles on it. 
2. After 200 easy break in miles, I replaced the exhaust with a Technigas Silent Pro.  The exhaust restrictions (intake and outlet) were removed. 
3. Jetting was raised to an 84 but the restrictor in the airbox inlet was left in place.  I live at 2700 feet above sea level.  Plug readings show light tan on the insulator. 
4. Just put on a Naraku unrestricted CDI from Racing Planet.  Was billed as an exacted replacement that would raise RPM. 
5. I have installed the unrestricted 20x38 bushing. 
6. Fuel is 92 octane unleaded, oil is Royal Purple full synthetic.

Stock mph (ideal conditions, uncorrected speedo reading) with a 215 pound rider was 28mph.

With the unrestricted bushing, 35mph.

With the jetting and Silent Pro Exhaust, 40mph.

That all held true until 250 miles.  Then the bike gradually began to loose top speed until it would only top out at 36mph.  Max RPM seems unchanged.  Engine runs well at all RPM levels.

At 300 miles, I installed the Naraku CDI.  No increase at all in RPM or top speed, still 36mph.

So here are my questions:

1. Why the gradual loss in top speed in the 50 miles before I put on the Naraku CDI?  Is it possible that the clutch or belt is slipping?  What's the best fix?  Do I need further modifications to the transmission to run with the small increase in horsepower that comes from the Technigas Silent Pro?

2. Why no RPM increase with the Naraku?  As an experiment, I removed the airbox restrictor.  Made no improvement at all.

Bottom line: I would like to get a consistent 40 to 45 mph under ideal conditions.  What will this take?

Thanks in advance to all who offer their ideas.

Tom

[245luigi]

I dont have all the answers but I can answer #2.

The stock Like 50 2T CDI comes with no rev limiter. There shouldnt be any reason to change it. I have no idea what the Naraku does to the bike but with my limited experience with Naraku...screw em.

I have had some experience playing with the airbox restriction and it only has led to bad times. It appears the stock carb cannot handle whatever happens when you remove that thing. Especially not being able to mess with the needle settings. When I removed it, I was able to tune my idle jet and main jet but had a lean spot with the needle. I feel its best to leave the restrictor in, espescially with the stock carb.

The loss in speed is very weird and I didnt experience it. I would wait for others to chime in. On the Like50, as well as other bikes it is recommended to change the variator/rollers/torque spring when adding the exhaust. You may see a higher top speed but you will definitley see better takeoff and acceleration once the CVT has been tuned.

[245luigi]

Oh I forgot your bottom line.

I could get consistent 43mph by having:

Tecnigas Next R Exhaust
90 Main Jet (im at sea level)
Stock Idle Jet
Stock Airbox with Restriction
Naraku Sports Variator (Do yourself a favor and go Malossi or Polini)
8g Rollers
1500 rpm Torque Spring
93 Octane

[wassonii]

Yes to all that, though I would also throw in the variator mix as a possibility Jasil/Top Racing. I would at least get comparable to the 1000rpm spring for your clutch. The rollers will have to get played with to find the set-up for you. Before getting my LeoVince, I had a Tecnigas Silent Sport and could get a decent top speed after playing with rollers.

[245luigi]

What wass said regarding the variator is correct. What I meant was anything but Naraku haha!

[Vintage MX]

Thanks so much for the good advice.  I have ordered a 1000 RPM torque spring from Racing Planet and will report back when it arrives.  If I need to do a Malossi or Polini variator, I'll try that next.

[ParaIndiana]

Some of the things that could cause you to lose some top speed:
Belt slipping causing wear
Rollers wearing down and losing weight/balance
Running lean causing cylinder damage, compression loss
Running rich causing buildup on the plug
Bad gas

I hope this helps!

[245luigi]

Wass and ParaIndiana have risen from the dead.

As a like 50 contributor thissss isss awesomeeeeeeeeeeeeee!

WOO HOO!!

[ParaIndiana]

I was not dead...only hibernating.