70cc 1e40qmb only 40mph

[1e40qmbchris]

Hi. I'm trying to tune the clutch and variator but with no luck. Iv tried rollers and contra springs. It sets off OK but it tops out at 40mph. It's got a naraku 70cc kit on it and a naraku hpc crank. It pulls hardest with 4.5 gram rollers and a 1500rpm contra spring but won't go over 40 unless going down a steep hill. Any ideas guys? To add to that my piston at tdc is about 1mm lower than the top of the cylinder. If I put a thinner base gasket on it and raise the compression is it going to be worth the work for the performance gain?

[pinkscoot]

What is your squish, sounds like it's pretty high. Check you compression and see what you have. What is the engine taching out at?

[90GTVert]

Is this the Naraku kit that does not include a new cylinder head with it? I've never used one, but I would assume that you may need to maintain a larger squish clearance to keep compression in check. Not really sure. Still, you could have a couple mm of squish clearance, which is a lot. As said, it would be best to figure out where the compression is before you make a move. Checking cranking compression is not terribly precise, but it gives an idea of what's up and most people have no desire to go through the long process of finding the actual compression ratio. Test multiple times and try to make sure it seals well.

Using a tach for tuning would be helpful.

[Zino]

For your Cvt
After finding your weigts that work best
do the sharpie test make a mark like this and go down th road full blast and see how much space is left in mm
most stock variators you can get under 3 mm


Squish
For the Snappiest builds under 1 mm- 1.5 mm is a good target .
If you can get below 1mm to ..8 to .9 that makes it even snappier

BBK kit
This is not a High Rpm kit so it might not add alot of top speed by itself
It has that Low end Grunt that gets you up to speed faster .

[1e40qmbchris]

Thanks guys I will try all of the above and report back with my results around this time tomorrow.

[1e40qmbchris]

Hi iv done a compression test and it comes in at 165psi cold with throttle closed and 175 psi cold with throttle open. My squish came out at 1.2 millimeters. I haven't had time to test any of the variator stuff yet. What do you guys think to those results?

[aeroxbud]

Compression sounds fine. Squish could be tighter. But perhaps it's designed like that if your using the 50cc head?

[1e40qmbchris]

I am using the 50cc head. So the compression is ok

[90GTVert]

Compression numbers are plenty high. I would not attempt to tighten squish with those figures. If you want to tighten squish up at some point, it would be best to get a head designed for the bore diameter with a squish band. Probably only minimal gains there, so I'd say it's not likely to be worth the extra money and time unless you start trying to push for more or have detonation issues at some point.

[Zino]

I agree with Brent
That is strong compression
I would not tighten squish up anymore than that .

3 things for speed power rpms and gear ratio

Your Kit has the power

If you have a tach
What peak rpms are you maxing out at.

Check final gear ratio
With your transmission cover off count how many times the clutch bell turns for every turn of the wheel.

Depending on if its Long Case Minarelli Being above 13 clutch turns holds you back .

Short case being above 11 holds you back .

[repherence2]

What size belt are you running?

[racegt50]

Have you tried a 2k contra spring? After I fitted my 70cc stage 6 kit I would top out at 45mph using 4.5g rollers for take off changed my contra to 2k and I can now do 60mph on the speedo, what exhaust do you have fitted aswell? A cheapo off eBay for 70 quid certainly changed how mine ran, I had a wider powerband than I do now with the technigas triops system I now have fitted that doesn't pull hard until 8kish.