Ct200u talk

[JimN]

Hi, I read your previous thread also and I'm thinking you're doing yourself a disservice by not being a little more specific with the information your imparting.
When you were changing parts did you do anything to bump up the compression or is that a stock length billet rod, stock piston, and stock head gasket?
Do you know the actual compression ratio?
Did you check clearances?
Your aluminum flywheel, do you know what timing your running?
What is your valve lash?
Have you looked at your spark plug and checked the gap? Is it the factory spark plug?
What is the air gap on your coil?
Did you do anything with the head? Can you check head temp?
Did you use a torque wrench?
Do you know what your TC is doing when your riding? Can you tell when the belt starts to shift and are you getting full belt shift?
(You swapped from a 40 sprocket to a 50 and only lost 2 mph. That is telling you something right there, and it is a good thing. If your engine is running good you need to keep dropping the gearing, I would suggest swapping the 10 tooth to an 8 tooth, it'll change you gear ratio from 5:1, 4.5 with belt shift, to 6.25:1, 5.6 w/belt shift.)
Have you tried any TC tuning with different springs?
Who is doing the testing you or your son? If gearing for your weight it will probably stand up on him right quick.
What distance are you dealing with when your doing a speed test?
As mentioned above, tach is really a necessity? Tach/temp would be better.

Have a good day, regards, Jim.

 

[Brandonmcgier192]

You shouldn't need a chain tensioner.

But why a straight chain? What gains do you expect to get? You will lose your low end.

I’m looking for more top end speed (street riding). Low end isn’t as important.

 

[Brandonmcgier192]

Hi, I read your previous thread also and I'm thinking you're doing yourself a disservice by not being a little more specific with the information your imparting.
When you were changing parts did you do anything to bump up the compression or is that a stock length billet rod, stock piston, and stock head gasket?
Do you know the actual compression ratio?
Did you check clearances?
Your aluminum flywheel, do you know what timing your running?
What is your valve lash?
Have you looked at your spark plug and checked the gap? Is it the factory spark plug?
What is the air gap on your coil?
Did you do anything with the head? Can you check head temp?
Did you use a torque wrench?
Do you know what your TC is doing when your riding? Can you tell when the belt starts to shift and are you getting full belt shift?
(You swapped from a 40 sprocket to a 50 and only lost 2 mph. That is telling you something right there, and it is a good thing. If your engine is running good you need to keep dropping the gearing, I would suggest swapping the 10 tooth to an 8 tooth, it'll change you gear ratio from 5:1, 4.5 with belt shift, to 6.25:1, 5.6 w/belt shift.)
Have you tried any TC tuning with different springs?
Who is doing the testing you or your son? If gearing for your weight it will probably stand up on him right quick.
What distance are you dealing with when your doing a speed test?
As mentioned above, tach is really a necessity? Tach/temp would be better.

Have a good day, regards, Jim.

I did not bump up the compression for the piston. Stock piston and head gasket. I do not know the compression ratio. I do not know if I checked the clearances. I left the stock timing key in for the aluminum flywheel - it came with a separate key but I don't know what the degrees affects. Valve lash is .005 intake and .004 exhaust. Its using the stock spark plug, but it is a little dirty from when it was running lean - I wiped it down a couple times with a towel so it isn't as bad. .030 air gap for the flywheel. I used a torque wrench when reinstalling parts and torque them to spec. The TC is shifting at top speeds - it looks fine to me. I haven't tried tunning with different springs. My son has been doing the testing - he is about 160. He rides on a 300 yard strip to measure the top speed. I'm not sure of the temps of the engines.

 

[JimN]

Valve lash is .005 intake and .004 exhaust.

Appreciate the reply. I think you valve lash is backwards. Is the cracked pipe the reason for the toasted ex. gasket? Or do you think something else is going on?
I plugged some numbers into this calculator http://www.csgnetwork.com/minibikepotentialspeedcalc.html , at a top speed of 38 mph with 10/50 sprockets for 5:1 gearing , approx. 4.5:1 after full belt shift. You're only turning about 3000/3100 rpms. If the belt only shifted to a 1:1 ratio instead of the .9:1 overdrive you only turning about 3400.

Here's the thing, when you had a top speed of 40 mph with the 10/40 tooth sprockets. 4:1, 3.6:1 with full belt shift, You were only turning 2600 rpm. About 2800 if the belt only shifted to a 1:1 ratio instead of .9:1. See where this is going. This is what @Strigoi and @SAS289 are alluding to.

With a tach that can be verified. The belt may not have even have shifted that far. That would have resulted in a higher rpm but also a lower (numerically higher) gear ratio. Say your running 10t/40t, if the belt only shifted to about a 1.9:1 ratio, you would at a 7.6:1 final ratio and be turning 5200 rpm but only going 38 mph. Granted it's only a mathematical calculation and reality will be different, but it is going to be close.

Your motor can't overcome the TC to get to the higher rpm it's capable of because the gearing is not right.

 

[Brandonmcgier192]

Appreciate the reply. I think you valve lash is backwards. Is the cracked pipe the reason for the toasted ex. gasket? Or do you think something else is going on?
I plugged some numbers into this calculator http://www.csgnetwork.com/minibikepotentialspeedcalc.html , at a top speed of 38 mph with 10/50 sprockets for 5:1 gearing , approx. 4.5:1 after full belt shift. You're only turning about 3000/3100 rpms. If the belt only shifted to a 1:1 ratio instead of the .9:1 overdrive you only turning about 3400.

Here's the thing, when you had a top speed of 40 mph with the 10/40 tooth sprockets. 4:1, 3.6:1 with full belt shift, You were only turning 2600 rpm. About 2800 if the belt only shifted to a 1:1 ratio instead of .9:1. See where this is going. This is what @Strigoi and @SAS289 are alluding to.

With a tach that can be verified. The belt may not have even have shifted that far. That would have resulted in a higher rpm but also a lower (numerically higher) gear ratio. Say your running 10t/40t, if the belt only shifted to about a 1.9:1 ratio, you would at a 7.6:1 final ratio and be turning 5200 rpm but only going 38 mph. Granted it's only a mathematical calculation and reality will be different, but it is going to be close.

Your motor can't overcome the TC to get to the higher rpm it's capable of because the gearing is not right.

What would be the best gearing to run with a t/c for street riding

 

[JimN]

Short answer is I don't know. Too many variables and I'm at the end of my wrench knowledge wise.
I think the cheapest way to start checking is to get the cheapo tach and change the 10t to an 8t sprocket and test from there. If you're still running the 50t rear.
That is if you have your exhuast sorted out and your confident of your engine tune.

Longer answer starts getting into cost, safety, and legal issues. Making these cheaply built bikes go beyond their design specs can get costly (in all 3 areas) quite quickly.

 

[SAS289]

Gearing is important but you will want more engine power. Look at post #3. He's not running a stage one 212 to get 60 mph.

And you may want to look at all engine options instead of just getting a Predator 212. You already have a rod and flywheel. The rod will not fit the two Predator 212's and the flywheel isn't a correct fit for either.

With the combos you ran so far there's no need for a billet rod and flywheel. Same with the straight chain you want to run.