New rps magician 250 - getting to 80mph

[slithica]

Update:



I drove it finally! Warmed up a little today and I had some time.


It drove and shifted fine, I still have trouble getting it into neutral while it's running.


Gotta feather it.



I sputter quite a bit at max throttle, so I believe it's running too rich, I'll go down a size on my jets and test it out.


I got up to 60, with about 70% throttle pretty easily, so I'm hoping with proper jetting to go faster soon when I can give it full throttle.



acceleration feels pretty good even with the gear ratio changes.

[China Rider 27]

Look forward to seeing your results. That 40 tooth sprocket is the key to speed. IMO, Break it in good for 500 miles before you lean on it too hard. You should not be hitting at WOT until you get some break in on it. The neutral is always tough during break in.

[Megadan]

The top speed will be a bit behind, and the neutral thing will eventually sort itself out, after you put a few hundred miles on it. Once the motor breaks in the top end will pick up more, usually after at least 300-400 miles.

[slithica]

Drove it for a short ride tonight, changed the jets out first.


main: 125
idle: 35


It had significantly more power and only sputtered once. I believe I may need to go down a jet to 120, I'm unsure.



I'll drive it for a good trip tomorrow probably around 120 miles.


So far it seems to run pretty well.

[slithica]

Update: drove it a fair bit, speedo is off by about 10mph at 60. It shows 70 on gauge, gps shows around 60.


The odometer seems to be off as well, a 54 mile drive shows as a 90 mile. Which is still incorrect in kilometers... soooo yeah, I wonder if there is any way to adjust this or maybe I'll just change the entire thing.



I do still sputter at 80%+ throttle.



I'm unsure if it's from running rich, I'm more leaning towards the exhaust being too restrictive, I'm going to gut the cat pretty soon and go from there.



At the moment, the top speed is about 63mph at 70-80% throttle. I can maintain that speed on even terrain, uphill I go down to about 55-58mph.


I will update after gutting the cat and driving it around a bit more. At the moment it seems to be getting about 80mpg. I'll have more concrete numbers later though.

[TxTaoRider]

After you do your top speed run for a few minutes, try pulling in the clutch and killing the engine. Coast to the roadside and pull the spark plug and see what color it is. Heck snap some pics so we can all go "ooh" and "ah" and give our opinions on whether you're rich or lean.

[slithica]

I looked at it, it's a nice light tan color. Basically what it should be. If anything I think it might be a tiny bit lean, either way based on the spark plug I could put a larger jet in. I am pretty sure it's the exhaust restriction. If not I'll have fun finding out what it is.



My next thing is gutting the cat.

[slithica]

For anyone curious about how this turned out, read the original post.

[Amateur]

The 50cc world speed record is 91mph.

Aerodynamics. You will almost surely need a fairing to accomplish your goal.

I know it can be done. It's really not that difficult and you don't need rocket boosters or 40hp china bike. You need to be slippery. However considering your bench racing approach and obsession with HP that you probably don't really know how to get from this motor. "Gutting the cat" in hopes of gaining measurable power tells all I need to know. I will personally never believe it happened without seeing a video of a gps speedo.

At 65mph things happen with wind vs. frontal area. Reaching 80 and holding 80 are two totally different animals.

[Amateur]

Originally Posted by China Rider 27

Look forward to seeing your results. That 40 tooth sprocket is the key to speed. IMO, Break it in good for 500 miles before you lean on it too hard. You should not be hitting at WOT until you get some break in on it. The neutral is always tough during break in.

Wide open throttle under load to redline through every gear is actually part of a good breakin process for a motor that's going to be pushed hard.

None of you have ever built a race motor and it shows.

[JerryHawk250]

Originally Posted by Amateur

Wide open throttle under load to redline through every gear is actually part of a good breakin process for a motor that's going to be pushed hard.

None of you have ever built a race motor and it shows.

You are absolutely correct. Most people on here never built a racing motor. But these Chinese engine are not racing motors and are not built to the same tolerance as a racing motor. Most of these engines are very tight from the factory and require a break in period. That's when you read those thread on here " I blew my engine up at WOT and don't know why" .
We are not here to bash other on there knowledge of motorcycle. We are here to help.

[franque]

Originally Posted by slithica

For anyone curious about how this turned out, read the original post.

Get the tires balanced, that's probably your wobble.


Also, @amateur, not everyone believes in a gentle break-in on this site, please don't make assumptions. How's about you make a new thread and show us the race motors *you've* built.

[Amateur]

If you want that bike to do 80 with no fairing, it's gonna need a race motor. That's my point.

Also, total BS. Every single engine can be broken in this way. Cylinder pressure is what seats the rings. You'll always make more power by breaking in a motor this way. You will never, ever blow up an engine by breaking it in the way I just told you to. Don't ever rev a new engine in neutral. Don't miss any shifts during the procedure.

I'm here to correct your misinformation. I know you don't like it.

Aerodynamics.

[Amateur]

Originally Posted by franque

Get the tires balanced, that's probably your wobble.


Also, @amateur, not everyone believes in a gentle break-in on this site, please don't make assumptions. How's about you make a new thread and show us the race motors *you've* built.

I totally would if this site supported pics bigger than a flea.

Don't try to make this thread about me. Read my input and get on with your life.

Or delete all of my posts and continue on telling your audience that you're always right. No biggie either way.

[China Rider 27]

Originally Posted by Amateur

I totally would if this site supported pics bigger than a flea.

Don't try to make this thread about me. Read my input and get on with your life.

Or delete all of my posts and continue on telling your audience that you're always right. No biggie either way.

What China bike do you own? The best evidence I have seen about engine break in is as follows and we see some wear with the ride it like you stole it. Words are words, evidence is evidence. Given the state of the tolerances and metallurgy on China Bikes I opt for an easier break in.