I just put a new hd air filter on my nt carb. Changed the jet from #70 to a #69. Put a carb ring on the intake tube. Now I can go a constant 23-24 but after a min it will over revv and lose power power( kinda like a govener in a typical car at top speed ) what's the deal. Open question in this thread (new content to nt tuning)
Nt Carb tuning
- Thread starter SavageBlunts904
- Start date
usually, running lean will make th motor over rev. From wot u describe it sounds like ur float level is set too low. With the carb off & the bowl & gasket removed, & the carb upside down it should b 21mm from the gasket seating surface 2 the highest point on the float, which will b the bottom of the float. This is the point that the needle & seat should shut off the fuel flow. Cheers
Ok, I just read back thru all 3 pages. If everything u have tried has not fixed ur problem, check 4 an air leak between the crankcases (soapy water & turn motor over, watch 4 bubbles). Mine had one new from factory & I've heard of others having same. I temorarily fixed with silicone till I tore down & replaced bearings etc. Cheers
What part of the engine is the crank case, I'm having a real problem of the engine bogginh after 23.5 mph. Like I said before it feels like a cars govenor.
This is a constant over 40 miles since my last post.
This is a constant over 40 miles since my last post.
Last edited:
The cases r wot the cylinder is sitting on top of. They join in the middle, all the way round. Mine leaked behind the cylinder, under the carb from the gasket between the case halves not being properly installed, but check all round the join. It sucks air in on piston upstroke & blows out on downstroke, causing leaning & power loss. A lean running motor will rev well but is gutless & runs hot. Exhaust note is thin & crackly. Cheers
Ivan please expand on your last post, go advanced for me please. All info is greatly appreciated!!!!!
Mate, I'm totally computer illiterate, posting from & old nokia phone & thats about my limit. Ok, where the front of the motor mounts to ur bike frame, c the vertical join, runs up 2 the cylinder & down under the motor all the way round 2 the rear mount then continues 2 the back of the cylinder (cylinder is the thing with all fins). That join is the join of the 2 crankcase halves. Cheers
The join runs right thru the middle of both front & rear mount, in the same plane as ur bike frame tubes the motor mounts 2. If u imagine splitting it where it sits on the bike, u'd have 1 crankcase half on either side of ur bike. Good luck with it. Cheers
Once u've found that join, mix up some water & dishwashing liquid. Slop some on the parts of the join facing upwards & turn ur rear wheel 2 turn the motor over. Look 4 it blowing out along the join. Do it all round the join. U'll need 2 turn bike upside down 2 do the bottom. If thats no it check crank seals. Cheers
Last edited:
Thanks again for all the help.
First you're right .73 was already too big and going bigger was only, well going the wrong way. I was getting 4 stroking at WOT, just didn't not recognizing it. I took pictures of my plug chops and found I was getting richer, so,,,,
I changed my mix to 40:1 and got the stock jet .68 and a .70 which is what it probably should have been. (I know patience, I drilled up two sizes in the beginning. I also )
While I was at it I got a free flow air cleaner and a new machined inlet manifold with new gasket. (No leaks for sure!) and a new NGK spark plug.
I put an expansion chamber on my bike but it didn't do that much, until I noticed that it was welded by a monkey. At least 25% of the pathway was blocked by a huge @$$ burr and misalignment, I took out my dremel and removed the burr and ground the flange until it matched the exhaust port. I've noticed a exhaust leak and I also got a new gasket.
Lastly I got a smaller sprocket 36 tooth vs my 44 I'll test it all tomorrow!
Last edited:
Glad to hear it's gonna come together for you.
It's a fine line when you get it close. A couple thousands of an inch in a main jet can make a huge performance difference.
It runs great lean, no 4 stroking wide open throttle but careful when the motor gets good and hot that it's not too lean. Nobody likes cooked brown seized up pistons.
Also cold dense fall and winter air makes mine want a little bit bigger jet than the hot humid summer air. Fickle 2- strokes.
TiM
It's a fine line when you get it close. A couple thousands of an inch in a main jet can make a huge performance difference.
It runs great lean, no 4 stroking wide open throttle but careful when the motor gets good and hot that it's not too lean. Nobody likes cooked brown seized up pistons.
Also cold dense fall and winter air makes mine want a little bit bigger jet than the hot humid summer air. Fickle 2- strokes.
TiM
Yeah back in the day we only worried about being too lean.
These are funny and flaky motors for sure!
These are funny and flaky motors for sure!
My broken in(about 5-600 miles of use) China 66cc 2 stroke 4 strokes at WOT. I am running 40 to 1 oil. How do I make the jet smaller? Is this the solder technique I have heard of? Pleae explain.
Hey leadfarmer the link below should help, read the post by VMB he has probably done a lot of jet soldering.
http://motorbicycling.com/showthread.php?t=36497
http://motorbicycling.com/showthread.php?t=36497
Last edited:
I read the thread you mentioned. Someone posted, why don't you just buy a smaller jegt? Is that an option of an NT carb? If so, that seems simpler. Are different jet sizes available for purchase?
Thatdax lists jets, but you may need a couple to get yours tuned. I find it quicker for me to solder it up and drill to what is needed, I did it back in the 80's on gas grills when converting from natural gas to propane. bigger drill bits but the same process.
http://thatsdax.com/
http://thatsdax.com/
The only problem with drilling out jets is, who has all the right bits?
I went to my old bosses shop (this man has all the toys! Mills, Lathes, tube benders, anything but not every metric drill bit) and I had to jump up two sizes because it was the drill we had. Now if you have a drill press and the right bits it is a piece of cake to solder and then drill to the correct size.
PistonBikes, Spooky, and Sick Bike pars all sell jets for less than 5 each.
I'd get the .64mm,.66mm, .68mm. and perhaps not a .70mm that may be too big.
One caution if you buy jets, make sure you're getting CNS or NT jets, the threads are different. NT jets also fit the stock carbs. CNS do not! (found out the hard way.)
The cost is small and it takes a morning or afternoon to tell you what you need.
Listen to the experienced guys here, they know their stuff.
I went to my old bosses shop (this man has all the toys! Mills, Lathes, tube benders, anything but not every metric drill bit) and I had to jump up two sizes because it was the drill we had. Now if you have a drill press and the right bits it is a piece of cake to solder and then drill to the correct size.
PistonBikes, Spooky, and Sick Bike pars all sell jets for less than 5 each.
I'd get the .64mm,.66mm, .68mm. and perhaps not a .70mm that may be too big.
One caution if you buy jets, make sure you're getting CNS or NT jets, the threads are different. NT jets also fit the stock carbs. CNS do not! (found out the hard way.)
The cost is small and it takes a morning or afternoon to tell you what you need.
Listen to the experienced guys here, they know their stuff.
Last edited:
Woo Hoo! Wow now my China girl is running brilliant!
Back to stock carb with stock jet. Speed demon expansion chamber with high flow air cleaner. I installed the 36 tooth sprocket and still have plenty of power at take off.
Now I have a top end that's a pleasant 28-30 mph without vibration.
After my brother and I keep loosing fender bolts and a few stress cracks decided that we no longer needed fenders so, off they went. He also noticed my chain guard was cracked and removed that too. It seems that I had some noise from all they loose and broken tins. Really happy with my bike. Thanks again for all the help.
Back to stock carb with stock jet. Speed demon expansion chamber with high flow air cleaner. I installed the 36 tooth sprocket and still have plenty of power at take off.
Now I have a top end that's a pleasant 28-30 mph without vibration.
After my brother and I keep loosing fender bolts and a few stress cracks decided that we no longer needed fenders so, off they went. He also noticed my chain guard was cracked and removed that too. It seems that I had some noise from all they loose and broken tins. Really happy with my bike. Thanks again for all the help.
When I started riding the 66cc motorized bicycle that I assembled back in April 2012, the bike would start up after popping clutch a few times, maybe more. In June, the same thing except not only would it start easier "less times", but I still had to give it gas to get going. Now here in well about September, with a 34 tooth sprocket, when I let out the clutch after going about 4-5mph - it starts every time and takes off without pedaling at all! And the coolest thing, all the times before I had to give it gas, pedal faster and pop clutch more times, had a 41 tooth sprocket!!.. the best part is it doesn't even rev high "IN IDLE"- How sweet is that?
Last edited: