Gas mileage

From what you've said in other posts, I think you are running super rich. Here watch this video.

You said you wouldn't go back to the stock NT carb in a different thread. Just put it on and see the difference. I got the HP carb a week after I put my first bike together and got it running (which took about a month, mainly from problems I created figuring out what the problem was). After almost two months I realized the HP carb was hurting performance more than helping. Only because of tuning though. You need to play around with jet sizes and find out which jet is PERFECT... you have to buy jets and I never found the right one. I didn't try very hard honestly either. With the NT stock carb you can adjust your fuel air ratio somewhat without rejetting. I live at 4,300 feet so I adjusted mine at the leanest setting and got the best results. Results may vary. But even with my HP carb I can go 30 miles on a tank without running out. My routine was 2 days at 15 miles commute round trip and refill. Never did I think I was close to running out.

There is a sticky on the NT carb in the forum. When I was brand new I read it and it made no sense to me. I'm about four months into the hobby and still learning every day. I reread that NT carb sticky thread again and with experience, I understood a lot more of it and it made me decide to finally remove the HP carb and give the NT a try. Honestly I was amazed. The issue of constantly being super gentle on the throttle to prevent fourstroking made riding the bike almost unenjoyable. Now with the NT back on, fourstroking is gone except for at wide open.

I just trying to encourage you to give that stock carb another try and play with the mixture. I think you'll be satisfied with the results.
 
personally, I only swapped out the NT bcs it is pretty small. it's not a bad carb at all, just it's 13 or 14mm,,
 
I have the hp carb on mine and when I first put in on I got 10 mph outta my top end but I been doing this n that little things like doubled my bottom cylinder or case gasket and dremeled a little out of exhaust ports on my cylinder and a tiny bit to the breathers and the intake manifold on the cylinder and so far I'm regretting it I lost about 8 mph out of my top end
 
I have the hp carb on mine and when I first put in on I got 10 mph outta my top end but I been doing this n that little things like doubled my bottom cylinder or case gasket and dremeled a little out of exhaust ports on my cylinder and a tiny bit to the breathers and the intake manifold on the cylinder and so far I'm regretting it I lost about 8 mph out of my top end

Well actually I lost 10 but I put on a bbr tuning volt master stage 2 today and got 2 mph back
 
A bigger carb can potentially make more power, but only if the rest of the system can handle it. It could be possible that without further mods to the rest of the engine (including exhaust) that you only impede performance adding a larger carb. There needs to be a minimum amount of air flowing through the carb before the venturi effect can work right. A single barrel carb meant for a car would never work on our tiny engines, let alone one designed for a 250. Even if you tried all the jet sizes available and even soldered/drilled your jets for broader sizing, unless your engine can pull air hard enough, it just won't work right. A slightly modded nt carb tuned right can easily out-perform a carb meant for a 125cc engine (try and tune it as I laugh) that can't breath well enough to even draw fuel till very high rpms.
Just do this one test. Stick a straw in a cup of water and blow hard across the top. You will see the water run up and spray off the top. Now try to do the same thing with a half inch pipe. Bet you barely even notice the water rise unless you have superman lungs. That's the simplest way to explain how a carb works. Bigger isn't always better till it can breath right to function correctly.
 
when you opened ports with the dremel, did you also change the top/bottom edges? that would change port timing from stock maybe a lot. you shouldn'tve lost top unless you went little too far,,
I learned only going wider like 2 or 3mm has a really nice punch, but the pipe has to match what your after. I hogged my first jug out n basically made it worthless (unless itll bolt on a 125cc lol.) they're cheap tho
 
Yeah I need to take more time at it and match my intake and manifold to match the cylinder.... I also need to do the piston. I just didnt take m time I was rushing...of I was considering just buying a cylinder already ported and setup for a reed valve. And a high performance head...I can get all of the above for right around a hundo. Which would de the best way to go in your opinion. Also I just put on the bbr tuning volt master stage 2 cdi. What's the best spark plug for that set up anyone have any suggestions ?
 
I also blew out my exaust manifold gasket...so .....i'm running with absolutely no gasket right now that may have something to do with the loss in top end.
 
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