'86 atc 250r

[ride_red_95]

Awhile back I blew the base gasket on my R, and finally got it rebuilt by a local shop. It's bored .40 over, has a 38mm keihn carb, vforce reeds, port and polished head, and an fmf header now. It fires right up on the first or second kick every time, it idles good and sounds good. But the thing is it feels real boggy and when the powerband kicks in it ain't like it used to be. It barely cuts out when your in the power band its hard to notice but its there. Kinda seems like its loadin up and gettin to much fuel. I've put several new spark plugs it in and it hasn't changed any. So now I'm Feelin like the jetting needs leaned out some but I don't anything bout jetting sizes. I could really use some help on this one and I'd appreciate it, thanks. BTW I always run with just 87 pump octane would 91 make any difference now that its beefed up a little more?

[bkm]

First thing to do is a compression test to see what type of gas you need to be using. At a minimum I always use the highest octane available at the pump. Next what type of oil do you use and what is it mixed at? The check the plug and see if its black and wet. You may need to come down on the jetting but first you need to copy what jets you have in the carb as it sits now to use as a baseline.

Its all about controlling all variables such as gas to oil ratio and sticking with it, then base lining the carb settings and performing plug chops at idle, part, and full. Buy a box of NGK B8ES plugs and play with the gap.

Very seldom does a bike go together after its been modified and it all falls into place.

[NOSBIGSHOT]

Lower the needle , and like he said ....bring a plug wrench .I also would watch how much oil you put in the air filter .

[ride_red_95]

I'm not real smart on messing with the carb. Lower the needle? Plug chops? What do you guys recommend for the oil to gas ratio?

[Lee350x]

If you shut your gas off while its running and drive around a bit the fuel in the bowl of the carb will start to burn out and it will lean your jetting. If its starts to run better with the gas off you know you need to go leaner.

[bkm]

If you shut your gas off while its running and drive around a bit the fuel in the bowl of the carb will start to burn out and it will lean your jetting. If its starts to run better with the gas off you know you need to go leaner.

I'm usually not one to bust somebody's chops when handing out advise, but that is horrible advise on how to tune a carb. You don't use the damn petcock to determine jetting.

ride_red: Before you can be helped we need to know what the current jetting is inside the carb as we speak, and you need to have a little knowledge on how to tune it or we're pretty much just pissing in the wind here.

[ceaserthethird]

link to - Jetting 101

Please read everything on this link !

http://www.3wheelerworld.com/showthread.php?55086-Carb-Jetting-101-Terms-Tips-and-Jetting-Theory

[ride_red_95]

Bkm- how can I tell what size my main jet is? Ceaser- very good info on that link, thanks. From what I've read my main jet is to rich. Idk what the stock size for the 38mm keihin, but when I found out how much smaller should I go as a starting point?

[mrmello]

I would say drop down one size at a time. Drop one size ride it and check the plug after a good wide open run. Dropping it too much would lean it out and you might end up melting down the piston

[bkm]

It will say the size on the bottom of the jet right next to the hole. It will be a 1xx number.