Carb Jetting 101: Terms, Tips and Jetting Theory

**Billy Golightly** · 03-04-2008, 07:13 PM

What your turning is more then likely an idle adjuster and not the air screw

**NOS_350X** · 03-04-2008, 08:40 PM

Also rember, what are you changeing, most the 4 stroke carbs dont control the air, it controls the fuel, so tighting it up will make it leaner. The 2 stroke carbs are controled by the air. Also some of the 2 stroke carbs you can turn the choke to adjust the idle. screw it in would be lean out would be rich.

**BELGIUM KXT250** · 03-05-2008, 04:42 AM

Hi,

Yes my carb is for a 2stroke engine (kxt tecate 86) and I was confused between the air screw and idle adjustment. You are right I must have adjusted the idle screw and not the air screw because this idle is the only screw located on the outside of the carb.

**zoomerman** · 03-13-2008, 03:58 PM

I recently put a 86 carb, power reeds, and dg national pipe and type two silencer on my bike( 83 250r) but haven't started it because of jetting issues. Around what size main jet should i start with? the stock main for the 86 carb was 142 and pilot 50?i was told well it has a 52 pilot jet in it and a 125 for a main jet. The 83 carb comes with a 50 pilot and a 130 main. I would like to start jetting rich like

stated, but i don't really have any idea. Should i buy a jet kit and start with a 138 or should i start bigger/smaller? any input would be helpful.

Thanks,

Evan

**Dammit!** · 03-13-2008, 07:49 PM

I'd start with the stock jetting for the 86 R carb. If I remember right it's either 145/42 or 142/45. Can't remember off the top of my head which one of those is right. When in doubt though, go big. Less risk of damage.

**Billy Golightly** · 04-28-2008, 09:57 PM

, I made this little guide thing for a plug a member posted in another thread, it might be a nice addition to the first post.

http://3wheelerworldforums.com/attac...1&d=1209435037

Edit: Fixed watermark overlap.

**dizasterzrfun69** · 04-28-2008, 10:01 PM

Originally Posted by Billy Golightly

, I made this little guide thing for a plug a member posted in another thread, it might be a nice addition to the first post.

http://3wheelerworldforums.com/attac...4&d=1209434047

pretty cool billy, except the watermark on the bottom right.

**Just-Tri-It** · 05-21-2008, 10:01 PM

I have a 1983 or 84 YTM 175. I premix the fuel as the oil tank was previously removed. I noticed that the vent tube which come out of the back bottom of the carb bowl is not vented to the crankcase cover next to the right rear wheel but hangs loose. When I hooked it up it filled the tube with gas and I had to take out the 3 screws to drain the casing. Why did it fill up with gas and is it important to have it hooked up there?

Could I hook it up elsewhere. One gentleman said he thought it effected the timing if it was unhooked. I know it doesn't need to be filling with gas but don't know its original purpose.
Thanks for any imput.
sheeptender

**Dammit!** · 05-22-2008, 12:17 AM

Originally Posted by sheeptender

I have a 1983 or 84 YTM 175. I premix the fuel as the oil tank was previously removed. I noticed that the vent tube which come out of the back bottom of the carb bowl is not vented to the crankcase cover next to the right rear wheel but hangs loose. When I hooked it up it filled the tube with gas and I had to take out the 3 screws to drain the casing. Why did it fill up with gas and is it important to have it hooked up there?

Could I hook it up elsewhere. One gentleman said he thought it effected the timing if it was unhooked. I know it doesn't need to be filling with gas but don't know its original purpose.
Thanks for any imput.
sheeptender

You'd have better luck posting this question in the main area. This thread is specific to jetting which is not part of your problem.

**Tecate250** · 05-23-2008, 03:35 PM

So the ground strap is where to look if you suspect ignition problems, The color on the porcelin inside the plud tells you rich/lean "gas and air" ? What would running a b7es plug in a b8es engine do? I know it is a hotter plug.

**Kintore** · 05-25-2008, 11:55 AM

Hey guys,

265 R PV motor, all mods in my sig

Runs fine first 3 gears then starts cuttin out the last 3.

Cleans out perfect but has a lil hesitation when you punch it after its been sitting a little bit.

Lean out my needle?

Thanks alot

**DeePa** · 05-25-2008, 12:00 PM

Canadaman, i have no idea for you. IS it cutting out lean, or is it rich? What you have in there for jets? The more load on the motor, the more fuel it need...i would think?

As for a jetting question...Does the needle effect the wide open throttle? Like if you have the needle clip to the bottom, making it rich as possible, will the trike run the same wide open as when the needle clip was all the way at the top, makign it as lean as possible? Or does the needle just effect from low to mid rpms?

Thanks

**Kintore** · 05-26-2008, 01:33 AM

Im going to drop the needle tomorrow and see,

wheres Doug when you need him!

**Kintore** · 05-26-2008, 10:33 PM

Leaned it out 1 clip and it did the same thing, going to go another clip up tomorrow and see!
Damn thing

**Dammit!** · 05-27-2008, 02:23 AM

Sorry I was out riding this weekend.

If you're saying it runs and revs out fine in the first three gears I'd be suspicious of the problem being something else. Electrical or maybe a crank seal. You're not being real clear though. Start with the main jet (see how it runs in all six gears wide open throttle). Get that running clean, then worry about the needle clip, then the pilot/air screw. If you can't get it cleared up with jetting, start testing electrical components. If you still don't have any luck it could be the left crank seal sucking some air.

Thread: Carb Jetting 101: Terms, Tips and Jetting Theory

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