Carb Jetting 101: Terms, Tips and Jetting Theory

[Bryan Raffa]

this is a spark plug with the threds cut off I have found this verry use full to find out how the bike is jetted.. for a long time I was only lookin at the verry tip of the plug for jetting.. this is where I look for proper jetting color.. hope this helps you guys...

Ttown it sounds like your lean at idle and ritch at your mid range

[TtownJoeShow]

lol its interesting! this jetting thing i mean...my 83R, the ring is always wet, the ground strap is just a tad lighter than black, but it runs pretty damn good!! (the mods are in the sig) just for the bigbore they call for a 135mj but i'm at 138, and the BRV says to drop 2-4 sizes plus i have the 86 carb and K&N....am i going to end up around 120 or 115 lol? mean while i have heared of some ppl on here running like 300 for a main!!! (or is that mikuni talk?) anyways i have ordered 6 smaller in sequence but they can't get 2 of them, so i'm going to haveto just work with what i get!!
thanks for all the help!
this is by far one of my fav threads!

[Frankencelery]

I have a 200s with a new aftermarket carb that I've always had trouble with. The bike must be choked for about 5 minutes before it will idle, and then the choke can be turned off. However, if you punch the throttle, it bogs big time. It doesn't do that if you leave the choke on. I have no trouble as long as I'm easy on the throttle, and the machine runs fine at WOT. I posted on this issue some months ago, and I never reported back in to say what happened.

At the time I played with the pilot screw and couldn't find anything to improve the situation. Then I moved the needle clip in both directions with no improvement. So I gave up, thinking I would just have to replace the carb. This week I had another idea, so I bought a 200s carb kit and replaced the carb's 38 and 88 jets with the kit's 35 and 100 jets. I thought the smaller pilot jet was odd, but that's what came in the kit, so I tried it. It required quite a bit of adjusting of the pilot screw to get it idling correctly again, and now it starts and runs fine, but it still bogs when I punch the throttle.

Does anyone have any ideas of where to go next on this? I'm stumped.

[Dammit!]

I usually adjust the air screw for best off idle throttle response. If that doesn't get rid of it, richen the needle clip one slot (at a time) and see if it improves.

Keep in mind, it's impossible to say for sure without hearing exactly what it's doing and knowing exactly where in the throttle it's bogging and how hard you're punching it. Even my 250R will bog a little off idle if you stab the throttle as hard as you can while it's idling.

[Frankencelery]

No, it's my only trike that does this. If I'm sitting at an idle and I push the throttle just hard enough to take off fast, it bogs. I have to let off or it will stall. However, if I'm at half throttle already, I don't have the problem. My buddy's 185 doesn't do this, nor does the 200x or the 250SX.

Tomorrow I'll go back to the needle clip and adjust it again with the bigger jets installed. i haven't tried that yet.

[Dammit!]

Sounds like the needle needs to be richer to me. Good luck with it. Let us know what happens.

[Frankencelery]

Ok, ......that sounds odd when I read it out loud. Anyway , I followed your suggestions, and moved the needle up one notch at a time. I ended up with the clip in the bottom slot and it's quite a bit better. It's still not quite like I think it should be, but at least now I can *almost* pull a wheelie off the line.

I've got the original carb rebuilt as well, and I might just throw that back in and see what happens. I did compare the two, and they are pretty much identical, so I can't see what the problem might be. I wonder if there's something engine related and not carburetor related?

[NOS_350X]

Here is a little trick to find out if your lean or rich. It dosent always work but does quite often. If your bike is sputtering and not running properly Turn the choke on 1/2 way if you can. See if that clears it up. If it does you know that in the rpm range your having the issue with you need to richen up your mixture. IF its a new 4 stroke fcr carb You can pull the hotstart that will lean out the mixture showing you if you need to go richer or leaner.

[Yamada]

Question. I finally repair the major leaks on my ytm-200 exhaust and now at idle the bike seems to run at lower rpm. It is also more difficult to start ( 2 pulls, 1 before with an very leaky exhaust. other than that, tthe bike run very well, i m able to wheelie the 3 first gear ( with a ytm-225 final drive). Should I check the pilot jet?

[Dammit!]

You will rarely ever have to change the pilot jet (unless you ride at a very high elevation). Just make sure it's good and clean and the stock size. You can fine tune that circuit with the pilot/air screw.

[3WW Star-CoeShow]

Frankencelery,

try putting the 38 pilot back in. Make sure it doesn't have some minor obstruction while its out. You may even want to purchase and install a 40.

Your issues sound to me to be pilot jet related.

Good luck and ride safely.

[tapper190]

Hi, I've done a few engine mods to my '84 200x, and was wondering how many jet sizes up I should start at? The things I've done is 1) installed a wisco piston (first bore over) 2) I believe the head was ported before I got the trike. The intake has been cleaned out. installed a new stock cam and valves. 3) uni air filter 4) cobra pipe and header. Thanks
Tapper

[dizasterzrfun69]

I got an 85 R with a PT high rev pipe and boyesen rad valve. When i try to run it it will bog out at bottom end and eventually die. I pulled the plug and its really dark with lots of carbon on it. Its a br8es plug and my main is a 145. My instinct would tell me to drop the main down like 2 sizes and try it there but its bogging on bottom end and not top end so what should i adjust?


I just checked the slow and the needle. The slow jet is a 52 like the book calls for and the needle is dropped all the way down.

[RedRider_AK]

play with your air screw and/or pilot jet. Also play with your needle.

[Dammit!]

I got an 85 R with a PT high rev pipe and boyesen rad valve. When i try to run it it will bog out at bottom end and eventually die. I pulled the plug and its really dark with lots of carbon on it. Its a br8es plug and my main is a 145. My instinct would tell me to drop the main down like 2 sizes and try it there but its bogging on bottom end and not top end so what should i adjust?


I just checked the slow and the needle. The slow jet is a 52 like the book calls for and the needle is dropped all the way down.

Are you running the stock round slide 85 carb? Where exactly in the throttle is it bogging? Will it idle? If it idles you don't need to mess with the pilot. My gut says your needle is too lean (can't trust plug readings in that range in my experience). I'd put the clip in the middle and see what it does.