How To Tell If Main Jet Is Rich or Lean [Jetting Symptoms]

[@MotocrossHideout]

Did you find this helpful? Learn how to easily tune the air/fuel screw in just a few minutes: 2 stroke - motocrosshideout.com/carb/ 4 stroke - motocrosshideout.com/fuel/

[@066motocross]

Thanks for giving the old guy about 8 good laughs Kelley! Your a hell of a 2 stroke impersonator! I'd love to hear your chainsaw cutting Minnesota trees lol. This is a great video about jetting. Even as long as I've been messing with these bikes I never quite understood the needle and clip positions very well. Do you have a video about that? If not I'd like to get a crash course on needle and clip positions. Thanks my friend. Keep the good stuff coming. I promise to get chip in on more videos when I get these medical bills to stop smothering me every week. Thanks buddy 😊

[@MotocrossHideout]

Haha, thanks. People seemed to like it in one of my other videos :D I don't have a video on the needle and clip yet, but I do have an article on my website that should explain it well enough: motocrosshideout.com/how-to-adjust-needle/ No pressure, John, I can imagine how difficult that must be...

[@Bargrabber]

Hi im currently working on a sym wolf 125 i bought carb rejet kit with 105 to 130 main jets and 38 to 68 pilot jets i have put on a spong 38mm air filter on my 2 different carbs that im using to test one is the stock cpz26 and the other is a honda pz27 The stock carb has a 35mm pilot and a 100 main And the other carb has a 35 pilot and a 102 main The problem im having is without the airbox and with a pod filter instead the main problem is when u put full throttle it will stop at 6 or 7k rpm and sounds terrible when i go richer it doesnt work but when i went closer to stock jets the bike sounded like it wanted to break apart lost all power and it couldt drive its working now itbdidnt break luckily but i am exteemely confused if i go rich it doesnt do much to help but go to lean and its sounds dangerous af im sorry im sorry im posting an essay but honestly i am stumped , the whole goal that i want to achieve is more power with the modded exhaust and pod filter i have also put the pod filter on a tube/pipe incase the intake effect caused a peoblem but yeah, any help would be extremely appreciated, than you and have a good day

[@darkogligorov3181]

So my 50cc 2 stroke yamaha aerox when i change to 70cc kit and new aftermarket exhusost i put biger main jet and pilot jet on 17.5 carburetor. So its start fine its ride fine but on cold start its start and after 2 minuts of idling its die. So i adjust the fuelmixturr screw to get more air but when its ref the idle is hang on a litl bit and after secoonds its settle and again want to die. So i assume my pilot jet now is to big right? What you think?? So i let you know the floath boath is adjustet right i watch your video and do it and the transsmision is all good. And i see the spark plug when just has idling its was black and has oil on it but when i ride it on like 5-10 minuts its has good has that brown color. So what you think??

[@Dastardly_X]

That low coolant / lean jet sounds interesting. I’m new to radiators.

[@MotocrossHideout]

Yeah, the low coolant can be caused by several things. Usually it's from overheating from low speeds/clutch use/not enough air flow. A lean main jet is one possible culprit, although not as common.

[@Dastardly_X]

@@MotocrossHideout Thanks for the reply !! 💖

[@jebi_jones]

i’m restoring a 1982 honda xr and just put a new carb in there. I keep adjusting air fuel mixture, and changing main jet going from not starting at all or it starts very well but redlines instantly and won’t come back down. I’m taking notes and turning air fuel mixture slowly but still, too much revs instantly or won’t start at all. Any tips?

[@MotocrossHideout]

Main jet doesn't really matter for starting and idling. Sounds like a possible air leak. Cracked air boot/intake manifold, loose carb clamp, fuel screw o-ring cracked/missing, or a cracked/missing a gasket/o-ring. That's what I'd check first.

[@roydavidjimenezcarganillo4825]

When the rubber seal in the idle screw has a little wear/ tear, does it also affect the tune of your carburetor?

[@ethan....]

Yes, it will allow more fuel to enter the circuit making it too rich. The broken seal can't limit the fuel thereby making an inconsistent idle condition as it wears out.

[@roydavidjimenezcarganillo4825]

@ethan.... I see thank you!

[@MotocrossHideout]

Are you referring to the idle/throttle screw or the air/fuel mixture screw? What bike/carb?

[@roydavidjimenezcarganillo4825]

@MotocrossHideout air/ fuel mixture screw. I'm from Philippines. It's a scooter bike. I have modified my bike and basically a loaded one. So I have changed my carburetor into 28mm. However, I just notice that my screw mixture seal has a little bit of tear in it. And I have little bit of trouble on tuning it. I don't really know if it was due to lean mixture or rich mixture. I sputters a lot when rev high.

[@MotocrossHideout]

Okay, gotcha. Yeah, if the air mixture o-ring is cracked, that can cause an air leak, making it run leaner. If it's sputtering at high RPM, it's probably rich, but the air screw only controls idle to about 1/4 turn throttle. Is this a new problem? Is the air filter clean?

[@blowup1213]

So for my yz85 I'm running 32:1 and it ran good for a while but now it's taking like 40 kicks just for it to start and then it just dies no matter what I do after a few seconds of it starting and I'm burning through a sparkplug everytime I try to start it do you know any way to fix it

[@MotocrossHideout]

Sounds like it might be low on compression, unfortunately! Here are some other common signs: kzbin.info/www/bejne/q4u7gmWKlNN7f7M

[@Jakob-lq6il]

my Yamaha YZ 125 has a hesitation right before the power band, and then after it gets past that it takes off good and if I stay in the power band and shift to the gears, it’s good, What would you say is wrong with it?

[@MotocrossHideout]

What throttle position when that happens? Have you tried anything to fix it yet? Has it always been like this?

[@Jakob-lq6il]

About 3/4 throttle I bought the bike blown up and rebuilt it it’s only been running a few days. The spark plug looked like it was running rich, so I dropped the needle one position leaner but that did not fully fix it

[@MotocrossHideout]

If it helped, I would probably try dropping it another. Are the reeds properly sealing?

[@Jakob-lq6il]

I dropped the needle all the way now it’s a little closer but still not quite right. I don’t know I haven’t checked. I’ll have to do that.

[@MotocrossHideout]

@@Jakob-lq6il Okay then there's probably something else going on. It's the stock needle, correct? I would also check the float height, it doesn't take much to bump that out of place, causing everything to be too rich.

[@redneck24-65]

What about revving to the moon after a rebuild? Is that a jetting problem? I’ve messed with air screws, replaced rubber boots, new carb, and cannot figure it out to save my life. Any help is appreciated

[@MotocrossHideout]

It didn't do that before the rebuild? It does sound like an air leak. Does it do that just when you first start it up? Any chance the throttle cable is pinched/stuck open or the idle screw turned in too far? It doesn't take much for it rev up high.

[@redneck24-65]

@ I didn’t own it before the rebuild so it’s hard to say. But no the throttle is closed all the way. I haven’t run it long enough to see if it will idle down because it revs so high I don’t want to blow it up. I’m just thinking it’s a jetting issue or I’ve heard some crank seals or some other seals or reed valves can cause this. The bike has new intake boot and everything though, it doesn’t make any sense

[@MotocrossHideout]

@@redneck24-65 Okay, I would maybe try start it and tapping the kill switch to keep the RPM down. If it wants to keep revving after 5-10 seconds, there's likely an air leak or the pilot might be too lean.

[@redneck24-65]

@ okay, yea I’ve done that with the kill switch for maybe 20 seconds a while back. So you think it could be pilot jet? Not the main jet?

[@redneck24-65]

@@MotocrossHideout it is a cheap carb, so I’m thinking it has to be that. If something wasn’t put together correctly in the top end, could that cause it? I wouldn’t think so, I’ve built a couple of these and never had the issue.

[@Hopeng-Youtube]

How about spark plug gaps, mean lean or rich?

[@MotocrossHideout]

Honestly, I don't remember the last time I've needed to adjust a spark plug gap on a dirt bike because they're typically set right when new. I doubt it will change if it's rich, but it might melt and bend if it's too hot (lean).

[@Hopeng-Youtube]

@MotocrossHideout I use a 150 cc Ninja motorbike that has been bored up to 180 cc, my question is: is it safe for the engine if the standard main jet of 260 is reduced to 200 after the bore up? now I use pilot jet 27.5 from the standard 22.5; main jet size 210, the engine sound is heard without any strange symptoms, only the exhaust sound becomes drier.

[@MotocrossHideout]

@@Hopeng-KZbin If the exhaust sounds different, or it's bogging or not revving out cleanly, it's most likely not tuned properly.

[@Hopeng-Youtube]

@@MotocrossHideout Does reducing the main jet number make it more economical, but not too lean, it can cause the engine to seize up?

[@Hopeng-Youtube]

@@MotocrossHideout If I use a 260 main jet, then the wind setting cannot be 1.5 openings, but if I use a 210 main jet, then the rpm will increase with a 1.5 air screw opening, is this also a sign that my main jet is rich?

[@Safet9876]

I am having all simptoms, am i cooked

[@kx_entertainment_801]

Phew thought I messed up my bike

[@SharkZoneGaming-m2r]

This has nothing to do with the video but do you know how to make ur dirt bike quiet? Bc I have a 110cc and it’s pretty loud and it annoys me and it’s loud for my neighbors bc they complain all the time abt it 😂

[@MotocrossHideout]

Best way is with a different exhaust pipe. More specifically the muffler. If it doesn't have packing or a baffle system, it's going to be loud.