Idle mixture adjustment (air or fuel screw adjustment)

[JustAnOrdinarySimmer]

What CC is that engine?

[thejunkman]

@JustAnOrdinarySimmer 125cc bored to a 140cc

[JustAnOrdinarySimmer]

@thejunkman can you tell me the exact make and model etc of it then please since this engine looks like it would fit straight into my bike

[thejunkman]

@JustAnOrdinarySimmer Well this engine is about 6 years old now. It fits into any CRF/XR50 based frame. This is 125cc GPX/Jialing 4 up bottom end with a TB 140cc BBK.

[kingwii2000]

I have a 350 warrior and i had a problem with fuel leaking out of the bottom overflow of the carb, so i took the carb out cleaned it and cleaked the floats.The floats were fine and puting it back together seemed to stop the leaking accept now the warrior idels at an isanly high rate. adjusting the idel screw does nothing same with the AF screw. My freind messed up the adjustment of the thottle on the carb but other than that. I just cleaned it with carb cleaner, reesmbled it and now this. HELP!

[thejunkman]

@kingwii2000 First adjust the throttle cable to have aprox 1/8 inch of play then adjust the idle speed screw. I would have replaced the floats as they could be suspect of leaking/cracking alowing them to sink and overflow the carb.

[Sk8rBoi4Lfe]

hey i need some help.your video helped me out alot. but im just wondering. my bike takes alot of kicks to start up but when it does i need to rev it alot or else it will die. im just wondering. would adjusting the idle help me out? and if so how would i do it exactly?

[thejunkman]

@Sk8rBoi4Lfe The idle is very simple. Find the screw that controls the idle speed (usually on the side in the middle of the carburetor) For example the idle speed screw is the screw with the black knob in the video. Turn the screw in until the RPM's raise. However if the thing won't idle at all you probably have a dirty pilot circuit.

[ThugsRmorons]

2:50 You said it took "hours and hours of testing" to get the proper a/f mixture for the idle, but a few turns of the screw, and a few twists of the throttle seems to set things up rather quickly?

Was there something else that you were tackling that took hours and hours?

[thejunkman]

@ThugsRmorons Ahhh, the beauty of the editing room. Actually I already knew where my optimal setting was for this particular engine setup, but when I built the engine and bought the carb it took hours and hours of testing to get the jetting right so it would start and run without either bogging or overheating. It was trial and error with different components to get this engine to run well. This is just a demonstration.

[ROBOTNINJA500]

i had stumbled across the information written a few days ago but this video was good just for practical experience :)

[thejunkman]

@ROBOTNINJA500 Thanks for watching! Like my facebook page for more tips and tricks like this.

[MrMethadrine]

is it a standard that u must have a high speed idle?

[thejunkman]

@MrMethadrine Well you are looking for the highest possible idle speed when setting the mixture. After that you can set the idle speed to what ever you want.

[DRMusicRoom]

@thejunkman So we should keep the tension of the throttle cable, when doing this, between loose and tight in order to adjust the idle speed using the idle screw? Thanks for the video.

[thejunkman]

@DRMusicRoom No, this video only shows how to adjust the idle mixture (air/fuel). The idle speed is an entirely different adjustment. The idle speed is adjusted by a different screw that is basically an adjustable stock for the carburetor slide. It has nothing to do with adjusting the air/fuel mix at idle.

[Boondogll]

Thanks for this video! First guy on youtube who REALLY knows what he's talking about. Excellent job explaining everything to. KEEP UP THE GREAT WORK!

[thejunkman]

@Boondogll Thanks for the kind words. I am no expert, but if you want more videos like this check out my website or Blip.TV show for other great how to and tip videos.

[mryamahadude]

Thank you for this! I knew how to do it but i didnt quite know what i was looking for! This helped!

[elshit1983]

hey junkman, I saw the video and saw the main jet, BUT it seems like i have to take off my carb to get to the main jet? is it under or something?

[thejunkman]

@elshit1983 Yes in most cases you have to remove the carburetor to access any of the jets in the carburetor.

[HopeForBipolar]

@thejunkman so.. if air screw was adjusted to get highest idle without hesitation and that setting was less then 1.5 turns out then i need a bigger slow jet/pilot jet? then i install the new jet and repeat previous steps to get proper adjustment between 1.5 & 3 turns out?

So are we choosing which to adjust... air screw or fuel screw or is it necessary to adjust both or are you saying carbs have one or the other and depending on that we adjust according to type we have?

[thejunkman]

@HopeForBipolar Carbs have one or the other not both. They are adjusted using the same proceedure just the operation of each is oposite. I cannot give a recomendation being I don't know what you have (an air of fuel screw) Towards the end I explain in general which way to go leaner/richer depending on what screw type you have.

[HopeForBipolar]

@thejunkman found that I have a air screw (close to air filter side) i think i got it adjusted right now thanks to you but as luck would have it i have a new question..this is all pertaining to a 1988 rm125. I was told the exhaust valve or power valve was turned to be off, i would like to re enable it but my clymer manual says not one word about adjustment..cylinder bored to .80 piston was also told be careful it don't hit piston..how can i safely check/adjust the exhaust/power valve

[thejunkman]

@HopeForBipolar Umm, I am not aware that you can "shut off" an exhaust valve, unless you remove the linkage that operates it (or its broken) Suzuki has a complicated exhaust valve that is prone to breakage from carbon build up. Only fix/diagnosis is to remove the top end and dissasemble the exhaust valve entirely and replace the parts.

[HopeForBipolar]

@thejunkman ok thanks, I kind thought that was the case. Thanks for replying..most don't bother.

[thejunkman]

@HopeForBipolar No problem. I just try to help.

[elshit1983]

with a cover and he put some take over half of the sport air filter, but then afterwards one day i took the tape and the cover off and its been stuttering when full throttle. So is the tape and cover the problem? is too much air going into the carburetor now? THANKS

[thejunkman]

@elshit1983 Sounds like your are way to lean now with that high flow air filter, thus the reason the mechanic might have put tape over half the air filter. Try going one step up on the main jet and see what that does first, then go from there.

[elshit1983]

@thejunkman Well is there any way i could keep the tape and cover off, and not have the bike stutter at full throttle? cause after i put the tape and cover back on it was fine, but what can I do to make it work without the cover and tape? anything at all? thanks and sorry for all the questions

[thejunkman]

@elshit1983 I gave you the answer in my previous reply. Richen the main jetting up one step and see how the engine runs. Just keep tweaking the jetting until it runs satisfactory.

[elshit1983]

@thejunkman yes, i know but where is the main jet on my carb, i don't even know what the main jet looks like or where it is...

[thejunkman]

@elshit1983 Find my carburetor diagnosis video and it will give you an idea on what your looking for. All carburetors function the same but look different. Find me on Facebook and subscribe/Like the page as I will probably do a jetting video in the future.

[elshit1983]

@thejunkman ok thanks man! ur online now!

[elshit1983]

hey, one more question, i've been seeing a "high jet" H on some websites, what screw is that? is it in this video? because my GY6 scooter 125 cc has been stuttering when full throttle, well the story is: originally this guy in a scooter shop changed my air filter into a sport one,

[thejunkman]

@elshit1983 Not sure what your talking about there, but some carburetors have a "jet" for high altitude (leans the overall jetting)

[elshit1983]

this was helpful thanks a bunch

[thejunkman]

@elshit1983 No problem. Check out the Facebook page for updates and to connect with me easier.

[salafibrouae]

nice video. My spark plugs are becoming black after some 35 kilos, so this means that my mix is too rich? So, doing ur test with the air screw should solve the problem? I am running a 500cc RE engine with a mukuni carb I believe it is a 33mm. Thanks.

[thejunkman]

@salafibrouae Yes you are running too rich, however the blackend spark plug is from overall jetting not just the idle mixture. This proceedure just adresses the air/fuel mix at idle so you don't foul plugs or over heat while idleing, as well as taking care of any tendency to "bog" off idle. Your problem lies within the main jet, jet needle or both.

[salafibrouae]

@thejunkman

Ok, thanks. So I need to address the main jet/jet needle or both. Will read up on this and get it to the shop. Thanks again.

[thejunkman]

@salafibrouae Well maybe both. It will just take time and testing to figure it out.

[salafibrouae]

@thejunkman I went out and got a few different main jets. I replaced the one that was in the 155 with a 145. I still got the same results; spark plug w/ black coating. It is a powder like coating and not oily. Do I need to go with even a smaller main jet, and just how small should I go?

thanks.

[thejunkman]

@salafibrouae I would go one more leaner. Then try messing with the needle clip position.

[salafibrouae]

@thejunkman

so, go with 140, and move the clip position one up?

[thejunkman]

@salafibrouae well I would do one or the other first and see what it does. Only do one thing at a time when testing before trying something else.

[djtooshort1]

when my bike is on the level and I give it gas it runs perfectly fine but when am going up a hill and gives it that extra exceleration in like say...second, third or even fourth gear...it tends to be holding back...as if it's not getting enough gas. I cleaned the air filter, cleaned the carburetor perfectly fine...went to the mechanic yesterday and he adjusted the air screw but still it runs over the hill like it's holding back. What do you think the problem is?

[thejunkman]

@djtooshort1 I responded to your inquirey on my website. Check your email.

[trrrmac]

didnt u said 2 turns out but instead u turn it half out? .. or is it a quarter turn counted as 1?

[thejunkman]

@trrrmac The video is edited so it only looks like 1/2 a turn

[trrrmac]

@thejunkman if the pilot-jet is too lean, i should then change it with a bigger number or a smaller one?

cause when i turn the air screw all the way in, the engine wont even stumble or stop running, and i'm still getting high rpm on idle, is that mean my pilot-jet is way too lean?

thanks for your reply junkman.

[thejunkman]

@trrrmac Yes your pilot jet is too lean, try one with a bigger number.

[xTSx100]

Great video thanks btw what is that second air filter for? ( the metal filter hanging from pipe) thanks

[MrMainoffice]

I am seeking adjustments, for 1998 RM-250 dirt-bike. If seating on it, the Idle screw is on the kick start side. Base center of carburetor. There is another screw towards the bottom. If you would personally help in this, I could take pics & send them to you. Would love to have this setup right. Please send me a confirm to, as i await for your reply. Ahead of time "Thanks" Sam....

[MrMainoffice]

I am seeking adjustments, for 1998 RM-250 dirt-bike. If seating on it, the Idle screw is on the kick start side. Base center of carburetor. There is another screw towards the bottom. If you would personally help in this, I could take pics & send them to you. Would love to have this setup right. Please send me a confirm would you help me here. Just say ha Sam. i await for your reply. Ahead of time "Thanks" Sam....

[thejunkman]

@MrMainoffice The screw on the side in the middle is the idle speed adjustment NOT a mixture screw. Your bike I believe has a FUEL screw it will be on the engine intake end of the carb on the botton and might be dificult to get to. The aftermarket makes extended fuel screws so the adjustment can be made easier with the carb installed.

[MrMainoffice]

@thejunkman Thanks, for the fast response. I had taken two-pics but can't seem ta find a way ta send them to ya. (But anyway, yes on the shifter side also fuel line side. There is the chock then just below that if I'm current Idle-screw. Bottom right corner, of the float bowl yes I see the screw.) So this is the "Air & Fuel" screw?? Just ta say I'm not really new ta this. But I think I'll count the turns just ta rem on the A & F screw. And find where that needs ta be set at.

[thejunkman]

@MrMainoffice You can contact me via my website. For the idle mixture there are two different kinds AIR or FUEL screws no carburetor has both. Your bike most likely has a fuel screw. Follow the instructions in the video. Contact me via my website and I can try to help you more if your still stumped.

[Unclechelu]

excellent vid and explanation junkman!

[thejunkman]

@Unclechelu Thank you. I will be uploading more.

[AReptileMan]

When you say turn is that 360 or 180 it seams most of the time it looks like a 1/2 turn?

Thanks

[thejunkman]

@AReptileMan 360 degrees. I edited me fully turning the screw to save some time, but when adjusting the screw you may only turn it 1/4 or 1/2 a turn in or out. All depends on how the jetting is for your altitude.