Adjusting the carburetor on a Honda CT90
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- เผยแพร่เมื่อ 9 ก.พ. 2025
- Same method is used on other small bike carburetors. Note that this should be done on a warm engine and choke off. If you can't get an initial idle at all then you may have other issues.
Thank you very much Finally I learned how to adjust idling my own bike after 56 years!!! It's amazing.
Great video!
Brillant! I just brought home a 1970, and it wouldn't idle without applying throttle. Knew I could find something to tinker with it. Thanks so much!
best ever, greatest, easy to follow video!!! THANK YOU!!!
Thank you! Very clear and concise! I have a CT110 and this was always a frustrating experience for me, I think this will really help me to understand the process better. Much appreciated. Be safe!
Just finishing my CT90 refurbishment and needed this advise , Thank You for showing me how to do it !!
Great video. Got my 1970 ct90 running 100% again.
Thank you! Just bought two of these, your vid helped me get one purring. The second one needs some work haha
Thanks, Phil! I just installed an exact (pretty much) Chinese copy carb in one of my 75 Honda ST90s, and it only would stay running on choke-mode. I did the all the way in and two-out adjustments you recommended, and it fired up on normal running mode, except with a very high idle rate, which I was easily able to remedy with further adjustments. I have two 1975 Honda ST90, and both of them now have the crappy Chinese-made carbs in them; however, I have purchased the rebuild kits for both the original Keihin carbs and plan to re-install them asap. Thanks for the carb adjusting tips, and take care!
Probably an air leak between the carb and manifold. Replace the gasket.
Thank you sir ! Now i got more idea about what i am going to do with my moped carb . Big apreciation for you .
Exactly what I was looking for, much appreciated!
Easiest video ever! I'm also surprised I'm not the only one with a trail 90 hahaha
I just picked up 3 CT90s. This will be very helpful. Thanks
Hi mate, thank you very much you helped me tune my ct90 trail cheers from Sydney Australia 👍
Excellent - just what I've been hoping to find. Thank you from Ireland. :)
The black knob that says "PULL" is for use in high altitude conditions. Normally it will stay pushed in.
Thank you!
Thank you. I was wondering about the Pull button.
Simple way I always think about it: tweak your mixture screw until you can get the highest rpm possible and then dial the idle back with the idle screw
for those wondering this also works for the ATC90 as well, basically same engine. thanks! time to ride!
Thanks so much for this informative video.
What’s the pull nob on the side of. Carb?
High altitude compensation.
Thanks for the video it was very well done and informative. May I ask what could a possible problem be if I took both idle screw and air screw out 2 turns and then started the bike... 1. The bike will only start with the choke on but it will not idle at all? Any idea what I should be looking at to solve this issue? Thanks
If the bike starts/runs with choke then one possible explanation is that there's an air leak between the carb and manifold or between the manifold and engine. If it runs at all you can spray something like carb cleaner in these areas, and if the idle changes, it means the carb cleaner is temporarily sealing the air leak. In this case it's a simple matter of replacing the gaskets in these locations. In a pinch you can use gasket sealer.
@@pburress06 Aaah that's a great idea, I have not used that trick yet but it sounds like a good one to know about. Thanks for that feedback.
@@my50bike Often this happens when the carb is removed and replaced without changing the gasket
That's funny, I came to this vid to see about adjusting carb on a 76' trail 90 and I noticed the truck in the background that's the same as my 65 F100 even in color
This is a 63 Unibody
great video on the process to get to a quality idle. Thank you!
Thanks followed ur steps I have no adjustment at all goes to full throttle?
Hmm check the slide which is where the throttle cable enters the carb, under the cap. Maybe it's stuck? If that the case maybe it's time for a carb rebuild
I've found this necessary to do at least twice a year when the oil companies move to winter and summer formulas.
Great information. I will be using this tonight. Thank you sir
What could be the cause for the engine RPM to have no effect when you turn the mixture screw? Mine has an air control screw and even when you screw it in full, the engine still runs. No noticeable effect when you back it out too..
Great video. Thank you.
I'm astounded at how many people don't know how to set up a carb! It's not rocket science...
What's the problem on a new carburetor when u turn to shut off it leaks? Thx
Thank you Phil
Have been trying to find the exact same carburetor as shown in this video. Ebay, Amazon, etc. etc.
The problem is the location of the 3 brass inlet/outlets. It is used on a ct90. Carb was made by
KEIHN.
Look forward to any comments/suggestions.
got an extra if you need one to buy!
I hsve 1970 CT90 trail bike, previous owner put on aftermarket? Its fkoodin when turn 📴 I hsve to let gas out reserve for it to start couple kicks compressions good new pkug ? Any💡 s thx
I'm not an expert... When you say turn off do you mean the petcock? If so replace the o-ring or the whole petcock so it doesn't leak. And if it has an aftermarket carb, maybe just replace it since those are inexpensive and usually work reasonably well. If it's the original carb, the rebuild is pretty easy if you have done any car work.
You should count your turns back out on air mixture after it stumbled then when it stumbles again count back exactly half that number... so if you turned 2 turns back out until it stumbled, you would go 1 turn back in
Exactly!
Really useful. Thank you. 😊
thanks for the video. For initial dial in what height is your pin?
Wouldn't it be better to do the airscrew first and when it runs at it's best you do the idle adjustment
Very good vidio brother!!
i have tried this on my honda c 90 cub,it has,nt worked you hav,nt warmed the bike up in advance,you hav,nt mentioned if you need to warm the bike up or not?
Yes you should warm it up! Sorry if I didn't mention that!
Which direction on the screw leans out the fuel mixture?
Counter clockwise.
What does it mean when you get it to idle fine and then all of a sudden it slowly revs higher by itself?
It's hard to say but I'd check for an air leak around the carb/manifold. I made this short video to show an easy way to do this: th-cam.com/video/4ja8Y62A72M/w-d-xo.htmlsi=k1XyPnNopFjIy0Ik
Otherwise, consider getting a kit and rebuilding the carb. It's pretty simple.
@@pburress06 ok thanks a lot 👍👍👍👍
thank you for video always wonder about that thing on carb that pushes in and out . what is the best position. i notice your is in. so i guess that is the best position.
It's for elevation above 6000 ft
That's the high altitude adjustment knob. When riding above 6000 feet, you pull the knob out. That changes the fuel air ratio for the thinner high altitude air. When below 6000 feet, you push the knob in.
Really nifty stuff. I'm glad it's there, it really does make a difference.
Thank you.
When riding, the choke remains in 'open' position? Or after the engine warmed up, turn choke in 'off' position and ride? Idk, just got a '73 but, currently need a seal kit. I may do both, put a new carb on now while rebuild the original.
Yes, the choke shoulder only be needed for a very short time. Longer when it's colder as it warms up, then all the way off. Rebuilding is not hard but make note of where everything goes and don't lose any parts. People usually report good results with the inexpensive replacement carbs. Be sure to replaced the gasket under the carb or you'll get an air leak
For mine I had to turn the air one the opposite way as you. Just fyi for others. Maybe just diff carburater.
Can you tell me what the PULL button is for? I just got an st90 and i do bot know what that is for. Thanks
when you get above 5000ft elevation pull out,
Yes, for use in high elevation where the air is thinner.
Is that an FJ 40 in the back ground?
1963 Ford F100 "Unibody"
Thanks! What does the "Pull" knob do?
Elevation above 6000 feet. Pull it and it adjust air to accommodate
@@brettgiles8311 Thanks! I have 2 Honda ST 90s(they haven't been started in 8 years) and one of the carb's pull button won't stay in the out position. I'm going to pull both carbs and ultra-sonic clean them or do a rebuild kit.. Thanks!
@@markh.2899 I have 3 ct90s 69,70,and 71. All running. The 71 has this carb
@@brettgiles8311 Very cool! I bought a very close match on ebay that I going to try while I rebuild the old carbs - They actually look very nice and good quality as well...
Hello Phil. What setting is your needle. Where is the e clip?. I have the same carb and have a runaway idle.
The needle is only capable of making very minor adjustments. What is very likely is the slide is binding in the throat of the carb. Try pulling the slide out, and make very sure you're putting it in correctly by looking at the notch on the side of the slide. It's very easy to put it in backwards. Or you might have dirt or junk built up in there. Try cleaning it.
I'm not sure; I've never changed the needle on a carb. If the engine is stock I don't see why you'd do that.
IS cd 90' carburetor same way ??
Wouldn't the two screw settings then be off once you let go of the choke? I'd imagine at least the air screw would need readjustment
They choke should be off, and the engine warmed up when you begin. It kind of like like I left the choke on a little bit but it should be off.
Thank for posting.
Great video. Where should the needle be set? I have a '72 CT-90 that seems to run fine until I after I have been riding for a while and the it wants to over rev or surge. Any thoughts?
Bradley Johnson not sure what you mean about "needle be set"! You mean the needle inside the carb?
Phil Burress Yes, the needle inside the slide.
As for your issue of your problem after you've been riding a while: Maybe there is a leak at the carb/manifold join that is occurring after it gets warm, resulting in it running lean. I first had the same issue on an old truck that ran great until it got warm, then it ran poorly. One clue was that it started occurring after I removed and replaced the carb, but did not replace the old gasket between the carb and the manifold. Once I replaced that gasket the leak was sealed, problem solved. You can check for an air leak like this with some spray carb cleaner. The carb cleaner fluid will temporarily seal the leak and you will hear a difference in idle. So get it warm and try that. As a matter of fact, I made another video about just this issue! Here it is: th-cam.com/video/4ja8Y62A72M/w-d-xo.html
Hmm, not positive about that needle! As I recall there are two grooves so you can make it go deeper? FWIW, if it runs fine when cold it's probably correct. I'm not an expert but I'm guessing that would not cause the problem with it running bad after warm up. I could be wrong though! I think I read up on that at one point because I had the same question but I can't remember now!
If you are on Facebook there is a Honda CT90 group and someone there can probably answer your needle question.
Very helpful thanks.
What does it mean if I start it and it has extremely high idle at these settings?
I'm not positive and also not a totall expert! I assume you've adjusted the idle screw all the way with no luck. I'd say check for an air leak, since it may be running lean(video). The gaskets under the carb and manifold get old. If it's not the original carb it could have a jet with a different size but I've never experienced that. Rebuilding these carbs is easy; basically you take it apart, clean it and put it back together with some new parts. The rebuild kits are cheap. th-cam.com/video/4ja8Y62A72M/w-d-xo.html
cool great video is this same for ct 70
Kevin Moa yes, it should be the same!
I tried this and it still wont idle
JDKeiffer if it won't idle there could be other issues that these carb adjustments won't fix. If there is a vacuum leak, clogged jet or dirty carb that will have to be fixed first.
Done did work in my dang old CT 70 too! Thank you Sir!
Are these adjustments made at operating temperature or from a cold startup?
Operating temperature.
On idle adjustment you started 3/4 turn
I think you're right! That initial 2 turns out is somewhat arbitrary.
my carb doesn’t look like that
good video, thanks
I'll give that again thanks
1:19. Count your turns again. Your off