Carburetor help
Discussion
Trying to fix up my new (to me) bike, it's a 2008 Yamaha XT 125 R.
Been setting up the carb myself, first time I've done one before, got it to idle fine, if a little fast, but the problem now is that any time I touch the throttle the engine stalls.
I get the feeling this could be due to the mixture being very rich, but I'm confused as it seems to idle ok.
The carb has been dismantled and re-assembled correctly, all spotless inside.
I've added a video here to demonstrate whats going on.
Anyone in the know care to comment on what could be causing this and the possible remedies?
Thanks
Video
Been setting up the carb myself, first time I've done one before, got it to idle fine, if a little fast, but the problem now is that any time I touch the throttle the engine stalls.
I get the feeling this could be due to the mixture being very rich, but I'm confused as it seems to idle ok.
The carb has been dismantled and re-assembled correctly, all spotless inside.
I've added a video here to demonstrate whats going on.
Anyone in the know care to comment on what could be causing this and the possible remedies?
Thanks
Video
The carburettor has two 'circuits or channels' (I can't think of a better word?)
One is the idle circuit and the other is the main running one.
The mixture of the idle circuit is usually adjustable for a smooth idle, but the main 'jet' is fixed.
The fact that it idles fine leads me to suspect a blocked main jet.
The main jet is usually a brass screw with a tiny hole in it located under the float. Whip it out and blow through it, check for crud blocking it etc.
One is the idle circuit and the other is the main running one.
The mixture of the idle circuit is usually adjustable for a smooth idle, but the main 'jet' is fixed.
The fact that it idles fine leads me to suspect a blocked main jet.
The main jet is usually a brass screw with a tiny hole in it located under the float. Whip it out and blow through it, check for crud blocking it etc.
odyssey2200 said:
has the needle dropped out of the slide, so that when you lift the slid eyou are leaving the needle behind?
Dr Doofenshmirtz said:
The carburettor has two 'circuits or channels' (I can't think of a better word?)
One is the idle circuit and the other is the main running one.
The mixture of the idle circuit is usually adjustable for a smooth idle, but the main 'jet' is fixed.
The fact that it idles fine leads me to suspect a blocked main jet.
The main jet is usually a brass screw with a tiny hole in it located under the float. Whip it out and blow through it, check for crud blocking it etc.
I'll check both these tomorrow as well, thanks!One is the idle circuit and the other is the main running one.
The mixture of the idle circuit is usually adjustable for a smooth idle, but the main 'jet' is fixed.
The fact that it idles fine leads me to suspect a blocked main jet.
The main jet is usually a brass screw with a tiny hole in it located under the float. Whip it out and blow through it, check for crud blocking it etc.
Edited by Robb F on Tuesday 14th June 23:06
Most of the single & twin bikes I've owned or worked on (including my sons mopeds & bikes)have involved tinkering with the carb settings. The usual mistake is with the throttle adjustment & air screw.
What I tend to do is make sure things like the needle(if adjustable) is set to the standard setting, ie if there are 3 slots on the needle I'd set it to the middle setting.
Then make sure there is no tension on the throttle cable, then adjust the air screw. The usual "ball park" setting is screw it in as far as it will go then back off the screw about 1 & 3/4 turns. then adjust the slide stop to get a decent tick over then take up any, but not all the excess throttle cable slack.
This should give you a good starting point. Obviously getting hold of the correct factory settings is better, but this set up it has worked for me on many 2 & 4 stroke bikes, Brit, Jap & Italian.
What I tend to do is make sure things like the needle(if adjustable) is set to the standard setting, ie if there are 3 slots on the needle I'd set it to the middle setting.
Then make sure there is no tension on the throttle cable, then adjust the air screw. The usual "ball park" setting is screw it in as far as it will go then back off the screw about 1 & 3/4 turns. then adjust the slide stop to get a decent tick over then take up any, but not all the excess throttle cable slack.
This should give you a good starting point. Obviously getting hold of the correct factory settings is better, but this set up it has worked for me on many 2 & 4 stroke bikes, Brit, Jap & Italian.
I resolved the issue I was having.
Turns out the problem was thus:
There is a small metal piece that guides the tapered pin into the fuel reservoir at the bottom of the carb. This part can physically be inserted either way, but if inserted correctly, will be flush with the bore of the air intake. It is supposed to protrude from the bore by about 2-3mm.
I rebuilt the carb putting this piece in correctly and all was well.
HTH.
now detach the carb from the air intake and from the engine and lift away. Don't turn it upside down or you'll get fuel everywhere.
It is also worth noting, if you are not entirely comfortable with removing the carb from the bike, it might be best to leave it to someone else to rebuild, as there lots of tiny fiddly parts and knowing how they all work together is essential. I don't mean that in a patronising way, and the best way to learn is to do it yourself, just make sure you go in with your eyes open that its not that easy.
Turns out the problem was thus:
There is a small metal piece that guides the tapered pin into the fuel reservoir at the bottom of the carb. This part can physically be inserted either way, but if inserted correctly, will be flush with the bore of the air intake. It is supposed to protrude from the bore by about 2-3mm.
I rebuilt the carb putting this piece in correctly and all was well.
HTH.
ktm301p said:
I'm hoping to bring this thread back to life. I'm currently in the same position as the OP - except I haven't removed the carburettor before and would find any advice on how to do so, invaluable.
Thanks
To remove the carb, take lots of clear photos of it installed correctly. These will be very useful if you forget where everything went! Then detach each pipe from the carb, labeling them as you go so you can put them back in the right place. Don't forget to block off the fuel line properly, although there should be a valve in the fuel tank to stop it all coming out.Thanks
now detach the carb from the air intake and from the engine and lift away. Don't turn it upside down or you'll get fuel everywhere.
It is also worth noting, if you are not entirely comfortable with removing the carb from the bike, it might be best to leave it to someone else to rebuild, as there lots of tiny fiddly parts and knowing how they all work together is essential. I don't mean that in a patronising way, and the best way to learn is to do it yourself, just make sure you go in with your eyes open that its not that easy.
Edited by Robb F on Monday 16th April 15:14
Robb F said:
To remove the carb, take lots of clear photos of it installed correctly. These will be very useful if you forget where everything went! Then detach each pipe from the carb, labeling them as you go so you can put them back in the right place. Don't forget to block off the fuel line properly, although there should be a valve in the fuel tank to stop it all coming out.
now detach the carb from the air intake and from the engine and lift away. Don't turn it upside down or you'll get fuel everywhere.
It is also worth noting, if you are not entirely comfortable with removing the carb from the bike, it might be best to leave it to someone else to rebuild, as there lots of tiny fiddly parts and knowing how they all work together is essential. I don't mean that in a patronising way, and the best way to learn is to do it yourself, just make sure you go in with your eyes open that its not that easy.
Thanks for your response, I'll remember to take as many pictures as possible and labelling the parts clearly. I'm also pretty comfortable with doing this myself, I think that as long as I do each stage slowly, patiently and carefully there shouldn't be a problem. now detach the carb from the air intake and from the engine and lift away. Don't turn it upside down or you'll get fuel everywhere.
It is also worth noting, if you are not entirely comfortable with removing the carb from the bike, it might be best to leave it to someone else to rebuild, as there lots of tiny fiddly parts and knowing how they all work together is essential. I don't mean that in a patronising way, and the best way to learn is to do it yourself, just make sure you go in with your eyes open that its not that easy.
Edited by Robb F on Monday 16th April 15:14
Thanks
Alex
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