YAMAHA XS250 CARB TUNING HELP!

Hey Crazypj
Im going to order new main jets today.
What size do you think i should get.
The standard is 110. Currently i have 122.5 because im running pods.
Should i go for 120 main jet? or should i perhaps get 117?
what do you suggest. ill wait to see what you think before i order the new main jet.

cheers!

Personally, I would get 115, 117.5 and 120, what works right now may not work right when you change/modify exhaust
If you 'play with motybikes long enough, you end up with lots of 'spares'
If cost is a problem, get the 117.5 first, if it's a bit lean top end you can always go slower until you get 120's ;D
BTW, were 'choke' plungers seating all the way down?

awesome mate,
i will get the 117.5 today.
Also in regards to the choke plungers i might attached a photo. to see what you think.

hi all,
I also have a problem with my FAZER XS250 ,it has starting problem n i m not getting the working of its carburetor .can any of u explain me the working of carburetor???or any link that guides me ???

Just to give you an update Crazy.
Well i put everything back together. and now for some reason the left carb is not getting any fuel. only the right one is getting fuel. so therefor only one cylinder is firing. the right one. the right pipe is hot. and the left is cold as ice. the problem is definitely because its getting no fuel.
So the bike isnt starting.

This is really driving me nuts. I dont understand it. the carbs are very clean. and i put them back together fine.
The floats are set. it makes no sense.

Now the only problem i think. well i dont think the float needles are in very good working order. the right one sits higher than the left. just when the bowls are off and they are sitting there. In saying this. the bike started great every time before i took the carbs apart this time.

Anyway. Do you have any suggestions why the right carb isnt getting any fuel?

-hey RIZ KHAN check out the second post on this topic there is links with all the information you need.

If the floats are different levels, they are not set.
If they are set correctly, the damper spring in shut off valve must be stuck.
Either way, carbs are still not as thet should be

so if the shut of value on the float needle is stuck/broken. that would cause no fuel to go into the bowl?

that would probably make sense.

Might be an idea for me to get new float needles. because everything else seems to be in place.

what you think?

There is a little spring loaded plunger on the end so tip isn't affected by vibration.
You can still set float level, the tip will just wear out quicker than normal (probably a few years instead of 30 yrs)
You are bending the little tang to set float level?
The shut off housings are fully seated?
It really sounds like your doing something wrong.
I have pics showing angle to hold carbs for setting but can't find them
I would get some new 'how to' pics but I cant do much until I get brace off my arm, one handed isn't going to work

Hi mate, sounds like you are having a tough time with the old bs32's.

Firstly I want you to know that I do not claim to be an expert on carbs and probably 99% of people on here have more knowledge about carbs than me.

I have an 81 xs250 that I am currently working on and hope that I can help by sharing what I have experienced.

My bike had 117.5 jets as per the Haynes manual.

The general consensus on xs carbs is that you should clean them again and again and again or get them ultrasonic cleaned as they hate the slightest bit of dirt. Some people get great results by boiling their carbs in diluted lemon juice but I have not tried that.

Are your pod filters attached directly to the carbs? It is recommended that you put the pods on the end of the stock air filter hoses as sometimes pods block intake passages.

Is you petcock freeflowing?

Are you running an inline fuel filter?

Do the rev's just jump to 5k rpm and stay there or do they hunt? If they hunt then I would suspect an air leak. What happens when you spray wd40 on the intake boots when it is running? Did you replace intake boot gaskets?

1.5 turns out on mixture is kind of lean as people usually set them around 3-3.5 turns out. This however, conflicts with your plug readings.

Do the floats have much lateral play that could make them get stuck?

When they hit 5k rpm what position is the slide in?

When you give it some throttle with the choke on, do the revs drop slowly?

...Good luck with sorting this out.

HI Porterhouse.
Even if you don't have a lot of experience with different carburetors you do sound like you've had a lot of experience with XS250 carbs

Thanks PJ but I am actually only building my first bike but I got heaps of help from the guys on xs400.com.

Hey guys,
Just to let you all know i ordered new float needles. and they just arrived today, so i will put them in this weekend and see how she goes.

Porterhouse thanks for the input, i will give you an update shortly.
the intake boots are new, new gaskets etc. the pods are straight onto the carbs. the petcock is new.

the last issue i had was that no fuel was getting into the left carb. so i got new float needles to fix that issue.

i will send an update soon.

Hey guys,
Ok i have been working on the bike. i fixed the issue with the left cylinder not fireing. it was because no petrol was getting to the bowl. this was because when i put the bowl on it was shutting the pin and stopping any fuel getting through. problem solved.

Now the issue is that. the bike wont idle without the choke on. and also once i give it a bit of throddle . it will stick. and once i take off the throddle then it will rev all the way up to 6000 rpm.

Does anyone know what i should do.

Also i had so much trouble with the floats. because in playing around with them, the bowl were moving also not just the flange. so they were all out of wack. i think that even though i cant measure the floats its also important to notice the cut off point on the pin. because they were measureing 28mm. but when i was putting the bowl on the bowl was pushing on the floats and cutting off fuel supply.

Anyway. what should i do next. the inlet manifiolds are new. there should be no leaks.
Does anyone know what the setting are for the throddle stop screw and also the idle screw.

cheers!

There isn't really a setting for idle screw, wind it out until bike 'dies', re-start, hold idle on the throttle and adjust idle screw until rpm starts to rise slightly, let go of throttle and adjust where you need it.
28mm sounds too high for float level, is that Yamaha spec for your specific carb?

hey mate,
yeah im a little confused with the float levels. because i have been told to put the levels at 28mm. the manual says 26mm.

but if you set them higher wouldnt that mean less fuel would get into the bowls? with pods on dont i want more fuel getting in the bowls?

Im a little confused. i had the floats at 28mm for example. and on the left carb the bowl was pushing against the float and causing it to shut off.

Anyway. I have no idea where to go from here. i change the float levels now they are about 25mm. and now i dont think its getting enough fuel to start. Im going insane!

I just need someone to give me the correct information and where to go from here.

Can you post some pics of what your doing?
I did some CB360 carbs and had a hell of a job to get left carb working properly.
The float support arm was ever so slightly bent plus the pivot point had been set at an angle (same on both cabs so it looked 'factory' )
I ended up taking a float out of my low mileage carbs to compare, then things became more obvious.
Needed an accurate straightedge and couple of pairs of special pliers to get pivot bar tweaked back to correct shape

what did you want me to take photos off?

The inside of carbs (floats, etc) and how your checking float height
I'll try and get a pic of carb to show correct method (I used to teach , 11-1/2 yrs until RIF last June)
OK, Just took some pics.
This carb has an angled gasket face but you can see the general concept

1. Manuals always show carb completely inverted, there may be instructions to tilt carb 20~30 degrees in the text



2. Tilting 90 degrees should have shut off valve completely open


3. Tilt until float tang just touches shut off valve without compressing it and measure highest point of float

Hey Crazy PJ,
sorry i have been away for a while.

Bike is pretty much done. however now i think i am having trouble with back pressure.
The bike starts and idles. but i tried to take it for a ride and once in first gear opened the throttle it then didnt go anywhere and conked out!
its doesnt seem to have enough power to pull me and the bike along.

What do you think the issue could be.

Also while idleing if i put the choke on. it will also cut out. not sure what the problem could be.

I hope you may have some answers!
cheers

Sounds like it's still too rich?
What colour are the plugs, still black?