Fair weather rider
got the carbs off today, taking them to a place in town for a clean and a rebuild, $300 (estimate) will tell them about the needles and tubes and see what they say, if no joy there i will be on the phone to the guy in CHCH to see what he can do, not sure how i can manage without my bike for over a week tho.
Fair weather rider
small update:
had them at the carb shop today, he stripped them down and is giving them a clean, tubes and needles look ok to him, but one of the main jets was blocked completely :S also mix setting were "all up the piss" suspect it started running rough on last owner and he just fiddled the mixes to make it sound/go right.
Hardcore Biker
Sounds like your problem is solved, cheaper than buying a set of carbs and getting them balanced and tuned.
Embracing mediocrity
Yep, that happens, had to replace a bleed screw in a carb because it had been wound right in and snapped the tapered end off in the hole when someone had fiddled with them.Originally Posted by dynamite9585
You'll probably find it goes a heap better after a clean, if all 4 cylinders are getting some petrol instead of just 3.
Riding cheap crappy old bikes badly since 1987
Tagorama maps: Transalpers map first 100 tags..................Map of tags 101-200......................Latest map, tag # 201-->
Hardcore Biker
Although $300 is a bit steep as rode my bike in to shop with fairings off and had same work done, cost me $300 and they replaced 4 spark plugs too with carbs fitted back on bike.
rode home sweet as.
Forum whore
Even better, I think the GSXR250 engine only uses 2 carbs.Yep, that happens, had to replace a bleed screw in a carb because it had been wound right in and snapped the tapered end off in the hole when someone had fiddled with them.
You'll probably find it goes a heap better after a clean, if all 4 cylinders are getting some petrol instead of just 3.
Fair weather rider
correct.
will be back up and running tomorrow by midday.
been googleing ect when it come to fine tuning the air fuel mix, is there a sound or anything in particular i should be loooking for so i know i'm on the money? and should this be done before or after i balance them?
oh yea, cost for strip and clean: $80
Hardcore Biker
thats your idle air mix screw, probably find its all the way in (not too tight) then something like 2.5 turns out <--- not actually 2.5 but ya see what ya do.
Should say in a workshop manual but would have though bike shop would have set for you.
Only other way to tune is to set needle height or rejet which I don't recommend.
I use an old o2 sensor from a car and put in exhaust and tune that way but only because I can.
'tart tourmenter
CV carb tuning info
A usefull guide I've had for a while - Emphasizes correct order of adjustments.
CV Carb Tuning
Follow steps in order....First, dial in:
1. Top end (full throttle / 7.5k to redline - Best Main Jet be selected before starting step 2!
Select Best Main Jet
To get the best, most even top end power (full throttle/after 7500 rpm), select the main jet that produces the highest top speed / pulls hardest at high rpm.
If the bike pulls harder at high rpm when cold and less hard when fully warmed up, the main jet is too large. Install a smaller main jet and retest until you find the main jet that pulls the hardest at high rpm when fully warmed up. This must be done first - before moving on to the other tuning ranges.
If the bike doesn't pull well at high rpm when cold and gets only slightly better when fully warmed up, the main jet is too small.
In order to properly tune the midrange and low rpm carburetion, THE MAIN JET MUST FIRST BE PROPERLY SELECTED after 10 to 15 minutes of hard use! Do not pay too much attention to the lowend richness when you are changing main jets - you still need to be using the main jets that produce the best power at high rpm. You will deal with the lowend / cruise later - after step 2.
2. Midrange (full throttle /5k-7k)
Select best needle clip position
To get the best power at full throttle / 5k-7k rpm, after you have already selected the best main jet.
If the engine pulls better on a full throttle roll-on starting at <3k, when cool but soft when at full operating temperature, it is too rich in the midrange and the needle should be lowered.
If the engine pulls better when fully warmed up but still not great between 5k-7k, try raising the needle to richen 5k-7k.
If the engine pulls equally well between 5k-7k when cooler as compared to fully warmed up, the needle height is probably properly set.
Do not pay too much attention to the lowend richness when you are changing needle clip positions - you still need to be using the clip position that produces the best full throttle / 5k-7k power in conjunction with the main jets that produce the best power at high rpm. You will deal with the lowend / cruise next.
3. Low end (full throttle / 2k-3k)
Float height (AKA fuel level & how to..)
To get best lowend power, set float height so that the engine will accept full throttle in 2nd gear from 2.5k to 3k rpm at minimum.
Float heights, unless otherwise specified in the installation guide, are measured from the "gasket surface" of the carb body to the highest part of the top of the float - with the float tang touching but not compressing the float valve spring.
If the engine has a "wet" rhythmic, soggy area at full throttle / 3k-4k rpm, that gets worse as the engine heats up, lower the fuel level by resetting the float height 1mm greater (if the original was 13mm - go to 14mm). This will lower the fuel level, making full throttle / 2k-3k rpm leaner.
If the engine is "dry" and flat between 2k to 3k rpm, raise the fuel level.
Example: change float height from 15mm to 14mm to richen up that area.
REMEMBER, since the main jet WILL affect low speed operation, the MAIN JET has to be within 1 or 2 sizes of correct before final float setting.
Warning: If the engine is left with the fuel level too high,, the engine may foul plugs on the street and will be "soft" and boggy at part throttle operation. Adjust Floats to raise/ lower the Fuel Level.
Base settings are usually given if a particular application has a history of fuel level
criticalness. The Fuel level height in the float bowl affects full throttle/low rpm and, also, richness or leanness at cruise/low rpm.
Reference: a bike that runs cleanly at small throttle openings when cold, but starts to show signs of richness as it heats up to full operating temperature, will usually be leaned out enough to be correct if the fuel level is LOWERED 1mm. Check out and RESET all: Suzuki (all), Yamaha (all) and Kawasaki (if low speed problems occur). Needless to say, FUEL LEVEL IS EXTREMELY IMPORTANT!!!
If there are lowend richness problems, even after lowering the fuel level much more than 1.5mm from our initial settings, also check for needle wear and needle jet (part of the emulsion tube). See Worn Needle and Worn Needle Jet diagram. It is VERY common for the brass needle jets (in the top of the"emulsion tube") in 36mm, 38mm and 40mm Mikuni CV carbs to wear out in as little as 5,000 miles.
Check them for "oblong" wear - the needle jet orifice starts out round! Factory Pro produces stock replacement needle jets / emulsion tubes for 36mm and 38mm Mikuni carbs.
4. Idle and low rpm cruise
Fuel Screw setting (AKA mixture screws)
There is usually a machined brass or aluminum cap over the fuel screws on all but newer Honda. It's about the diameter of a pencil. Cap removal details. Newer Honda carbs use a special "D" shaped driver, usually supplied in the carb recal kit.
Set for smoothest idle and 2nd gear, 4k rpm, steady state cruise operation. Set mixture screws at recommended settings, as a starting point. For smoothest idle, 2nd gear 4000 rpm steady state cruise , and 1/8 throttle high rpm operation.
Pilot fuel mixture screw settings, float level AND pilot jet size are the primary sources of mixture delivery during 4000 rpm steady state cruise operation.
If lean surging is encountered, richen mixture screws (turn out) in 1/2 turn increments.
Alternative pilot jets are supplied when normally required.
Pilot fuel mixture screw settings, float level and pilot jet size also affect high-rpm, 0 to 1/8 throttle maneuvers. Too lean, will cause surging problems when the engine is operated at high rpm at small throttle openings! Opening the mixture screws and/or increasing pilot jet size will usually cure the problem.
NOTE: A rich problem gets worse as the engine heats up. If the throttle is lightly "blipped" at idle, and the rpm drops below the set idle speed, then rises up to the set idle speed, the low speed mixture screws are probably set too rich: try 1/2 turn in, to lean the idle mixture.
NOTE: A lean problem gets better as the engine heats up. If the throttle is lightly "blipped" at idle, and the rpm "hangs up" before dropping to the set idle speed, and there are no intake leaks and the idle speed is set at less than 1000 rpm, the mixture screws are probably too lean: try 1/2 turn out, to richen mixture. Be sure there are no intake leaks and the idle speed is set at less than 1000 rpm!
Carb tuning is a combination of science, art, intuition and a lot of wizardry.
Suck, Squeeze, Bang, Blow aren’t just the 4 cycles of an engine
Scooter boy
Ok so from this I have questions:
1. Roughly what should the mileage from a 250 Bandit be normally then?
2. Hard starting? like having to twist the throttle right round then hit the go button?
Awesome answer by the way, a fair amount of info there
'tart tourmenter
Start with full choke & no throttle.
Suck, Squeeze, Bang, Blow aren’t just the 4 cycles of an engine
Fair weather rider
wow!!! fantastic information there!!!!! thanks.
as for Techno's issue, imo sounds like it's dumping fuel in the carbs and flooding.
but that just my opinion based on that your having to give it all the air you can to get a combustable mix.
Scooter boy
Yeah that used to work but over the last couple of months I've found that I need to crank the handle more and more, I only really noticed it a couple of days ago (as with all things that build up slowly you don't notice straight away). Once it's been running it's ok, but the next morning back to the same.
So your thinking is that it's just pouring fuel in but it's not getting enough air until the throttle is opened? Are we talking a job for my local friendly bike storewow!!! fantastic information there!!!!! thanks.
as for Techno's issue, imo sounds like it's dumping fuel in the carbs and flooding.
but that just my opinion based on that your having to give it all the air you can to get a combustable mix.
Fair weather rider
possibly, but thats just my inturpretation of it.
i THINK bandits have the same carbs as the gsxr, so could be the wearing that was mentioned earlier
Fair weather rider
will this ever end??!!!!
got it all back together now the carbs are in desperate need of a tune, but i can't seem to find anything on it that screams this is the screw your looking for. down to the bike shop tomorrow i think..... sigh
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