Carb problems, possibly?

[nzdeveth]

Hi everyone
im writing as a new member to the website, and to road bikes altogether for that mater.
i brought a 1990 fzr250 3ln a few weeks ago with the knowledge that it wasnt running quite rite. being semi mechanically minded i thought id be able to fix it.....i was wrong. Heres the problem if anyone can help id be very grateful

when you try to start the bike wether it be 5min or five hours after the last ride if wont rev up. the bike will start if you give it full throttle and will run at idle speed if you keep the throttle wide open, however, if you let the thrott off at all itll stall, to get it running normally again you have to turn the fuel off, let it idle away for 2-3min (with thrott full open), then all of a sudden it becomes completely responsive again and revs rite up. originally after reading a few posts on this website i figured it was a carb problem so i went about trying to fix it. 4hrs later i realized how little i knew about carbs so i put the bike back together and took it to the local yamy shop where they
-stripped and cleaned the carbs
-set float heights
-balanced carbs and
-set mixtures an speeds

I went and picked the bike up and it ran like a dream, problem solved..... not quite i filled it up with fuel and the problem came back i also noticed its running rough below 8000rpm and its quite slugish above 8000 but only when the tanks roughly above half full, it seems like excess fuel is being forced into the carbs under its own weight???

if thats at all posable or anyones got any ideas id love to hear them, dont realy want to keep paying the bike shop to not fix the problem if i dont have to haha

cheers, steve

[Trev084]

What sort of fuel did you put in?

If you don't mine me asking how much was it to get the carbs done?

[dontz125]

Sounds like you're flooding (bad float needles) and possibly you have no pump.

[deadbirds]

or might be a problem with the line.. does it work better on the reserve line?

[nzdeveth]

hi guys thanks for the quick replies,
um fuel wise ive tried both 95 & 91 octane with the same result, also got the fuel from different servos each time so relatively confident its not the fuel itself, paid 240 nzd including tax for the carb work, iv told the yamy shop they didnt fix the problem and there willing to do a cheeper rate to look at it again. id just rather have a rough idea of the problem before i take it back in, ive had bad experiences with cars so dont fully trust mechanics.
I took the bike for a ride this morning and ran it on reserve with no real improvements also had a look at the fuel lines they seem to be in pretty good nick. the fuel pumps running normally as far as i can tell (took the fuel line off, turned the key on and the pump started making noises and fuel came out)
Is there a way to check the float needles without any special equipment/knowledge

steve

[dave]

To Check the float level you only need a piece of clear tube that fits over the carb drain outlets.Then open the drain tap with a screwdriver. Get the bike perfectly upright and test all carbs one at a time. Start the engine to see if the levels move around.

Attached pipe like such... Dimensions are for 2KR carbs...



This pic is 3LN carbs with the levels marked on the carbs

[nzdeveth]

hi dave thanks for that. i did the test this morning, all four carbs are reading a fuel level about 9mm above the line irrespective of wether the bike is running or not, is that likely to be causing a problem?

cheers steve

[dave]

It sounds much like it is running rich because of the elevated float bowl levels.

I found this post
viewtopic.php?f=20&t=1487 and I will quote the relevant line,

Some documentation says that the stock level is 10.5mm above the float indicator. Iono I just set mine to the line. Worked just dandy.

Hope that helps. Read the fzr 400 manual on this website, viewtopic.php?t=327 chapter 6 page 11 - it tells you how to set the level.

[Trev084]

Dave thanks for all your tech input, Very rarely do you see an admin/mod going out of their way to make tech posts.

[PhTanJo1]

dude...if still you have the problem,try to check the valve clearance,i have problem with same like yours(starting in full throttle and wait for couple of minutes to become the throttle responsive)and with dave helps i've found out most of the valves don't have clearances anymore,try it anyway it is easy to do and worth it.....

[garyhoons]

Hey mate, it really sounds to me that your float needles are stuffing up and screwing you around.

I have a 2KR so I'm not sure how yours compares being a 1990 because your tank is a little different, but in my case my float needles were that old that the o-rings seating them in had perished enough such that they snapped when I removed them. Also the Veriton tips of the needles had edges worn in them.

IE, there is a small hole in the float needles seat that the fuel flows through. A rubber coated needle is pushed into the hole to block the fuel once the float rises up. If the tip is worn, then it may not be able to withstand the pressure of the fuel flowing into it, especially with a fuel pump trying to hammer it through relying on the needles to seat. When you first go to start your bike and the fuel pump primes it may not stop pumping straight away and float over, OR, if you have the model where the fuel tank sits ABOVE and a bit behind the carbies, as opposed to my 2KR which sits behind the carbies, then when you fill the tank up and the fuel level in the tank rises above the carbies then gravity and the law of fluids will try to force into the carbs and again, your needles and seats might not seal well enough to stop it.

Either way, i would suggest you whip your carbies out, slip the pin out that holds the float on, take the float off and then pull the needle out and inspect the end for a step worn into the rubber tip. If its got a step worn into its probably borderline useless and you should replace the needle and seat as a set.

Struggling to stay awake at the moment so if i left every third word and i didn't make any sense, then i'm sorry !

P.S (If you do need them, whip em out ( undo the screw and pull gently with large pliers wrapped in clothe if they won't just wiggle out) pop the mesh grill off the bottom with a screw driver and look for the number stamped on the bottom telling you the hole size. If its 1.2 then call up the guy from www.mikunioz.com and tell him you need 1FN-14107-12 which will cost you 35 each from memory and i THINK is the 3LN size. Otherwise, if they are 1.0 you need the same part number with 10 instead of 12. Be prepared for the shock of $52 from Yamaha as they stock em and no one else does because Mikuni stopped producing them in 2007.)

[P071]

Hi, I'm new to the board. One problem I turn to you. Start the bike (fzr250r 3ln 90 ') goes well, no choking, is idle, all right, but when the speed would increase over the 4000 return will blow the exhaust gas and choking the engine. Is that until 4000 I can only pull the throttle but it is up to 5000. I think that this might cause blockage in the carburetor. What do you think? What are your experiences?

I'm sorry because of the terrible English! : D

[Trev084]

Sounds more like the EXUP valve is in the closed position, can you hear the servo cycle when you turn the key and switch on?

[dave]

Could be the EXUP valve not opening, carburetor problem, or electrical problem.


Check exup valve.
http://www.thunderace.host.sk/thunderac ... owto/exup/


Carburetor
Check air filters are clean.
Check float levels are correct
Dismantle and clean carbs. note - jet sizes different between carbs, do not mix up.

Check charging circuit, rectifier/regulator problems can cause erratic behavior.
Check the battery voltage with the engine running and above 3000rpm and you should see 13.5 to 14.5 volts dropping to 12.5 - 13volts when idling. This indicates that your battery is charged and alternator and R/R is working ok.

[P071]

Sounds more like the EXUP valve is in the closed position, can you hear the servo cycle when you turn the key and switch on?

The valve exup picked apart, but we put it back, it is also a video that I made. Sometimes I pull the throttle more, sometimes less so. This is why we think that it is not the exup valve problem. The servo motor normally runs a test if I give him ignition. I barely opened the state to launch and fully opens and closes - but not quite.

[url]The valve exup picked apart, but we put it back, it is also a video that I made. Sometimes I pull the throttle more, sometimes less so. This is why we think that it is not the exup valve problem. The servo motor normally runs a test if I give him ignition. I barely opened the state to launch and fully opens and closes - but not quite.

http://sportmotor.hu/motoros_videok/kip ... ppal-69665