Another attempt to stop carb from overflowing

[angus3xv]

Hi

On the old forum you guys were extremely helpful in offering advise on my rear carb that keeps leaking from the overflow tube.

The carb is removed from the bike and about to go in an ultrasonic cleaner (fingers crossed). While its off is there anything else I can do to hopefully mean this is the last time I have to remove it. I vaguely remember someone saying there is a filter where the fuel line goes into the carb. I cannot see this...could it be missing or do things need to be removed to see it?

The other thing is that the bike will not run well when the bike fuel tap is on ON. It feels restricted...when set to PRIM it run wells. Is this linked into the above? I'm checking all the pipes for leaks etc and also taken the fuel tab off the tank. The tank is mint inside & the filter on the tab is clean. What else could this be? I'm replacing the fuel lines and circlips etc to make sure all fits snug, but while its all apart (AGAIN) is there anything I can try?

Thanks again for any advice, pictures to help with the above.

Cheers...Angus

[Warwick]

If everything is clean and in good order and the fuel needle valve is clean and sound, are you sure the float heights are set correctly?  With the float bowl removed and the carb body held upside down, the measurement between the bottom edge of the carb body and the bottom of the float should be in the range 15-17mm (assuming R model carbs - I'd need to look up the SP float height setting).

The tap working on 'Prime', but not on 'ON' suggests a problem with the vacuum set-up. Is the vacuum hose between the upper cyl carb and and the fuel tap connected and in good order? Have you stripped and checked the tap?

The little fuel filter sits inside the fuel feed stub on teh carb. You should be able to see the plastic rm of it poking out of the top of the fuel intake stub allowing you to pull it out with pliers. These can get clogged with tank debris so do check if it's there. If not you can either replace it with a new one or leave it out if you'd rather (If you tank's as clean as you say it shouldn't be a problem to leave it out).

Hope that's of help
 

   

[angus3xv]

Hi

Thanks for your help...I've just checked the float height and adjusted it to 17mm. Its an RS model.

I'll check the hose from the upper cyl carb to the fuel tap...not done that yet. Hopefully that will sort out the vacum issue....just waiting on a couple of other pipes to arrive to allow me to put it back together...fingers crossed.

The fuel tap seemed ok in that I could only blow through it when on PRIM. Do I also need to take apart the tap?? What would I look for it to be a problem??

Cheers

Angus

[wullie3XV9]

What about the o-ring seal around the outside of each of the brass float needle seats, have you checked to see if they're split / perished on the offending carb ?  That would allow fuel to bypass the float needle into the float bowl causing the flooding.

If you're in the U.K., I sourced new o-rings from ALLENS PERFORMANCE Ltd. in Bingham, Notts.  Their phone No. is :-  01949 836733.
The o-ring Pt. No. you need is :-  616-23002.  Two o-rings plus postage cost me £ 4.61 back in January '09.   
You can order on-line, just "google" Allens Performance, then look in MIKUNI carb spares, & take it from there.

Be very carefull / gentle when pulling out the brass seats as they're easily damaged. Use a small set of snipe, ( pointed ), nosed pliers
& a bit of old rag to remove them, then check the seals. If they're the originals, they'll be well past there best !!
Both of mine were perished after being in there for 15 years !!

                        Hope this helps Angus, regards, Wullie.   

[Kingy62]

the carb overflowing probs on my 3xv was down to a build up of debris/corrosion on the inside of the fuel inlet stubs,every now and then a tiny piece would break off,causing the fuel needle valves to stick open,some gentle rubbing with some cotton buds and autosol or some very fine wet and dry  seems to have cured this, (i dont have those little filters,just an aftermarket filter fitted between the tank and carb,hope this helps, Ian  

[ash33]

What about the o-ring seal around the outside of each of the brass float needle seats, have you checked to see if they're split / perished on the offending carb ?  That would allow fuel to bypass the float needle into the float bowl causing the flooding.

Be very carefull / gentle when pulling out the brass seats as they're easily damaged. Use a small set of snipe, ( pointed ), nosed pliers
& a bit of old rag to remove them, then check the seals. If they're the originals, they'll be well past there best !!
Both of mine were perished after being in there for 15 years !!

                        Hope this helps Angus, regards, Wullie.   

Was thinking the same thing, if the float heights are right it would have to be the O rings in the float needle. Although that doesn't explain the "prime" and "on" issue.

[Warwick]

Easiest way to test the tap is probably just to suck on the vac pipe while it's in the on position. If fuel flows freely the tap is probably fine.  Check the vac  hose isn't perished or kinked etc too, so that it is actually making a vacuum at the tap with the motor running. Useful tip from Kingy re: the inlet stubs too. Try to make sure all the fuel system is as clean as possible. 

[angus3xv]

Thanks for your help on this.

I have also replaced the complete float needle, including the O ring previously but it still did not cure the problem. I'll check the inlet stub & clean that up further, but after the blast in the ultrasonic cleaner most areas look great.

Once I get it started again I'll check the vacum on the tap. I'll also check all the pipes from the T bar piece to ensure there are no kinks or damaged pipes.

Fingers crossed....

[Warwick]

It really can't be much at all. In my own experience it's always been tanki debris that's been the problem whenever i;ve had a bit of leakage. How far out was that float? And did you check the float for holes and cracks while you were re-setting it?

Also if you leave it standing on PRIME that will put more strain on the fuel valve than it should have (ie: none when the motor isn't running) so that probably wouldn't have been helping things if you were in the habit of doing that before? It'd therefore be sensible to find out why the tap isnt working properly on the ON position and sort that to prevent stressing the float valve.

[essarjayauto]

This might sound like a daft question but how do these tap's work ? I looked at mine and i only have
 three position's. on,prime,reserve. Which off these serve as the 'off' ?
 I took a look inside and it seemed that the position's of the tap did not relate to
 the position's indicated by out side plate. No fuel came through with reserve or on, only
 on prime. Does the engine have to be running ?

[wullie3XV9]

... Does the engine have to be running ?

In a word, Yes.   
There's a vacuum operated spring loaded valve inside the tap assembly.  A piece of small bore pipe goes between the small stub on the tap assembly & a stub on the R/H side of the venturi on the L/H carb. When the engine's NOT running, the small spring inside the tap closes the valve, stopping fuel getting down to the carbs. "PRIME" overrides the spring loaded valve to allow fuel to the carbs after any maintenance on them.

                             

[TZR-V4]

If the 3XV tap is similar to RD500 and TZR 2MA
 - ON and RESERVE work with the vacuum line from one of the intake rubber so engine runs => fuel flows
 - PRIME is an open position to get the tank empty.

See the http://tzr250.com/forums/index.php?topic=112.0;topicseen to convert the tap is more classic one : ON / RESERVE & OFF without vacuum line.

Olivier.

[angus3xv]

Right then....finally got time to strip the carb, put in through an ultrasonic tank then rebuild it. I also replaced the fuel tap as a precaution although I couldn't see anything wrong with the old. I also replaced all the fuel pipe I could while the bike was apart.

Fired up on about the 5th kick but only ran on the left hand side until I was able to rev the bike. Then  eventually the other side fired up.

The original issue of the rear carb overflowing seems to be cured for the time being (been here before many times), however things are still not right. I have to really feather the throttle for the first few minutes as it will not rev, and heave to catch it right to rev higher. Eventually things all fire up and after taking it for a short ride idles fine.

The issue is the bike does not run well on ON or RES. Its like when you run of of petrol & have to switch to RES on a normal bike. The bike only runs well on PRIM. Then it goes as expected. However if I leave the bike on PRIM when parked it overflows (seems to be for about every tube!!..to be expected I guess). So I leave it on ON & for the time being its not leaking.

So any idea why it will not run well on ON. New fuel tap, carb all cleaned out (No filter in the inlet of the carb). The only thing I've not touched is the front carb. This does not overflow.

Any help really appreciated. Basically its a bitch to start, then when it does start it only works well on PRIM.

Cheers...Angus

[slinger]

Right then....finally got time to strip the carb, put in through an ultrasonic tank then rebuild it. I also replaced the fuel tap as a precaution although I couldn't see anything wrong with the old. I also replaced all the fuel pipe I could while the bike was apart.

Fired up on about the 5th kick but only ran on the left hand side until I was able to rev the bike. Then  eventually the other side fired up.

The original issue of the rear carb overflowing seems to be cured for the time being (been here before many times), however things are still not right. I have to really feather the throttle for the first few minutes as it will not rev, and heave to catch it right to rev higher. Eventually things all fire up and after taking it for a short ride idles fine.

The issue is the bike does not run well on ON or RES. Its like when you run of of petrol & have to switch to RES on a normal bike. The bike only runs well on PRIM. Then it goes as expected. However if I leave the bike on PRIM when parked it overflows (seems to be for about every tube!!..to be expected I guess). So I leave it on ON & for the time being its not leaking.

So any idea why it will not run well on ON. New fuel tap, carb all cleaned out (No filter in the inlet of the carb). The only thing I've not touched is the front carb. This does not overflow.

Any help really appreciated. Basically its a bitch to start, then when it does start it only works well on PRIM.

Cheers...Angus

Is the vacume pipe connected the fuel tap?

Had something similar with the starting and it was the choke, well the very small hole in the carb bowl. Even thou I cleaned it, it was blocked solid once clean it started a treat.

If your starting it from cold and have the feather the throttle then it's running lean ie choke not working proper.

[Warwick]

I'm with Mr. Slinger. Sounds like you've two problems: an issue with the vacuum set-up (you never did confirm that that was connected and sound etc? - Switch the tap to 'on' and suck gently on the carb end of the vac hose to test it), and a problem either ioin the choke or the pilot circuit. My money's joining Slingers on it being a clogged choke fuel pick-up from your description.