Hey guys,

So a few times now on my NSR I have gone to start it and have had to kick and kick and kick, then once it fires fuel shoots out the stingers and of course all over the bike!

I have forgotten to turn the fuel off a few times and had this happen but now its starting to do it even with the fuel off. I have tested the petcock and it works fine.

I suspect the needle and seats in the carbs. When I first got the bike I inspected them and set the float levels, they seemed to be ok. Three or four times now I have gone to my bike only to find a puddle of fuel underneath it. The lower cyl must have had the piston up and the fuel leaks out the exhaust flange and down the pipe.

Any ideas on this one?
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Andre E. Benguerel
1996 Honda NSR250R
Daijiro Kato/Fortuna Replica #74

2000 Honda RS250R (NX5)
2008 Honda RS250R (NXA)
AFM Expert #430


Last edited by andreb on Mon Nov 24, 2008 10:39 pm; edited 1 time in total

Only advice is be careful, I managed to hyrolock my gsxr750 and bend a conrod due to a bad carb.

I'd get it sorted asap

I would take a close look at the needle and seats. I've had this kind of problem on other bikes and after chasing my tail it was just worn seats. NSR's are getting up there in years and these types of mechanicals are going to become more common.

I was also thinking a leaky float but in all my years of working on carbs I have never found one that leaked.

I think I'll order new needle and seats anyways and just replace them when I inspect and clean the carbs. I don't want to have them apart and then figure out I need them.
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Andre E. Benguerel
1996 Honda NSR250R
Daijiro Kato/Fortuna Replica #74

2000 Honda RS250R (NX5)
2008 Honda RS250R (NXA)
AFM Expert #430

I agree on the float. It's always a solution that get's mentioned, but like you I've never seen one full of fuel on any bike no matter how old.

If it was the float seal, it wouldn't really explin the fuel in the engine when the tnk is turned off.

How is it getting from the carb into the cylinder when the only fuel available is from the flot bowl?

Have you checked that the tank tap ctually turns the fuel off - and that you're not rotting it to reserve?
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

Yeah, not sure really! I was thinking maybe pressure in the tank or fuel line forced it past the seats or petcock? My tank vents to a catch bottle. Maybe the line is pinched? I do run a fuel filter and between that and the line to the tank there would still be gravity pressure on any fuel in the line.

I would say the amount of fuel that shoots out the pipes is about the amount in the fuel line and carb bowls.

I have had the tank off a thousand times and I know the petcock works. Each position has a nice snap to it when you hit the detent. I know I had it in the off position and its done this twice now. I am certainly going to test it again. It's been a few months since I had the tank off. Maybe the seal in the petcock has failed.

It's always when its on the side stand too, never when it's on the rear stand. I am going to pull the carbs and check them out regardless, petcock too. Funny thing is it never pushes fuel out the bowl vents which I think would happen first before it pushes its way past the seats.

My thinking is it`s probably just the float level is set too high.
If this is the case, even with the petrol tap turned off. The level of fuel in the carburetor will still be too high.
With the bike on the side stand the excess fuel can leak out of the pilot & needle jet orifices into the engine. Also, as the float level setting is out, it won`t allow the floats to actually close the float valve.
This means the fuel left in the fuel line and filter can drain down, refilling the bowl, in turn leaking more fuel into the engine.
You may want to check that the overflow tube isn`t blocked anywhere also. Not just the plastic pipe but the brass tube sticking up inside the float bowl too.
The float bowl vents are a bit higher than the jet drillings into the venturi throat, so any fuel will reach there first.
The workshop section on this site should explain how to check and set the float levels.
Hope you find the problem.
Cheers, Roy.

Might be worth cracking the drain screw on the dodgy bowl to let a little out and see if tht helps?
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

Sorry, just realised that you said you`ve checked the float levels.
As long as you are sure they are right then you`ll have to check the valves actually close. You can do this by blowing down the fuel feed pipe and holding the float valves closed by hand.
Sorry if I`m stating the obvious but, you do know when checking the float heights you start by holding the carbs upright, then slowly rotate them until the valve closes and the float tab just lightly sits against the sping loaded plunger on the valve needle? Then measure from the gasket face to the bottom of the float.

Another thing you can try before pulling the thing apart is take the bike for a good run to clear out any crap in the cases and exhaust. Before puting the bike in the garage, turn off the fuel tap and run the engine until it dies from emptying the float bowls. If it still floods after this it`s a good indicator of the fuel tap leaking.

i had that problem on mine, cleaned the float valve seat with brasso on a cotton bud attached to my cordles drill. just smooths out any imperfections.
also drilled out the rivetts in the fuel tap/petcock ad put new o rings in the tap as it leaked, (not really enough to notice but over the course of a night parked up the amount still build up)

Pull the fuel tap apart, check the seals. Then check the float level, then the seats and needle.
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The Chopster

Thanks guys. I set the float levels properly when I first cleaned the carbs out. I can't imagine they would change that much but I will check to make sure. I thought I had pulled the petcock apart once but that may have been another bike, I have too many to keep them all straight.

I am going to try and tinker a bit with it this weekend. I also thought about your suggestion Chester. If I drain the carbs and park it over night, I can see if its leaking by just looking at the fuel filter. But even if it is leaking, the needle and seats should prevent fuel from flowing into the engine.

Hey Andre I wouldn't worry to much about the petcock. You said you removed the tank with it in the off position and no fuel flowed out. But like you say even if you leave it on the needles shouldn't allow any fuel to drain in to the engine. Just for reference my petcock is in the on position right now just like it always is and I've never had a problem.

A stuck needle will usually overflow out the carbs overflow tubes. A worn seat or needle will do what your describing. Replace the seat and needle just to eliminate that issue. They aren't that expensive and fresh carb parts are always a good thing.

andreb wrote:Thanks guys. I set the float levels properly when I first cleaned the carbs out. I can't imagine they would change that much but I will check to make sure. I thought I had pulled the petcock apart once but that may have been another bike, I have too many to keep them all straight.

I am going to try and tinker a bit with it this weekend. I also thought about your suggestion Chester. If I drain the carbs and park it over night, I can see if its leaking by just looking at the fuel filter. But even if it is leaking, the needle and seats should prevent fuel from flowing into the engine.

As apexxn says above &, as I said before in my first post, I do think the float valves must be letting fuel past somehow. Whether it`s worn valves or them being out of adjustment.
If you suspect them of sticking, (meaning they are worn usually, can also be dirt/debris, although you have a filter), tapping the float bowl area sharply can shock the valve closed. As has been mentioned, you would normally see fuel leaking from the overflow. That`s why I wondered if the overflow may be blocked?
Also, I`m pretty sure the overflow tube in the bowl sits to the right hand side. Meaning it will be raised slightly in relation to the fuel level when on the side stand.
Good luck. I`m sure you will find it in the end.