fuel starvation

[julie-nsr-125]

i have been having few problems wit my nsr125 '91 model (unfaired).

the bike will only run on choke, it works fine if you put fuel directly into carb but with all fuel pipes attatched properly will not run unless choke is on.

fuel is getting through pipes ok, whole carb and jets have been soaked in white spirit overnight and cleaned thoroughly.

have been advised it may be the vacuum operator cap but have no idea where to find this.

any advice on my problem will be much appreciated.

J x

[Trixie]

Could be the problem lies with the fuel tap. Do you have an "off" position or a "prime" position? It could also be a bit of crap in the tank that's jammed in by the filters on the fuel tap.

Have you checked your plugs? If you need the choke for the bike to run it may be running quite lean, which isn't good.
____________________
Dead nobodies in company cars...

[StealthDJ]

Er.

Hope I'm not sounding patronising, but you sure they didn't mean 'vacuum operated tap'? Would make a little more sense.

There's usually a diaphragm in the fuel tap operated by vacuum from the inlet. It's possible that either the diaphragm or the vacuum line leading from the inlet to it are damaged. Easiest way to check is to set to the fuel tap to 'prime' (if it actually has a prime setting) and see if that cures it.

There are other possibilities though - does it make any difference if you run the bike with the fuel cap off/open? You might have a blocked breather in the tank. It might also be the fuel tank's internal filter, something that will require draining the tank to change/clear, unfortunately.
____________________
Current garage: VFR800 FI-W | RD500LC YPVS | SV650 K2 | MZ TS250/1 | MZ ETZ251 | BSA WDB40
Previous notables: H100 S2 | CB250NA/B | CB250T | GT250X7 | Z650 B1 | SR650
Still owned, but long gone: RD250LC | CB750F2 SOHC | C50

[julie-nsr-125]

the mixture seems fine doesn't seem t be lean it has been running great until this happened.

ahhhh not patronising that makes more sense.

Dont think fuel tap has prime setting. Have not tried it wit fuel cap off, but assumed that when all pipes are liked up that it would not even run on choke if it was a blocked breather in tank.

i was told that the vacuum operated tap came from the carb to let fuel into engine. i prob sound stupid lol you can tell i am new to this.

[Trixie]

If your fuel tap has a "prime" position, the tap should be in the horizontal position, as it would be for "off" on other models. If you look closely, it should be marked as either "prime" or "off".
____________________
Dead nobodies in company cars...

[Kickstart]

Hi

Fairly certain it doesn't have a vacuum fuel tap.

I would normally suggest a blocked fuel filter, but think the NSR does without one, even in the carb itself. Next suggestion would be the fuel tank breather being blocked.

However if the breather was blocked (or anything else restricting fuel flow) then pulling the choke on would just manage to keep it running for a bit longer. It would still die when the fuel in the carb was used up.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[StealthDJ]

[julie-nsr-125]

will check the fuel tap on bike see if i can see that.

The nsr i have is imported model and does have fuel filter, we replaced it last week so that should not be the problem.

Am not sure if it is breather as when running on choke it will quite happily keep running without dying until you take choke off.

[Kickstart]

[StealthDJ]

[julie-nsr-125]

only one pipe goes from tap to carb and the two run off the carb.

the only marking on my tap are on/off/reserve.

did not take float out to clean no, didnt want to touch it to be honest.

[julie-nsr-125]

we already checked the clip on the needle was to manufacturers settings. it really has me stumped.

not sure if bike has a fuel filter inside the actual tank will have to check this thanks

x

[StealthDJ]

[julie-nsr-125]

ha ha well that mechanics for you lol thats what they said it would be.

will try cleaning the floats to see if there any filth gathered and check that they not damaged.

how would i know if float is damaged?

[StealthDJ]

It's not the float that you want to clean, particularly, it's the valve that it opens and closes (which you have to remove the float to get to). On some bikes they drop straight out, on others, you need to remove a retaining collar - I'm not sure which it is in your case.

A damaged float usually sinks and floods the carb - you'd be having the exact opposite of the problems you're having.
____________________
Current garage: VFR800 FI-W | RD500LC YPVS | SV650 K2 | MZ TS250/1 | MZ ETZ251 | BSA WDB40
Previous notables: H100 S2 | CB250NA/B | CB250T | GT250X7 | Z650 B1 | SR650
Still owned, but long gone: RD250LC | CB750F2 SOHC | C50

[Kickstart]

Hi

If I am reading this correctly:-

1) Engine will not start or run without choke taking fuel from the tank.
2) Engine will start and run with choke on taking fuel from the tank, and continue to run indefinatly.
3) Engine will start and run fine if you put a funnel full of petrol directly the the fuel pipe on the carb.

These seem contradictory to me, so I suspect I am missreading your description of the problem.

Could you go through in detail the exact symptoms and what you have tried (whether it worked or not) to get around it.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[julie-nsr-125]

so its just the valve we need to clean

[julie-nsr-125]

hi

the bike will not fire up without the choke on.

when we fire it up with choke on it seems fine although when choke is off the bike will die.

we removed fuel pipe and poured a bit of petrol directly into the carb (where the air filter sits) and bike fires up and runs until petrol is used up.

[Kickstart]

[Kickstart]

[julie-nsr-125]

the symptoms are listed above,

so far we have cleaned the carb and jets,

we have reset needle to manufacturer settings,

we have now tested the float system which seems fine (but have not cleaned float system),

we have changed the fuel pipes and fuel filter that runs through pipes.

[julie-nsr-125]

thanks keith

we will try all you have suggested and see if that helps.

x