Completely gutless

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    Juan Skinner

    I’ve got an NRG 50 which was really very nippy when it was new. Now it’s output has dwindled to such a point that it can barely carry its own weight up a hill. On the flat, it tops out at around 30mph. It used to do 65mph. The engine still runs smoothly but power decreases when warm.
    I’ve changed the plug, cleaned the air filter, checked for fuel delivery to the carb from the vacuum operated fuel tap. The plug colour is healthy and plume is normal.
    I did find a load of water in the EGR filter, so this was dried and cleaned. I don’t know where this water came from, I have never jetwashed the bike, it’s always been sponge and bucket.
    I’m really scratching my head over this one. I have wondered about the EGR system and confess that I know little about what detrimental effects could occur due to a fault in this area.
    I’m just about to take off the air filter and run it up so I can check to see if the automatic choke is working.
    Anyone have any thoughts on this?

    Juan Skinner

    I blanked off the EGR and found it made no discernable difference.
    I’ve found a crack in the rubber inlet duct between the carb and reed block.
    Not sure if it goes right through but its my prime suspect at this stage.

    GSX Rat

    sounds pretty likely….

    mind you, if it was pulling air the plug should have shown that up.

    I slept with faith and found a corpse in my arms on awakening; I drank and danced all night with doubt and found her a virgin in the morning.
    Aleister Crowley (1875 – 1947)

    Blackboard paint – Covers a multitude of sins!

    Juan Skinner

    Grr, yes the plug would have looked chalky I guess. I had the inlet duct off and it was quite deeply split but not all the way through. A good blob of silicon sealant was applied just to eliminate any doubt but sadly, this wasn’t the cure. I did notice though that there was what looked like drops of water right on the reed valve. The bike is the liquid cooled version btw. The crankcase had some fluid swishing about in it, perhaps only 1cc of the stuff but i’ve never seen a 2 stroke crankcase looking this wet. It had a viscosity more like oil than water and there was no sign of rust on the crank.
    Next thing I suppose is to look at the ignition circuit. This is a pig because loads of plastic has to come off to get at the cdi box.
    It’s all done in one unit, cdi, flashers et al. My indicators often start blinking fast so this unit has been suspect for quite a while now.
    I’m hoping to get these overalls off one day and go for a proper raz without having to push it up hills!

    Juan Skinner

    Oh if only it were that simple! Of course your right, the plug would have looked chalky if this were the problem. When I finally found my T30 Torx

    tamperproof driver bit and took the duct off, it appeared split but not enough to penetrate right through. A healthy blob of plumbers silicon sealant was

    gobbed around it just to be sure. It still ran completely gutless, worse when the throttle was wide open and worse as it got warmer.
    I had checked the automatic choke. Although the carb is plumbed into the coolant, my assumption now is this is just a de-icer. Had me thrown for a while.

    The carb is a DellOrto PVHA and the automatic choke is done instead by an element heated by the lighting coil which extends a brass rod, acting as a slide

    valve, to cut off a bypass drilling and associated choke jet. It showed a good low resistance and extended from 11mm when cold to 14mm after a couple of

    Next, I’m going to go for the sparks side of things. It’s a bit of a pig because getting at the module involves taking off loads of plastic. The module does

    cdi and a whole bunch of other things such as flashers. My indicators have spates of flashing very fast, as if a bulb has gone but it happens both sides and

    all four bulbs are fine. This unit has always been under suspicion.

    One fine day, I’ll get out of this boiler suit and go for a very enjoyable raz, till then I’m still scratching my head over this one.

    A little about the bike

    This NRG 50 liquid cooled, dual disk brake bike has a bit of history behind it. It was bought originally by a millionaire as a pit bike for the gumball

    rally. He had it derestriced, keeping the original pipe but blanking off the resonant tube. I guess the variator nylon washers have been removed but I can’t

    find any other modifications.



    Just a thought. I’ve seen these symptoms on a bike which had a duff battery. It sometimes registered full voltage (12V or 6V depending on your battery) but because it was half empty on the electrolyte level, the plates were buckling and causing a few strange errors. The battery effectively ‘drags’ the voltage down in the system so that you get quirky symptoms. CDI units need a steady & stable voltage to work well. Worth a check if you haven’t already. One other thing, carbs are very susceptible to blocking – even if they look totally clean the jets are often the culprit when you have a gutless bike.

    Have you tried a plug chop?

    Juan Skinner

    Hey, i turns out I was wrong about the unit, it’s called a lighting regulator unit and does, as far as I can see, alternator field current, rectification and flashers but not as I originally thought cdi.
    The cdi is actually built into the coil which is why I couldn’t find the bugger in the first place.
    The battery is 12v gel type and spins the motor over very well over an extended period so I don’t suspect this could be a problem.

    I take your point though, on my CB125 import, it was cutting out on what I thought was the overrun. Thinking on, this is when the brakes are applied. 21W bulb brought into circuit, nearly 2A drain from the battery and the result is weak sparks. The battery is new, and I’ll check tomorrow but I suspect it’s not charging.

    Back to the scooter, it’s getting worse day by day. When I go on a test run, people are now swearing and gesticulating at me as if I’m trying to piss them off. If only they knew who was *really* pissed off. As it degenerates, it is obviously missing, going in fits and starts on full throttle.

    A new cdi/coil is £45 which is fine if it solves the problem. If not I’ll be £45 worse off and still have the original problem.
    My only reservation is that I do not have a timing light. Can anyone recommend a good basic (active not passive) one? I swore an oath against petrol engines being a diesel head by nature but I forgot all about bikes. Bad mistake to make.


    Juan Skinner

    Hey I’ve sussed it!
    There’s this little blanking screw which is in the exhaust right near the exhaust port. I took is out and went for a spin. Hey presto, power is restored. Makes me sound like a right jonny boy but I think it proves a point – it’s my exhaust bunged up! Gives me a good excuse to get a nice stainless job for it.


    Great, thanks for posting the solution. Is that the restrictor screw? If so it should still not perform that bad with the screw in (unless it was wound in too far). Maybe you still have a problem but that extra bit of power makes it feel a whole lot better? I hope for your sake it’s cured and that you can at last enjoy the bike without your boiler suit!

    Juan Skinner

    I’m not sure what this thing is for exactly, possibly it’s to measure exhaust emissions as the exhaust has a catylitic converter. It is a ten millimetere fine thread blanking screw
    It does not restrict gas flow as such, but just taps into the downpipe.
    I wonder if anything can be done with a standard pipe to unblock it

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