Piaggio NRG 50 Carb - revving itself up

Hi guys. My first post on here. Im a 36 year old guy who bought the above scoot as a cheap mode of transport but it's got problems. I need a few basic answers and some pointers please from somebody in the know. I believe this has the standard Dellorto? carb, certainly looks like it. Its not been modified as far as Im aware other than a different exhaust and the secondary air system has been blocked off which I believe is par for the course.

It went into a local garage who charged me a fortune and did f&*k all. He said the carb was doing what is should be doing now. The auto choke had been disconnected, he reconnected it and reckoned it was 'ticking over alright now'. It was ticking over at just over 1000rpm which I though was slow. Well, I got it home and the mixture screw was 1 1/4 from fully closed which I thought was a bit wrong? As I understand it the rough setting is 2 1/2 (or 2 1/4?) from fully closed. So 1 1/4 seems just plain out. First question lies therein. What is the rough setting for both idle screw and mixture screw? Second question from here so I can understand whats going on. With the standard dellorto carb what action is being taken by screwing IN the mixture screw and idle screw. My guess is that screwing IN the mixture screw is strengthening the mixture? not weakening it? and that screwing IN the idle screw INCREASES tickover? not decreases it? Screwing the mixture screw out causes the engine to rev more and more - there seems to be no limit to this.

Anyway, to continue, the scooter has a tendency to hover around 5000 - 7000 RPM once it has been revved up. I adjusted the mixture to 2 1/2 turns out (the standard rough setting?) and the thing goes nuts - rev rev rev all on its own. I turned the mixture screw in to roughly what the garage has set it to, 1 1/4 and it calmed down...for a while before going ballistic again.

So now Im at the stage that Ive messed around with the mixture and idle settings so much I havent a clue where I am with them.

Are there any 'rough settings' for idle screw and mixture screw for me to start again from? and any thoughts as to why the thing revs itself up or doesnt return to idle as it should do? I have had suggestions that there may be an 'air leak' but this means nothing to me. I have no ides where to start looking of proving this so I'd really appreciate peoples' input as to what may be causing this or how to troubleshoot it. Im guessing somewhere on the inlet manifold but how I access this is a bit of a grey area. I need help! I have no faith in the local scooter dealer who charged me £200 for basically nothing and want to try to sort it myself. Im an intelligent enough guy, just need some advice. Thanks, in anticipation.

I hope my explanation makes sense.

Rob.

 

Hi rhbmcse ive a NRG 50 too is yours an aircooled version or water

I hope to be checking the jetting on mine also as mine is drinking fuel at the min

Good post there terro i will check my carb also

 

Hi Acid,
Mine is the air cooled variant.
Im about to get the overalls on and annoy the neighbours early on a sunday morning.
From what I've read, spraying some WD40 (dont have carb cleaner) around the base of the inlet manifold should cause the engine to rev (even more!!!) if there is a leak there. Whilst im in there Im going to see what jet the previous owner put in there too. He could have upjetted it I guess. This thing has had a different exhaust put on it too but I have no idea whether it would require an upjet because of this. Mine too drinks fuel at an alarming rate Acid, so let me know how you get on.

Thanks for the info tErr0

I will revert once i've stipped it down and got mucky.

 

Interesting. Stripped the carb apart. Float appears to be moving freely. Needle jet is not sticking at all. Cleaned the whole thing down with some brake cleaner I found in the garage. Jets are currently soaking in it too. I found that the main jet is a 65. Am I correct in saying thats a pretty big jet for a stock NRG 50? Like I said the only thing it has had is a different exhaust fitted. It did have a new piston and head fitted around 4000 miles ago but I believe theyre standard because the thing only hits 45 max unless youre going downhill!!! Would this cause the problem with the engine revving itself up or am I still looking for an air leak? I dont know what the standard jet would be? Anybody know? I looked where the manifold is and there are two torx screws holding the inlet on with a sodding pin head in the middle so I cant use a standard torx to get it off and examine. Off to HellFrauds to pick up a security Torx bit set ... another sodding £20. Also of course I didnt take note of the position of the idle screw before I removed and cleaned it. Should I just give it a few turns from fully closed? Manufacturers are a pain in the ass with this sort of thing...Sorry there are so many questions, just hope somebody has some answers!!! Thanks. Rob.

 

OK. Update. More questions. Removed the security torx screws T30 with bits from HellFrauds. Found the reeds - all good BUT I would have expected to see a gasket here? Between where the fuel filter / reeds drop into the cylinder and where they mate up with the inlet from the carb. Maybe IM just being naive but wouldnt there be a gasket to stop air leaks???

 

i have found out that the stock jet is 58 - 60

Rub some instant gasket into the carb manifold (bodge trick to see if its leaking) it seals it up better covers cracks ect.

The reed to engine should have a gasket (cornflake's box is fine for making some)

Mine does 48 on flat ground (gps speedo)

Rob could you throttle cable be binding I seen it on lots of bikes (I worked in a bike shop). simple way to check is take off the airbox lid and check to see if the carb is closed on when you have no throttle, then turn the handlebars full lock to both sides and see if the cable is pulling the car open, if yes then reroute the cable so there isnt any tension on it.

Second thing to try is to look down the carb and open the throttle with the twist grip, then let go does the carb slide slam shut or does it slowly return, if so then lube the cable, clean the twist grip and if it still then replace the cable.

hope some of this helps

I,m only getting to start working on mine now

Karl

 

Well I just spent 8 hours working solidly on it. Cheers for the tips Karl. I had the same thought as you and bought some instant gasket whilst I was out. I popped the reeds on a bed of it and also put some on top of the reeds between then and the inlet hose for the carb. Put it all back together and started it up and it revved its knackers off. I realised the needle was obviosuly sticking because the throttle didnt feel right. A quick lube with wd40 and re-assembly and it started up nicely. But not for long. I adjusted the carb until it seemed about right and took it for a spin. Same problem, no difference. Worse when warm. Pullled it onto the driveway and up it went... 5000 - 7000 RPM. I dont think it's the needle valve sticking beccause I can get it ticking over at about 1200 quite happily and then it will start gradually creeping up until it revs itself into oblivion. If I kill the ignition and leave it until it's nearly dead then start it again sometimes it will rev itself up, other times it will clam down again. Not sure now if Ive got an engine seal gone somewhere but thats a job for a garage. Im now fairly confident that I dont have a leak on the inlet manifold. I did note the 65 jet fitted but this does have an aftermarket exhaust so that may not be too far out, plus it's derestricted. I got best results with the mixture screw about 1 1/4 turns from fully closed. It seemed to go 'less ballistic' at this setting but when I went for a run there was quite a lot of smoke initially but that seemed to calm down but it is drinking fuel again. Any suggestions??? Heeeeeelp!!! 8 hours and no further forward, or at least I think I know now what it ISNT???...

 

Hi rob spent today at my local piaggio dealer taking about stuff. You want to hear some of the horror stories that he told me. Then some guy arived with a runner 125, saying the breaks were bad. Turned out he has worn through the pad the backing plate and was half way throught the piston !!!! :rant:

I really think that your throttle slide is sticking hence why the bike is reving its nuts off once warmed up. You carb slide could be worn and thats causing the need to miss the hole hence sticking, have you checked that it moves up and down freely ?

I ordered a service kit for my carb so that i could get it back to stock, as my jets and stuff is showing signs of wear, and this way i will know everything is correct. :thumbsup:

Maybe a complete over haul of the carb would help you too. I,m sure like mine your as been abused.


I will keep up updated on mine

karl

 

Hi Karl,
doesnt look like a carb issue on mine, it's looking like an air leak. You dont have to touch the throttle, and it will rev itself up and it sounds lean like its sucking in air too. I have checked the carb over completely. Needle is sliding beautifully (I lubricated it) even checked the electronic choke. Started it up tonight and it idled OK for a few minutes before it started to get frisky again. Never touched the throttle. Leave it running it continues to rev, turn if off and back on again sometimes it calms down, other times it revs itself back up again so Ime positive its not the throttle sticking any way. The bike has been sat for 6 months so its likely the crank case seals have dried up with not being used and hence - leaking. The thing is I down know how to change crank case seals, where they sit, or how to get at them. Is it a head off job or can it be done is situ in the bike?

 

Found the stock settings for are carb rob
set the mixture screw 2.5 turns out from being all the way in,the mixture screw is on the back of the carb near where the air filter rubber meets the carb on the right hand side.the tickover screw is just to the right of it in the middle of the carb screw it in until the rear wheel just starts to turn a fraction now and again,this is how piaggio tell you to do it.

Any joy with yours ?

 

i jus take the pin thing in the middle out with a flat head and use a standard torx key to take it out i knw its kinda bodge

 

Mine is doing exactly the same, did you manage to sort it out ? it revs its nuts off. its an original carb but a different engine, i have just replaced the engine with a 2nd hand 1, the carb was running fine with the old engine.... could it be an air leak somewhere ?

Mick

 

If its reving up on its own it sounds like an air leak on the inlet side,vibration could make the problem worse,try squirting easy start around the carb while pulling it about a bit,wd 40 will do the trick as well,remove the carb and give it a clean out or at least open the float bowl drain screw and dump out old water,particles of rust.check also that the fuel flows uninterupted by filling a jar with the petrol pipe removed from the carb,good luck

 

did you sort this??