Cant go over 50% throttle...Stalling

Graham Mcmillan /

Hi there,

Last week i noticed my moped would lose power at anything over 50% throttle. I did a little research and found out the carb could be dirty. So today, i cleaned the carb and reinstalled it and it's even worse than before. Everytime i go over 50% throttle, the revs will drop very quickly and the engine will stall.

I dont know what else to do. I tried running without the air filter, and it was the same result. Could the carb be getting too much air or too much fuel? If so, how do i fix it to the right amount? I havent checked the spark plug yet, but i will. But at the minute im out of ideas. Can anyone help? Please :-(

Re: Cant go over 50% throttle...Stalling

Assuming you did absolutely nothing unusual to the bike, something may have come loose.. check for vacuum leaks and check compression.

The bike could be starving for fuel.. check fuel flow from top to bottom.. Start with the vent in the gas cap and work your way down.

Properly cleaning a carb cannot make a bike run worse.. you may want to clean it again. But since your 'cleaning' made a negative impact, this might be a clue. There's a chance that the carb is the problem and you aggravated it, perhaps by pushing a piece of crud deeper into a passage.

Re: Cant go over 50% throttle...Stalling

Graham Mcmillan /

Thanx for the fast reply.

Ill check the compression tomorrow. Since i dont have a tester, ill just use my thumb. When i was putting it back together, i made sure all the hoses etc were completely on. Also checked the carb when the throttle needle was put back in and all seemed fine.

It took forever to start, ended up having to kickstart it. Even when it moves, there's barely any power. How would you recommend cleaning a carb? I just used spray cleaner. It seemed clean, but i suppose you can never tell.

Somebody mentioned it could be my variator, since my bike is an automatic. I was messing around with the variator last week to see if it was derestricted, but i dont think i damaged anything. Besides, it's been down on power well before then. I guess ill check it's getting into top gear anyway. But as you said, cleaning the carb shouldnt make the problem worse, so it must be carb related.

Re: Cant go over 50% throttle...Stalling

Robert Dingman /

yeah i have a 82 qt50 and when i go past 50% throttle it like completly slows down doesnt stall but slows down any sujestions

Re: Cant go over 50% throttle...Stalling

Carb cleaning is a simple thing but doing it right is a lot of work.. complete disassembly.. soaking parts in a solvent.. compressed air to blow out all the hidden passages.. careful examination under a strong like with magnification.

And every component of the fuel system deserves equal attention. It seems like the vast majority of problems in this forum turns out to be fuel-delivery related.

Re: Cant go over 50% throttle...Stalling

Graham Mcmillan /

Well i took the carb off again and cleaned it thoroughly. The engine ran a little better, but as soon as i go full throttle, it will just drop the revs and die again. Im guessing it's too much fuel in the mix. I checked the spark plug too and it's black and oily, i think it's carbon fouled. Any ideas?

Re: Cant go over 50% throttle...Stalling

Jason Luther /

pull the gas line off of the carb and see if gas is pouring out of the tank. are you out of gas?-jason

Re: Cant go over 50% throttle...Stalling

Ben Van Zoest /

What ped, how many miles?

Re: Cant go over 50% throttle...Stalling

Graham Mcmillan /

Im not out of gas, there is some gas coming out of the line, but it stops after a while. I assume it has a pump which pumps gas whenever it needs it. My bike is a 2004 Piaggio Nrg 50cc. It's only got 5800 miles. I've double checked and it feels like there is air coming from the carb.

When i took the carb off the hose from the engine, there was a really tight clip on it. I had to destroy the clip to get it off and i just used a tie wrap to reconnect it. I dont think it's good enough though. So ill have to find a jubilee clip and tighten it. I also cleaned the spark plug, my dad had a look and thought the contact points were a little too wide. So we cleaned that and tightened the contacts. But it's still running like crap at anything over 50%.

I havent tried riding it, but yesterday when i tried it, i was getting about 8mph. Any more gas and it would stall. My dad thinks the choke may be sticking. I think the choke is electronically controlled. It has a needle going into the carb and wires coming from it, but i dont think this would cause the problem, especially in 7,000+ rpm.

A couple months ago, i switched from unleaded to super unleaded. I was told it was better, i dont suppose this could be a factor could it?

Re: Cant go over 50% throttle...Stalling

I don't know your scoot but it probably has a vaccum type fuel valve. Sometimes here is a filter under the gas tank or somewhere between the tank the carb. This filter may need to be cleaned.

See if you can get a shop manual for your bike and check the fuel system from the tank to carb.

Re: Cant go over 50% throttle...Stalling

Graham Mcmillan /

Yeah thats what i was going to try next. There's a black box at the other side of my bike and it looks like fuel lines going into it. Im guessing it's a fuel regulator or something, so ill try cleaning that if nothing else works. I bought my bike second hand, and the guy didnt freakin keep the manual. I guess ill have to call the bike shop. I think i've just voided my warranty too :-(

Re: Cant go over 50% throttle...Stalling

This might not be much help, but if 'some fuel comes out', as in, it is actually .leaking. fuel, then you need to get that taken care of before anything else... you should also just put in a brand new fuel line, they are cheap as dirt.

If it just dies at over 50% throttle, as far as I know it could be a lot of things, but most likely are timing (if it is off just the right ammount it might work at lower rpm's) and dirty carb.

Clean the carb first and try some 93 octane gas, because as I read before, it combusts at a higher temp, and will help to keep the piston from compusting the gas rather than the spark plug, IF that is the problem.

So... clean the carb, good gas premix (PRE MIX IT!), check the fuel valve, new fuel line, in-line filter, and if all that doesnt help, check the timing and clean the points.

Most of that is general maint. stuff anyway, no reason not to do it, especially the fuel stuff if you are having problems.

Re: Cant go over 50% throttle...Stalling

Heh, I just read "My bike is a 2004 Piaggio Nrg 50cc", which I know nothing about. If youve got some kind of funky fuel pump on there (why they used those I will never know) then that is probably your issue.

Re: Cant go over 50% throttle...Stalling

Graham Mcmillan /

Well, i dont need to premix my fuel and oil. It's a modern moped, so the oil mixes in the carb. I was thinking it could be timing related too. I dont have any fuel leaks at all, just feels like an air leak from the carb. So ill fix that and see how it runs. Oh yeah, what was that fuel you were talking about? I live in ireland and we got a choice between unleaded and super unleaded. Super is supposed to be cleaner and better for the engine...

Re: Cant go over 50% throttle...Stalling

Jason Luther /

you have a fuel delivery problem. either your 'pump' isnt working, or a filter is clogged.-jason

Re: Cant go over 50% throttle...Stalling

Graham Mcmillan /

you have a fuel delivery problem. either your ‘pump’ isnt working, or a filter is clogged.-jason

How can you be so sure? Cant this be caused by too much fuel too? Maybe it's excessively rich causing it to choke when i open the throttle. I checked the spark plug and it's carbon fouled, so i dont think i have any fuel delivery problems. But ill check it out anyway.

Re: Cant go over 50% throttle...Stalling

Jason is right... its that pump on there. I am sure someone, somewhere, knows how to modify it so that you can remove it entirely. Maybe it is similar to other modern peds that have pumps, in that respect?

Re: Cant go over 50% throttle...Stalling

Graham Mcmillan /

When i rev it halfway though, it will reach max rpm (Just over 7,000). So if there was a pump problem, why wouldnt it affect it at half throttle. Maybe as it demands more fuel, it cant get through or something? Ill check it out......Just wanna get this damn thing fixed......Failing that ill pour petrol over the thing and light it lol :-)

Re: Cant go over 50% throttle...Stalling

Heh, your ganna have to get some nuts and rip that pump offa there and tear it apart and clean it, however that is done. Same should go for carb..er, lemme just go with

CLEAN YOUR ENTIRE FUEL SYSTEM!

Re: Cant go over 50% throttle...Stalling

Graham Mcmillan /

Ok well, i put a new spark plug on it and put a really tight clip around the hose to the carb. It stays alive at full throttle now, but it's as it was before. When im riding it at half throttle, it'll go just over 7,200 rpm, but when full throttle it will go to about 6,800. The guy in the bike shop reckons the exhaust may be full of crap.

Apparently i wasnt using the proper oil, so i got some semi synthetic stuff. I drained the oil out of the bike and filled it with the new stuff. At least it rides now, and if it can stay together till next week, ill take it to the bike shop. Get this: For a new exhaust it is

Re: Cant go over 50% throttle...Stalling

Ben Van Zoest /

Hell man you'r close to fixing it, take the exhaust off if she runs noticeable better disassemble the muffler and soak it in cleaner solution. That's a lot of smackers for a new pipe!

Re: Cant go over 50% throttle...Stalling

Graham Mcmillan /

I thought the only way to clean an exhaust is to burn the crap out of it? I was gonna get a sports exhaust for it anyway, give it a bit more power....So im not really losing out. I was gonna take the exhaust off yesterday and run it, but i have very grumpy neighbours! Ill try it at the weekend, i just hope it's nothing more serious...

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