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I recently managed to get the moped running properly, albeit for only a short time. Things were looking up: I replaced the spark plug, cleaned out the exhaust, adjusted the idle / fuel screws, and even replaced the brakes (I can stop now!). So everything was looking good. I was test-riding it after a short hiatus, and the moped was running fine. Near the end of my ride, I stopped at an intersection to make a left turn. I revved the engine while still stationary in anticipation of the light turning green – I didn’t want to hold up traffic, and the 50cc engine takes a while to get going. I pushed off from standstill, the scooter started moving fine, but soon thereafter started lagging. It absolutely refused to go past 20 MPH even though I’d usually go 27-28 on the same stretch of road. It was consistently going slower afterwards, and I scurried back home as best as I could. I’ve revved the engine like this in the past (with the moped stationary), but for shorter durations. This time I’d say I was on full throttle ~5-10 seconds while stationary. A couple of days later I fired it up, but it ran horribly. I managed to get it moving, but it hit 10-12 MPH on mostly flat land (where 27 MPH was common). It felt as if the engine was providing power for a couple of seconds, then stopped the power delivery for a couple of seconds, and it kept doing this over and over. It was so weak that I had to push it up a hill to get it back to my residence. I thought – for just a second – that I smelled a burning clutch when I was riding it back home after the intersection incident. After I got home, I “smelled” around, but couldn’t pick up any burnt clutch scent. I sincerely hope the clutch isn’t the culprit, since it’s an expensive fix. Please let me know if you have any ideas as to where I can start troubleshooting (aside from the clutch, of course), as the weather’s nice and I’m hoping to get it going this weekend – fingers crossed! 7/10/10 Update I swear guys, I’m not crazy. There was a problem with the moped. This morning I fired it up the usual way, hoping to analyze how it runs. It hit 29 MPH on flat land like nobody’s business and I rode it around for a good half hour with no problems. I have no idea what changed in the last couple of weeks – perhaps it had some time to think about its problems and resolved them. I have a feeling this won’t be the last time this problem pops up. I will most likely be coming back to this post sometime in the future :) Thanks for all the replies!
Always start with checking for strong spark, a bad condenser can put out strong spark when cold, but will quickly fade. Arcing across the points is a good indication of a bad condenser. Assuming that the ignition system is in tip-top shape, that sounds like a fuel related issue. I would start with checking fuel flow, as well as the fuel level in the tank. With a gravity feed fuel system, a clogged gascap vent, or misrouted/to long of a fuel line are common culprits, especially as the fuel level gets lower in the tank. If the tank is venting properly, and fuel flowing well to the carburetor, I’d clean the carb. Pay close attention to the small holes in the carburetor jets, just because you can see light through the hole does not mean it’s not restricted by residue left from evaporating fuel causing a lean fuel mixture. Poking a small piece of soft copper wire through all the holes, followed by a good blast of air or carb cleaner works well. Do not use steel or anything to hard to clean out the jet, you may accidently enlarge the jet, changing the fuel mixture. If the bike does not idle smoothly or takes a long time to settle back down to idle speed, and you’ve already cleaned the carburetor, you may have an airleak. Airleaks can be caused by a bad seal in the engine, or in the intake/carburetor joints. You can sometimes track down an airleak by spraying carburetor cleaner on a suspect sealing/joint area and listening closely to see if the engine RPM’s change (sucking carb cleaner fumes into carburetor will also do this, so be careful when working near the carburetor). Hope those suggestions help!
Drain the gas tank completely and wash it out with some fresh gas. Condensates from sitting for a long time may have clogged the hoses and filters plus you may have some water condensation in the lines now or particulate matter.
Well I think you should spray started fluid then clean off spot plug and spray hoses and make Sure your hoses are tight
My fa50 Suzuki 1985 had the same prob, i could rev it a lil but as soon as i revved it while on it, it would cut off. My neighbor suggested that all older motorcycles have same issue. Simply get your hammer and tap away. I tapped the carborater and the thing next to the carborater pretty good and it started up and ran faster than b4! It is suppose to loosen a needle that controls gas flow.
I had the same issue with my SYM Euro Jet, I had cleaned the carb and exhaust. However still bogging out, I took it in to a shop for service, they said sell for parts. What I ended up doing was replace the seals on the Piston head and Exhaust myself and it has been running fine for another $8000ks :-) Update I have also fallen victim to cheap 2stroke Oil, which was found to cause buildup on the Spark Plug and in the Exhaust. Never again
A small engine like that that idles ok but bogs under acceleration is usually one of three things; 1) air leak at the intake boot. A squirt of starter fluid at the boot while running will tell you. If it revs you have a vacuum leak. 2) the main jet is clogged (it could also be the main jet is too small but sounds like it was previously fine, so that’s unlikely) you’ll need to take the carb apart and give it a good cleaning. It’s not hard to do, it just takes some time.
I have a 50 cc moped new carb an spark plug every so often it will bog out an die. Then it’s hard to start what could it
For some reason the air fuel mixture isn’t right, too much air not enough fuel. Is the carb tight on the intake boot? Is the air filter clean? If its a new carb is the air/fuel screw set correctly for your scooter- generically 1 1/4 turns out.
Why isn’t my moped why isn’t my moped running but I have spark and gas
Mine is doing the exact same thing!! It will get to about 30 mph no problem, but then immediately begin to loose acceleration and slows way down. Then, if I let go of the gas and let it idle almost all the way down and then hit the gas back, it shoots right back up to about 30 mph only to drop speed right back down repeating the same process over and over. My mechanic tried everything you can think of to no avail. Now he’s saying it is probably the timing chain because he eliminated all the little issues it could have been. I wish I knew for sure and that he wasn’t ripping me off, but most people on this thread have not brought up the timing chain, so it’s not giving me the advice I was hoping for. Wish someone knew more on here!
I am having same issues. He took out the cam cover and then had no power from the clutch side. I had the D and S mode not working either. I suspect it’s an uneven air Fuel ratio. Now it’s just running on rich fuel
having the same issues with my engine 50cc gilera runner sp drives fine but sometimes when i pull the throttle all the way it takes some time to kick in and i get a surge of power like ive got turbo on my bike then sometimes i go up a hill fine and other times the same hill the engine dies on me won’t get enough revs to go up bought it as a non runner stripped the bike down and engine cleaned everything bought a new carb as the throttle pin was bent in the old carb dont know how put it all back together managed to get it running with some carb spray it was loud sputtering popping the lot turned it off took it to my local mechanic and he said it was a mixture of jet was to small on the carb i bought ,crankshaft seal was worn so engine did have compression but would loose it as it built up started off at 50 psi before crankshaft seal was replaced so anyway the mechanic replaced all seals and gaskets in the engine happy days picked it up drove it about 20 miles home drove it for a few days thats when i started to notice the surge of power and loss randomly took the crankshaft case off today to inspect the belt clutch and variator first thing clutch had rust on the inside were the belt rubs against which isn’t good belt looks new variator i took off cleaned checked the rollers they dont have bold spots tho they feel like there about 3 grams each i think honestly the last person tried to make is faster and just screwed the balance of the engine up so i’m going to buy a new clutch the variator and new belt that all match the same specs as if you buy a sport clutch and a normal variator i’ve been told can mess things up and you have to change jet sizes as you make the bike more powerful so ill be taking the bike back to the mechanic next week and let you guys know think the main lesson here with moped’s is know the history because one part gets swapped out that’s sporty like exhaust system everything else will struggle and need upgrading with it that’s why most of the time people will buy the whole kit a lesson im learning
