MOPED ARMY

You have an air leak. Between the carb and intake, or the intake and engine.

Air leak for sure

thats all weird it sound like its fuel starved at certain points, mainly at starting. If its not an airleak anywhere, Id go back to the carb. lets back up

you said it was fine and stalled at a light = could be the idle jet clogged, flooded ,any number of things .

Did you mess with the carb before all this happened? if so what did you do? these carbs have to be level otherwise your float wont work properly.

"then it would actually be revving instead of idling" maybe you put the needle sleeve in backwards? that would cause the high rev at start.

[i"]take the jet needle (#18 in the attached diagram) completely out and try starting her. And she started right up and idled beautifully. I rode her around for a couple of minutes and she seemed to run great."[/i] I never heard of this troubleshooting technique before what are you doing? this is weird so you are having difficultly starting but not when the needle jet is gone? but with needle in it wont start unless you choke it ( means it needs gas) normally.

If you take the needle out then you have no secondary jet no 1/4-3/4 gas range, just air movement and the main working fully open (again this points to needing gas)

tear the carb back down (all the way) and clean it 2x, make sure you put it back together correctly this includes the needle and sleeve, take a look at your throttle/choke cap to make sure the seal is in good condition and sealing. pay special attention to the idle circuit.

When you got it back on the bike look down the throat of the carb and work your throttle back and forth too see if your needle is working correctly, make sure at no throttle the jet is in the main and at full throttle it all the way up out of sight. with it not running of course. and check your compression

Hi Jayson,

Actually before I even touched the carb, I popped off the petcock and gave it a good cleaning. It was pretty nasty on the fuel tank side, but I carefully cleaned it all out and made sure everything was flowing through well. I'm certain that the fuel line is delivering plenty of gas to the carb.

When I get some time this weekend, give the carb another thorough cleaning, particularly at the fuel intake to make sure it is flowing in properly. If that passageway was clogged, would it make sense that it will start up with it choked?

compression guage (auto parts store) but if it was running ok before your all good and probaably dont need it but its nice to have to see where your at with the psi's. a good carb cleanin is your solution air compressor is great for blowing out all the passages. if your needle jet is working right then yeah you got it in right. dint mean to knock you down over the needle jet removal just never heard of anyone running without it before hahaha

Well I feel pretty silly. You guys were right about the carb needing another cleaning. I took it apart and went over everything one more time and noticed the pilot jet had gotten clogged since I cleaned it the first time (I'm certain I cleaned it the first time because I passed a wire through it). After putting everything together again the first time, something must have gotten passed down from the petcock or fuel line and plugged it up causing the fuel starvation.

I have it all cleaned out, cleaned the petcock again, replaced the fuel line and added an inline filter and she's running like a champ again! Even more responsive and a better idle than before.

I appreciate everyone's help and now have a much better understanding of the carb and how to troubleshoot it.

Thanks guys!

My QT 50 will start easy and idle ok in the START key position, but as I put it in the Run key position it dies. (warm or cold engine temp) Has no spark in the RUN position. Any help would be awesome !!

Sounds like my QT50 only runs with choke open so I bought a new carb got it put on and still will only run with the choke on also put a new top end on with no difference, only thing left is crank seals or reeds.

So I just picked up a Yamaha Riva Ca50

And bought it knowing it had carb issues.

I figured bad gas and need the carb cleaned but so far haven’t found myself to be so lucky. The bike would start and idle fine. But as soon as I went to accelerate it would die. I took the carb apart and cleaned it thoroughly. The plunger assembly seemed a bit floppy and it was hard to line up correctly almost like it had been taken apart too many times before.

After putting it together and messing with it more I can’t even get it to idle now.

I’ve tried to find s plunger assembly online but they’re all unavailable for this bike.

I see these other 19 mm 50cc 2 stroke carbs available online cheep but I’m not sure of the fit. I’ve even found one for a newer riva with an electric choke but almost the same but not quite. So not sure if I’d take the chance trying it .

Any ideas guys?, where can I get a carb for this thing or even a rebuilt kit?