2017 Yamasaki 50cc manual clutch

[4T_Goblin]

I have a 2017 Yamasaki 50cc 139FMB with 4 gears. Grom clone with horizontal engine.

The carb is unserviceable, I have another one ready to go but im holding off on it just yet.

I can get the bike to turn on and idle with the choke on. When i turn the choke off it starts to die out. I have gotten it up to 3rd on my short street but i lose power when letting off the throttle and downshift. So it does run its just having some horrible tuning issues - not sure if its a compression thing or failing tubes / carb.

My spark plug is black. dry black.

I cannot get enough power but im not sure if im just riding it wrong..Im not opening up to WoT because im in a neighborhood full of stop signs and speeding cars (i live in the hood) so maybe im idling the bike too much and driving at low speeds....is that an actual problem? I keep having to turn the bike on after it dies so im really working the battery down every time, unfortunately.

The petcock valve is a vacuum petcock valve, not a switch.

I just replaced the fuel line from the petcock valve with temporary clear vinyl tubing so i can see what's going on with the fuel. Yesterday after i replaced it it appeared that I could not get the vacuum strong enough to suction the fuel from the petcock to the carb upon cranking but i did see it trying...it almost made it all the way.
This morning the line was full, no air gaps, and some fuel had leaked out (through the drain line bottom of carb) I'm not sure if the petcock valve is bad or if the Carb was just flooded from me trying to crank it...but over night without pressure from cranking...im not quite sure how it would have passed through ..unless the petcock is bad.

So my black spark plug - research tells me it could be a lean condition - too much air not enough fuel. I checked it last night after running it - reminder - it is a new spark plug...so I could definitely tell it was getting fouled. Dry black...not wet.

Could it be the wrong temperature range? its an NGK CR7HSA 4549 replacing an A7TC (which was already in the bike...yes i bought it used =) )

I have not checked valve clearances yet but i do not hear any rattling or ticking from the engine...

my work schedule is killing me at the moment...i bought the bike to mess with during quarantine but we are back to work so that plan has been shot haha.

So the issues im having - petcock valve, fouled spark plug, not enough power sometimes, engine dies with choke off...i have to keep it on to keep it running.

Im still learning a ton about bikes and I think im close to an answer but i feel so far away from one...any help with these problems would be very much appreciated.

Pictures and video - this forum has shite sizing for pictures so If you want to see pictures, bear with me because our phones shoot in low MB but the forum only allows even smaller KB =(

Thanks all

[culcune]

Originally Posted by 4T_Goblin

I have not checked valve clearances yet but i do not hear any rattling or ticking from the engine...

People can confirm or reject what I say (I am no engine expert), but you won't necessarily hear anything from the valves. They just get tight over time and need to be adjusted periodically. I would go ahead and do those just to eliminate valves as a culprit, and if they were extremely tight, that might actually fix the issue.

[China Rider 27]

I agree with with Culcune, check the valves first to make sure your mechanical is in good adjustment prior to further tuning. After that, it sounds like a carburetor tuning issue. Not sure what you mean by the Carburetor is "unserviceable" but what you are describing are all symptoms of valve adjustment and/or carburetor tuning issues. What kind of carburetor is it?

[4T_Goblin]

Originally Posted by culcune

People can confirm or reject what I say (I am no engine expert), but you won't necessarily hear anything from the valves. They just get tight over time and need to be adjusted periodically. I would go ahead and do those just to eliminate valves as a culprit, and if they were extremely tight, that might actually fix the issue.

It's the most free thing to do but also the most intimidating, gonna try again knock it out this coming weekend

[4T_Goblin]

Originally Posted by China Rider 27

I agree with with Culcune, check the valves first to make sure your mechanical is in good adjustment prior to further tuning. After that, it sounds like a carburetor tuning issue. Not sure what you mean by the Carburetor is "unserviceable" but what you are describing are all symptoms of valve adjustment and/or carburetor tuning issues. What kind of carburetor is it?

By unserviceable I mean most of the screws are plugged or soldered. I would have to drill them out. The carb is a You-All 19mm left side choke.
I cannot really keep the bike running with the choke off. But when warm I can start it choke off and in first gear

Part of the reason I haven't taken it out very far is because the battery is low and I don't want to get stranded. Battery low from cranking the bike so many times.

[Falkon45]

The pictures are gone, but the carb was a mikuni knockoff. Go ahead and swap it out. Check the valve clearances. Get some feeler gauges and hop to it. It's easier than you think. If you're having problems with the petcock and all the other emissions stuff, delete it, or swap it out. A simpler engine runs better.

[4T_Goblin]

Originally Posted by Falkon45

The pictures are gone, but the carb was a mikuni knockoff. Go ahead and swap it out. Check the valve clearances. Get some feeler gauges and hop to it. It's easier than you think. If you're having problems with the petcock and all the other emissions stuff, delete it, or swap it out. A simpler engine runs better.

I started a new thread with a cleaner presentation and better question. You-All is what it came with so I'll probably swap it soon.

What would I put in place of the petcock...a manual switch or another vacuum valve?

I had held off on buying the EGR delete...I don't want to have to buy a pod filter because I don't want to rejet... But if I'm swapping the carb... Might as well rejet?

Can you recommend a source for choosing the right jet size for a 50cc with a pod filter?

Thanks

[Falkon45]

Originally Posted by 4T_Goblin

I started a new thread with a cleaner presentation and better question. You-All is what it came with so I'll probably swap it soon.

What would I put in place of the petcock...a manual switch or another vacuum valve?

I had held off on buying the EGR delete...I don't want to have to buy a pod filter because I don't want to rejet... But if I'm swapping the carb... Might as well rejet?

Can you recommend a source for choosing the right jet size for a 50cc with a pod filter?

Thanks

Unfortunately, I don't really know carbs. More than likely, the extra carb you have is on the rich side I'd go ahead and swap it in, then check the plug. For the petcock, just a ball valve type. Fewer fail points.

It is a cool looking bike. You could always do a 125 or 150 swap later, also.

[China Rider 27]

I would make the stock carb "serviceable" if only to see what jetting is inside. That will be your clue. In a stock unmodified bike, that is the jetting you should start with. You say you have another carburetor to install but if it is larger than the PZ19 you have which I assume is stock, it will create a bunch more tuning issues and may not be tunable at all. In this case I would suggest tuning the stock carb. In my experience with a 125cc motor these smaller displacement engines can be very particular about carburetor size. If it is another PZ19 or equivalent then the jetting should be very similar. Welcome to the world of China Bikes, the first lesson is generally carburetor tuning so time to go to school.

[4T_Goblin]

Originally Posted by China Rider 27

I would make the stock carb "serviceable" if only to see what jetting is inside. That will be your clue. In a stock unmodified bike, that is the jetting you should start with. You say you have another carburetor to install but if it is larger than the PZ19 you have which I assume is stock, it will create a bunch more tuning issues and may not be tunable at all. In this case I would suggest tuning the stock carb. In my experience with a 125cc motor these smaller displacement engines can be very particular about carburetor size. If it is another PZ19 or equivalent then the jetting should be very similar. Welcome to the world of China Bikes, the first lesson is generally carburetor tuning so time to go to school.

The replacement carb is a PZ19, it's pretty much the same in appearance on the outside.

The air idle screw (with the spring) is the one I have the most trouble with. It's marked on its original spot on the stock carb, but on the new carb I'm unsure where to start but I have found some good videos from Matthew MC Repair talking about adjusting his 50s and 70s.

I think I need 1 and a half turns out on the fuel mixture.

This weekend I plan on swapping the carb and getting the screws and bolts off of the valve cover so I can check the clearance. I gotta figure out exactly which plate on the Yamasaki is the one for turning the flywheel to TDC, but it looks like there's a little cover on the case cover that could come off and make it easier, we shall see

[4T_Goblin]

Originally Posted by Falkon45

Unfortunately, I don't really know carbs. More than likely, the extra carb you have is on the rich side I'd go ahead and swap it in, then check the plug. For the petcock, just a ball valve type. Fewer fail points.

It is a cool looking bike. You could always do a 125 or 150 swap later, also.

My petcock has 3 hoses, 1 from tank, 1 to carb, 1 to the EGR /intake for vacuum.

The more I think about it, I was considering buying a newer X-Pro 125, but perhaps I'll do an engine swap once I get this 50cc going... But it couldn't hurt to have 2 Chinese bikes now could it?

[Falkon45]

Originally Posted by 4T_Goblin

My petcock has 3 hoses, 1 from tank, 1 to carb, 1 to the EGR /intake for vacuum.

The more I think about it, I was considering buying a newer X-Pro 125, but perhaps I'll do an engine swap once I get this 50cc going... But it couldn't hurt to have 2 Chinese bikes now could it?

Yeah, just delete the hose going to the intake. Basically, it acts as an automatic open\close valve. Go ahead and install a normal petcock, and delete the intake hose. Just remember to kill the fuel after you're done riding for the day. Even my 2000 ZX-7R has a manual petcock.

[China Rider 27]

Here is a link to some general tuning info with links to the different circuits for tuning.

https://www.motorcyclezombies.com/re...orcycle-carbs/

[4T_Goblin]

Originally Posted by China Rider 27

Here is a link to some general tuning info with links to the different circuits for tuning.

https://www.motorcyclezombies.com/re...orcycle-carbs/

I set my valves to .003 intake and .005 exhaust and installed the new carb. Also deleted the EGR system.

The old carb was throttle clip was on the lowest setting(the needle is lower in the carb). The new carb was 2 higher.


Started the bike up it was idling higher, and stayed running with the choke off so next step I'm going to tune the carb and update the thread.

[4T_Goblin]

I set the idle screw 1.5 turns out to sit slightly above 1500rpm.

I can idle the bike with the choke on, and I can idle it with the choke off.
thats an upgrade from before

currently bogging on acceleration with choke off, accelerating with the choke on


at low rpm its bogging. the spark plug black again. i gapped it to .6mm ~.023in
ran it again, spark plug black.

here is the bike when i made the post


here is the bike after the valve clearance - .003 intake and .005 exhaust - it was easy to do but i have no idea if its correct - im leaning to the its wrong side - but i wont open them back up until tomorrow


here is an example acceleration