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Post by prodigit on May 28, 2013 13:39:57 GMT -5
So I finally managed to get my Roketa MC-05-127 running, adjusted the idle to ~1000RPM. It started up right away when warm, but did needed to take 2 or 3 starts when cold.
I have a choke. When opening the choke completely it starts fine on cold but soon would bog down.
I'd have to put the choke in the middle.
When I took it out for a spin, I noticed while riding, when putting the choke fully opened, the engine would bog down. When I'd fully close it, it would skip strokes, and die down too.
I had quite the hard time starting it up again, but it did, and I rode it to the next street. I noticed the bike had best performance with the choke halfway.
It bogged down on me, in the middle of the street (after doing only 2km), and I had to push it home. I started it several times but nothing.
I have spark, and think perhaps something is blocking the fuel flow?
Well in any case, I don't know what it is or what to do?
I was also thinking that perhaps I should do a valve adjustment?
I also upped idle but to no effect.
The carburetor is not the standard 50cc carburetor. The throttle cable is connected directly to a needle, that has to be inserted in the carburetor and tightened, much like those from the 2 stroke engine kits for bicycles.
I found the idle adjustment screw, but did not find an A/F screw. Where can I find it?
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Post by devo344a on May 28, 2013 14:50:12 GMT -5
kinda sounds like a vacum leak Check around the intake the rubber cracks and the gaskets theres a plastic spacer between the intake and the head. If you have it running and spray some either or carb cleaner around that area and the engine revs up theres a leak
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Post by jerseyboy on May 28, 2013 17:19:46 GMT -5
If its running good on half choke sounds like you have poor fuel flow(filter/petcock screen),dirt in the carb(jetting),and or possible poor venting fuel cap.Check your flow at carb,,if good,,clean out jets and carb,and see if there is a little brass cap on that carb,,sometimes they hide the air/fuel screw under a cap,you need to drill it out and open it up a little if its in the front of carb,,if its in back of carb by air throat,,screw it in a little,,less air more fuel!!!
BTW-Air leaks comment was a good idea to look for also,,and I would do a valve lash adjustment,,why not,,just check it,,make sure they are not too tight.
Good luck!!
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Post by prodigit on May 29, 2013 0:32:11 GMT -5
Ok, at first sight there does not seem to be any vacuum leak. All hoses are connected, they're new, undamaged.
I unplugged the fuel hose, and fuel came streaming out.
I opened the carb drain screw and a lot of fuel came out.
I closed and opened the fuelvalve, got everything together again, took out the spark plug (somewhat black, can't blame it, I've been starting for the past 6 hours or so), there's compression, but no fuel damp.
Closed the spark plug, surprisingly the motor started, but only with the choke in open position.
Bogs down when I close it.
I adjusted the idle to very high (like 2k rpm), and choke open. It still died after about 15-20 seconds of barely staying alive. The carb drain was full of gasoline again.
Funny thing is that it started when cold...
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Post by prodigit on May 29, 2013 13:34:01 GMT -5
The carburetor somewhat looks like this:  Except on the top there's a steel throttle cable, not a hose. (like the throttle cable is directly connected to the needle) It has a choke, so I suspect it does not have an auto enricher? |
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Post by oldbikerider on May 29, 2013 17:10:25 GMT -5
From the picture and your description, you are set up kind of like an old Mikuni from the 70's, it will not have an enrichener. Sounds like jetting is not right or the position or size of the slide needle is wrong. The needle is attached to the inside of the slide and it controls the running mixture ( not the idle mixture). Mikunis have 3 to 5 grooves in the needle jet that are adjusted by moving the "e" clip to another position. Try raising or lowering the slide needle clip. If I remember correctly, moving the clip down richens it, moving the clip up leans the mixture.
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Post by prodigit on May 29, 2013 20:29:04 GMT -5
Is that the running or idle mixture that enriches when resetting the clip? Because it doesn't start, so idle mixture may be off. Here's a pic of the needle before installing:  |
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Post by oldbikerider on May 29, 2013 21:09:13 GMT -5
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Post by scootnwinn on May 29, 2013 21:44:39 GMT -5
Moving the needle will affect all throttle positions
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Post by prodigit on May 30, 2013 4:46:46 GMT -5
The funny thing was, that I got it to start, but after running for a few minutes, it died, and doesn't want to start anymore. The exhaust does not smell to gasoline, The plug is foul (black) from the choke I believe and when taking out the spark plug I don't notice any gasoline in the mixture, and I can't smell it coming from the open spark plug hole (where I removed the spark plug to test compression, which I have. The carb bowl gets filled with gasoline after starting a few times (is that ok?) The company told me to put something in the air filter, to initiate better startup. Don't know what they told me to put in there. Why would it work, halfway riding 0.5 miles, and die on me; not start, when I drain the carb bowl, and try starting on a cold engine, starts for a sec, then dies, and remains dead? I tried starting again on a cold engine but the battery is empty now from starting (is charging). Some things don't make a lot of sense to me. There might be a possibility that the jets haven't been adjusted, as this is a 127cc engine, not a 125 (and the carb might be tuned for a 125cc?). I don't know if it's a mikuni carb, as I don't have a tube on the top, but the needle with cable goes in there. The carb is in a hard to reach position, not much I can show you as my cam can't reach there. but this is what I have:   and behind the watch:   I have a premonition, that it might have to do with the fuel supply. I connected the fuel supply (after fuel filter) straight to the carb. It might need to pass via the petcock; but I don't see where I could connect it to the petcock. There are 2 hoses from the carburetor (with at least one of them a vacuum line) going to a black box, which I can barely show here:  The black thing is behind the left top screw, behind the frame. I don't know what it is? |
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Post by prodigit on May 30, 2013 5:25:51 GMT -5
Ok, I just opened the carb,
the needle is non-adjustable. But even if it was, I would be able to do the same, by tensioning the cable a bit through the adjuster near the handle/lever.
When I start the engine, with open throttle, the starter seems to be able to rotate faster, but it does not start.
Same with throttle closed.
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Post by oldbikerider on May 30, 2013 9:00:56 GMT -5
Tightening the cable is like twisting the throttle, it is not the way to adjust anything but cable free play. The carb is a Chinese Mikuni clone and should be similar, I hate to hear the needle is non adjustable. The tube on the top is a cable protector.
Do not reuse a fouled plug to troubleshoot carb problems, put a new one in you may just have a faulty resistor plug.
How does the choke work ( is it like pull the knob out to start then push in once it is going)?
Let me see if I got this right. You drained the float chamber and the bike runs till it refills the chamber? There should be some fuel in the bowl, but the level must be correct. It is possible that the float level is wrong or the needle is not seating to keep the fuel level correct. This will flood the engine and foul the plug.
If a bike is running rich, cold starts are not a problem but after it warms up it will foul the plug and die. If the bike is lean, cold starts will be hard to do without excessive choke but once warm the bike will run but it will have pops on deceleration and pinging on acceleration.
Since this is a new bike I'd seriously consider getting another carb under the warranty.
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Post by prodigit on May 30, 2013 15:21:22 GMT -5
Ok, I've got some more info on it.
Seemingly I can start the bike, only when the battery level is good, and the starter goes fast.
I can only start the bike when the engine is cold, and the choke is fully opened.
The engine warms up really fast, but any closing the choke, makes it bog down and die (even the least reduction in choke).
Once the engine is warmed up, it just dies, and does not start anymore. throttle does not keep it alive.
concerning adjusting the cable, you can reduce throttle play with it, but if you adjust it any further, it'll do exactly the same as opening the throttle a tiny bit, or re-setting the needle clip (as resetting it would basically only raise the needle a bit).
I can not adjust the needle on this carb.
All this searching, narrows down the problem to the carburetor and the choke.
It might be jetted incorrectly (perhaps running too rich, or too lean?). I live near to ocean level.
I presume that the choke enriches the mixture when cold.
Thus it needs more fuel (running too lean).
Closing the choke while cold makes it bog down and die.
Leaving the choke opened while the engine heats up, causes it to die too.
This is a quote from a website describing another carburetor:
Does anyone know if this bi-metal is found in these type of carburetors, or is this bi-metal the enricher?
The spark plug is black, foul, indicating a too rich mixture. The strange thing is, that if the mixture would be too rich, I should be able to close the choke, to allow better airflow, no?
Doing so, makes it bog down (skip strokes), and die.
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Post by prodigit on May 30, 2013 15:52:11 GMT -5
The choke has a black plastic, black, round thing mounted on it; like on this picture:  I don't have the lever (a cable solution going to a choke on the handlebars), but the black round plastic thing is there. Is it an adjustable knob? Also, on the other side, there's the idle adjustment screw. Right next to it (on the left) there's a rivet; which I believe should be the A/F mixture screw, but I'm not sure. It's very hard to see. I'll try drilling it out. |
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Post by oldbikerider on May 30, 2013 17:19:49 GMT -5
Looks like moving the lever away from the bolts closes the choke plate for starting and moving the lever towards the bolts opens the choke plate for running. With the choke closed the mixture will be extremely rich which is great for starting, but you don't want that plate closed long or you will foul plugs. if you ran with the choke closed too long you will have fouled the plug. A choked carb is not like an enrichener carb, they work differently.
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