Scooter Carb Issues

[pennstump]

Hi. I'm new here, but let me say I've been searching all through this site for the past 2 weeks and learned lots of valuable tips, but now I'm hoping that someone here can help me finally put all the "pieces" together.

A neighbor moved out last month and offered me his 2004 Jetmoto 50cc scooter (GY6 engine) with 581 miles for free. Of course I said yes. I have another scooter now and a few in the past. This one is hopefully going to be an Xmas gift.

At first, it wouldn't start at all. My first thought was the carb. I went to dismantle it and clean it out and found that all the screws were stripped. So, I went to extracting them to replace with hex cap screws, but one around the electric choke wouldn't budge, so I tried to cut the cap with a dremel -- no good, it never came out. So, I found a replacement on Amazon of all places for $29. It shows up, I install as is and it starts first try. I'm excited, but I notice that it won't rev without bogging down. It started to bog down somewhere between half throttle and full throttle and would die every time within 20 seconds of full throttle. I pulled the plug and it looked black and sooty. I thought 'rich.'

So, I pulled this carb and raised the clip on the needle jet. 2nd from the top of 5; it was originally on the lowest setting. I also replaced the #75 main jet that came with the new carb with the one that was in the old carb. I believe it's also a #75 or very close to it. I don't have any tools to measure it precisely.

Put it all together and it started first kick. Also, for some reason the electric starter rarely actually starts it, but the kick starter was working first try at this point. It idles fine at this point, cold or warm. It also reved the whole throttle up until WOT, then it would die. So, this was an improvement. I had the whole throttle except WOT. At this point I started searching this site and did the following:

1. Replaced spark plug (0.023" gap)
2. Cleaned air filter with soapy water, rinsed, dried, replaced.
3. Checked air hoses and found that the air filter cover hadn't been on "the whole way" since I got the thing. It had another snap to fully close.
4. Checked the vacuum lines. All look good, gas flows from petcock, and I capped it off the manifold and I got the same running state.
5. Confirmed battery is good.
6. Tested with gas cap off. No change.
7. Checked out gas filter, seems fine, but I did NOT replace it, yet.
8. Checked oil level. It's a little above the last indent on the dipstick.

None of these diagnostic steps seemed to do anything. Then I removed the intake from the carb and used my hand as a choke directly on the carb. When I would cover roughly 2/3 of the carb's intake with my hand, the engine would sound great and and would run through the whole throttle without any problems.

PROBLEM FIXED, right? No. I thought that meant that I was running lean. I put the air breather back on and started to adjust the air mixture screw on the carb (bad idea on my part). Nothing seemed to help. Now, I've tried to reset the air mixture screw 2 full turns from all in, but now the engine starts really poorly and difficult. Also, I thought it seemed like it was running lean, but when I pull the plug it's still black and sooty.

So, here's where I'm at:

• spark plug is black and sooty
• using my hand as a choke, without the air breather, seems to fix all my problems
• the bike is now incredibly difficult to start now

Things I didn't do:

• Check valves. I don't know how.
• Check cylinder compression. I don't have the tools, but it runs fine except for WOT already.

Questions:

1. Is the fact that I finally now have the air filter cover on fully making it harder it to start?
2. Am I running too lean or too rich? Seems like both.
3. Could the black soot on the sparkplug be from burnt oil?
4. Why does the kick start work more often that the electric start?
5. What do I do next?

Thanks everyone! Sorry for the long story, but I wanted to be as detailed as possible.

[Weldangrind]

Welcome!

Excellent detail. I'll just address a few items to start, and we'll see if you make any progress.

1. What material is the air filter? If it's foam, it needs to be oiled; that would explain why it's running lean. I use Maxima Fab1 spray oil, but there are several good options.
2. How do you know that the battery is good? I suspect that a good battery would make it start easier than kicking it.
3. Did you clean the original main jet before installing it in the replacement carb? Have you tried the jet that came with the replacement carb?

Replace the fuel filter and the fuel hose with good quality stuff. Totally worth it.

[pennstump]

Originally Posted by Weldangrind

Welcome!

Excellent detail. I'll just address a few items to start, and we'll see if you make any progress.

1. What material is the air filter? If it's foam, it needs to be oiled; that would explain why it's running lean. I use Maxima Fab1 spray oil, but there are several good options.
2. How do you know that the battery is good? I suspect that a good battery would make it start easier than kicking it.
3. Did you clean the original main jet before installing it in the replacement carb? Have you tried the jet that came with the replacement carb?

Replace the fuel filter and the fuel hose with good quality stuff. Totally worth it.

Thanks for your help!

1. It's foam and I oiled it with some fresh 10W-30 and let it drain over night. Is that "too heavy?"

2. The battery is new and I've been recharging it overnight with my trickle charger.

3. I did my best. It soaked in carb cleaner for about an hour and was blown out. I haven't tried the #75 that came with the new carb since I changed it. I think I'll try that first tomorrow.

4. I can replace the fuel lines and filter, but is this a when I get around to it kind of suggestion or could this be causing these problems?


Thanks again!

[Weldangrind]

10W30 is ok, just wring the excess out. I'm starting to wonder if that's where the sooty plug is coming from.

A single strand from a wire brush makes a good jet cleaning tool, especially for slow jets.

The filter could be minimizing fuel flow, and that can cause a lean condition, although it usually presents a feeling of running out of fuel (the bogging that you describe). The cheap fuel hose might deposit bits of junk in the carb.

I think its not getting enough fuel.

[pennstump]

OK, I have a quick update. I haven't checked the valve clearance, but that's next for me. I put the main jet #75 that came with the new carb back on, lowered the clip on the needle jet, and found out that my air breather tube wasn't fully seated on the carb. So, I fixed that. There shouldn't be any air flow besides the intake/filter setup now. I also replaced the fuel filter and fuel lines. This fuel filter is clear so I know there's gas in the line now....

However, the same condition happened. It wouldn't rev all the way to WOT. But, I noticed a couple times it seemed like it did rev the whole way through the throttle. Then, it started to get dark and I noticed sparking from the green wire that goes into the ignition coil. So, to be 100% clear, there are 2 wires that go into the side of the ignition coil that faces the back of the bike. One is black and one is green. Both have clear wire protectors over them, but the crimp on the green one sparks occasionally from multiple points. The connection seems solid and the crimp to the wire is good.

Is this a clue?

[pennstump]

Fixed the crimp; no change. I guess I'll check the valve clearances tomorrow.

[pennstump]

I checked the valve clearance and they were exactly 0.05mm (0.002"), which is where the manual said they should be.

What else is there?

- Too much oil?
- Not enough electrical output for high RPMs?
- Bad air/fuel mixture?[/list]

[Weldangrind]

Originally Posted by pennstump

Fixed the crimp; no change. I guess I'll check the valve clearances tomorrow.

Does it still spark from the green wire? That's the ground.

[katoranger]

This is from.
http://www.scrappydogscooters.com/Te..._with_Mo_.html

BIKE NOT RUNNING PAST 3/4 THROTTLE
got from scooterdogs an 80 cc.cylinder kit for my 50 cc. Rocketa scooter.It's aQMB139 moter.All went well runs .Had 2 rides only notticed it needed to break in.Now I cant get it beyond 3/4 throtle without it wantting to die,unless I lower the throtle quickly. The timming is allright,spark continues, carberettor is fine .I gave it a spray shot of gas when it was dieing but no saving it.Ignition and carb. don't seem at fault. Do you think a valve spring is broke? even though it seems fine up to 3/4 throtle,or about 3000 RPM.

Me again. I adjusted the valves and it still didn't work past 3/4 throtle. I tried the spray gas in the carb. idea and this time it made a diferance' for the better. so I guess it is carburetion after all. Funny it rode well the first 2 times' but maybe since it wasent broke in yet and now is more so the piston is pulling in more gas now. Carb. is a CVK with # 78 h maine fule jet and # 34 h low speed jet. low speed seems o.k.

What do I do now scrappin dog?
Hope you can help! Thanks

Without being able to see what has been changed or modified, it's difficult to tell. I'm inferring by your statement that your spraying gas in that you've removed the stock airbox? This might explain some things. These airboxes are very restrictive to pass DOT noise regulations. When this restriction is removed in the pursuit of suppossedly more power, the vaccuum is grealy reduced at the venturi nozzle point, which leads to a lean-below stoic condition. This is very common for scooters to just not want to run when airboxes are removed. It's even more common to hear all the subjective analysis that everthing was working fine "until" this or that was done, or it worked like that before eg. "it's not the carb because I spuirted gas into the carb with no change". The piston seal will improve with proper break-in, but not to that degree to make that kind of difference. I'd recommend replacing the stock airbox for baseline test. I normally install a #85 main whenever I remove the airbox, and even then, because of resonance differences, a substantial loss in bottom end power results.

Last of all, when all else fails, seek a professional that can tactilly repair your vehicle. (hard to find I know) If it was possible I'd invite you to Arlen Ness motorcycles where I consult part-time for a challenge fix. Was this CVK a stock carb or a later addition? MO!


Me again.You really know your stuff, I'm glad your there man.I put the air filter box back on like original.And it runs great now! I had taken it off in place of a new 3"round x 2"tall chrome air filter.Looked great,but I guess it's running right is better than looks. I'll bet you get in opperation vs.looks with Arlen Ness sometimes.ha.ha. Your not scrap to me man. Have a good day.and thanks

[pennstump]

The green wire doesn't spark anymore after I fixed the crimp.

Thanks. That's a good read, but I still have my stock airbox and filter. Are you thinking that it could be my air filter? I haven't found a leak or a hole in my air intake, any tricks to try and find one?

[katoranger]

I was thinking it may not have enough restriction. Try covering part of the air inlet to the airbox.

My honda elite would not rev without a stock filter in place.

[pennstump]

I tried this and it didn't seem to make a difference. I have the stock filter on.

[pennstump]

I've never had a rig take this much time. This thing is now the bane of my existence. I'm exploring electrical options while my compression test 10mm adapter comes in the mail.

Since I have spark does that mean the ignition coil is OK? If not, how do I test it?

I've seen lots of posts on here about testing the pickup coil and the stator; I'm going to attempt. Which is the correct way?

[katoranger]

It may be the CDI box. They are very cheap and might be worth trying.