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My Eternal Project, or the Scooter That Refuses to Live. Any Ideas?

4313 Views 59 Replies 11 Participants Last post by  Unkle Krusty
And the scooter is dead for a third time now...I’m running out of things to replace.

If you’ve not been following my CF Moto saga, here’s a recap:

First Revival

Acquired in November from a fellow Gambler 500 team member. I replaced the battery, the carburetor, and learned the starter solenoid was installed backwards by a previous owner. It sat for roughly two years without running and I made a gamble that I can make the old fuel burn again. While I was successful in that, I made two critical errors:

1. I didn’t replace the fuel filter.

2. I rode it every day for a month, not really ever allowing it to get to running temperatures.

Despite that, the scooter was good for 75mph, impressive acceleration, and it all around it ran absolutely perfectly. I felt I had myself a good score and with actual fresh fuel I’d probably even break 80mph. I proceeded to daily it for a month, taking it everywhere.

Fixing my Original Mistake

I made sure I ran all the bad fuel out of the tank and made sure the tank wasn’t rusty. Then I filled it with good fuel.

I then replaced all the fuel lines, the fuel filter, and the carburetor. I then installed a pod filter. I also closed off the crankcase vent to the airbox. Instead, the crank vents out into the outside. The original problem with not being able to start after getting hot remained, but at least I was no longer fouling my air filter and carb with particulate matter (air filter material) and oil. Top speed was about 40. Figured I would get more speed from restricting the pod filter, but first I really wanted to address the problem with not being able to restart with a warm engine.

Take Three

I decided to replace basically everything else I didn’t touch. I took the panels off and replaced the air filter so I can ditch the pod filter and go back to the factory setup (I still have the crank venting to the outside, though) and not have to jet the carb. Then I replaced any old vacuum lines that remained. All this work resulted in no change. It does cold starts well, but introduce any heat and it’s dead. The engine tries to fire, but it just won’t.

You can get it to start on starting fluid, and then it will go on to run like it’s misfiring and it’ll die as soon as you stop moving...then fail to start again.

Only thing I haven’t replaced is the spark plug (because the bloody thing has a spark plug that requires a bigger socket than the one I have for my smarts), but I fear it’ll be a waste of time.

Is there anything else I’m missing or do you think the spark plug will be my magic bullet?

This was supposed to be an easy project, but it certainly has taught me a lot about motorcycle/scooter repair! If the spark plug doesn’t fix it I’ll probably get rid of it. I’m just not sure how much I would be able to trust it at that point..And I'd hate to do that because when this thing was running well it was an awesome way to get around. 75mph top speed and everything.

For a TL;DR - here’s everything I replaced:

- Battery
- Fuel Lines
- Vacuum Lines
- Carburetor (built in electric choke)(2 times)
- Air Filter
- Fuel Filter
- Oil
- Fuel

Only thing I can think to replace now is little sparky..
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How does the gas tank vent?
Maybe it's blocked and forming a vacuum? When it wont start or runs like **** remove the gas cap and see if it works better then.
Is there a fuel pump that could be bad or is it gravity feed? Check flow?
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Fuel pump is vacuum based. When I replaced the vacuum lines and fuel lines I went almost clear with everything so I can see it all in action. IIRC, the tank vents through the petrol cap, which I'll probably give a good clean to make sure it isn't blocked.
I'm not sure how to troubleshoot a vacuum fuel pump system.. how does that even work? How does it start? The fact that you can get it started with fluid has me wondering...

To check the vent can you just leave the cap loose for a test?

Fuel pump is vacuum based. When I replaced the vacuum lines and fuel lines I went almost clear with everything so I can see it all in action. IIRC, the tank vents through the petrol cap, which I'll probably give a good clean to make sure it isn't blocked.
I'll give that a try! I'll be honest, given that it's a Chinese bike there could be something wonky internal with the engine (valves!) so if changing the spark and trying to vent the fuel better doesn't work I'll probably just get rid of it.
Good luck with it Miss M. :thumbsup:
I wouldn't give up on that thing yet.
First, you need to figure out whether or not its a fuel issue, a spark issue, or a mechanical issue.
A fuel issue is pretty easy to check, turn off the fuel, and see if it'll start when its hot on starting fluid, or better yet, a shot of carb cleaner, (just make sure its the flammable kind, like 2+2 or such).

Spark is easy to check for, crank it over with a fresh spark plug in hand, make sure the threaded part of the plug is touching the something metal on the motor and crank the engine with the key on. You should have bright, blue spark.

The motor and mechanical is another issue. You need good compression and proper timing for a motor to run. Since it runs cold, we can eliminate the big stuff, the timing is likely fine in that it ran long enough to get hot, and I suppose it runs fine till you turn it off and try to restart it?

Something I've run into with those Chinese motors is that the valve clearance tends to close up as the motor gets some miles on it. Usually its nothing more than a simple valve adjustment to get them running right again.
What happens is that when the engine is cold, the valves have sufficient clearance and the engine starts right up, as the motor warms up, the valve clearances get tighter, often to a point where the valves aren't seating fully when hot. They close enough to let it keep running, but the motor will be down on compression enough not to start hot.

I'm not sure what the motor looks like on your particular scooter but I've seen two styles, one has and external valve adjustment, the other is like an old Honda where you either remove a small valve cover or unscrew and a pair of access caps on the cylinder head. There's likely a few videos on youtube showing you how to check and set valve clearance.
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Rusty beat me.
Thinking about what can happen when things get hot. Valve clearances can close, causing a drop in compression.
The carburetor can get too hot, and the fuel does not vaporize correctly.
Early push rod Volvo and some British cars had that problem. 1/4" spaces helped.
Does the fuel pump push fuel up? Or is it a vacuum to suck the fuel from the tank. If it is a vacuum, fuel should flow in the prime position. If it is a pump, check for fuel flow while cranking. then check for spark, and check compression. Some coils fail when hot. Sometimes you have spark when testing, but not enough spark when the plug is in the hole. Open the plug gap to 50 thou, or cut off the tip, and check for spark.

Bon chance. UK
I used to work with a guy who used to check for spark by spitting in his hand, then he would grab the bare end of the plug wire and rest his hand on the cylinder head, then he would hit the starter button. You could tell how strong the spark was on the other side of the shop by how loud he grunted.
He quit doing that when HEI came out.

We had a Honda clone motor on a little go cart a few years ago that I bought at auction that wouldn't start unless it was dead cold. I adjusted the valves and all was good until the clutch/belt transmission blew up.
Thankfully, having an IT background means I apply my work to my projects. :) I've ruled out the fuel as the issue after replacing the lines, carburetor, and actually already having done the tests you've mentioned above. It's vacuum based fuel delivery, so I made sure that was good, too.

I have the service manual for this little scoot (poorly translated to English, but it works) and thankfully the valve adjustments are pretty easy as well. I actually didn't know valves could even be a factor here and heck, it's worth a shot.

I see some of these things with 20+k miles on them so they can go for a long time when they do work right.
You can't give up, it's not in your DNA
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I do have the ability to give up, but that's usually when I lose attachment to the thing I'm trying to work on. I really really like this scooter, hence me trying to do all I can to get it back working 100%. :)
If you DO end up giving up, make sure the scooter goes out in style. Maybe burn it or something.

+1 on the valve adjustment - very important.

Where is the fuel tank on that scooter? The vacuum fuel pump probably uses a diaphragm inside which tend to stiffen up when exposed to ethanol - seen it a bunch of times with those types of pump.

Are you able to post a close-up photo of the engine/pump area?
Depending on how these repairs go it may or may not become my vehicle for May's Gambler 500...which is about the most "metal" way to retire a vehicle from service.

Fuel tank is in front of the seat under the floorboard. The vacuum fuel pump is just in front and under the carburetor. That was one part I didn't replace when I first got the scooter because it appeared to be working. It appears to be doing its job for now, but I'll check it out and I definitely can get a pic later today or this weekend. :)
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I know some folks who do the Gambler events - they actually used their retired service van for it last time to retire it.
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Last year I was supposed to take that 150cc Chinese Ruckus clone I have, but I couldn't get my new tyres installed in time. I ended up "Gambling" my daily driver (a mostly stock smart fortwo). We lost more than half the entire field of vehicles at the first offroad park and somehow the little smart with only 5.5 inches of ground clearance wasn't one of them. :D

This year I want to crank up the crazy and bring an even more unfit vehicle. Thought about picking up a beat up Ninja 250 or Rebel 250 because an offroading sportbike or cruiser would be hilarious. But knowing that falling/crashing is a definite possibility I think I'll stick to last year's idea of bringing a scooter that isn't going to pin me to the ground when I fall. That or I'll just run my smart again (because that was hilariously fun).
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Alright, so tonight I will make some progress on this one. I'm getting antsy waiting for the new wires to come in so I'm taking matters into my own hands.

First, I will remove the spark plug, examine it, then replace it with a new one. Then I will test the tank for vapor lock. If this doesn't work, I'll move on to replacing the coil and doing a valve adjustment. If absolute none of those work, the scooter is going to get sold.

A 1984 Honda Elite 125 popped up on my radar and I'll likely pick it up on Friday. The Elite will replace this scooter as my work commuter. If I get this scooter running well again, it'll become my new Gambler, replacing the Ruckus clone. Such will bring me down to just one Chinese bike, and it'll only exist to be an offroader.
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Didn't take you long to turn on the Chinese............
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Didn't take you long to turn on the Chinese............
Ah, you got me there! :grin:

Yeah, as much as I can appreciate how stupidly simple a Chinese bike is, I'm very much not liking the trade off of not being able to trust it to get me home.
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Ah so! Cheap Chinese junk!
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