Scooter carb adjustment hell

"Full of the sound of the Gran Fury, signifying nothing." (granfury) 07/24/2016 at 22:23 • Filed to: None

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Trying to get this 800-mile cheap Chinese scooter running reliably and it seems be down to a fuel/air mixture issue, even with a new carb and fuel and air filters. I need a little advice on how to get this thing starting and running without a lot of manual intervention. I’ve never really worked with carbs, so I’m not sure what I’m getting wrong.

1) There’s a hose connection on the manifold between the engine and carb. There’s a plug on that connection, but if the plug is pulled (more air into the engine) the engine starts, but doesn’t run well until that plug is replaced. Starting the engine without that plug in place is almost impossible.

2) The only two adjustments that I can see are the low speed mixture adjustment and the throttle position. I’ve followed most of the advice and turned the low speed mixture screw all the way in and then backed it out 1.5 to 2 turns. Backing it out further doesn’t have a major effect when the engine is running, but it is noticeable; when backed out further the engine seems a little less responsive to throttle inputs.

3) The engine doesn’t seem to run well with the stock airbox in place, so a washable cone air filter was installed and it seems to run stronger. It runs about the same with either the cone filter or no filter installed making me think that there is some sort of obstruction in the airbox (currently bypassed)

I’d like to see this engine start reliably without having to pull any hoses, and I think it should have a steady idle without enough revs to turn the rear wheel when on the center stand. What am I missing, and what can be done to turn this temperamental PoS into a reliable commuter vehicle?

Berang > Full of the sound of the Gran Fury, signifying nothing. 07/24/2016 at 22:32

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Vacuum leak in the manifold? What does the hose on the manifold connect to?

Also in any centrifugal clutch moped I’ve had, the rear wheel should be spinning when on the stand, but only slightly.

Raymundo > Full of the sound of the Gran Fury, signifying nothing. 07/24/2016 at 22:34

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Question: Does this carb belong on this engine? Also, are the jets sized appropriately for this configuration? It sounds like you’re getting too much fuel. What does the exhaust setup consist of?

Decay buys too many beaters > Full of the sound of the Gran Fury, signifying nothing. 07/24/2016 at 22:40

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Is it a 2-stroke? If so could be oil/gas mix.

Also you can tweak the overall mixture leaner by spiking the fuel with a little e85. Try playing around with different length PVC tubes to increase the post filter intake manifold volume.

How is the plug?

OversteerMyBagel > Raymundo 07/24/2016 at 22:40

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This, exactly!

Full of the sound of the Gran Fury, signifying nothing. > Raymundo 07/24/2016 at 22:42

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The exhaust system is the stock TaoTao 50 part. The carb was purchased on Amazon and was chosen for use on this 50cc engine and thus has the stock 18mm intake; it came with an extra jet, but considering that this engine doesn’t have any performance mods there didn’t seem to be a need to use it. The jet that is in the carb isn’t marked, but the extra one does have a size marked (I don’t know where it is so I can’t tell you the size...)

Full of the sound of the Gran Fury, signifying nothing. > Decay buys too many beaters 07/24/2016 at 22:44

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Plug is a new CR7HIX, the good iridium-tipped unit. It’s a four-stroke and running pump gas

Raymundo > Full of the sound of the Gran Fury, signifying nothing. 07/24/2016 at 22:45

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Can you take your exhaust/muffler off, try to start the engine, and report back?

Decay buys too many beaters > Full of the sound of the Gran Fury, signifying nothing. 07/24/2016 at 22:48

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Try a copper plug, sometimes little engines have trouble lighting off iridium. More resistivity and all that...

Full of the sound of the Gran Fury, signifying nothing. > Raymundo 07/24/2016 at 22:58

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I’ll have to contact the owner and see if he wants to try this during this 100 degree heat. What could be wrong with the exhaust? This thing doesn’t even have 1000 miles on it.

Raymundo > Full of the sound of the Gran Fury, signifying nothing. 07/24/2016 at 23:09

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Nothing. I’m still not convinced the jets are correct. All your symptoms point to too much fuel. If you remove the muffler or the whole exhaust and it runs better, then you certainly have too much fuel.

Full of the sound of the Gran Fury, signifying nothing. > Raymundo 07/24/2016 at 23:14

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I tend to agree with the diagnosis of too much fuel. Opening up that port on the intake manifold and having the engine start up better tells me it needs more air, although I question why it runs like crap with that port unplugged after starting.

I’ll ask that he try the stock carb again and see if that makes a difference. I don’t think we’ve tried that one after getting the valves and timing adjusted.

Raymundo > Full of the sound of the Gran Fury, signifying nothing. 07/24/2016 at 23:19

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Definitely do that. Let us know what comes of that.

RangerSmith > Full of the sound of the Gran Fury, signifying nothing. 07/25/2016 at 01:24

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Have you gapped the intake and exhaust valves? These scooters are recommended to have this done as part of routine maintenence, every 300 or so miles. Only costs a few bucks for the shim tool, and a little bit of time on the Youtube.

Full of the sound of the Gran Fury, signifying nothing. > RangerSmith 07/25/2016 at 02:43

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Yup. That job was just done just before this ordeal began. This step alone made a big difference, but it still has issues.