cabrinha
Scoot Member
Posts: 22 
Location: Hellas
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Post by cabrinha on Dec 14, 2018 18:31:27 GMT -5
Hello again.
Tomorrow morning (Saturday) I will have some time to deal with my scooter (and shops are open). So I want, for once more, your knowledge.
After replacing the stock carburetor (12mm Dellorto Phva) with a cheap chinese (17mm) and removing the exhaust restrictor my scooter runs better than ever before.
BUT
1.The air mixture screw does not make any difference whether it is fully screwed or not. Nevertheless it idles fine. 2.When I turn the engine on (after sitting for several hours) the engine is revving up (as it would do a car with a faulty idle air valve) and if I blip the throttle couple of times it goes to normal idle speed (normal for cold start) . If then the engine (and the auto choke) warms up the idle rpms go even lower to normal idle speed. If then I pull the throttle to start moving the engine hesitates for 2-3 seconds, the exhaust makes a lot of smoke and then it starts and works perfectly. The scooter had the same behaviour (hesitation on first throttle twist and lots of smoke) before I had the fuel cock replaced (it was leaking).
Here is a video of what I describe above.
My first concern is to solve the problem with air screw not responding. And I believe that this problem correlates with above problem no.2. I am thinking that either the float height level is set wrong or the pilot jet is bigger than it should be. I remind you that the engine works perfectly on partial and full throttle.
So, how can I find the correct float level height for the new carburetor in order to check whether it is set up properly? Is there any way or I have to just set the float parallel to bowl?
What size pilot jet should I buy? One number smaller or even smaller? Any other suggestion?
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Post by aeroxbud on Dec 14, 2018 19:18:45 GMT -5
Have you had a look at the plug to see what colour it is?
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cabrinha
Scoot Member
Posts: 22
Location: Hellas
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Post by cabrinha on Dec 14, 2018 19:22:30 GMT -5
Have you had a look at the plug to see what colour it is? Here is a pic.  |
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Post by benji on Dec 14, 2018 21:21:05 GMT -5
Kinda sounds like your "cheap Chinese carburetor" has developed an air leak somewhere. I'm guessing the airscrew maybe since it has no effect. The cheap Chinese carbs are horrible, your lucky you got one that works ok haha. I would suggest getting a Dellorto 17mm, itll probably run better and tune easier.
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Post by geoffh on Dec 15, 2018 10:48:18 GMT -5
Cabrina,please stick to one thread for your scoot,these engines need everything to be in tune and one area effects the other.I suggested you change the plug and then show us,the air box needs to be sealed up good ,we are here to help,post pictures of the air box and plug.
Geoff
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cabrinha
Scoot Member
Posts: 22
Location: Hellas
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Post by cabrinha on Dec 15, 2018 11:22:06 GMT -5
Kinda sounds like your "cheap Chinese carburetor" has developed an air leak somewhere. I'm guessing the airscrew maybe since it has no effect. The cheap Chinese carbs are horrible, your lucky you got one that works ok haha. I would suggest getting a Dellorto 17mm, itll probably run better and tune easier. Scooter runs rich at idle. If there was an air leak mixture would be lean. Today I changed-lowered the needle (raised clip from position 3/5 to 1/5, needle got deeper in the carb) in order to lessen fuel. Air screw started to respond (very little though) and partial throttle to full throttle shows a slight hesitation (almost not perceivable).
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Post by benji on Dec 15, 2018 20:51:45 GMT -5
The needle effects the main jet, not the pilot jet. If changing the needle position effected the way it idled, I would think you have an air leak causing it to draw fuel from the mj. Or something else wrong with the carburetor. You should be able to completely remove the main jet and tune your idle circuit without even having the ability to rev up to half throttle.
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cabrinha
Scoot Member
Posts: 22
Location: Hellas
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Post by cabrinha on Dec 16, 2018 5:37:26 GMT -5
The needle effects the main jet, not the pilot jet. If changing the needle position effected the way it idled, I would think you have an air leak causing it to draw fuel from the mj. Or something else wrong with the carburetor. You should be able to completely remove the main jet and tune your idle circuit without even having the ability to rev up to half throttle. I see your point and you are right. When I changed clip position the air screw started to respond. It was not responding as it should but when it was fully closed the rpms got lower. When unscrewed 3 turns rpms slightly rose. Is this normal? youtu.be/EZg8pp0f1aU |
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cabrinha
Scoot Member
Posts: 22
Location: Hellas
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Post by cabrinha on Dec 19, 2018 19:34:00 GMT -5
What type of pilot jet is this? I cant find it in stores here so I have to order online.   |
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Post by aeroxbud on Dec 19, 2018 20:50:41 GMT -5
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cabrinha
Scoot Member
Posts: 22
Location: Hellas
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Post by cabrinha on Dec 20, 2018 14:57:02 GMT -5
It looks different the keihin one.
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Post by benji on Dec 21, 2018 17:14:11 GMT -5
It looks different the keihin one. the other downside to Chinese carbs. Parts don't fit. I would go to jetsrus.com and email em a pic of the jet. |
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