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Post by pinkscoot on Oct 30, 2017 17:27:17 GMT -5
When you went to the smaller pilot jet did you readjust your A/F screw? Here is a link to Brent tutorial on adjusting it 49ccscoot.proboards.com/thread/429 on the video the info on the screw is at 4:20.
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Post by twitchytoes on Oct 30, 2017 17:55:11 GMT -5
When you went to the smaller pilot jet did you readjust your A/F screw? Here is a link to Brent tutorial on adjusting it 49ccscoot.proboards.com/thread/429 on the video the info on the screw is at 4:20. A/F screw ran best at fully closed in both 30 and 34. 32 as well.
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Post by twitchytoes on Oct 30, 2017 18:17:36 GMT -5
I just went ahead and ordered a replacement genuine keihin one. I feel like it might be a case of more than one thing being just slightly off or maybe even just a bad carb but not super bad.
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Post by AtariGuy on Oct 30, 2017 20:22:29 GMT -5
Even replacement carbs aren't a simple plug and play.
First, what size cylinder bore are you running? Stock or performance cam? What diameter carb? Stock airbox, altered, or k&n/foam filter?
Second, when the air/fuel mix screw is closer to the air intake, it's -generally- gating the air. If its closer to the cylinder, it's metering the fuel flow. So if the screw gates the airflow and you're turned in closed, you're trying to run rich. That means you should go smaller. Make sure you use genuine branded jets. The no-brand jets suffer from lack of quality. jetsrus.com has genuine keihin if you're looking for some.
Other notes - adjusting needle positions only really affects 1/4-3/4 throttle mixture, it won't fix idle issues, and doesn't really do much during the moment of let-on. If you're looking for a more instant action carb, you should get a slide carb instead of a diaphragm carb. And always use fresh white plugs for plug chops - swap into the fresh plug while the engine is at operating temp - and only run it for a moment just to set the color. Using it for warm-up or doing a 15 minute run would black out the color you're trying to read.
And the emulsion holes that ya'll were talking about earlier, they're found in the atomizer, its a tube just above the jet where the needle seats. Its primary purpose is to shred the fuel droplets into much smaller droplets - helps them mix with the air flow racing through the carb...
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Post by twitchytoes on Oct 30, 2017 21:01:03 GMT -5
Even replacement carbs aren't a simple plug and play. First, what size cylinder bore are you running? Stock or performance cam? What diameter carb? Stock airbox, altered, or k&n/foam filter? Second, when the air/fuel mix screw is closer to the air intake, it's -generally- gating the air. If its closer to the cylinder, it's metering the fuel flow. So if the screw gates the airflow and you're turned in closed, you're trying to run rich. That means you should go smaller. Make sure you use genuine branded jets. The no-brand jets suffer from lack of quality. jetsrus.com has genuine keihin if you're looking for some. Other notes - adjusting needle positions only really affects 1/4-3/4 throttle mixture, it won't fix idle issues, and doesn't really do much during the moment of let-on. If you're looking for a more instant action carb, you should get a slide carb instead of a diaphragm carb. And always use fresh white plugs for plug chops - swap into the fresh plug while the engine is at operating temp - and only run it for a moment just to set the color. Using it for warm-up or doing a 15 minute run would black out the color you're trying to read. And the emulsion holes that ya'll were talking about earlier, they're found in the atomizer, its a tube just above the jet where the needle seats. Its primary purpose is to shred the fuel droplets into much smaller droplets - helps them mix with the air flow racing through the carb... Running all stock engine. Air/fuel mix screw for idle is on the cylinder side, it effects fuel. I was just attempting the needle change for sake of sanity check as I had moved it from the stock position previously. I'll take your advice on the jets, I wasn't aware there was significant enough difference. I have a 78 main that is keihin brand, and a 34, 38 pilot that are. The carb I ordered has an 85 and 33 in it, and I was running 34 and 85 (main seemed to perform better than the 80 I had, came 78 stock). I plan to see how it performs in its stock state and I'll go from there with that. This carb now seems to be a clone of a CVK carb of some sort as it has Japan standards or made in Japan somewhere on it. I can't remember what exactly it said, it was ordered off of ebay. It has the gold colored metal cap. The stock carb in the scooter had a tamper proof mix screw and if I recall, blocked off bowl screws. I know swapping in a new carb isn't plug and play but my gut tells me something is wrong in this carb.
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Post by cagiva4ever on Oct 31, 2017 6:05:19 GMT -5
Alright, I tried swapping my pilot jet down after doing a 15 minute idle plug chop, and the plug had come out black then (34 jet). I jumped down to a 30 jet and repeated that, plug was black. I've adjusted my float up and down, most recent attempt being down and the plug is still coming up black. My choke appears to work as the idle does start high, then levels off. When I give it 1/8 to 1/4 throttle, I get grey and black smoke. So it seems all I've accomplished today is narrowing it to a severely rich condition but not why.. Highly debating on replacing the carb entirely because I can't seem to find it. Additionally, forgot to mention I also attempted leaning the needle 1 step to see if that mattered. this is all irrelevant work basically, if Acceleration pumps isnt De-activated, or atleast its progressive lever isnt checked for dissformation.... be aware that Float height is adjusted/tuned in tiny amounts like 0,5mm or less. Only huge out of Specs require changes in millimetres. if you would change Float Height out of Spec by 1~2mm , it would be Monsuun disaster fludding, or opposite Dry, in layman terms. BUT, even if your Float height/Fuel level would be correct in Specs, its ruined if using Jet's that have wrong Structure : the point where tru jet hole bore starts, Equals into how deep they are in float bowl.....Like ive mentioned in past China made Jet's varie. i have here idle jets etc that have about 2mm difference.... Anything China made can varie. even Atomizers/Emulsifiers might have different lenght....due no proper manufacturing calibration.... i havent either seen you say anything if your "Fuel screw" at intake manifold side-cylinder side , has its Tip in proper form. not mushroomed not mangeled not bend etc. hopefully the new ordered carb "as is bolt on" fixes it all, or you need to go these Basic things through still all again.
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Post by twitchytoes on Oct 31, 2017 12:24:04 GMT -5
Alright, I tried swapping my pilot jet down after doing a 15 minute idle plug chop, and the plug had come out black then (34 jet). I jumped down to a 30 jet and repeated that, plug was black. I've adjusted my float up and down, most recent attempt being down and the plug is still coming up black. My choke appears to work as the idle does start high, then levels off. When I give it 1/8 to 1/4 throttle, I get grey and black smoke. So it seems all I've accomplished today is narrowing it to a severely rich condition but not why.. Highly debating on replacing the carb entirely because I can't seem to find it. Additionally, forgot to mention I also attempted leaning the needle 1 step to see if that mattered. this is all irrelevant work basically, if Acceleration pumps isnt De-activated, or atleast its progressive lever isnt checked for dissformation.... be aware that Float height is adjusted/tuned in tiny amounts like 0,5mm or less. Only huge out of Specs require changes in millimetres. if you would change Float Height out of Spec by 1~2mm , it would be Monsuun disaster fludding, or opposite Dry, in layman terms. BUT, even if your Float height/Fuel level would be correct in Specs, its ruined if using Jet's that have wrong Structure : the point where tru jet hole bore starts, Equals into how deep they are in float bowl.....Like ive mentioned in past China made Jet's varie. i have here idle jets etc that have about 2mm difference.... Anything China made can varie. even Atomizers/Emulsifiers might have different lenght....due no proper manufacturing calibration.... i havent either seen you say anything if your "Fuel screw" at intake manifold side-cylinder side , has its Tip in proper form. not mushroomed not mangeled not bend etc. hopefully the new ordered carb "as is bolt on" fixes it all, or you need to go these Basic things through still all again. Firstly, the air/fuel mix location is mentioned in the OP, and I recall asking in another post in this thread whether or not being on that side, and fully tightened being closing as much fuel as possible, if I needed a smaller jet. Regarding the acceleration pump, while i had it apart, I toyed with the mechanism for it a bit and it seemed to be unbent, and functioning properly. Not only that, during my idle tests, WHICH WERE IDLE ONLY TESTS, I started, usually with kick start unless I ran out of energy trying to enough fuel into the carb kicking (pulling vacuum to activate the petcock for the carb fuel), and I would leave it to run at FULL IDLE for 10-15 minutes. I only say 10-15 because one of them was like 12 minutes because my lunch had finished cooking. As far as adjusting the float, I was doing it by eye in small amounts to what appeared to be parallel with the top of the carb, as I have been suggested for that type of adjustment MANY times. In buying the new carb, I'm going with my gut instinct telling me something, somewhere, is wrong with this carb.
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Post by AtariGuy on Oct 31, 2017 18:10:17 GMT -5
Cagiva is just offering help. Just keep mind, english isn't his native language.
The accelerator pump he's referring to is a mechanism within the carb that, as you twist the throttle, it primes an extra mini-shot of fuel into the air column. There should be a little spring tab that rides the cam (the half circle the throttle cable is attached to) that, as the cam rotates, the tab/lever presses outward from the cam into a tiny pump button - that primes the fuel into the carb.
In the olden days of carburated autos, you'd have to mash the gas pedal once or twice before you'd turn the key. Its to prime the fuel for them. Then as you'd turn the key, you'd slowly press into the gas pedal to give it one more slow shot to help the engine start to fire. It's also there to help with sudden acceleration. If you're at a low idle rpm, and you mash the throttle, all you'd be doing is opening the throttle valve. The engine isn't running fast enough to draw the extra fuel as that happens (sudden drop in air velocity as the venturi opens - they say), so your engine would choke on air and stumble - if not die. Now if we added a forced shot of fuel, the engine would have something to combust, rpms jump, and the increased air velocity takes over drawing fuel from the bowl.
That's why its called an accelerator pump - and that technology still carries over into our scoots today, specifically in these style carbs.
What cagiva is suggesting is to temporarily bypass the accelerator pump while you do your plug reads - the extra shots of fuel as you bump the throttle will mess with the reading you're trying to get at idle. And we all have to bump that throttle a couple times at some point to get the idle to sit still.
Anyway, considering you're getting a new carb, keep us updated on it. I hope we can hear good news and you get a fine running machine soon!
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Post by twitchytoes on Oct 31, 2017 18:22:43 GMT -5
Cagiva is just offering help. Just keep mind, english isn't his native language. The accelerator pump he's referring to is a mechanism within the carb that, as you twist the throttle, it primes an extra mini-shot of fuel into the air column. There should be a little spring tab that rides the cam (the half circle the throttle cable is attached to) that, as the cam rotates, the tab/lever presses outward from the cam into a tiny pump button - that primes the fuel into the carb. In the olden days of carburated autos, you'd have to mash the gas pedal once or twice before you'd turn the key. Its to prime the fuel for them. Then as you'd turn the key, you'd slowly press into the gas pedal to give it one more slow shot to help the engine start to fire. It's also there to help with sudden acceleration. If you're at a low idle rpm, and you mash the throttle, all you'd be doing is opening the throttle valve. The engine isn't running fast enough to draw the extra fuel as that happens (sudden drop in air velocity as the venturi opens - they say), so your engine would choke on air and stumble - if not die. Now if we added a forced shot of fuel, the engine would have something to combust, rpms jump, and the increased air velocity takes over drawing fuel from the bowl. That's why its called an accelerator pump - and that technology still carries over into our scoots today, specifically in these style carbs. What cagiva is suggesting is to temporarily bypass the accelerator pump while you do your plug reads - the extra shots of fuel as you bump the throttle will mess with the reading you're trying to get at idle. And we all have to bump that throttle a couple times at some point to get the idle to sit still. Anyway, considering you're getting a new carb, keep us updated on it. I hope we can hear good news and you get a fine running machine soon! When I was cleaning out the bowl and just looking things over, I kinda toyed with the pump and had a decent idea of how it worked. With this one in particular, I don't have to do anything to keep it idling unless it's REALLY cold, like 20-30. I blame this due to running as rich as it is. I start it, it engages the choke and runs high, then slows down to normal idle. However, say I try to take off once it slows down, it stumbles really hard most of the time. I've logged most, if not all, things I've tried in this thread somewhere. Like I said, my gut instinct tells me something is wrong with this carb, I'm just not sure what, so that's why I went with replacement. Also, I know he's trying to help but he completely skipped over something in the very first post and that kinda irked me a bit, not to mention bashing over and over on I should take the accel pump apart/deactivate it when the test I'm running is strictly idle at the moment.
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Post by cagiva4ever on Nov 1, 2017 5:34:35 GMT -5
the thing is that 1st you should Verify that Critical parts are in correct specs, or the test results are irrelevant, unless you know how to read them test results.
for example your idle jet #34 could be equal in size to #31 if the jet bore structure is different on them 2 (i.e #31 sits swims deeper in FloatBowl). if you dont know take into consideration it, the results are irrelevant how the idle behaves.
your Float height could be out of spec from Factory, if you dont take exact mm measurement and Fuel level measurements, its again all irrelevant if you dont keep Track on adjustments accurately.
your Float could also be pinholed, floating too deep, rising fuel level=static fuel pressure -> causing Richer mixture.
you can also have an intake path Airleak.
acceleration pump progressive lever is often very soft, it can Bend even under normal usage.
also before doing anything Carb adjusting tests, as i mentioned parts need to be checked to be in correct Specs, like the Fuel Screw TIP has to be in correct form-shape. Often they can be over tightened mushroomed bend. mangeled Adjuster screw like that wont work correctly.
that was already what 7+ variables and their combos. and i havent seen you taken any Critical info out of them by Measuring.
problem is that you are basically just "bolt on" swopping parts and doing adjustments without really knowing what you are doing.
carburettor related things are Multi complex in terms of ripple effect. especially these diaphram CVK's are basically way more complex on behaviour Vs "traditional carbs".
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Post by AtariGuy on Nov 1, 2017 9:08:41 GMT -5
Well for the sake of being redundant, lets check off what you've accomplished. First, you said you cleaned the carb (and even toyed with it - good, the more familiar you are looking at it, the better). You've adjusted jetting and needle positions. Can i ask what pilot and main is currently in the carb and where you have the needle set? Also, you went over fuel mixture and idle settings.
Theres the basics. Next you went through the enricher (choke), it works. You checked the diaphragm, it doesn't have any leaks, but you did say a tiny lip of the seal may be slightly folded/pinched? You've checked the float level which works well enough. Upside-down level and the seam of the is level with the level surface.
Ok, back to troubleshooting. The bog happens as you accelerate through quarter to half throttle. Bogging usually indicates a rich condition - lagging is lean - so that points to too much fuel. Some options to toy with are to set a smaller pilot and retune the idle. Next, look into the air box. If you left it alone originally, you could open it up by removing some stock restrictors. That improved airflow should match your jetting better. Then try leaning your needle some. Moving the clip up leaves the needle in the seat longer restricting the fuel somewhere in the 1/4-3/4 throttle range - more so in the earlier throttle.
Best i can do at the moment for you...
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Post by twitchytoes on Nov 1, 2017 20:04:41 GMT -5
Well for the sake of being redundant, lets check off what you've accomplished. First, you said you cleaned the carb (and even toyed with it - good, the more familiar you are looking at it, the better). You've adjusted jetting and needle positions. Can i ask what pilot and main is currently in the carb and where you have the needle set? Also, you went over fuel mixture and idle settings. Theres the basics. Next you went through the enricher (choke), it works. You checked the diaphragm, it doesn't have any leaks, but you did say a tiny lip of the seal may be slightly folded/pinched? You've checked the float level which works well enough. Upside-down level and the seam of the is level with the level surface. Ok, back to troubleshooting. The bog happens as you accelerate through quarter to half throttle. Bogging usually indicates a rich condition - lagging is lean - so that points to too much fuel. Some options to toy with are to set a smaller pilot and retune the idle. Next, look into the air box. If you left it alone originally, you could open it up by removing some stock restrictors. That improved airflow should match your jetting better. Then try leaning your needle some. Moving the clip up leaves the needle in the seat longer restricting the fuel somewhere in the 1/4-3/4 throttle range - more so in the earlier throttle. Best i can do at the moment for you... New carb is in and I have done a few short rides for errands, I always let it warm up a bit before I head out. It's 45F today, and as far as the air box, I have the diameter restrictor removed but have kept the cap with the 4 big holes and 1 small hole in it on there. I was unable to open the carb to verify jets as, even with extreme care, one of the screws was in super tight and stripped the head out when I went to remove it to verify. I decided to go ahead and try using it as it were, and a review on the product says it comes with a 33 pilot and 85 main. I had tightened and screwed the mixture screw (on intake manifold side) inward, then turned it out 2 turns as my initial point. I have experimented in both directions a bit during my errand rides but nothing super in depth yet. Acceleration is greatly improved, but a small hesitation when taking off. Nothing nearly as bad as before. Top speed has improved slightly, as well. Idle is a lot more stable and doesn't sound ragged. Something I also noted, the throttle is a lot smoother. (I.E more lubrication.)
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