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Post by twitchytoes on Oct 24, 2017 16:01:40 GMT -5
I've been having this issue since I first swapped the new carb in (not new, but new to it. First one was sealed all around). It came stock with a 34 pilot and 78 main. I've upped the main to an 85 with good results, and put the needle on the second to richest setting, also with good results. I've checked valve clearances, and adjusted to .003" intake .004" exhaust, helped a bit. It doesn't bog/die nearly as badly as it used to, but it's still there. I can't quite determine whether it's being flooded with I throttle or if it's not getting enough. I've got pilot jets from 30 to 55, so I can change that pretty easily. As of now, the mixture screw is fully tightened, and it is on the intake manifold side, so I'm assuming it effects fuel flow, so as little fuel flow as possible. (?) Does that mean I need a smaller jet?
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melc
Scoot Junior
Posts: 6 
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Post by melc on Oct 24, 2017 18:07:23 GMT -5
Mine was doing that and it turned out to be the cv carb diaphragm. once i changed it it idled and accelerated perfectly.
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Post by twitchytoes on Oct 24, 2017 18:29:18 GMT -5
Mine was doing that and it turned out to be the cv carb diaphragm. once i changed it it idled and accelerated perfectly. How can I tell if the diaphragm is damaged? I didn't notice any cracking of any sort, and I know dropping my needle did help. I haven't tried the richest position yet though. |
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melc
Scoot Junior
Posts: 6
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Post by melc on Oct 24, 2017 19:01:23 GMT -5
I also adjusted the needle before it was spotted it helped slightly, but didnt cure it. i had a really tiny pin hole in mine just under where it connected to the slide tube. initial inspection i didnt spot it, but my 18 year old son spotted it when he checked it. we held the diaphragm with a light behind it shining through it.
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Post by twitchytoes on Oct 24, 2017 19:07:05 GMT -5
I also adjusted the needle before it was spotted it helped slightly, but didnt cure it. i had a really tiny pin hole in mine just under where it connected to the slide tube. initial inspection i didnt spot it, but my 18 year old son spotted it when he checked it. we held the diaphragm with a light behind it shining through it. I'll take a look at it. I may have a damaged carb around here and if I still do, I'll see if the diaphragm in it is salvageable. I have accidentally poked the needle against the bottom, missing the hole slightly when reseating it, so I may have damaged it. Any idea where to get a diaphragm for a stock style CVK carb? |
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Post by pinkscoot on Oct 25, 2017 11:55:58 GMT -5
You also need to be sure that its seated perfectly on the top. Here is a video to show how to test the slide when the carb is off the scoot: CAUTION, BE SURE THAT THERE IS NO GAS IN THE CARB WHEN YOU DO THIS:
If the carb is on the scoot remove the air box and start the engine, open the throttle and see if the needle raises: Caution be sure there is gas in the carb or it won't start.
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Post by twitchytoes on Oct 25, 2017 15:58:04 GMT -5
You also need to be sure that its seated perfectly on the top. Here is a video to show how to test the slide when the carb is off the scoot: CAUTION, BE SURE THAT THERE IS NO GAS IN THE CARB WHEN YOU DO THIS:If the carb is on the scoot remove the air box and start the engine, open the throttle and see if the needle raises: Caution be sure there is gas in the carb or it won't start.So with the carb on there, pull the airbox off the air intake end of the carb and watch for the needle to rise when throttle is pulled? With engine running, of course. I have been playing with my pilot jets today to see if there was any effect and for the most part it seems like placebo but I did manage to catch a video with it held in the bog position and it almost seems like it is waiting on fuel, maybe the fuel filter is clogged and needs the stronger vacuum of high rpm? Video was done with a 30 pilot jet 85 main but I'm gonna try again with the stock 34 and see if it's similar. www.youtube.com/watch?v=2fK0C2Bw_gA. Additionally, I noticed my 34 pilot has a symbol by the 34 and it seems to be smaller looking through it. Here's it compared to the 31. imgur.com/jrpfKnd also, fixed the formatting here. Going to take a video of the bog on 34 jet. edit2: 34 jet video www.youtube.com/watch?v=enlsBAmfzVA, little longer because I wasn't quite getting as much reaction so tested an extra time or two. |
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Post by cagiva4ever on Oct 26, 2017 6:03:45 GMT -5
have you read what ive recently wrote about idle jet structure differences ? regarding static fuel pressure effect...
also notice, that as these parts are China made, there is no same "calibration" among different manufacs.. basically none of the same size marked jet's are truly same size...
also notice how at your sample photo, the Air emulsion holes look rough as badgers ar*e....This also has huge effect into air/fuel emulsion mixture...its ratio and how it gets mixed...
if this were "Nozzle for needle/emulsifier", it would be lotsa more effects, havoc.........having such crappy emulsion air holes....etc
also, De-activate the Acceleration pump Function. as this is 4T, it behaves different Vs 2T.
your pump might basically Flood the low rpm's 1/8th throttle opening. but that doesnt mean that your idle Circuit alone is good.............................you might have combo issues..............
yet again a China thingy... even 1 identical 139qmb carbs might have diff Acceleration pump jetting, no Jet bore calibration etc issues...
Even the "Air Cut of Valve" diaphram might act up ! , that is there to eliminate Exhaust popping etc when Throttle closed from "higher rpm's"
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Post by twitchytoes on Oct 26, 2017 7:16:56 GMT -5
have you read what ive recently wrote about idle jet structure differences ? regarding static fuel pressure effect... also notice, that as these parts are China made, there is no same "calibration" among different manufacs.. basically none of the same size marked jet's are truly same size... also notice how at your sample photo, the Air emulsion holes look rough as badgers ar*e....This also has huge effect into air/fuel emulsion mixture...its ratio and how it gets mixed... if this were "Nozzle for needle/emulsifier", it would be lotsa more effects, havoc.........having such crappy emulsion air holes....etc also, De-activate the Acceleration pump Function. as this is 4T, it behaves different Vs 2T. your pump might basically Flood the low rpm's 1/8th throttle opening. but that doesnt mean that your idle Circuit alone is good.............................you might have combo issues.............. yet again a China thingy... even 1 identical 139qmb carbs might have diff Acceleration pump jetting, no Jet bore calibration etc issues... Even the "Air Cut of Valve" diaphram might act up ! , that is there to eliminate Exhaust popping etc when Throttle closed from "higher rpm's" Really not quite sure what you're getting at other then disabling the acceleration pump, and I'm not sure how to do that. |
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Post by cagiva4ever on Oct 26, 2017 8:48:11 GMT -5
well, look at the Pump how it works, dismantle it de-activate it, Block its Jet. many options how to "De-activate it"
if you cannot do that, then take the carb to Proper mechanic. you are chasing your own tail if you dont do the fault finding procedure Properly.
read what i have written about idle jet Bore.......... take photos of your #31 and #34 from proper photo angle....Comparison photo, to show Bore hole.
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Post by pinkscoot on Oct 26, 2017 10:27:06 GMT -5
cagiva4ever thank you for "Air emulsion holes look rough as badgers ar*e...." it told me everything I needed to know without looking at the picture. I will have to save that for future use.
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Post by cagiva4ever on Oct 26, 2017 14:47:24 GMT -5
well..looking at the idle jet photo again and again zooming.. it has reflections shakyness shades and holes at opposite site are peaking visible at the photo angle...at 1st glance holes looked non-symmetric etc..
but still, manytimes, china jets are rough.. including emulsifiers. Especially emulsifiers need to sit/seat in Depth they are designed to, or the Air emulsion holes change their Throttle opening effectiveness area....
if buying asian made jet's, id go for taiwanise Naraku brand, unless Keihin oem is exact fit match to our 139qmb CVK's.
pin hole damage at Diaphram may also exist under the center part/plate which attaches the diaphram into Slide.
or diaphrams edge may be hardened even from 1 tiny spot.....
often also Needle(s) are bend from/at Factory production line....
in anycase, every single 139qmb owner should alwasy own have at least 1 DRY perfect Diaphram at Spares. WHY ? because even a perfectly good used1 is often Swallen from petrol, and is often difficult to put back on, can be pinched or doesnt sit well in grooves and leaks when re-attached...
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Post by twitchytoes on Oct 26, 2017 15:11:04 GMT -5
well..looking at the idle jet photo again and again zooming.. it has reflections shakyness shades and holes at opposite site are peaking visible at the photo angle...at 1st glance holes looked non-symmetric etc.. but still, manytimes, china jets are rough.. including emulsifiers. Especially emulsifiers need to sit/seat in Depth they are designed to, or the Air emulsion holes change their Throttle opening effectiveness area.... if buying asian made jet's, id go for taiwanise Naraku brand, unless Keihin oem is exact fit match to our 139qmb CVK's. pin hole damage at Diaphram may also exist under the center part/plate which attaches the diaphram into Slide. or diaphrams edge may be hardened even from 1 tiny spot..... often also Needle(s) are bend from/at Factory production line.... in anycase, every single 139qmb owner should alwasy own have at least 1 DRY perfect Diaphram at Spares. WHY ? because even a perfectly good used1 is often Swallen from petrol, and is often difficult to put back on, can be pinched or doesnt sit well in grooves and leaks when re-attached... Not sure I see what you mean about the emulsifiers, it might be that I'm using a cell phone camera. It was super windy today and I didn't feel too great when I woke up so I haven't done anything other than swap the fuel filter I just received in. Tomorrow I'll probably pop the carb apart so I can get bore pics on the 34 jet and I'll take pics of the 32 and 35 for up and down comparisons, but it will still be a cellphone camera. They may have come a long way but they still aren't magnificent. I looked over my diaphragm with a bright flashlight and didn't notice any light leaking in, only thing I did notice was a spot on the top where it seats into the groove for the gasket, there seemed to be a point where it wasn't perfectly circular and a small fold happened, like when you press in the sides of a bottle of soda with only air in it. However, with the gasket seated, I didn't notice any area that was not covered around the seat. I assumed it was designed that way as this is my first venture into stuff like this. I planned on buying a new diaphragm soon just to have one on hand, as well as to test and see if that was my issue to begin with. My previous pic of the pilots was to take note of the symbol beside the number that stands out more as the difference to me than the bores, as I suspect the 34 has the 34 size bore throughout, where the others have it, then it widens out near the end to smooth the flow, like a duct on a fan. Additionally, if the idle is best with screw fully tightened, that means I need a smaller pilot, right? Edit2: I only have access to one gas station with 90+ octane and it has 87 89 and 93. The 87 and 89 have 10% ethanol while the 93 isn't designated. Would 93 octane be too much for a 49cc and cause predet? Should I try 89 with 10% ethanol? |
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Post by cagiva4ever on Oct 27, 2017 3:14:32 GMT -5
if you need to learn "Basic principals of Carburettor" , download free dellorto PDF "Dellorto basic principals" 2nd edition print ,or both 1st and 2nd. it covers many things that are same to 4T CVK.
i say that book Because it has best photos and best explanations for Emulsifiers etc Venturi's etc.
Best explanations for Fuel level/Float height and Static Fuel Pressure are on other pdf which is Privateer diy version...best ever.
Swallen china CVK diaphrams basically need roomtemp drying time 24~48hours, to Shrink back into std dimensions.
that is why every1 should own DRY spare, 1 or 2, to have on-the-go if needed Ready for use instantly.
i live in Northern europe, so i have most likely very different Fuel rating scaling specs than you. we have pumpfuel Octane 95RON 98RON 99RON.
our 95 has max 10% ethanol content in it. our 98 has 0~5% ethanol content.
Stock 49cc 139QMB defenitely need minium of 95RON. but 98 is ok good.
if 139QMB is tuned then 95RON is substandard......Due ethanol and Detonation issues.
139qmb cylinder heads etc parts run very hot (if low on engine oil) . Valve seats are mostly poorly made etc issues. hot temps, ethanol , Detonations etc issues are bad combos eat destroy engines rapidly.......
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Post by twitchytoes on Oct 30, 2017 17:15:39 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.
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