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Post by katt on Sept 30, 2018 14:07:47 GMT -5
Man i gona have to buy new plug to have clean results.
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Post by Sir Scoots-A-Lot on Sept 30, 2018 17:13:00 GMT -5
Why hunt "real 20mm" carb and pay like $50 when you can get legit 24mm carb for (125/150cc) for around $20 of amazon/ebay?
I want to install 24mm carb on 80cc QMB139 will this work?
From what i understand you cannot go wrong with bigger carb, air ratio will be proper even if theres bigger air flow trough carb engine only consumes as much air as it needs.
Yes it will undoubtedly work in a very similar fashion to many others running an 18mm or 19mm with #88-#95 main jets. Of course I think you will need a different intake boot running from your carb to your cylinder and you may need a different air filter to fit the larger carb, depending on what you are running. This guy in the link below runs a 24mm carb, apparently no problems and he goes around 45mph, which as I understand is about a normal honest speed in good favorable wind conditions on very smooth and approximately flat ground on a long stretch with tuned CVT etc. Link to his Youtube: youtu.be/CS5O_2TsRKU I apologixe if you need to copy and paste the link, not sure if you will be able to just click it or not. The thing about these CVK Keihin clone style carbs usually with accelerator pumps is there is a very broad range for what size jet and venturi you can use that will work in a very similar fashion because the engine vacuum determines to a large degree how much fuel is sucked thru
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Post by Sir Scoots-A-Lot on Sept 30, 2018 17:26:43 GMT -5
I personally tend to find plug chops pretty hard to read if you are trying to use them to fine tune a carb....I mean sure if you are running way rich or way lean you should be able to tell...but other than that it could be hard to tell the difference between say a difference of 5 extra parts of air per each part of gas by plug chops alone or something along those lines because there is a range in which the engine will run ok without stalling and in a similar manner, it might have trouble starting if too rich or too lean and may bog down during acceleration if too rich or struggle if way too lean..it will also need different idle screw adjustments at different tunes of richer and leaner..plug chops are also very subjective to user experience....that being said i'm sure scoot veterans like the guys giving advice above whom I have a lot of respect for, Im sure they could see way more than me on a plug chop. I find listening to the scoot when you rev it or feel the acceleration differences after changing the tune is easier for a newbie like me. even the air/fuel mix screw being adjusted a few turns on my scoot seems to make the scoot act a little different/ sound a little different if I give it a quick rev and then let go of the throttle when stopped with the brake on. Maybe if you tune it rich with different main jets then tune it lean with smaller main jets you will learn the differences from experience also. If you post pics of plug chops Im sure some of these guys can give you good advice and it is another way of learning to tune along with listening and feeling and observing how the scooter runs with different tunes. I wish I was experienced enough to be able to tell how to tune better, but a lot of what I do is still trial and error as I am a relative carb newbie, only owned one car with carbs, played with a dirtbike briefly as a teen and now getting into scoots a but late. Learning thru all of these methods is a very possible and useful tool for everyone to be a better tuner
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Post by katt on Sept 30, 2018 18:12:25 GMT -5
I wanna do plug test, being in a center of Los Angeles is tough all streets are short and have traffic lights lights, i might need to drive couple miles away from the center to run a good test and also at night time where there's no traffic.
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Post by Sir Scoots-A-Lot on Sept 30, 2018 18:24:24 GMT -5
I wanna do plug test, being in a center of Los Angeles is tough all streets are short and have traffic lights lights, i might need to drive couple miles away from the center to run a good test and also at night time where there's no traffic. I can imagine all the stop lights in your big city can be very tough on a scooter. Scooters often run fine while going but then can try to stall out at stop signs sometimes. Me- I am always adjusting my idle here as it can be 45 degrees around dawn and 75 degrees in the afternoon and my idle speed is different from when I start the scooter to when it warms up, plus I have hills here and although I am in a small suburb this entire state is heavily traveled with cars and technically part of the most densely populated part of the USA on the East Coast. I suggest you post pics of the plug test especially if you don't know how to read them the guys on here are very experienced and good Are you close to the freeways? I haven't been to L.A. in years but I remember the freeways some and lane splitting is legal out there so I don't know how strict they are telling people to not drive 50cc on freeways but if it is rush hour maybe you could take your little scoot on the freeway and go around all the traffic would be cool. In CT where I live there is no way I could take a 50cc 4 stroke scooter on the highways even during rush hour where cars go like 5-40mph for an hr or two around the city I live near with big bore kit people drive way too fast and crazy if given any chance to usually and the police would get me.
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ratdog
Scoot Enthusiast
Posts: 342
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Post by ratdog on Oct 2, 2018 12:54:55 GMT -5
Scoots... the problem with “seat of the pants” testing is, frankly, you will often get better preformance from an engine running too lean. While that’s fine for my drag bikes, that only run a min or 2 at a time, it can be real bad for street bikes driven in traffic. I’m sure you have seen some of my posts where someone posts a pic, and someone else sz “ well the tip of that is black, so you are running way too rich...”. And I frankly write back no no, look at the pure white insulator! It’s much too lean!!! this is a plug I pulled from Red Bike last weekend. I’m very happy with this mixture. (I’m running a CR8HSA btw). Red bike is very highly modified and will pull in the low 50s on the flat. I could most likely get another mile per hour by dropping from the current “97” main to a 95 or even 93, but that would push the heat way up and I don’t want the heat for driving on the road.
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Post by eclark5483 on Oct 3, 2018 22:17:01 GMT -5
Scoots... the problem with “seat of the pants” testing is, frankly, you will often get better preformance from an engine running too lean. While that’s fine for my drag bikes, that only run a min or 2 at a time, it can be real bad for street bikes driven in traffic. I’m sure you have seen some of my posts where someone posts a pic, and someone else sz “ well the tip of that is black, so you are running way too rich...”. And I frankly write back no no, look at the pure white insulator! It’s much too lean!!! this is a plug I pulled from Red Bike last weekend. I’m very happy with this mixture. (I’m running a CR8HSA btw). Red bike is very highly modified and will pull in the low 50s on the flat. I could most likely get another mile per hour by dropping from the current “97” main to a 95 or even 93, but that would push the heat way up and I don’t want the heat for driving on the road. That plug looks 100% correct and balls to the wall accurate for short spurt use, but looks lean for everyday traffic use. Great example and explanation.
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Post by katt on Oct 3, 2018 23:14:08 GMT -5
Main jet #90 in 24mm carb its both idle and city miles, gap measures 0.60-0.65mm
By the way this new plug failed in just under 100mils for some reason spark is there when i test it, but it would not start, put new plug and it fired right away, like my ignition is frying this cheap NGK C7HSA plugs, NO resistor plug so i don't understand know how it could have failed so quick.
can it be parasitic curent that kills them or they overheat because they run lean and burn out?
Its not first time this happens, i drove home it was all fine no problems power excellent until the moment i parked the scooter then few hours later it would not start at all just almost catch on ignition for half seconds every 5 seconds of turning the starter but nothing would happen.
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Post by gsx600racer on Oct 3, 2018 23:40:23 GMT -5
Main jet #90 in 24mm carb its both idle and city miles, gap measures 0.60-0.65mm
By the way this new plug failed in just under 100mils for some reason spark is there when i test it, but it would not start, put new plug and it fired right away, like my ignition is frying this cheap NGK C7HSA plugs, NO resistor plug so i don't understand know how it could have failed so quick.
can it be parasitic curent that kills them or they overheat because they run lean and burn out?
Its not first time this happens, i drove home it was all fine no problems power excellent until the moment i parked the scooter then few hours later it would not start at all just almost catch on ignition for half seconds every 5 seconds of turning the starter but nothing would happen.
The highlighted areas is melted aluminum from the piston. That plug is way to white. Running lean no doubt.
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Post by katt on Oct 3, 2018 23:55:10 GMT -5
Why plug fails though?
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Post by katt on Oct 4, 2018 2:27:52 GMT -5
The highlighted areas is melted aluminum from the piston. That plug is way to white. Running lean no doubt. You saying my piston melting, because it overheats? I think i have detonations, been feeling some kicks when i apply gas recently like strong vibrations that travel trough entire frame i feel them with my butt and feet, soon as i let throttle go they go away so i know its coming from engine.
Going to test tomorrow and up the main jet to size 98 for time being then run for a while and check the plug. I don't need to worry about idle jet being lean too much since detonations don't happen when it idles right?
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ratdog
Scoot Enthusiast
Posts: 342
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Post by ratdog on Oct 4, 2018 10:04:21 GMT -5
As far as I’m concerned, it looks like your engine I’d eating it’s self from the inside. My thought is WAY TO LEAN. What gas are you running? With a plug looking like that, I would run 93 octane I would increase the main jet size a LOT more then 2 points.id jump up to a “100” A problem you are having is that the bike is running way too hot. It needs more gas, and it needs more octane. I would also go to a C8HSA plug. To run best, plugs are designed to retain a certain amount of heat. The lower the number on the plug, generally, the more heat it retained. In the NGK line, the “7” is “ normal”. An “8” will blend heat faster and live longer in your too hot engine. It really surprises me that a “90” jet is this lean. Makes me wonder if your anso sucking air. i would also do an oil change. In my BBK engines, I run 20w-50 air cooled engine oil. You would be surprised how much that will help when your running so hot. id bet that if the plug has not failed on you, it would look more like this in a hundred miles more
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Post by gsx600racer on Oct 4, 2018 13:18:40 GMT -5
Its funny that you're more concerned about the color of the plug than you are about the aluminum dingleberries that are splattered all over the end of the plug.... There are plenty of plug charts online that show you how to read a plug.
Others have said that the carb was too big. You say it runs 30% better with the bigger carb. Its running so lean of course its going to run better at the cost of failing spark plugs, overheating, and the top of you're piston going bye bye. Remember I mentioned that the larger carb will effect the fuel delivery circuits with the lower velocity/vacuum, it's not going to deliver the correct mixture. Upjetting is just bandaid-ing the problem
Common sense says go back to the smaller carb and jet according, or keep the big carb and upjet a lot and burn more fuel in the process and band-aid the real problem.
Or you can keep throwing spark plugs at it till it grenades, and blame the ignition/coil or faulty spark plugs.
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Post by gsx600racer on Oct 4, 2018 13:23:38 GMT -5
As far as I’m concerned, it looks like your engine I’d eating it’s self from the inside. My thought is WAY TO LEAN. What gas are you running? With a plug looking like that, I would run 93 octane I would increase the main jet size a LOT more then 2 points.id jump up to a “100” A problem you are having is that the bike is running way too hot. It needs more gas, and it needs more octane. I would also go to a C8HSA plug. To run best, plugs are designed to retain a certain amount of heat. The lower the number on the plug, generally, the more heat it retained. In the NGK line, the “7” is “ normal”. An “8” will blend heat faster and live longer in your too hot engine. It really surprises me that a “90” jet is this lean. Makes me wonder if your anso sucking air. i would also do an oil change. In my BBK engines, I run 20w-50 air cooled engine oil. You would be surprised how much that will help when your running so hot. id bet that if the plug has not failed on you, it would look more like this in a hundred miles more When he is running a 24mm carb and probably a open type air filter vs running a 20mm carb, that 90 jet is just not going to cut it.
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Post by dexameth on Oct 4, 2018 13:55:01 GMT -5
I skipped by a lot of reading to throw in my 2 cents. I have ran a 24mm GY6 carb on my 82cc builds and up. 50mm bore ran a 105 main, 52mm bore ran a 110 main and when I did the stroker/52mm setup I have a 112 main. All with the same stock GY6 24mm carburetor and intake manifold. When I popped that baby on there it was NIGHT AND DAY difference. I had pull finally. I could feel the motor actually tugging at me to go when I'd blip the throttle. Not just revving up. I understand the physics of venturi and vacuum and blah blah, and yeah there's a time when you can over-carb. I even did a 24mm carb on a Chinese 50mm kit (crappy ports, smaller valves, standard piston) and that motor saw a big improvement over the stock carb. Where you REALLY see improvements is with a nice Taiwanese head like the SSP-G/Hoca 50mm or 52mm heads. The valves aren't huge, but the porting is absolutely amazing. Intake starts at 23mm and tapers to 21.5 at the valve. Exhaust is tapered just the same. 24mm carb, to 23mm intake manifold, into the tapered port, it's an awesome design and what I run now. Hint: those heads are 10% off right now
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