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Post by tricci1009 on May 28, 2022 18:57:01 GMT -5
Really hoping someone can help. I bought a 50cc Tao Tao from Amazon. It was so slow barely got to 20mph and it was way to lean I couldn’t even twist the throttle without it bogging. But it always started on the first try no matter what. So I bought a Kehin carb and a package of main jets. Tried different jets until I got the best results. It hits about 40mph now. I also played with the needle for the best results. And put different weights in the cvt. I put a yellow clutch spring in but it was way to strong and popped the belt off so I went back to original spring. Well when it’s running it’s got great throttle response and is pretty fast but I will kill the battery trying to get it started. Takes me almost 40 min to get it started. I’ve messed with the mixture screw and best spot when it’s idling is about 1-1.5 turns. Once it’s hot and have been running it will start on the first try but if it sits for more than an hour it’s almost impossible to start. Even with starting fluid in the carb. And sometimes I’ll be cranking away hearing it barrely start to turn over but when I kick start it I’ll get it going a little bit but it’s like barely running low low quiet revs like it’s starving of fuel then after doing that for a while it will spring to life. That’s happened a couple times but mostly it just takes for ever to start and then once it starts it’s fine. I’m wondering if I should have changed the pilot jet too I figured the stock one was fine I think it’s a 36 maybe??? But If I take the carb off and put the original sealed and super lean Chinese carb back on it will start right back up. Maybe put the original air box back on? Or change needle position. I can’t imagine that it needs valves done it only has 500 miles and it has always done this since the new carb which was done almost immediately after buying it new. And also because it starts right up with the stock carb. Please help it’s really annoying
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Post by FrankenMech on May 28, 2022 21:20:49 GMT -5
The air box is part of a stock carb fuel system, the engine will not operate without it. The flow resistance increases the pressure differential across all the jets to draw the proper amount of fuel from the fuel bowl. Replacing the carb and/or making ANY change to the air box means you must re-tune the entire fuel system. Any 'stock replacement' carb purchased from XYZ retailer will give you big fuel delivery problems and a lengthy tuning process. The 'stock replacement' carbs are just the carbs left over from some manufacturer's production run which is why they are so cheap. The Original Equipment Manufacturers (OEM) have engineers and test equipment to set up carbs and fuel systems at the factory. There are 'performance' carbs that will operate with a tiny amount of idle mixture and speed adjustment without a filter or with a very low resistance pod/cone filter right out of the shipping box. The problem with performance carbs is keeping out dirt, bugs, and water while riding.
There may have been a defect in your original carb. Get a replacement from the distributor you bought your scoot from. Any need to tune with the new carb should be minimal USING THE ORIGINAL STOCK AIRBOX.
Your original enrichment unit may also be bad so buy a replacement and install it. Check some of the vids and manuals on how the enricher works.
I personally found the electric enricher to be a real PITA and eliminated mine with some additional carb tuning and modifications that come from a lifetime of working with carbs on all types of vehicles.
Perform only ONE change at a time. Throwing performanc parts or mods at your scoot will cause difficulties. Never use 'RACE' parts unless you know precisely how they work and why.
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br4inl3ss
Scoot Enthusiast
Posts: 448
Location: Québec
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Post by br4inl3ss on May 28, 2022 21:34:09 GMT -5
valve job has been done on many brand new car. less than 500 miles... i dont think its your case, but really possible. remember that nowadays if big brand name cant make a decent car without 100 defect and 3 recall, then what about chinese ? lol. ( car dealer experience i know it all about modern shit they sell us ).
have you checked the auto choke ?
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Post by tricci1009 on May 29, 2022 6:22:54 GMT -5
I removed the stock carb because It needed to be tuned and I didn’t want to deal with drilling thee plugs out. The new carb has a bigger main jet. I’m not sure what size pilot jet came with the new carb but. If I take the new Keihen carb off and put the stock carb back on it fires right up on first try. Without the stock air box. Only a pod filter. I don’t think the air box is my problem. I do believe there may be some benefit to using the stock air box but with the jet I’m using it wasn’t getting enough air. Its not the valve clearance either again if i put the original carb back on it starts up first try. It has to be either the automatic enricher or the pilot jet is too big. I’m going to try swapping enricher with the stock carb. I’m also going to drill the plugs out and open up the stock carb and put then pilot jet in the new carb. Question. I’m assuming that when I bought this new carb possibly for a 150 when it came with bigger jets installed the pilot it came with was too big for my little 50cc. I only bought main jets to tune it because the problem I had was with the main jet. But if it came with a bigger pilot jet already installed which I didn’t touch it might be why it’s always been really hard to start.
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Post by tricci1009 on May 29, 2022 6:23:30 GMT -5
Also. How can I close the enricher circuit to see if it will start easier?
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Post by aeroxbud on May 29, 2022 12:54:34 GMT -5
If you connect the choke to a 12V supply it will cut off the enrichment circuit after a couple of minutes. This is what normally happens when the bike is running.
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Post by GrumpyUnk on May 30, 2022 7:14:21 GMT -5
Did you happen to note the diameter of the venturi? The standard is about 18mm as I recall. If you got a carb sized for a 150cc engine, you have way too much carb(3X!!). It will be hard to start, hard to turn, and likely not give very good performance. I could be wrong, but I do think it will take effort to make it usable. The cold start problem is likely the 'byvalve', or enrichment system. On the intake side of the carb, around the 'clock' of the intake, there will be a circular port in line with the enrichment valve(if you have one). The port is the air supply to the byvalve. If you take a length of rubber tubing and push it into the byvalve port, it will(should) flow air when things are cold. Once warmed up, there should be no airflow through the byvalve port. If you remove the retainer (two screws) holding the byvalve, you may be able to see the air passage looking towards the inlet side of the carb. The air comes in and mixes with fuel drawn from the float bowl via a tube that dips into the bowl, inside a hole drilled into the carb. There is a small hole which allows fuel into the bore drilled into the float bowl. If plugged, you will not get any 'cold start' help from the byvalve. tom
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Post by tricci1009 on May 31, 2022 6:48:25 GMT -5
The carb is the same size as the stock one. I actually fixed it this weekend. I adjusted the valves and it starts on the first try every try now no matter how long it sits. I changed the 33 pilot to the stock number 30 and it idles perfectly now. I had a 95 main jet in I decided to try the 100 main jet and I don’t think I notice a difference. However there’s a new problem and it has to be either from the valve adjustment or from swapping the jet to a 100. The bike has never died on me. The other night (after the valve adjustment and jet swaps. Running better than ever) I’m going full speed down some back roads and started going downhill once I really started getting some speed about 50mph from the engine and the momentum all the sudden it died. Like it ran out of fuel. It took a few minutes before it would start again. Then yesterday same thing on a different road going downhill really gaining some speed then like it ran out of fuel. I’m wondering if the 100 main jet is letting the fuel out faster than the vaccuum can replace the fuel at those really high rpm’s when gaining extra speed down hill. I’ve read some stuff about stalling going down hill but I think this has more to do with gaining the extra speed than it does the angle of the bike. It’s like I gain the extra speed flying down a hill and the motor sucks up all the fuel. But this never happend before with any other jet including the 95. It’s the same backroads I use to tune the bike and cruise down all the time. It’s my little loop and I’ve done it a million times never had the bike stall out. Any thoughts??
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Post by GrumpyUnk on Jun 1, 2022 8:59:25 GMT -5
I'd check the actual flow rate from the tank/petcock/filter/hose to the carb inlet. The fuel flow should be unrestricted at the full diameter of the fuel line with suction/vacuum applied to the petcock diaphragm. If the flow is restricted, could be the tank outlet debris screen, clogging in the petcock, filter clogged, or the fuel line deteriorating. Last could be a sticking float bowl needle valve needle. The latter could restrict fuel filling the bowl when it is being pulled out at high useage rates... Does closing the throttle rather than continuing WOT make a difference? is it possible you have a 'rev limited' that cuts off the ignition if rpms exceed a set point? Could your CDI be a bit sensitive and unable to keep up with the demand(rpm sensitive)? Lastly, when you have this problem occur, if you can pull over immediately(Yeah. Put on the brakes so you can check before things change) and see if you have fuel in the float bowl. Clamp the fuel line so it can't refill while you fiddle, and then open the float bowl drain screw, catching any fuel that comes out. If things lack fuel, you won't get much. If it is NOT a fuel supply problem, you should get a 'float bowl full' of fuel. Lastly, could a lack of vacuum(WOT... down hill... lack of vacuum?) cause the petcock to slow/stop the fuel flow? You can test by having a 'IV style fuel supply' to test without use of a vacuum petcock. Rig up a plastic soda bottle & fuel line. Drill a too-small hole in the cap, feed fuel line in. Remove normal fuel line & plug. Connect the plastic line, with the soda bottle filled with some fuel. Place under the seat using ties so you can test with an unrestricted fuel flow(it will STOP after vacuum gets too high inside, so test accordingly). If the IV works, you have a fuel supply problem... tom
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Post by tricci1009 on Jun 1, 2022 12:48:46 GMT -5
Thanks those are all great ideas. The carb is brand new and was cleaned just recently I don’t think the float is sticking. It’s an aftermarket cdi and it’s more like running out of fuel than ignition being cut. It sputters and bogs down and dies. I did suck on the last vaccuum Line and see plenty of fuel shoot out the fuel line. It seems to not happen if I let off the gas a little bit when going down hill. I really think it’s gotta be from the main jet being too big. It started happening as soon as I put the 100 main jet in place of the 95. And the 95 was running fine I just wanted to see what the 100 would be like. It’s only happened twice now that I’m aware of it I try to back off the gas when I’m really flying downhill and it hasn’t happened. I’m going to swap the jet back to the 95 and go try the same hills that it stalled out on before. I feel like that has to be it
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