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Post by blakewatson26 on Mar 21, 2021 22:53:23 GMT -5
So I have a 1994 yamaha jog CY50. I bought a chinese 70cc bbk from gy6store on ebay, bought an unbranded aftermarket exhaust, still on stock carb and airbox, but I cannot get it to run right for anything. It ran okay-ish right after I did the bbk, and had the stock pilot jet in and an 85 main, but I was stoned, and thought that the drill bit I had would be perfect size to drill out the pilot jet to make it run perfect. That was a mistake. It had a 42 stock pilot jet and a 76 stock main. It's a teikei 19mm carb I believe. I bought a replacement pilot jet from jetsrus because I can't find an entire jet set for the teikei carb. I bought a 47.5 pilot jet, cost me $20. I figured that would work but apparently not. I've tried every damn needle clip position, and every main hey combination I can think of and it still runs like dung. Any suggestions?
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Post by Zino on Mar 22, 2021 7:27:33 GMT -5
post a pic of your plug It may be fouled Swap in a fresh plug If all you changed was drilling pilot start there Go back to 85 main jet and needle in the middle . That is a big jump up size wise in pilot jets . A pipe usually doesnt need a pilot jet up grade or a very small one under 5%. OEm Teikei pilot jets are hard to come by . I have only been able to get them from yamaha Brent has a good carb tuning process www.49ccscoot.com/faq/carbtune.html# |
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Post by blakewatson26 on Mar 23, 2021 0:50:04 GMT -5
Is that really that much of a jump from 42 to 47.5? Hell I thought it was reasonably less than the equivalent I went up in the main jet. 10 sizes to 5.5. But I don't know because I just started getting into moped here recently when I got one given to me. Right now I have a 95 main in and I swear it runs better than it was with the 85. Hell I've tried everything from 75 which is stock, to now 95. It's just extremely slow taking off but builds speed. To be honest It seems like it's getting to much air on take off. Which would be lean and I checked my plug and it definitely is running lean. Which confused me because when I had the stock pilot and an 85 main it ran rich-ish. But now I went up on the pilot and way up on the main jet and it's lean? Talk about a headache 🤯 lol
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Post by aeroxbud on Mar 23, 2021 4:24:08 GMT -5
If you have only drilled the pilot jet. It shouldn't effect the running from half throttle at all. The fact it's running bad everywhere, suggests you have other issues too.
I would go back to the original main jet you were running, when it ran ok. Then check over everything again.
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Post by blakewatson26 on Mar 23, 2021 10:49:44 GMT -5
I bought a pilot jet from jetsrus. I was just saying that I drilled the original pilot jet, ruining it, causing me to have to buy a new one, which I bought a 47.5 pilot. The original was 42. The idle is fine but taking off is where I have the problem. And I checked the plug and its running extremely lean, so going back down to an 85 main jet doesn't make sense to me since I'm at a 95 now.
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Post by aeroxbud on Mar 23, 2021 13:45:37 GMT -5
If your running a 95 jet, and it's extremely lean. Something is wrong. You must have an air leak of some sort. You shouldn't need to be more than 25% richer than you were bafore.
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Post by Zino on Mar 23, 2021 17:44:59 GMT -5
I am betting a air leak .
Intake leak check
With the scooter running
I like to use a unlit propane torch and run it along the seams of the intake and listen for a change in rpms .
Exhaust leak Check
With the scooter running Rake a gloved hnd with a wet cloth and plug the end of the exhaust if it kills quick You are good if it keeps running you have a leak If it is at the head gasket that is a problem if it is at the silencer not dangerous .
The way I check is with a soapy bottle of water and spray it on the silencer seams while running
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Post by Zino on Mar 23, 2021 17:46:56 GMT -5
If you put on a expansion pipe You may neeed stiffer clutch springs to get in the power band for best take off and a notch lighter weights in the variator
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Post by ThaiGyro on Mar 23, 2021 19:29:17 GMT -5
What the guys are implying here...and don't feel bad...is that you tried to do too many things at once, "hoping" for great results.
In the two stroke world, there is no magic, but there are tricks. Just go back to your GOOD running setup, if you can. A bit more top end jetting with a BBK is OK.
Look through these vast pages of "how to" and you will soon see. I have an early '80s Honda 49CC engine, that is still sporting OEM guts, but with some love and care. It has a few carb options to go with a few pipe options. Different combo's, different operations, but both work well...on the leaner side. Ignition timing...do not forget!! Do it FIRST!!
It took me many hours and much Thailand sweat to get these setups right. DO NOT WORRY! You will too. One step at a time will make your personal light bulb brighter.
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Post by pinkscoot on Mar 24, 2021 9:26:51 GMT -5
 It's a process and the first one is always a long process. My first BBK was the same one you have and I'm still running it on my Pinkscoot. It had a few soft seizes and taught me a lot about these 2 strokes.
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Post by blakewatson26 on Mar 28, 2021 4:01:20 GMT -5
I think I found the issue. On the underside of the cylinder it appeared that it was leaking oil/fuel slightly between the base gasket and the cylinder. So I had to take it apart and I some gasket maker along with the base gasket. Just waiting for it to be 24 hours so I can test and see if that fixes it or not.
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Post by aeroxbud on Mar 28, 2021 5:37:16 GMT -5
That's good you found it.
Its always a good idea after a couple of heat cycles. To torque down the head again. They usually loosen up a little.
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Post by captincvmn on Mar 28, 2021 10:32:39 GMT -5
Small engines are simple when they run
When they don’t run they’re simply frustrating
Read some builds in the build folder. Pick some with many pages started by posters with experience. Even those have trial and error in the process but guided by experience.
I ask for help whenever I am stuck and I am quite fortunate to have found this place.
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Post by blakewatson26 on May 26, 2021 22:44:13 GMT -5
So I was wrong when assuming I found the issue. It's been a nightmare since I last posted. I ended up over tightening one of the head nuts, breaking the stud. Having to buy studs, put it back together but not having a base gasket because it fell apart pulling it off so I used just Permatex gasket maker copper. Still didn't fix the problem so ordered new base gaskets and tried it again. Still didn't fix it. Then I thought maybe it's my carb. Bought a new carb. Still wasn't it. Then my cheap Chinese exhaust broke on the neck of the exhaust right behind the flange where it meets the exhaust port on the cylinder. Welded it. Still didn't work. By this time I've driven it quite a bit since I put it back together from getting a new base gasket. I notice it looks like It's leaking down by the base gasket again so I check the head nuts / bolts and sure enough they're not all the way tight. So I retighten them. Still doesn't fix problem. I at this point have no idea what it could be. For some reason initially I thought maybe it was the crankcase center gasket/seal was leaking. (Before I noticed it was the base gasket. Could that be be a possibility? I'm ready to ghost ride it into oncoming traffic
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Post by aeroxbud on May 26, 2021 23:15:04 GMT -5
I would put a steel rule across the bottom of the cylinder. Make sure it's flat. Some of these cheap kits don't ever run right. The port timings are off.
Perhaps do a leak down test. If your bikes not sealing somewhere, it will never run right.
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It's a process and the first one is always a long process. My first BBK was the same one you have and I'm still running it on my Pinkscoot. It had a few soft seizes and taught me a lot about these 2 strokes.
