|
Post by albongo on Mar 13, 2015 15:01:53 GMT -5
Okay so I've fitted a 72cc bbk, stainless steel eBay exhaust and a Chinese free flow air filter. All have 200km since install. The scooter seems to have developed a stumble/cough/hesitation at random times when past half throttle. It feels like the engine loses power with an auditable change in engine sound, scooter drastically slows for a second and then recovers. I rode for about 4 miles and then the engine lost power and died like it was suffocating. Pushed it to a safe place and then tried to start back up. Fired up 3rd kick! Rode back home very slowly staying around half throttle. Stumble happened only once and I made it home. Pulled the spark plug, looked like Not sure what is happening at base of ground electrode Main jet is 90 with needle clip moved 1 place lower. I have pulled the carb to clean. Given the mass of experience on the forum can anyone help figure out why this is happening Please?
|
|
|
Post by 90GTVert on Mar 13, 2015 15:43:21 GMT -5
Pictures won't enlarge for me, but a 90 main jet sounds very small for your setup. I'd try a larger main jet, or better yet a few larger jets and see which works best.
|
|
|
Post by albongo on Mar 13, 2015 16:03:52 GMT -5
Is this better? The plug. The base of ground electrode. I will get the hang of posting pictures eventually.
|
|
|
Post by Fox on Mar 13, 2015 16:29:04 GMT -5
Have you tried running the kit with the stock air box to see if the stumble disappears? You can open up a stock air box a few different ways to increase air flow. 1: Remove the plug in the end of the snorkel if so equipped: 2: Remove the small rubber tube inside the air box cover. 3: Drill holes in the air box cover. Better to drill one hole and test than to drill too many holes.
|
|
|
Post by albongo on Mar 13, 2015 16:55:04 GMT -5
Fox, Stock air box is broken, I bought a replacement from a scooter of the same make and model, engine size and year of production but it doesn't fit! Chinese quality control! So I'm stuck with the pod filter. I'm going to try upjetting, see what a 93 jet is like.
|
|
|
Post by Fox on Mar 13, 2015 16:59:26 GMT -5
Why doesn't it fit?
|
|
|
Post by niz76 on Mar 13, 2015 17:28:40 GMT -5
Sounds like you're running waayyyy lean and overheating your engine to the point of failure. I was running a 91 main jet on a 4t with BBK and that was with stock airbox. That free flow air filter is pulling in way more air than the stock box would. You'll need to upjet considerably to get the air/fuel back to the correct ratio. You'll more than likely end up over 100 mj... Maybe way over.
|
|
|
Post by Fox on Mar 13, 2015 17:45:42 GMT -5
Maybe he can reduce the air flow some with some strategically placed duct tape.
|
|
|
Post by niz76 on Mar 13, 2015 21:16:42 GMT -5
Must admit I've done it before when running an open filter but didn't have large enough jets atm but I wanted to RIDE!
|
|
|
Post by Fox on Mar 13, 2015 22:07:07 GMT -5
Yeah I believe you niz. He didn't say exactly why his replacement air box wouldn't fit on there but you can believe I would make it work somehow. LOL
|
|
|
Post by albongo on Mar 14, 2015 0:55:10 GMT -5
Sorry, the replacement air box is exactly the same as my previous one but the 'hose' that connects to the carb doesn't reach. Even though it is from exactly the same bike! Just goes to prove no 2 Chinese bikes are the same or I'm just very unlucky.
The spark plug looks a nice tan colour but the symptoms do sound like it is lean! Just not all the time!
My largest MJ is 99 after that I'm using duct tape.
|
|
|
Post by stevec on Mar 14, 2015 5:21:48 GMT -5
the ring on the plug is black which is from being rich, the tan doesn't look bad, it is not coated. i always used a pod filter on the 72cc upgrades, usually works well with a #85 or #90 mail and a #35 pilot jet. half to 3/4 throttle is the pin setting, 3/4 to full is the main jet. make sure the diaphragm is not leaking, should have no tears and be seated properly all the way around, if it is not working properly or leaking it will cause what you are describing.
|
|
|
Post by albongo on Mar 14, 2015 17:36:24 GMT -5
Carb cleaning tonight! Diaphragm looks good, no tears. When I stripped the part the main jet is screwed into (main jet housing?) It looked like it was gunked up. So I'm going to clean, replace and reinstall with the 90 main jet fitted. Could this gunk have cause the issue?
|
|
|
Post by Fox on Mar 14, 2015 17:43:22 GMT -5
Gunk is never good in the carb. but it looks like the little holes are clear so I don't think that was the issue but it may have disrupted the flow in there some. Move the needle clip all the way to the bottom and check the plug after a ride. Better to err on the rich side so you don't run too hot and damage the piston. I have seen posts where guys will actually install a tiny washer under the clip to raise the needle even higher.
|
|
|
Post by albongo on Mar 15, 2015 6:23:18 GMT -5
After all the excellent advice I cleaned and reinstalled the carb with a 96MJ. I could barely make it to the end of my street!! Bogging down really bad and really loud. So if I started with my MJ at 90 and 96 made it worse I should drop it below 90. Installed an 85 (my next size down) and went for a spin, scoot is quieter but the cough still happens occasionally. my next jet down is an 80. Is this too low? I don't want to damage the engine.
|
|