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Post by deejays50 on Oct 11, 2013 9:51:48 GMT -5
Hey guys. First of all, I am new here and would like to introduce myself. My name is Martin. I found this forum to be a bit more technical than some other forums. Many other forums just know how to bolt things on but don't know the technical aspects of things or they never reply. I feel this may the right place.  Here's my story: I recently put the stock head back on my BBK (exhaust studs snapped on other head, figured it was easier to swap the old head) and went for a ride. I added a digital tach that same day and must have set it up wrong (I thought 1 piston 1 fire per rev? guess not!) My RPM was reading 5000k (which was probably 10k?) flying down a hill and I blew the top half of the motor to smithereens, and was hot as blazes. The kit that was installed by the previous owner was an AIRSAL 80cc with that funny looking cone shaped piston (higher comp?) I want to do an 80cc kit --nothing more. I currently have a MRP exhaust, Polini Variator with 7g rollers, Malossi clutch,open cone air filter, orange coil, orange CDI (i guess performance hence no rev limiter) and I believe a  or  main jet. Do I need to go bigger with the main jet? Also, where is the most trusted place to buy BBK's from with quality in mind? I want to do the large head as well. Do you think this kit is any good? LINK
I've never run my scoot at this high of an RPM before and I think that's why the engine cooked. If I had to guess, I would say lack of fuel caused the damage to the piston and head? Or something else? Thank you guys in advance PICS 1) i41.tinypic.com/28mfva9.jpg 2) i40.tinypic.com/2yorbx3.jpg My Scoot is a 2009 Kymco Agility 50 |
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Post by jeepsteve92xj on Oct 11, 2013 11:24:45 GMT -5
you didn't drop a valve, but something was loose in there.
Nothing is white like it was run lean. But I can't quite make out the center of the sparkplug.
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Post by deejays50 on Oct 11, 2013 11:36:28 GMT -5
you didn't drop a valve, but something was loose in there. Nothing is white like it was run lean. But I can't quite make out the center of the sparkplug. I'll take a pic of the plug. The piston lost a good chunk of itself from the ring area. That's what was bouncing around in there. Any info about reputable kits? |
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Post by jeepsteve92xj on Oct 11, 2013 11:53:46 GMT -5
I have no experience with any kits, yet.
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Post by pmatulew on Oct 11, 2013 12:04:22 GMT -5
Yikes. Piston lost top edge 1 o'clock to 5 o'clock and I suspect the ring with it.
Looks like a do-over.
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Post by sailracer on Oct 11, 2013 12:18:25 GMT -5
The airsal kit you got is one of the best quality kits out there.They are designed for use with a stock head. The digital tach shoukd be set on 2. 1 spark per revolution Even though it's a 4 stroke, the plug fires on every revolution. I suspect that with the uni filter, you probably ran too lean and too hot. The weird thing is the color, but that may be due to oil after it lost a ring. I would either upjet, or use the stock airbox. I have an airsal. stock head, A9 cam, jet and stock airbox, and I'm very happy. Try again, but watch the mixture. You must've been at wot and too lean. |
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Post by deejays50 on Oct 11, 2013 12:24:45 GMT -5
The airsal kit you got is one of the best quality kits out there.They are designed for use with a stock head. The digital tach shoukd be set on 2. 1 spark per revolution Even though it's a 4 stroke, the plug fires on every revolution. I suspect that with the uni filter, you probably ran too lean and too hot. The weird thing is the color, but that may be due to oil after it lost a ring. I would either upjet, or use the stock airbox. I have an airsal. stock head, A9 cam, jet and stock airbox, and I'm very happy. Try again, but watch the mixture. You must've been at wot and too lean. I tried putting my stock air box on awhile ago and all the engine would do was bog and rev and bog again. What would cause this behavior? With uni filter no bog,ever |
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Post by JerryScript on Oct 11, 2013 13:40:37 GMT -5
Stock air box is too restrictive for a BBK. I had the exact same experience trying my stock air box, bog like crazy. Put the uni back on, and vroom vroom!
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Post by deejays50 on Oct 11, 2013 14:03:30 GMT -5
Just ordered a 47mm 80cc kit from scrappydog and a 47mm head to match.
Hopefully we get this baby up and running before its too cold to ride. My girlfriend was ready to ride her Roketa alongside me this fall! (too hot outside, she will not go!)
I will keep you guys updated.
This leads me to think I may still need to go up a jet. What do you think? The engine was fine all up until i wen't too fast down that hill.
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Post by alleyoop on Oct 11, 2013 15:09:20 GMT -5
Yes, do not let a 4 stroke rev above 8K unless your a racer and do not mind changing blown motors.
4 strokes the red line starts at 8K and the motor is screaming at those RPMS.
Alleyoop
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Post by deejays50 on Oct 11, 2013 18:32:55 GMT -5
105 main jet?
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Post by sailracer on Oct 11, 2013 18:37:50 GMT -5
I use my stock airbox, and my airsal BBK screams. If you have the right fuel-air ratio, the stock airbox is Not too restrictive. Its all in how you tune it. I have a 2 stroke type exhaust with the expansion chamber, and it came stock on the scooter. I kept the stock airbox too. Jusy=t to let you know, I originally got a scrappydog BBk and head. I made holes in my airbox to let in more air. Guess what? too lean, and it soft seized and destroyed the piston.I than got a hoca piston, but the compression was too high, I couldn't get it to run right. One of our fellow members suggested the airsal. I got that and a keihin carb, and I couldn't be happier. You don't need to suck in all kinds of air to get performance. The trick is, the right air/fuel ratio. A lot of people right away put unifilters and open exhausts on right away thinking it will get them a lot of performance. WRONG! The right jetting can give you the proper ratio of fuel to air. By sucking in too much air, you blow up your BBK fast. I know, I did it, and learned the hard way.
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Post by deejays50 on Oct 11, 2013 22:58:47 GMT -5
I use my stock airbox, and my airsal BBK screams. If you have the right fuel-air ratio, the stock airbox is Not too restrictive. Its all in how you tune it. I have a 2 stroke type exhaust with the expansion chamber, and it came stock on the scooter. I kept the stock airbox too. Jusy=t to let you know, I originally got a scrappydog BBk and head. I made holes in my airbox to let in more air. Guess what? too lean, and it soft seized and destroyed the piston.I than got a hoca piston, but the compression was too high, I couldn't get it to run right. One of our fellow members suggested the airsal. I got that and a keihin carb, and I couldn't be happier. You don't need to suck in all kinds of air to get performance. The trick is, the right air/fuel ratio. A lot of people right away put unifilters and open exhausts on right away thinking it will get them a lot of performance. WRONG! The right jetting can give you the proper ratio of fuel to air. By sucking in too much air, you blow up your BBK fast. I know, I did it, and learned the hard way. That's going to be my focus. Finally finding the safe and proper a/f. I'll throw the stock airbox back on with the new bbk and see where that leads me. I've had issues from day one starting the scoot. It would always hit TDC and stop the starter. I didn't realize this airsal bbk had higher compression until I saw the shape of the piston. Hopefully the new bbk will be easier to tune, but doubt it!! |
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Post by sailracer on Oct 12, 2013 8:53:05 GMT -5
I just noticed you say you went wot downhill.WOT down a hill will definitely danage the motor. You probably were closer to 11,000 rpm. I have 16/50 gearing in mine, and on long wot runs I do 9,000-9200 rpm on a regular basis. with no adverse effects. When you re-build, make sure you set the tach to 1 plug fire per revolution. This way, you can keep an eye on it. And I would suggest you Up-gear
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Post by deejays50 on Oct 12, 2013 8:57:59 GMT -5
My scoot absolutely flies off the line and gets to 45 something really quick. I've been wanting to find a way to get the rpm down and the speed up. I only weigh 135 so I have options.
Where should I look for an up gear set? Not sure which to get either.
And my tach is set to 1 and I thought I need to set it to 2....
Edit: I currently have 7g rollers and want to get sliders. Should I stay with close to 7g or get 8 or higher if I can find them?
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or 
main jet. Do I need to go bigger with the main jet? 
..BAD TO THE BONE..