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Post by 90GTVert on Sept 25, 2009 6:40:35 GMT -5
I looked through my BBK install pics to see if my memory was correct concerning the pistons in relation to deck... 50 70 Also note that the bbk's piston is dished. I must admit, I'm starting to regret the $100 bbk now. The really sad part is that I bought it because it was cheaper and included a head, which i thought would have larger valves. In reality, it's a stock head with a bit milled out of the combustion chamber. Knowing what I do now, i woulda just bought Enviromoto's $100 bbk that doesn;t include the head or any extras. The thing is, I had heard everyone say "just go with enviro's kit" over at SD... but no one explained why other than Jeremy giving good service. Had someone went in depth as I am doing here and said the cheap kits kill your compression, I woulda passed on the cheaper one. Then again, maybe I'm wrong and the other kit is the same way? It does look like the piston is dished in the pics on 139QMB.com too. What ever happened to flat top or domed pistons with big bore kits? I always had great luck with the kits for midbikes that included them. I moved up from 108cc to 114cc, which is a pretty tiny difference in comparison to the 50-70cc, and it was like a different engine thanks to the compression it created.
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Post by stepthrutuner on Sept 25, 2009 9:15:37 GMT -5
Yeah. I agree with you. So little info and pictures are given by most vendors that you mostly don't know what you're going to get.... and getting info over the phone is usually not much better. It's pretty much a crap shoot and about half the time you wind up disappointed.
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Post by 90GTVert on Sept 25, 2009 11:53:30 GMT -5
Well, even if you asked most vendors what the distance from deck is, the type of piston, compression, valve sizes, whatever... I have a feeling many would tell you they didn't know or just pull numbers out of the sky. It might be a winter project to pull this thing back apart and see what I can do with it, whether that's a different kit altogether or milling or a piston, who knows. I hate to pull it off the road again when time is already running out for my father to ride in decent weather. I can't see him wanting to suit up in the cold. I'll still do what I can without pulling the engine and having the scoot down for a bit though... which pretty much just leaves me to ignition advance, finishing the carb tuning for mid/low/idle, and fixing the exhaust leak. If I can get a tach working I'll see if it's got the 9000RPM limited CDI or not... or if it even revs that high. this is just so disappointing to have all this time and money into something that doesn't wanna go 40MPH. I'm sure I can tuck down sometime and get 40+, but 40 cruising seemed like a low goal when I started this project. Silly rabbit, 4 strokes are for kids.
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Post by 90GTVert on Sept 25, 2009 14:49:26 GMT -5
Fixed the exhaust leak. It's not a bad sounding pipe. It's deeper in person. Just a shame it doesn't run as good as it sounds.
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Post by stepthrutuner on Sept 25, 2009 15:32:32 GMT -5
That is a nice deep throb for 72cc. Love it.
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Post by 190mech on Sept 25, 2009 19:56:25 GMT -5
I've never worked on one of those types,would it be too much work to advance the cam timing by slotting the cam sprocket? Done it a bunch on Honda engines with good results...
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Post by 90GTVert on Sept 25, 2009 20:28:47 GMT -5
Slotting the cam sprocket? I had thought of just moving it a tooth. I advanced the ignition timing by dremeling the pickup so I could move it. I took it for a quick ride, about 5 miles. It ran better, with more pep and it was cruising at 38MPH at one point. I was doing 36MPH up a slight incline. Finally, I was beginning to be happy with it. Still slow compared to 2 strokes, but at least it was showing potential. After getting it home, I fired it up again for a moment and it was missing a little. I drained all of the 87 octane and filled it with 93 octane. It started up and acted just fine. I planned to back out just a little timing to make sure I didn't have any issues with it anyway. Before I did that, my father decided he wanted to ride. I told him about the issues, but said it should be alright for a little bit, 'cause it ran great for me earlier. We got about 1 mile down the road and he said it hesitated or missed a little. I told him to avoid WOT then, and I'll just follow you so you go whatever speed you feel safe with. I've said it before, but I'll say it now anway... my father was a mechanic for 35 year and used to do dyno tuning in the 70s and owned a speed shop. He knew the whole situation with the timing, so I figured if it got any worse or whatever he would stop and tell me we need to head back to the house. 10 miles later, he starts slowing way down. I revved the engine on my scoot, trying to get him to go, and he shook his head as if saying no. Just as I thought "$%!@", it slowed to a halt with flames shooting from the exhaust and small puffs of smoke. I went and got a truck and got it back home. It has a little compression, but not much. The plug is nearly pure white, with peppering from detonation. No melting or signs of damage at least. Then my father lays this one on me... " I was really hoping we could ride Saturday night and maybe some Sunday. I didn't really care if we rode tonight." So I took a chance to let him ride tonight, that ended bad, and ruined a decent weekend for riding. Nice. At least the fire was pretty cool looking.
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Post by Enviromoto on Sept 25, 2009 22:23:51 GMT -5
Damn.
You can not catch a break on this one.
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Post by 90GTVert on Sept 25, 2009 23:55:24 GMT -5
Burnt exhaust valve. I coulda prob replaced it and put the engine back togehter, but when I removed the engine shroud I noticed the cam chain tensioner sitting up kinda high. Then I saw that the bolt was busted...
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Post by 90GTVert on Sept 26, 2009 0:01:07 GMT -5
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Post by 190mech on Sept 26, 2009 6:09:54 GMT -5
Sorry for my stupidity!I now see the GY6 has a fixed cam sprocket.The only change that could be made is to reorient the crank sprocket,which is a bear..Does not this machine have timing marks on the flywheel for timing light checks?If so you could check your total advance at high RPM and know if you went too far.Looks like the saga continues,,Good Luck!!
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Post by 90GTVert on Sept 26, 2009 6:18:56 GMT -5
It's got timing marks, but my timing light refuses to work with this scoot. Works fine on cars and my other scoot.
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Post by 90GTVert on Sept 26, 2009 12:13:35 GMT -5
I pulled the valve out. I knew I had knicked the seat, that's why I lapped it. I never could get the knick all the way out. I know that a valve that can't seat properly can get burnt. I'm wondering if that knick wasn't the cause rather than the timing. Maybe just a combo of both. Many hours of work, ruined by a split second slip with a dremel.
I'm not sure how to protect the seat when grinding. It's enough to leave the valve in for port matching, but that doesn't work so well for making big changes in these tiny passages. Tools barely fit, so you need all the angles you can get.
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Post by 190mech on Sept 26, 2009 20:40:14 GMT -5
Yep,a nick in the seat will allow the burnt gasses to funnel thru that slot making a big mess in short order.Did you lap it with a drill motor attached to the valve stem?I know we should hand lap a valve,but if we dont have a seat cutter and pilot,sometimes this will clean up a seat to seal well..
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Post by stepthrutuner on Sept 26, 2009 21:38:47 GMT -5
Brent Your luck with this scooter makes ME want to cry! I can only imagine that you have dreams at night about cutting torches or band saws or explosives and this scooter. The word albatross comes to mind. I feel for ya, dude.
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