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Post by Zino on Feb 25, 2020 22:54:11 GMT -5
The main jet really should not effect idle . 3/4 throttle is needle and over lap of main Get a tach it makes it easier for tuning carb and cvt Main jet is tuned by running wide open . I take a bunch of jets run down the road wide open and note top speed by gps and feel. If two jets hit the same top speed i go with the larger jet if it feels right . I then move onto the needle mark the throttle grip with tape so you always open it to half way so you are fully on the needle . Repeat process take notes on throttle feel as you work down from the top needle to lower is richer When i find two that feel the same I take the richer setting. The stock vino carb is a mikuni clone here is a good mikuni web page to help you . www.iwt.com.au/mikunicarb.htm
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Post by scootandboot on Feb 27, 2020 17:49:25 GMT -5
Okay guys so I got the rpm meter and have been testing and adjusting the carb and now cvt. Best rpm I can get is 3200 maybe 3400 if I'm lucky. Looking at the service manual it says 5000 rpm as a number to check the charging system with. Where could I be losing engine rpm?
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Post by Zino on Feb 27, 2020 18:22:35 GMT -5
You only get 3400 rpm when wide open ? That is really low 8500 would be healthier. These scoots tend to idle in the 1500-2000 rpm range . I would think pipe is holding you back or you have extremely low compression restricted cdis cut out around 7000 rpms and the stock vinos is unrestricted so i would not look there .
Have you derestricted the pipe at the head of the exhust pipe yamaha puts a restriction in there if the exhaust pipe has a dime sized hole you still have a restriction when fully restricted it is closer to a quarter size opening .
Check compression 140 plus very good below 100 bad
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Post by scootandboot on Feb 27, 2020 18:28:08 GMT -5
Idle reads 1000 when running a really low idle and closer to 1500-2000 normally so I'm guessing the tach is right. I'll check compression tomorrow and update.
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Post by Zino on Feb 27, 2020 19:30:53 GMT -5
20 mph is real slow these do about 30 mph with stock engine with exhaust restriction and variator ring
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Post by scootandboot on Feb 28, 2020 9:35:47 GMT -5
Compression is at 90-maybe 100 (cold) if I really hope my fitting were a little lose. But okay so problem. Should I pull the head and check for damage? or is some other troubleshooting worth trying first. Keep in mind I have a new cylinder piston rings, and clips so swapping the engine isn't out of the question. I picked up some copper spray rtv would it be worth checking squish clearance and possibly. Losing the head gasket to copper rtv to up compression?
Also worth mentioning the exhaust is hugely suspect to me. My old moped I burned out the exhaust and most issues went away. I'll give it a go but in the mean time would having the exhaust off effect compression measurements.
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Post by scootandboot on Feb 28, 2020 11:10:24 GMT -5
Tested compression again cold and hot. still around 90-95 psi. Manual specs says that's above the minimum but it still sucks. I pulled the cylinder head and found not much wall look really nice ports don't look clogged. Piston head had some carbon build up so I cleaned it. Cylinder head also had buildup so I cleaned that as well. Checked clearances and I'd be okay to lose the head gasket but before I go there. How much should a piston wiggle? is it worth replacing the gaskets and putting on new piston rings? Or just move on and hold off on going there. Ideally I want to leave this cylinder stock maybe light porting but the free 50cc clone cylinder I have I'd like to be a bit more bold with.
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Post by scootandboot on Feb 28, 2020 11:29:08 GMT -5
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Post by scootandboot on Feb 28, 2020 12:19:34 GMT -5
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Post by geoffh on Feb 28, 2020 15:44:17 GMT -5
That looks pretty bad IMO,are the piston rings moving freely or stuck in one spot they look carboned up ,you may have had some soft siezes in the past,I would replace the barrel piston and rings ect and start fresh,the are guides to compression testing in the tech sec,let us know.
Geoff
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Post by scootandboot on Feb 28, 2020 16:18:17 GMT -5
Thank you so much that was the direction I was going to go. Just wanted to be sure it was worth going there and wasn't something as simple as cleaning the exhaust port. I ended up burning out the exhaust it was almost completely clogged so I'm guessing that hasn't been helping performance.
I'll drop a new piston/rings ect in it tonight and see if I've made any improvement. Also I spent the afternoon cleaning the cylinder exhaust port getting all of the carbon off it. I figure if it was carbon buildup it'll be worth it in the long run to spend the time cleaning it.
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Post by Zino on Feb 28, 2020 18:13:47 GMT -5
I agree totally with geoff If you have a dremel and the right bit you can open up the exhaust port a little bit the stock yamahas are 1/3 closed over the 50 cc and 70 cc upgrade. I would just upgrade to 70cc and get the bbk smile going on A malossi wild lion exhaust is a nice upgrade for stock cylinder also Either one would push you low 40s and together mid to high 40's
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Post by scootandboot on Feb 29, 2020 12:59:02 GMT -5
Can I use a 50 cc cylinder head with a 70cc cylinder?
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Post by repherence2 on Feb 29, 2020 13:13:22 GMT -5
in this picture your lower piston ring is cracked.
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Post by repherence2 on Feb 29, 2020 13:15:30 GMT -5
Can I use a 50 cc cylinder head with a 70cc cylinder?
I wouldn't try it. you might end up burning a hole in your piston.
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