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Post by oldgeek on Jul 3, 2017 5:24:48 GMT -5
Another low end issue on a 70 set up like yours could be the contra spring is too weak. Using heavy clutch springs to bypass the weak low end often causes the CVT to start shifting before you even start moving. It was a real issue for a heavy rider like me.
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Post by ThaiGyro on Jul 3, 2017 6:03:01 GMT -5
I am with Old Geek on most carb points. Your intake will certainly have some back flow if reed leakage of any kind...even weak reeds, or old.
Seems as though everyone has different ways to get narrowed to the real tuning. I live in Thailand...my 50cc tuning looks like USA 70cc on the air side, slightly lower on the fuel end.
One of the earlier threads said it best...freshen up EVERYTHING, then start carb tuning.
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Post by tsimi on Jul 3, 2017 6:27:18 GMT -5
oldgeekYeah that might very well be. It is my 3rd stock Yamaha contra spring that I use. I have a Malossi yellow and a Stage6 pink in the pipeline but some parts are back ordered so I'll have to be patient. Also my new Polini 2G clutch is in that order so there are still a few things I can try before opening her up.
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Post by ryan_ott on Jul 3, 2017 8:34:59 GMT -5
I have found that the W8 needle gives me a crisper throttle response but is leaner at cruise speeds with the same jets used with a W7. Check the images of the needle tapers. That being said with these carbs if you change one thing double check other stages. I'm a Keihin guy I've been using them for 10-15 years, this is my first go around with a 21phbg and it's time consuming to say the least. But fuel economy is great.
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Post by tsimi on Jul 3, 2017 18:44:31 GMT -5
Another low end issue on a 70 set up like yours could be the contra spring is too weak. Using heavy clutch springs to bypass the weak low end often causes the CVT to start shifting before you even start moving. It was a real issue for a heavy rider like me. That my friend could be the culprit. Now that you mention it I bought a after market torque spring long time ago which had a +5% rating. The spring looked identical to the stock Yamaha spring, color and size. But she was a bit stiffer. So I maybe was using that after market spring that lasted quite long and I replaced that with a stock Yamaha which lasted me 1 month. So this could be all just a simple confusion of springs. I will try to find that spring again, its something I bought at a store here let's see if it can solve the issue till my other ordered stuff arrives.
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Post by tsimi on Jul 5, 2017 6:29:39 GMT -5
Went to the bike store today and got that 3% up spring that I think used before. Got late so couldn't test drive anymore but tomorrow I take her to work and see how she goes.
Can someone help me refresh my memory again? What was it, stiffer torque spring => lighter roller weights? Or heavier roller weights?
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Post by oldgeek on Jul 5, 2017 6:47:05 GMT -5
In general. You may need heavier weights to counteract the heavier spring if you loose some top end. (contra pulley not opening all of the way) I would start with what you have to see where you are, then go from there. I have put in a heavier spring, and heavier weights and found I could tune the same performance as a lighter spring combined with lighter weights. But with the heavier setup I also added considerable heat to the CVT which is not good.
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Post by tsimi on Jul 5, 2017 18:36:44 GMT -5
Just arrived at my work and performance definitely has improved. She is snappier now and she responded well at mid-range. However there still is a bit of a lag at the bottom. Before I could go from 0-WOT and she would lift the wheel easy. But considering that I don't run with my stiffest clutch springs at the moment and my jetting is still a bit off, she does drive great, almost as before.
Ryan is getting my necessary jets and a new clutch is already ordered so hopefully I will be able to get her back to old glory.
I also could use a stiffer torque spring. I just bought one that says +3% rating. They have a +10% at the store so I might grab that one too till my Malossi(+35%) arrives.
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Post by tsimi on Jul 19, 2017 19:21:39 GMT -5
Got my new jets from Ryan. Finally I was able to tune my carb the way it was meant to. So I got the low end almost perfect, maybe still a tiny bit rich but at those outside temps I rather have it that way.
Now I am running 35/96, W7 2nd from top. Mixture screw 2 1/4 turns out.
What jet is affecting the following; When I quickly twist the throttle to WOT it sputters and then picks up normal. Is that a main jet issue?
I also installed the Polini 2G Evo II clutch which I like very much. Easy to setup and good, strong bite. Also installed the Malossi torsion control on the torque driver side which makes my torque spring now a bit stiffer and therefore I get decent performance. Also installed the Wingbell which I thought might not fit because of the cooling fins around it but it fits a Jog CVT cover without touching it. All in all great progress. Except for that sputter at quick twist to WOT.
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Post by ryan_ott on Jul 19, 2017 20:35:05 GMT -5
Your sputter is likely just the engine can't react to the sudden rush of fuel from idle to wot. The vacuum signal gets weak and can't atomize the fuel correctly or something technical like that.
Is that jetting with the uni filter, premx? That jetting wouldn't work for me here at sea level... I get a idle hang with a 42.
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Post by tsimi on Jul 19, 2017 20:50:07 GMT -5
What you are saying makes sense. How can I fix that? Besides raising the rpms for the clutch engagement.
Current setup (35/96) is with the slightly modified stock airbox with Malossi airbox filter/sponge. Premix at 40:1 ratio.
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Post by spaz12 on Jul 19, 2017 23:21:16 GMT -5
I'm with Ryan on thinking that your pilot is sorta small. Have you gone bigger? What were the results?
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Post by tsimi on Jul 19, 2017 23:23:24 GMT -5
I'm with Ryan on thinking that your pilot is sorta small. Have you gone bigger? What were the results? Next bigger would be a 37 which is what I had in there previous.
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Post by spaz12 on Jul 20, 2017 2:28:50 GMT -5
I'm with Ryan on thinking that your pilot is sorta small. Have you gone bigger? What were the results? Next bigger would be a 37 which is what I had in there previous. Have you tried a 40? Or even larger?
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Post by tsimi on Jul 20, 2017 2:51:11 GMT -5
40 or larger? Once I tried a 42 and I barely could move her forward. Way too rich. The spark plug got all wet. Highest I ever went after that was 38 (winter season). When the outside temps are around 5-20 degrees Celsius then #38 is good. When temps started to go up to around 25-35 degrees Celsius I swapped it for the #37 since I was able to start the scoot without choke which tells me I was running rich. But even the 37 was a bit too rich. Now with the #35 I have to pull the choke to start her, which is good, and besides that slight sputter at quick twist to WOT all seems to be good. I even thought to lower the main from 96 to 95.
I still need to try a couple more adjustments and see how that goes. Maybe the engine/cylinder it self lost a bit compression and therefore the carb has trouble sucking the needed fuel quickly? I don't really know at this point. I just know that now even at 1/4 or 1/2 normal throttle use the scoot drives good and gives me steady power until I reach power band. I think oldgeek was right, before I used very hard clutch springs to skip the low end so no matter how shitty the tuning was as long the main jet was good she pulled great. Now my clutch engages at 7000rpms and is around 500-1000 rpms short to previous setting. But according to the Polini manual 1mm = 500rpms/min so I guess I'll take that clutch apart again and see what I can do.
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