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Post by parkmice on May 9, 2020 18:52:51 GMT -5
Hi,
I've just installed a Polini 70cc big-bore kit on my buddy's Kymco People50. I'm staying with the stock gearing, stock 14mm Kehin carb, and stock exhaust. I plan to pull the snorkel from the stock airbox. The stock carb has a size 75 jet. I have 90, 88, 85 & 82 jets for it.
I'm in Seattle so we're at sea level, with lots of hills under 500 feet in elevation.
Anyone want to take a stab at suggesting which main jet to start with?
Thanks,
-Mark
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Post by Zino on May 9, 2020 19:38:20 GMT -5
Since you did not change your pipe .
The polini has mild port timing .
Most Times you stay the same or go up 5% .
Taking snorkle out adds one more jet size
Since 75 is your stock
82 is probably close to right 85 probably gets too rich .
With most kits you need to lower the needle one clip rich since you spend more time at mid throttle .
Do you have a temp gauge ?
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Post by parkmice on May 10, 2020 2:07:43 GMT -5
Since you did not change your pipe . The polini has mild port timing . Most Times you stay the same or go up 5% . Taking snorkle out adds one more jet size Since 75 is your stock 82 is probably close to right 85 probably gets too rich . With most kits you need to lower the needle one clip rich since you spend more time at mid throttle . Do you have a temp gauge ? No, unfortunately no temp gauge. |
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Post by Zino on May 10, 2020 6:23:11 GMT -5
The Temp gauge imho is one of the best safety and tuning mods for a scoot, it will tip you off to high temps and help you get your jetting in line faster . If you have not tuned carbs before here is a good resource www.49ccscoot.com/faq/symptoms.htmlwww.49ccscoot.com/faq/symptoms.htmlThat polini is a good cylinder and gives plenty of power without overreving your cylinder. Treat it right with Oil and proper jetting and you will get thousands of miles . |
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Post by christopher on May 10, 2020 7:10:42 GMT -5
Get a temperature gauge so you know if your running to lean. Most people up jet for wide open throttle. Then they ignore the midrange and wonder why there is a hole in the top of their piston.
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Post by parkmice on May 10, 2020 15:01:11 GMT -5
Get a temperature gauge so you know if your running to lean. Most people up jet for wide open throttle. Then they ignore the midrange and wonder why there is a hole in the top of their piston. Yes, I'm with you. I want to follow the recommended break-in procedure so I won't be running it at full throttle yet. So, I can't really get a good spark plug read until I do that. Usually when I jet I go richer than what I really expect, then step down leaner from there. But I've never jetted with a brand new piston & cylinder, so I've been able to go out and run at full throttle and take a plug read. That's why I'm looking for advice, hoping to land close enough to be safe until the preak in is done. Polini recommends no more than 3/4 throttle for the first 200km. I will be raising the needle 1 notch richer (lowering the clip 1 notch). |
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Post by Zino on May 10, 2020 15:18:14 GMT -5
You dont have over jet a new cylinder.
You can hear real lean and real rich .
Lean is Zingy and Rich is deeper sound .
I would still look at the plug even if I was going 3/4 throttle .
If she has some Graham cracker to chocolate color good enough if she is grey go up a jet.
Alot of kits burn up on mid throttle or decelerating .
I would Juice the throttle a few times as you decelerate to give a couple blasts of cooling fuel mixture when you let off the throttle.
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Post by christopher on May 10, 2020 16:34:37 GMT -5
Get a temperature gauge so you know if your running to lean. Most people up jet for wide open throttle. Then they ignore the midrange and wonder why there is a hole in the top of their piston. Yes, I'm with you. I want to follow the recommended break-in procedure so I won't be running it at full throttle yet. So, I can't really get a good spark plug read until I do that. Usually when I jet I go richer than what I really expect, then step down leaner from there. But I've never jetted with a brand new piston & cylinder, so I've been able to go out and run at full throttle and take a plug read. That's why I'm looking for advice, hoping to land close enough to be safe until the preak in is done. Polini recommends no more than 3/4 throttle for the first 200km. I will be raising the needle 1 notch richer (lowering the clip 1 notch). I perform testing and plug reads at 1/4, 1/2, 3/4 and WOT. No need to limit yourself to just WOT. I've also gotten lazy in my old age and have started using an air fuel ratio (AFR) meter. I bought one from PLX that uses your phone as a display and connects to it using bluetooth. I also use a spare battery and put the stuff in the trunk under the seat. The only permanent fixture is the hole in the pipe for the bung for the sensor. AFR meters are great to tune with easily, not a guess you get real time data and know where your at. I used one on my 1950 Ford with a flathead 6 and dual carburetors when I was tuning it. Also on my 2007 Stella with a bbk. |
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Post by parkmice on May 10, 2020 16:52:28 GMT -5
Yes, I'm with you. I want to follow the recommended break-in procedure so I won't be running it at full throttle yet. So, I can't really get a good spark plug read until I do that. Usually when I jet I go richer than what I really expect, then step down leaner from there. But I've never jetted with a brand new piston & cylinder, so I've been able to go out and run at full throttle and take a plug read. That's why I'm looking for advice, hoping to land close enough to be safe until the preak in is done. Polini recommends no more than 3/4 throttle for the first 200km. I will be raising the needle 1 notch richer (lowering the clip 1 notch). I perform testing and plug reads at 1/4, 1/2, 3/4 and WOT. No need to limit yourself to just WOT. I've also gotten lazy in my old age and have started using an air fuel ratio (AFR) meter. I bought one from PLX that uses your phone as a display and connects to it using bluetooth. I also use a spare battery and put the stuff in the trunk under the seat. The only permanent fixture is the hole in the pipe for the bung for the sensor. AFR meters are great to tune with easily, not a guess you get real time data and know where your at. I used one on my 1950 Ford with a flathead 6 and dual carburetors when I was tuning it. Also on my 2007 Stella with a bbk. Ya, but I don't want to run at full throttle for the first 200km, per the Polini break-in procedure. So I'm hoping someone here can help get me close with my main jet with some good advice, so it's not a total shot in the dark. I'm leaning toward a 82 at this point, I'd rather err too rich than too lean, until I can do a full throttle plug read. |
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Post by aeroxbud on May 10, 2020 17:18:54 GMT -5
The thing is, no two scooters will be the same. Even with the same setup.
I would always go richer than you think. If it is very rich it will be quite noticeable. Then go down 2 sizes of main jet at a time, until it runs clean.
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Post by harleyracer59 on May 16, 2020 13:47:00 GMT -5
You dont have over jet a new cylinder. You can hear real lean and real rich . Lean is Zingy and Rich is deeper sound . I would still look at the plug even if I was going 3/4 throttle . If she has some Graham cracker to chocolate color good enough if she is grey go up a jet. Alot of kits burn up on mid throttle or decelerating . I would Juice the throttle a few times as you decelerate to give a couple blasts of cooling fuel mixture when you let off the throttle. hot lean almost to seizure point gets dull as well. when on a run and the exhaust goes from whaaaaaa to whoooooow. let off immediately if she revs fast and then the exhaust note gets deeper and it reves real slow. youre smearing melted piston on the cylinder walls.... |
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Post by parkmice on Jun 30, 2020 22:26:11 GMT -5
Hi all. I ended up having to replace the exhaust too, it had a broken baffle. I replaced it with a LeoVince Touring exhaust. Of course I removed the restrictor funnel.
Stock jetting was 35 pilot and 75 main. I ended up at 45 pilot and 95 main, with intake snorkel removed. I did 15 miles of mostly full throttle and could see that sweet chocolate color starting to form on the brand new spark plug.
Thanks all for chiming in!
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Post by Mech Warrior on Jul 10, 2020 11:51:35 GMT -5
Glad we could help you and welcome to the Forum parkmice  |
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