Am I maybe too rich?? Polini CP 21mm carb

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eclark5483
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Am I maybe too rich?? Polini CP 21mm carb

Post by eclark5483 »

So I'm trying to dial in the correct idle adjustments on my Spree, and I just can't seem to get it right

Details:

I'm using a Polini 21mm CP carb, according to Polini's website I should be at 40 on the pilot and 100 on the main. I have not switched jets from the ones that come with it stock.

I went to adjust my mix and here's what happened.. The mix screw was set all the way in, and I take it back 1 and 1/2 turns as a starting point, I then set my fast idle screw as low as I can go without killing it... around 1200rpm..

From there, I started turning the mix screw out and watch my tach. I turn it out at 1/2 turn increments and each time I do, rpm increases.

I keep going till I can get to a point where RPM decreases, but it never happens. I get to a point where my rpm's are into the 1800-1900+ range and do not dip, but I start to see a bit of gas dripping coming from the screw so I know I'm way out there yet RPM's keep going up, not dropping.

I take the bike for a spin, and it will die when I come to a stop. It starts right away with a bit of throttle and runs fine otherwise. Acceleration is where I would expect it to be with such high gears, but you kind of have to play with it to find a sweet spot till the pilot point ends and the main kicks in. After the main kicks in, that thing flys!!

So what am I screwing up here? Is my pilot maybe too rich? Never had this problem on my other scoots, and I'm not very familiar with the Polini carbs.

Given that it is an AF05 engine (with Taz BBK of course), I'm thinking maybe my pilot is too high (40) ??? Recommendations? Stock carb pilot is what... 34?
Last edited by eclark5483 on Mon Feb 20, 2017 1:26 pm, edited 1 time in total.
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Re: Am I maybe too rich??

Post by eclark5483 »

And while I'm on the subject of Polini jet sizes, was curious about my main. Should I try other sizes on that as well? If so, should I go higher or lower? SSS sells them in 80-98 and 100-118. Don't wanna buy 2 kits. Already have some pilot jets in the shopping cart, holding back from purchasing till I get some feedback here.
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Re: Am I maybe too rich??

Post by Meatball »

Im sort-of in the same boat. Im trying to figure out the pilot on a 21mm CP. It comes out of the box with 40/100 jets installed and I bought the 32-40 pilot kit. Im down to the 32 jet now and still think its rich. Im frustrated with it for now. Wish I could be of some help but unfortunately not. :sad:
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Re: Am I maybe too rich??

Post by eclark5483 »

Yeah, I HAVE TO BE running super rich without a doubt. It smokes like crazy at idle. Also, I'm thinking I might possibly need the 19mm CP carb for better atomisation and fuel delivery. The take off using the 15:81 gears is terrible... well, not the worst, but then it's what one should expect... but still, I'm guessing the smaller 19mm CP might be better considering the Mikuni kit sold on webike.net is an 18.5. You'd think a smaller CP would be easier to tune as well.

EDIT: And before anybody asks.. NO, not doing plug chop at this time. Still using the winter VP110/91 Premium fuel mix till I run out. Did a gallon of each last fall and have only used a bit over half of that, so I don't want to get too aggressive with the tuning till I'm back on street gas to see what's up. Might be contributing to the problem as well, but I'll sort that out later on. Plug chop at this point is kind of pointless.

Otherwise, runs awesome!! Highest temp so far on the CHT has been 341 degrees after maintaining 40mph (round 8,000 rpm) for a couple miles. Didn't dare go any faster at this point, but still had plenty of throttle to spare.
Last edited by eclark5483 on Mon Feb 20, 2017 12:57 am, edited 1 time in total.
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Re: Am I maybe too rich??

Post by Meatball »

My buddy has a bone stock Spree with the only mod being TAZ gears and it holds 35 all day long. However, its a complete pig on take-offs. Basically have to Flintstone it to get going.

It would be nice to adjust the clutch to engage at a higher rpm's. Maybe tighter springs would get it out of the bog zone a bit.
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Re: Am I maybe too rich??

Post by eclark5483 »

I'm using the RED Leo Vince springs right now (2000 rpm). According to the tach, it catches at just over 1800 rpm when I adjust fast idle screw. I'm thinking of also going higher and using the yellow springs. And yeah... FLINTSTONE takeoffs!! LOL

The red would probably be just fine for a 13T or 12T gear though.
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Re: Am I maybe too rich??

Post by eclark5483 »

Meatball wrote:I bought the 32-40 pilot kit. Im down to the 32 jet now and still think its rich.
Have you played with the air brake setting on it yet?

Section 9
http://www.polini.com/en/technical-area ... tructions/

What I'm getting from it though... and it might be because the English translation is a bit off, is that by adjusting it to "2-stroke" mode (closing the air brake), that this will enrich my mix coming in.

I haven't messed with that adjustment yet, but it seems to me being too rich is already the problem. Don't know how it comes stock, but might be worth a look.

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Re: Am I maybe too rich?? Polini CP 21mm carb

Post by Meatball »

Im unfamiliar with Air Brake adjustment but I understand its function. Its explanation is unclear however. Open the air brake to increase the airflow to the emulsifier by exposing its upper holes to increased air resulting in lean. Am I reading it correctly that this increased airflow is for a 4-stroke application? I tried to unscrew it but its deep in its socket and cant be pulled out without dismantling the carb. Its not an "adjustment" type screw like the idle or mixture since it doesn't stay put with a spring etc...Once its cracked free, its loose in its threads like a main/pilot jet. Leads me to believe its meant to be replaced with a different size or simply removed altogether. Any input from the masses on air brake adjustments out there?
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Re: Am I maybe too rich?? Polini CP 21mm carb

Post by Meatball »

Also, can someone clarify the "fuel * depression" and 'Mixer" bungs on top of the carb? I have them capped off. Is this correct?
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Re: Am I maybe too rich?? Polini CP 21mm carb

Post by Meloshameless »

I was running the 21 cp on my variated afo5 with malossi kit and intake. My jetting was 34-36 and 104-106. So urs is prob rich on the pilot.
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Re: Am I maybe too rich?? Polini CP 21mm carb

Post by veedubh20 »

The pilot jet is rich 40 , down. Pilot jet 35. C clip on the top needle.

32:1 premix 710 oil
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