19mm carb vs stock carb

[stevo52]

Been running the arreche 19mm for a couple tank fulls now. It seems the low to mid range is nearly identical to the stock carb . The top end seems a bit better with +5 mph. Although I have no reason to go 55mph. 45mph or so is fine on city streets. The performance increase vs the mpg doesn't seem worth it.

Maybe this sounds weird.... but I think I'm going back to the stock carb at least that got me 60mpg vs 45mpg with the 19mm. I'll just sell the 19mm and buy more Motul 710 and just ride ;D.

[reveeen]

And your point is.................

A larger carb difference is ONLY going to be seen "on the top", as the stock carb flows more than enough on the low and mid range.

You are forgetting though that if you go back to the stock carb you likely are going to have to up-jet it a bit.

[jmkjr72]

also with anything less then a 17.5mm you will burn that athena kit up faster

[stevo52]

Maybe my tuning is still off....it seems like the last 20% of throttle there isn't much there its kind of flat but then sometimes it pulls smoothly up to 50+mph. Seems very inconsistent...the stocker is more consistent. I was just riding it and I was riding into the wind ~10mph and it would only go 43 mph WOT lol. I got a good deal on this carb it was used maybe there is something wrong with it....

Yeah I know to upjet the stocker I ran a 77.5 up from a 70 for the first 500 miles on my 70cc.

[stevo52]

Update after some research on kymco forums:

I was reading that having the carb slide go pass WOT can cause performance problems. So I checked mine and sure enough the throttle is open too much. It's going pass WOT above the hole of the carb opening. This may be causing turbulent flow and the unstable performance I'm getting. I switched to the stock carb today for a comparo... I was able to hit 9.8k rpm. I couldn't really go over 9k or so with the 19mm. No way the stocker should out rev the 19mm something is very wrong. Sound like a good theory? Kinda tired of tuning constantly lol...

[stevo52]

I've been swapping the stock carb and arreche back and forth. Here's my observations:

Arreche 19mm - more power everywhere except very top end where it hits a wall at 9.3k rpm WOT. Running out of fuel?
Stock carb - less power on low end and especially the mid range. However able to get more rpm 9.8K up top WOT. So somethings not right with the arreche.

Not sure if its lean or rich. Plug chops are grayish on the electrode but black on the insulator. If I up the main jet all I get is hesitation/sputtering when I crack the throttle from low speeds. I'm desperately trying to get to this thing tuned. I'm scared to go leaner on the main to a 75 because the electrode already looks leanish. Bike runs fine for 20+ miles trips thought.

Any thoughts? Maybe I need a smaller pilot so I can then up the main? Seems like the circuits overlap alot. The main jet definitively effects the mid throttle range.

[51cc]

check your throttle cable. check the carb, take it off and look and check and see if it's openning all the way. i got this off some other stupid post recently. so there. yoru asnwer. and it could be lean. figure out which. :lmao:

[skuttadawg]

I have a 19mm unsure of brand it says Japan and was told it was a PWK or PK and the jet is a 70 . It runs perfect and I can hit 50 mph with my 200 lb self on my 2011 Jonway Magnum . I put on an unlimited cdi and lighter rollers but dang it still only hits 8,000 rpms grrr . I read some carbs can support up to 10,000 rpms . Would a flat needle perform better ? Yers I know the cable is diff for them

[stevo52]

The throttle cable is adjusted fine. Its opening all the way I have the motion pro cable.

[stevo52]

The throttle cable is adjusted fine. Its opening all the way I have the motion pro cable. I took in my head and block in today to clean it at work and a guy there who has a Puch 250cc twin (2 stroke) says the plug looks rich. I think most of the throttle range except the top end is rich. The plug base and insulator is dark brown/black. The electrode is tan. I think the solution is to drop the pilot to a 15 and up the main to an 85. If I up the main more that an 80 it sputters at mid throttle.

I like the smoother power of the 19mm but the stock carb tends to pull more rpms up top which is strange.

[skuttadawg]

www.4secondsflat.com/plug_chart.html

[lbo]

I have the Arreche 19mm carb as well. I found that the stock needle is difficult to tune, so I got the S1 needle and tuning became a breeze. I had to either drop it a notch or raise it (can't remember) but it made a huge difference.

[stevo52]

Thanks for the response lbo. What pilot, main, needle position are you running? So I can compare. I run a 20, 80, middle with the S1 needle. I's say its pretty much in tune in the midrange the S1 needle fixed that like you said. I do have a hesitation sometimes if I crack the throttle WOT from a stop. My plugs look rich though and its much harder to start than the stock carb. I really think I need to go down on the pilot.

[lbo]

Sounds like you are just about there, I would adjust the needle before swapping jets......... needle position had more of an affect on the PJ than I realized or thought it would.

I have a 73cc Polini and "modified" the airbox. If memory serves me I have a 20PJ, (25 was too rich) and a drilled out 90MJ that is a tad smaller than the 95MJ. 90 was too lean and 95 was rich. The needle I believe I have set up one notch.......... but not 100% certain where it all is. All I do remember was finally finding the sweet spot with the needle clip position and jet sizing and the performance was much improved......... no hesitations or lean conditions. I had to fine tune with the A/F mix too but finally got it dialed in.

My exhaust is a Next R from Technigas suited for 50cc's. If I ever get the RS-II then I will probably have to go up in size for the MJ as that pipe will produce more revs and breath better.