AF05 carb on AF16 // PA 31M vs PA 35J carb differences

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AF05 carb on AF16 // PA 31M vs PA 35J carb differences

Post by burnt_toast »

Trying to pinpoint source of a fuel cut issue, and leading me to carb. Motor is AF16, all stock beside a KymcoZX50 pipe
Have a spare stock carb from a '93 SR (AF05), figure I'd try it since on hand.

from noiseguy's carb ident thread & Honda service manual:

88 - 93 Elite (SA50)
PA 31M
Jetting: 88

94 - 02 Elite (SA50/Dio)
PA 35J
Jetting: 78

Has anyone had the pleasure of trying such a "downgrade"?? :?:
I know the PA 35J is about 14mm, but what about the PA 31M? Venturi diam looks smaller, but how much smaller
And whats the deal with the fatter 88 vs 78 jetting, seems counter-intuitive for a smaller carb..

Likely won't stick with this setup if it chokes the bike, but driving me crazy not having a decent reliable daily scoot..
trying to mend that with this stopgap measure :?
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Re: AF05 carb on AF16 // PA 31M vs PA 35J carb differences

Post by burnt_toast »

Pulled off both carbs for comparison tonight, both are same venturi diameter size 13mm (not 14). Minor differences overall. Took a bunch of pics, will post some later.

Running out of daylight to further test this carb swap, but still baffled as to the 88 vs 78 main jetting difference in this case :crazy:

since carbs look very very similar, only theory is there are internal differences I am not seeing OR the af05 case/bore is less efficient therefore requiring more fuel vs af16 dio style case/bore, or combo of both. just odd off the bat since both are 50cc displacement and similar in design. (vertical orientation, side case intake)

anyways ima keep on truckin and report back. although surely someone must've tried this already, plz post if so! :love:
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Re: AF05 carb on AF16 // PA 31M vs PA 35J carb differences

Post by Meatball »

Where exactly are you measuring? I have an SE50 carb lying around I can throw a micrometer on if you want. Says 31D
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Re: AF05 carb on AF16 // PA 31M vs PA 35J carb differences

Post by mousewheels »

Beyond the main jet, the emulsion tube and needle are tuning components which change between different carb tags.

Try swapping the AF16 e-tube, needle and jet in the AF05 carb.


See this link for e tube comparisons. It gives an idea of variations. However I do not have a pic of the 88-93 etube. Please take a photo of yours.
http://www.hondaspree.net/phpBB3/viewto ... 15#p262332
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Re: AF05 carb on AF16 // PA 31M vs PA 35J carb differences

Post by burnt_toast »

Meatball wrote:Where exactly are you measuring? I have an SE50 carb lying around I can throw a micrometer on if you want. Says 31D
needle slide. right at 13mm, verified w caliper
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Re: AF05 carb on AF16 // PA 31M vs PA 35J carb differences

Post by burnt_toast »

mousewheels wrote:Beyond the main jet, the emulsion tube and needle are tuning components which change between different carb tags.

Try swapping the AF16 e-tube, needle and jet in the AF05 carb.


See this link for e tube comparisons. It gives an idea of variations. However I do not have a pic of the 88-93 etube. Please take a photo of yours.
http://www.hondaspree.net/phpBB3/viewto ... 15#p262332
interesting. so you think this could account for the +10 mainjet size huh. will give it a shot!

that is an amazing thread btw, treasure trove of stock carb info :thumbsup:
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Re: AF05 carb on AF16 // PA 31M vs PA 35J carb differences

Post by ped »

mousewheels wrote:Beyond the main jet, the emulsion tube and needle are tuning components which change between different carb tags.

Try swapping the AF16 e-tube, needle and jet in the AF05 carb.


See this link for e tube comparisons. It gives an idea of variations. However I do not have a pic of the 88-93 etube. Please take a photo of yours.
http://www.hondaspree.net/phpBB3/viewto ... 15#p262332
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Re: AF05 carb on AF16 // PA 31M vs PA 35J carb differences

Post by mousewheels »

interesting. so you think this could account for the +10 mainjet size huh. will give it a shot!
I not sure the e-tube/needle accounts for all the jet difference. It may be airbox/exhaust etc differences between Aero/SE50/88-93 Elite vs AF16 are larger.
But swapping an AF05 carb to AF16 as you are doing, those are the parts which differ.

On a similar note I get AF05 carbs running on Gyro's by swapping the e-tube/needle and jets over to Gyro parts.
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Re: AF05 carb on AF16 // PA 31M vs PA 35J carb differences

Post by ped »

mousewheels wrote:
interesting. so you think this could account for the +10 mainjet size huh. will give it a shot!
I not sure the e-tube/needle accounts for all the jet difference. It may be airbox/exhaust etc differences between Aero/SE50/88-93 Elite vs AF16 are larger.
But swapping an AF05 carb to AF16 as you are doing, those are the parts which differ.

On a similar note I get AF05 carbs running on Gyro's by swapping the e-tube/needle and jets over to Gyro parts.
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Re: AF05 carb on AF16 // PA 31M vs PA 35J carb differences

Post by Meatball »

Measured the slide on the SE50 carb and its at 13mm also. Then just for fun I checked a Polini 21mm CP carb and the slide measured 24mm...who knows?


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Re: AF05 carb on AF16 // PA 31M vs PA 35J carb differences

Post by Meatball »

Heres a post from another forum explaining the proper measurement of a carb...(hes actually explaining for a 22mm Mikuni)

Take the needle slide out of the carb, and look through the carb as the air would flow,

the portion where the slide was that you can now see through is the venturi,

it will look oval'ish (more of an upright rectangle with rounded corners).



The narrowest point (across the width) should be around 20mm and the widest point (across the height) should be around 24mm, the average gives the overall size e.g, 22mm


My cheapie caliper's arms for measuring INSIDE are too short to reach inside to the carb's verturi so I cant get an accurate number. Of course, the caliper arms for OUTSIDE measurements are very long but wont help us here.
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Re: AF05 carb on AF16 // PA 31M vs PA 35J carb differences

Post by burnt_toast »

Meatball wrote:
Remember that episode of Seinfeld when Jerry was dating that girl with "Man Hands"? :bowrofl:
bwahaha :lol:

still a nice welcome pic lol
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Re: AF05 carb on AF16 // PA 31M vs PA 35J carb differences

Post by burnt_toast »

So major update, but no pics been slacking sorry.

Did some more fiddling with the carbs yesterday. How da heck does that emulsion tube come out?!? looks pressed in?? no recess to twist out..

Not wanting to damage the carb, but really wanting to ride, I cobbled together the following:
PA 31M carb (with existing e-tube)
PA 35J needle (since that was already on throttle cable)
90 main jet, logic being since stock for af05 is 88 and I'm running ZX50 pipe with better flow

Having a feeling it would be way rich, I tried just open carb. no filter, nothin. started right up! up and down the street, ran like a top
hmm okay, next threw airbox on. would idle and not much more just burbble and obviously too rich.
back to open carb, runs like a top! loud, but i like it.
next up, how about airbox back on, but airbox cover off. ran OKAY, but noticeably less power than open carb and still felt rich.

And with that, I deemed open carb to be the winner! And with only 30min to spare to get to an ATT store accross town to fix my phone, i obviously had NO OTHER option than to try my newly untested but promising setup. :eyeroll: remember the initial reason for this carb swap was to cure my most dreaded problem: FUEL CUT

promptly cut some screen mesh type material and hose clamped it, and rode off into the sunset. literally. with liberal amounts of WOT for miles, talking MILES. on hwy frontage rd. and guess what? NO FUEL CUT!! temps even stayed nice, consistent 290-300F avg, 310F or so peak. even more surprisingly part throttle is not bad at all, with only minor hesitation at low throttle but its to be expected with no filter/airbox.

Anyway, long story short. I made the roughly 13mi round trip unscathed, and no blown top end. howbout that. even gps'd a top speed of 44.3 mph :shock: surprised me since stock gears, only mods are the ZX pipe and 3.5-10 rear S1 tire, and i guess this open stock upjetted carb if u want to count it. cvt cover is untouched and all cvt is stock! virgin block

Just to verify some more did another 30mi+ trip today to downtown, all around and back. again with copious amounts of WOT, and again solid 300 temps, no fuel cut, running great. I could not be happier :love:

except when I got passed by a grom who assumed i was a stupid tao tao.. or when a lexus suv purposely raced me at a stoplight only to slow down, point and laugh. NO. FN. WAY. :evil: :evil: :evil:

so as much fun as the stock carb meddling is. the above experience fueled a flame thats been gassed out for ages.
no more silly groms or suv *, time to do a real Dio build. :twisted:
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