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View Full Version : Wrong pilot jets (28mm Carb.)



jokerio
04-05-2009, 09:36 AM
I recently bought a U.S. spec RS125 and the thing was almost unridable due to what felt like a way lean carb setting. The parts book says the pilot jet should be a 36 ?
I took my carb apart and found it had a S35 in it, O. K. I thought, that's close, but still couldn't figure out why it ran so poorly.
My dealer finally got a hold of the Aprilia Rep and as it turns out, its supposed to be a S45 pilot jet.
I put the correct jet in and what a difference !
Now when getting back on the throttle at higher rpm's the 1 to 2 second lag time of the engine feeling like you hit the kill switch is gone, along with the very annoying, ka-chung, ka-chung (Technical term) back-lash felt through the chassis when rolling off for slower corners.
I understand that when new, these motors can be very tight feeling but this just didn't feel like a new "tight" motor to me, that just needed break-in.
Now I know why...
Anybody else out there with the same problem ?

ThisEndUp
04-05-2009, 12:12 PM
along with the very annoying, ka-chung, ka-chung (Technical term) back-lash felt through the chassis when rolling off for slower corners.
I understand that when new, these motors can be very tight feeling but this just didn't feel like a new "tight" motor to me, that just needed break-in.
Now I know why...
Anybody else out there with the same problem ?

I can relate to the Ka-chung.

'Checking jet tonight. :cheers:

ThisEndUp
04-07-2009, 03:46 PM
S35 in mine too.

the 45 is what was supposed to be in there?

O.K., what jet IS this?
Idle jet? Yes?
According to AF1 diagram of carb, the 36 is what it should come with.

I'm confused.

strowph
05-17-2009, 12:04 PM
I don't have access to my bike to check the jets, but I do know that the bike was running so lean that I had the engine seize on the track the first time out. Had done 11 careful heat cycles over four days and a little running in the parking lot prior to taking it out for a few "gentle" break in laps seemed to be running fine untill second time down the back straight when it seized. nothing that can't be fixed with a new piston and resleeving but do check your bikes carefully. my plug checks after the heat cycles looked good to me but in retrospect they were so light that I should have realized that the bike was running too lean for cool days. something close the a chocolate brown would have been better than the light tan/ Short version picked up bike on Saturday took it back Wed broke

Gman2005
05-17-2009, 12:17 PM
right lads, your bikes don't have any restriction do they? The manuel is more then likely stating the extra fuel the cats need to work properly. I hope I make sence

frankd_nm
05-18-2009, 05:18 PM
I haven't checked my pilot jet size, but I can tell you that I adjusted my fuel screw to about full open. I started by trying to set it like I would on a 4-stroke, but then thought about my fuel/oil mix when decelerating. I figure I can run rich at and just off idle for the sake of lubrication.

the brit
05-19-2009, 09:47 AM
I guess I should pull my plug and check, ha. I'm up to about 750kms of break-in so far, and the engine's finally starting to losen up. Seems to be starting a little better too, but it's probably part my imagination, part the warmer weather in general.

odie_trackie
05-19-2009, 07:54 PM
Oh, I can totally relate to the ka-chung, ka-chung.

So, this is about the idle jet?

Is the idle jet really item 3 on this (http://www.af1racing.com/store/Scripts/prodList.asp?idCategory=1549) page?

There is another "idle jet" here (http://www.af1racing.com/store/Scripts/prodList.asp?idCategory=1547)


I recently bought a U.S. spec RS125 and the thing was almost unridable due to what felt like a way lean carb setting. The parts book says the pilot jet should be a 36 ?
I took my carb apart and found it had a S35 in it, O. K. I thought, that's close, but still couldn't figure out why it ran so poorly.
My dealer finally got a hold of the Aprilia Rep and as it turns out, its supposed to be a S45 pilot jet.
I put the correct jet in and what a difference !
Now when getting back on the throttle at higher rpm's the 1 to 2 second lag time of the engine feeling like you hit the kill switch is gone, along with the very annoying, ka-chung, ka-chung (Technical term) back-lash felt through the chassis when rolling off for slower corners.
I understand that when new, these motors can be very tight feeling but this just didn't feel like a new "tight" motor to me, that just needed break-in.
Now I know why...
Anybody else out there with the same problem ?

odie_trackie
05-19-2009, 08:06 PM
Ok, as I read the original post, jokerio said "pilot jet". Which one is the pilot jet?

odie_trackie
05-20-2009, 11:59 AM
After doing some digging into this, I think jokerio is was right on the money. Micah seems to agree and I do think my bike (which is absolutely bone stock) is running lean. I found a Dellorto ePaper going into their small displacement carbs. Very informative. Helps locate everything.

Here (http://www.scribd.com/doc/9641108/Dellorto-Manual) is the link. Now, I just need to find out what I have in my carb (I am guessing it's going to be a S35) and find a S45. I would assume AF1 can supply me one. AF1 guys, is this correct?

Oh, and if I am not wrong, the carb in our bikes (or at least they used to be) is a Dellorto PHBH28.

Gman2005
05-20-2009, 03:18 PM
well if you can find an Rotax dealer in the USA, it will be cheaper then what AF1 can offer.

odie_trackie
05-20-2009, 04:53 PM
Oh, check this out. It's a Dell Orto dealer in SF.

Here's the link (http://www.dellortodirect.com/)

odie_trackie
05-31-2009, 06:49 PM
Ok, so I did the S35 -> S45 idle jet swap and just went for a little ride. Way better, much better. No "ka-chung", "ka-chung", "ka-chung" anymore.

The idle screw was out 3 turns and I turned it in 1/2 turn, for a total of 2.5 turns out. Not sure if that's right.

The idle speed screw was turned out a handful of turns but now is only out maybe a turn or possibly two (didn't measure that just yet). The bike starts right up, idles way more consistent and come back down from a high revs like one would expect.

For anyone in the states that has one of these that's still bone stock, I would definitely check their idle jet and change it if it's not the right one.

Thanks to everyone one here who gave help figuring this out.

quagmire
06-01-2009, 11:07 AM
Ok, so I did the S35 -> S45 idle jet swap and just went for a little ride. Way better, much better. No "ka-chung", "ka-chung", "ka-chung" anymore.

The idle screw was out 3 turns and I turned it in 1/2 turn, for a total of 2.5 turns out. Not sure if that's right.

The idle speed screw was turned out a handful of turns but now is only out maybe a turn or possibly two (didn't measure that just yet). The bike starts right up, idles way more consistent and come back down from a high revs like one would expect.

For anyone in the states that has one of these that's still bone stock, I would definitely check their idle jet and change it if it's not the right one.

Thanks to everyone one here who gave help figuring this out.

Where did you get this jet?

odie_trackie
06-01-2009, 12:05 PM
I got it from my Aprilia Dealer. We have one in Downtown San Diego. Only reason why I didn't go through AF1 was the lead time was about half.
The jet was about $20.


Where did you get this jet?

jokerio
06-02-2009, 12:45 PM
Thanks to everyone one here who gave help figuring this out.
You are welcome !

jokerio
06-02-2009, 12:51 PM
If you really want it to run much better, get yourself the 34mm carb that AF1 sells along with the manifold available here...
http://www.af1racing.com/store/Scripts/prodView.asp?idproduct=6888

odie_trackie
06-02-2009, 01:04 PM
Well, of course!! All in good time.


If you really want it to run much better, get yourself the 34mm carb that AF1 sells along with the manifold available here...
http://www.af1racing.com/store/Scripts/prodView.asp?idproduct=6888

odie_trackie
06-02-2009, 01:09 PM
Jokerio,
can you read off the Dell'Orto part # off your 34mm carb? It should be P???34 or something like that.


If you really want it to run much better, get yourself the 34mm carb that AF1 sells along with the manifold available here...
http://www.af1racing.com/store/Scripts/prodView.asp?idproduct=6888

jokerio
06-02-2009, 01:20 PM
Vhsb34

the brit
06-05-2009, 12:56 PM
Just spoke to my local dealer regarding the bike's first service, they mentioned they have been using S65 jets as a fix and have had decent success with them. Sounded like it was a known issue for them. I'll see if it helps after the service :)