2012 Stella 4T jets

Crew · Post by **Crew** » Fri Nov 09, 2012 11:30 pm

I'm living in the Pacific North West and purchased my Stella 4 stroke in August of this year. During the break-in period I was checking the plug and noticed that the scooter was running very lean (I'm at sea level) so adjustments were made to the fuel mixture which helped the bottom end but the engine was still lean at hyway speeds. Now that winter is here and because of the air temp getting down towards zero Celsius the scooter is once again very lean and performance has dropped off at higher throttle settings. I am going to change the jets and was wondering if anyone has an idea of the stock jet sizes that the scooter comes with?
Crew

Crew · Post by **Crew** » Wed Nov 14, 2012 2:27 am

Well seeing as I have had no response to my query I decided after seeing a video on Vimeo to remove the carb and check the jet sizes as well as check the fuel bowl for any debris which I did find. I also ran a fishing line through the jets to free up any contaminants and made sure they were clear. The scooter idles a bit better now and the jet sizes were 40 for the slow jet and 90 for the main jet. Seeing as I'm at sea level and the temps are averaging 40+ deg the Stella is running exceptionally lean, it was a bit lean during the summer as well but now there is a definite loss of power in the mid to high end. So I will be ordering a few jets to enrich the mix. Would anyone in North America know of a place that carries the correct jets for the Stella 4T carb?

magnato1 · Post by **magnato1** » Wed Nov 14, 2012 5:19 am

I'd call Scooterworks, they're supposed to be the supplier for all things Genuine (you probably already know this, but thought I'd state the obvious). They're located in Chicago.

Crew · Post by **Crew** » Wed Nov 14, 2012 7:10 am

Thanks magnato1, I,ll check with them.

magnato1 · Post by **magnato1** » Wed Nov 14, 2012 8:44 am

Crew,

Sorry I can't be of more help, but I only have 300 miles on my Stella and I'm not sure about the jetting myself. Good luck and let us know what you find out.

Crew · Post by **Crew** » Fri Nov 16, 2012 5:07 am

Just thought I would give an update as to the lean problem I have with my Stella. The scooter shop that I deal with contacted the Genuine Scooter Company and was told where to get the correct jets for the Keihin carburetor (which they said was a 17.5mm carb, PB series) in order to enrich the mix. They also recommended adjusting the needle first by raising it and see if that would help before replacing the jet. So tomorrow I'll start with that recommendation and see how it goes. Although we found the main jet to use which is a number 92 (one size up from stock) we were unable so far to find an idle jet, so the search continues. I'm looking forward to getting some power back in the upper rpm range that the cold has robbed me of.

az_slynch · Post by **az_slynch** » Fri Nov 16, 2012 5:13 pm

How about these?

https://www.denniskirk.com/genuine-keih ... tid=727471

Crew · Post by **Crew** » Fri Nov 16, 2012 5:32 pm

Those are a little big I think. Everything is still stock on the scooter and main jets I have. Looking now for idle jets to fit a Keinin PB18 side draft.
Thanks anyway.

jartist · Post by **jartist** » Sat Nov 17, 2012 5:44 pm

I've done a little bit of carb tuning on a carb with a slide needle on a motorcycle and every carb has different overlap of the circuits but here's what I found. I had mid range lean surging and raising the needle one shim fixed it. Basically raising the needle will make the main come on sooner but won't change wide open throttle at all. Idle jet shouldn't make that much difference on the top end but it will minutely. 3/4 to full throttle you'll get the most response changing the main jet so I'd want to start there myself based on what you want. Main thing is to go slow, only change one thing at a time and don't be afraid to go back to baseline. I'd want to make the change as simple as possible if you're going to have to make seasonal changes unless you can perfect it to be a compromise for all season riding.

Crew · Post by **Crew** » Sat Nov 17, 2012 6:39 pm

jartist, thanks for the insight. I believe you are right. I did raise the needle yesterday and it made a world of difference. She comes on strong in the mid-range and the idle is now more stable. I am concerned about WOT as I do a fair amount of commuting between towns, so I will take your advice regarding the main jet for WOT and change it from a #90 to a #92.
One thing I found when raising the needle was that there were no adjustment slots for the circlip. There is only one slot which is factory set. What I did was add a 1/32 flat nylon washer to the bottom of the circlip to raise the needle and it worked beautifully.

jartist · Post by **jartist** » Sun Nov 18, 2012 12:14 am

Glad shimming the needle out worked for you. If that gave you the top end you wanted you could probably stop there. I don't think there's as much worry about engine seizures on the 4t as with a 2t, especially with stock jetting but one size up couldn't hurt anything. I'll bet you end up keeping the same carb settings in the summer

Crew · Post by **Crew** » Sun Nov 18, 2012 12:19 am

It was lean in the summer, your right I'll keep the settings next summer. I just got back from a ride and it still needs a wee bit more at the top end so I'll try the main jet later next week.

Crew · Post by **Crew** » Sat Nov 24, 2012 10:46 pm

Well I have now changed the main jet to a number 92 and the scooter runs strong through the entire range and the idle is solid. This scooter was way too lean from the factory and the difference is like night and day. Compared to the way it is running now I'd say that when new it was running sickly.
I am now considering the summer and the fact that it might be a tad rich so I am considering opening the stock pipe and removing the foil used in the exhaust and giving it a less restricted flow as well as looking at a slight modification to the air filter but that is another day., for now it is a very nice ride.

jartist · Post by **jartist** » Sun Nov 25, 2012 6:17 am

I'm glad you got it sorted by using tried and true methods. I'll bet more people end up following you're lead on this one.

Maximus53 · Post by **Maximus53** » Sun Nov 25, 2012 3:59 pm

I have seen a lot of information on doing 'plug chops' on 2-strokes, is the process the same on a 4-stroke?

Crew · Post by **Crew** » Sun Nov 25, 2012 9:35 pm

Not that I am an authority on the subject but from my research so far and the from results that I've seen the settings for the four stroke are not as critical as the two stroke. Still with that in mind it would be an advantage for a four stroke tuned without any unnecessary heat do to a lean mix for longevity sake. Just a note to my improvements, I am at sea level with an average temp between 38 and 44 degrees at this time of year and I am running an NGK CR7EH-9 plug with an NGK spark plug cap.

Crew · Post by **Crew** » Tue Nov 27, 2012 5:50 am

I was noticing that after the changes I have made to the carb that it seemed a tad rich so I pulled the plug today and sure enough it was. I then removed the nylon washer I had used as a spacer to raise the needle and sanded it down by half its original thickness and tried that. Well it still pulls smooth and strong through the full range in each gear but now has even more power in so much that it pulls harder and is quicker to get through the power band and has a nice bark to the pipe. I believe I've found the sweet spot for this lovely little scooter. The cost to get the Stella running like a champ is one main jet at about four bucks and a nylon washer at about ten cents (oh yes, and a little Sea Foam for carb maintenance).

jartist · Post by **jartist** » Tue Nov 27, 2012 8:36 am

You might find a brass washer is a bit thinner than the nylon ones. The klr650 guys use little brass washers but I don't know if they'd be too big for the little Stella carb.

Crew · Post by **Crew** » Tue Nov 27, 2012 8:41 am

OK Jartist I'll look into it. Thank You