Re-Jetting a Stella 4T

djp4059 · Post by **djp4059** » Mon May 26, 2014 10:52 pm

If anyone is thinking about re-jetting your scooter, because you modified your air intake or put on a performance exhaust, jetsrus.com has them. The main jets are here http://www.jetsrus.com/a_jets_by_carbur ... 38-xxx.htm the stock main jet is a 90. The slow jets are here http://www.jetsrus.com/a_jets_by_carbur ... 27-xxx.htm the stock slow jet is a 40.

I put on a Sito Plus exhaust and just swapped out the jets, put in a 92 main jet and a 42 slow jet. Performance is pretty good I may move up to a 45 main jet or raise the needle jet by lowering the clip one notch.

Does anyone know of a good intake mod (better air filter or box modification)?

az_slynch · Post by **az_slynch** » Wed May 28, 2014 4:08 am

djp4059 wrote: Does anyone know of a good intake mod (better air filter or box modification)?

Try this on for size:

https://www.treatland.tv/SearchResults. ... air+filter

https://www.treatland.tv/SearchResults. ... air+filter

https://www.treatland.tv/SearchResults. ... air+filter

I picked up a Pinasco kit from jimmbomb for a buddy's bike (which is still down...) and got this one to go with it:

https://www.treatland.tv/polini-PHBG-ai ... 3.0080.htm

slotrod65 · Post by **slotrod65** » Wed May 28, 2014 4:55 pm

Thanks for the jetting info.

I have a Tasso orange coil, a Brisk plug, a Ram Air foam air filter and a GPR exhaust. I checked the plugs and I am running a little lean.

Orange coil (Tasso) - HT Coil Hi Power with plug cap - Part No: VE50053

Plug: AOR14LGS Brisk High Performance Motor Cycle Special Silver Electrode Spark Plug - Ebay item#: 360394108178

Below is the filter I am using. Just a word: The air box muffles a lot of miscellaneous sounds. With the Ram on I can hear gurgling from the carb, and what I believe is some valve train clatter. The guys on the LML UK forum say this is normal. Besides, once I got the GPR exhaust on, it drowned this all out.

http://www.ebay.com/itm/Ramair-Pod-filt ... 43c7440acd

djp4059 · Post by **djp4059** » Wed May 28, 2014 7:37 pm

Thanks for the info on the air filters guys.

Slotrod, as far as reading your spark plug. I have read that there is a certain way of doing this pertaining to motorcycles, ATV's and scooters. They say to do it like this.

"Use a fresh plug or one that has only a few passes on it. This works best in top gear or an upper gear on a slight uphill area. After running the engine at full throttle for about 8 to 10 seconds ( do not run up on the rev limiter as this will give a false reading of the plugs) do the following at the same time: pull in the clutch and hit the kill switch to stop the engine. DO NOT let the engine idle and DO NOT let the clutch out until the vehicle has come to a stop. Remove the spark plug and examine the INSULATOR (the porcelain) color. White is lean and black is rich. Best color is a tan to grayish-white. White means main jet is too small (lean) and black means main jet is too big (rich)."

I had always thought that all you had to do is pull the plug and check the electrode, but evidently I've been doing it wrong.

slotrod65 · Post by **slotrod65** » Wed May 28, 2014 11:51 pm

So how much difference does the idle jet make? I haven't' heard of changing that jet in the past.

djp4059 · Post by **djp4059** » Thu May 29, 2014 9:07 am

According to some jetting charts, the idle jet supplies fuel to the engine through out the throttle range.

http://www.arcticchat.com/forum/attachm ... rcuits.jpg

And they say its the first thing you should change if you need to re-jet your carb.

http://www.jetsrus.com/FAQs/FAQ_rejetti ... _rejet.htm

misterbrackets · Post by **misterbrackets** » Thu May 29, 2014 6:00 pm

slotrod65 wrote: Below is the filter I am using. Just a word: The air box muffles a lot of miscellaneous sounds. With the Ram on I can hear gurgling from the carb, and what I believe is some valve train clatter. The guys on the LML UK forum say this is normal. Besides, once I got the GPR exhaust on, it drowned this all out.

http://www.ebay.com/itm/Ramair-Pod-filt ... 43c7440acd

I assume you're using this with the stock Keihin carb (?) I may try one of these. I'm currently using a RamAir filter, but I put it in the airbox in place of the old one (I bought a size that would fit correctly in there) I'd like to try hooking one up directly to the carb.

Currently I have a Pinasco exhaust and a 98 main and 42 idle jet. It's a tad rich, but was a little lean with the 95. Maybe a slight change in air filter will balance it out. Still, the Stella seems to be running great. (I left the needle where it was originally - after trying it a little lower/higher)

djp4059 · Post by **djp4059** » Thu May 29, 2014 10:07 pm

Currently I have a Pinasco exhaust and a 98 main and 42 idle jet. It's a tad rich, but was a little lean with the 95. Maybe a slight change in air filter will balance it out. Still, the Stella seems to be running great. (I left the needle where it was originally - after trying it a little lower/higher)

You went all the way up to a 98 on the main, I got the 92 and 95 and thought about getting the 98 but thought that would be kind of pushing it to rich, I installed the 95 today and it ran pretty good. I ordered the K&N RC-2310 air filter, its suppose to be delivered tomorrow, and I'm going to put it on when it arrives and see what it does. I'm also going to stop and get a NGK CR9EIX spark plug tomorrow.

If anyone needs to know the outside diameter of the intake side of a Keihin PB-18 its 40.5mm.

djp4059 · Post by **djp4059** » Fri May 30, 2014 10:42 pm

I was going to install my new K & N RC-2310 filter today but it looks like I'll have to remove the entire air box since the rubber intake pipe to the carb is attached to the box, I had thought that all I would have to do is take it off of the air box. I don't want to cut it off of the box incase I want to put it back on later. I also noticed a vacuum line on the intake pipe, looks like it goes to the EVAP (if thats what its called). Since my new air filter has a chrome cap on the end of it, I was thinking about drilling a hole into it and putting a nipple on it to attach the vacuum line. Does anyone have any other ideas about what to do with this vacuum line?

djp4059 · Post by **djp4059** » Sat May 31, 2014 10:14 pm

Here's a pic of what I came up with as far as installing a vacuum line to my air filter.

UPDATE: This didn't work, the vacuum fitting sticks out to far and hits the rear shock absorber.

Tipper · Post by **Tipper** » Sun Jun 01, 2014 8:20 am

The rubber pipe just pulls out of the air box you don't need to cut it.

slotrod65 · Post by **slotrod65** » Tue Jun 03, 2014 7:11 pm

The rubber pipe on my Stella was glued into the airbox. Work it out using a screwdriver.

djp4059 · Post by **djp4059** » Thu Jun 05, 2014 9:10 pm

Since I couldn't connect the EVAP to my last air filter setup, I came up with another idea. I bought a UNI UP-4229AST 2 Stage Pod (angled) with a 2 1/4" ID. I'll have to remove the air box to install this config. I also noticed that the engine breather connects to the air box, so I'll have to find some kind of way to connect that to the vacuum line since its a larger diameter hose.

Has anyone ever tried to connect a mechanical fuel pump like the one below to their scooter. Its a Mikuni Pulse pump.

Neurotic-Hapi-Snak · Post by **Neurotic-Hapi-Snak** » Fri Jun 06, 2014 2:22 am

For the jets, should I go with the genuine Keihin or the generic? Anybody have experience with the generic jets?

slotrod65 · Post by **slotrod65** » Fri Jun 13, 2014 3:48 pm

I finally got to my jetting. Again, I have a Brisk plug, Ram air filter, Tasso hot coil, and a GPR exhaust.

I up jetted to a 93 main and a 42 idle. The scoot seems to run strongly, but she doesn't want to idle, even if I raise the idle screw. She idles for a few minutes and then slows down until she conks out. It is raining like all h&ll, so no road tests today.

Does anyone have any thoughts on the idle situation? Is there anything else I need to adjust after changing the jets?

I also removed the majority of the evap system, if that matters.

misterbrackets · Post by **misterbrackets** » Fri Jun 13, 2014 5:10 pm

You probably need to adjust the mixture screw, which is behind that black plastic cover, if you haven't already removed it. It's a brass-colored screw with a head that requires a small pliers to turn. There are some good tutorials on getting your mixture set properly .... I'll see if I can find one and post it.

djp4059 · Post by **djp4059** » Fri Jun 13, 2014 7:23 pm

Yeah, you need to adjust the the slow jet mixture screw, its to the right of the idle screw, it doesn't have a slot for a flathead screwdriver but you can turn it with needle nose pliers (I took it out and used a dremel with a cutting disc and cut a slot into it). To adjust it you need a tach. First before you start the engine turn the screw all the way in until it seats lightly, then turn it out one and a half turns. Then start your engine, let it warm up then turn the screw a quarter turn either way wait about 10 seconds and see what your rpm's are. You want to adjust this screw until you find its highest rpm (only turn 1/4 turn at a time and wait 10 seconds each time to allow the engine to react). If the rpm's go down when you turn it in one direction, then turn it the opposite way. They say if you have to turn it out more then 2 and a half times to get your highest rpm's then you need to up the jet one more size. Once you find its highest rpm then adjust your idle screw to around 1100 rpm's.

misterbrackets · Post by **misterbrackets** » Fri Jun 13, 2014 8:45 pm

djp4059 wrote:Yeah, you need to adjust the the slow jet mixture screw, its to the right of the idle screw, it doesn't have a slot for a flathead screwdriver but you can turn it with needle nose pliers (I took it out and used a dremel with a cutting disc and cut a slot into it). To adjust it you need a tach. First before you start the engine turn the screw all the way in until it seats lightly, then turn it out one and a half turns. Then start your engine, let it warm up then turn the screw a quarter turn either way wait about 10 seconds and see what your rpm's are. You want to adjust this screw until you find its highest rpm (only turn 1/4 turn at a time and wait 10 seconds each time to allow the engine to react). If the rpm's go down when you turn it in one direction, then turn it the opposite way. They say if you have to turn it out more then 2 and a half times to get your highest rpm's then you need to up the jet one more size. Once you find its highest rpm then adjust your idle screw to around 1100 rpm's.

Yeah --- these are the steps I went through when I did mine. One thing I might add is that it's easier to adjust the mixture if you set the idle a little high - like 1500 or so - then dial it back down after you've gotten the mixture set. Also, you don't absolutely need a tachometer to do it because you can hear the changes in revs when you turn the mixture screw, but it takes out the guesswork.

Oh --- and definitely make sure the engine is nice and warmed up. Take it for a short spin if the rain lets up momentarily.....

djp4059 · Post by **djp4059** » Sat Jun 14, 2014 1:13 am

Here's a good webpage that details the re-jetting procedure

http://www.jetsrus.com/FAQs/FAQ_rejetti ... _rejet.htm

slotrod65 · Post by **slotrod65** » Sat Jun 14, 2014 11:44 am

Thanks guys, I do have a tach. So I will give this a try and let you know how I make out.

Neurotic-Hapi-Snak · Post by **Neurotic-Hapi-Snak** » Sat Jun 14, 2014 12:39 pm

What kind of tach are you guys using? The laser/optical kind or the induction (spark plug wire) kind? Any suggestions on a good one?

djp4059 · Post by **djp4059** » Sat Jun 14, 2014 7:19 pm

I bought a Tiny Tach which I'll mount in my scooter one of these days.

http://www.tinytach.com/tinytach.php

And there are some others on this thread topic27226.html that are quite nice also.

And I recently bought an Innova 3340A Digital Automotive Tester which has a tach built into it.

http://www.amazon.com/INNOVA-3340-Autom ... B000KIMHRQ

Both wrap the spark plug wire.

slotrod65 · Post by **slotrod65** » Sun Jun 15, 2014 1:28 am

So I had some time this evening, and adjusted the idle mixture. I ended up backing it out a total of 2 1/4 turns, and I could probably go up another jet size. But, on the test run, the backfire and popping are almost gone when I let off the throttle at speed, and she just pulls in the mid range. In 4th gear, She used to really lug, but now she pulls instead. Even as low as 30 mph. I will drive her as is for now and see how things go.

Modern Buddy

Re-Jetting a Stella 4T

Re-Jetting a Stella 4T

Re: Re-Jetting a Stella 4T