Polini carb kit and Gianelli pipe installed.

[sippin.fnordies]

I ordered the Polini carb kit and Gianelli pipe from SIP awhile back and installed them yesterday. I'm pretty impressed so far.
It turns out the polini carb kit is a mikuni carb with a polini intake manifold. Aside from some fiddling with the new "choke" everything went together smoothly and fit wonderfully. I did end up matching the phenolic spacer to the intake manifold with a dremel, but that wasn't strictly necessary.
The Gianelli pipe also fit pretty well though I had to do a little "adjusting" to get everything where I needed it at the back. A few minutes with a length of pipe fitted over the tailpipe moved everything to where I wanted it to be.

I still need to do some fine tuning on the carb (today), but I couldn't be happier with everything.
Sound is great, low and rumbly without being particularly loud. Engine now pulls a little harder and doesn't run out of breath like it used to. Easily pulls all the way to 45-48mph in 3rd. Haven't gotten it out on the highway to see if the top speed improved yet, but I won't be surprised if I can hit and hold 70 (indicated) on the flats.
Seems to climb steep hills as well as it ever did. No real gains in torque, but that will all change when I get the 165cc BBK.

To all of those that said that doing intake and exhaust mods on a 4t is pointless...Ya'll are wrong. The difference isn't magic, but it is noticeable. Feels less restricted. Totally worth it.







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[JohnKiniston]

Way cool.

What jetting are you running?

Does the pipe block the oil drain plug?

[az_slynch]

Way cool.

What jetting are you running?

Does the pipe block the oil drain plug?

John, keep in mind that different manufacturers use different numbering schemes for their jets. His number's won't translate to Dell'Ortos.

Sippin.fnordies, thank you for taking the next step. The 4T has so much potential and it rocks to see someone tappin' into it.

[JohnKiniston]

Way cool.

John, keep in mind that different manufacturers use different numbering schemes for their jets. His number's won't translate to Dell'Ortos.

I know, It's still information that could help someone else out in the future.

[sippin.fnordies]

Currently running the jets that come with the kit. Main is a 100, not sure what the slow jet is, I couldn't find a marking on it . I'm planning on tuning it today, but riding around yesterday I'm pretty sure the jetting is damn close to perfect. The mixture screw is located in the worst place ever...not sure how im going to adjust without removing the carb...then Im not sure how I will ever get it right if I have to take the carb on and off to adjust.

As for the exhaust blocking the oil drain, it doesn't seem to at all. Im sure a few drips will make it onto the exhaust during oil changes, but it shouldn't be in the way. That was one of the first things I checked when I got the pipe on. edit:it looks way worse in the picture, must be the angle

[sippin.fnordies]

Just got back from a ride. Top speed seems to have changed little. 65mph indicated (no windscreen, full tuck). I did feel it might have gone a bit faster, traffic had other ideas.
Man what a fun bike
I ordered a small tach to try and figure out what this motor is revving to, seems like over 7k, maybe 8k or so...I'll let ya'll know.

on a tangential note...
Does anyone know where I may be able to get a cam? just looking for a stock one...thought I might do a little re-grinding and see what kind of gains/losses i get. I have a feeling these little motors are a lot more capable than they are generally given credit for. Looking at the head casting there is A LOT to be improved there too. I plan on doing a little port/polish work when I have the motor apart for the 165cc kit (it'll be awhile)
I also have plans to make the timing a bit more adjustable. I may work on that one today.
I know our bikes come tuned for economy and I know I could spend a bit less money ultimately on a 2t and make it go quite a bit faster, but I don't like the massive pollution factor of a 2stroke.

[az_slynch]

You should be able to order OE parts from Genuine. Our local dealer was able to order a new stator for John and is ordering me a few engine gasket kits.

You can try WebCam for re-grinding a camshaft. Might consider using a motocross (MX) profile in order to get mid to high-end power. I'm studying a similar mod for my Elite 80 build. I plan to do a comparison between the "stock" and "high-lift, high-rpm" cam that Endrigo Racing makes for CN250 motors (Helix), as I'm working on rebuilding and tuning one for a local and MB'er who wants to "power tour" on his Helix.

They also offer a heavily ported head for the Helix, which I think will be useful for his build, but also for looking at "where to port" when I finally get my 4T Stella. I totally agree; the porting on the 4T is very restrictive and could flow much beter with appropriate porting.

For timing, MRP made a stepped woodruff key which could move timing on a GY6 by +/- 5 degrees. I'd need to look at John's 4T Stella again to see if it would work in this application. The 4T uses the same CDI box as the Honda Elite 80, the Dio line and other smaller Hondas from the 80's and '90s. I know there are several boxes out there that have adjustable advance curves and some have selectable retard-points. Use the key to advance timing off a traffic light, then retard for high-end power. Another trick I've read of was to tack a bit of metal onto the leading edge of the flywheel tab to trigger the pulser coil earlier.

[JohnKiniston]

Here's an adjustable CDI marketed for the Star which is the Stella overseas.

http://www.ekmpowershop2.com/ekmps/shop ... 6130-p.asp

Here's a pair of cheap CDI's on ebay that may also work based on our findings with the Honda CDI:

http://www.ebay.com/itm/400434533055?ss ... 1438.l2649

http://www.ebay.com/itm/280970264330?ss ... 1438.l2649

[ericalm]

Just got back from a ride. Top speed seems to have changed little. 65mph indicated (no windscreen, full tuck). I did feel it might have gone a bit faster, traffic had other ideas.

YESSS!

That's what I want to hear!

[sippin.fnordies]

just a cheap-o one, induction type. The sample rate is really poor, so it's only good for things like adjusting idle and recording max RPMs.
here is the cool part...under certain conditions I've hit about 8600 rpm and the engine pulls all the way to about 7800-8000 before it levels off. According to the factory specs, peak hp is 6500-6800 rpm. So the carb and pipe freed up 1000-2000 rpm up top
Now hopefully someone else will install a tach and confirm the stock motor runs out breath at 6500...either that or I will have to re-install the stock carb and exhaust just to test it

[viney266]

YES, a mikuni carb!. Something you can adjust and get parts for CHEAP. Thank God. I fooled with one of the Dell ortos on the pinasco kit and could NOT get it to quit fouling plugs down low...just terrible. ...and believe me I tried.

Really excited to see this kit...The "expansion chamber" on the pipe is a bit odd on a 4t?

[magnato1]

YES, a mikuni carb!. Something you can adjust and get parts for CHEAP. Thank God. I fooled with one of the Dell ortos on the pinasco kit and could NOT get it to quit fouling plugs down low...just terrible. ...and believe me I tried.

Really excited to see this kit...The "expansion chamber" on the pipe is a bit odd on a 4t?

Agreed, the expansion chamber is really weird. Anybody have an explanation for it?

[sippin.fnordies]

Yeah, agreed. The expansion chamber is probably wasted on the 4T...
That said, the engine should "recognize" the large diameter change as the end of the pipe. This effectively works like a open header, but with the benefit of a muffler (I find loud pipes annoying ).
When I start playing with cam profiles on this thing I may be able to get a nice bit of power in the top end because of the design. The only time 4 strokes benefit from the negative pressure wave (like an expansion chamber provides) is at fairly narrow and high RPM range and when running a fairly big cam with a LOT of overlap. There are better ways to design exhaust to make this happen, but I didn't have to design this one, just buy it
this pic may be of a porsche engine, but it does demonstrate an 4 stroke exhaust system that both significantly quiets and doesn't rob hp...
http://quiethorsepower.com/images/side_914-6.jpg
notice the expansion chamber...
(I know it is of a completely different design, but that may be more because of space constraints of a flat 6 in the rear of a Porsche. I really don't know.)

[az_slynch]

YES, a mikuni carb!. Something you can adjust and get parts for CHEAP. Thank God. I fooled with one of the Dell ortos on the pinasco kit and could NOT get it to quit fouling plugs down low...just terrible. ...and believe me I tried.

Working on the Dell'Orto problem after Amerivespa. The problem is that it's not my 4T. Can't wait until I have my own to tinker with!

I'd bet that the biggest issue with that carb, based on the issues described by you and others, is that the throttle slide is wrong. It's a #30 slide, which generates serious vacuum at low throttle (idle to half). I'd swap with a #40 slide to reduce low speed vacuum.

[Cmarsh]

where is the idle screw?

[Johnny O]

Idle screw is on the side. That is the one you can adjust easily with everything assembled. The air screw is likely what you're looking for...its under the intake venturi in front of the carb. You should be able to get a aftermarket air screw that can be adjusted without having to remove the carb. I haven't tried to replace mine yet. Follow instruction for tuning here:

http://www.mikuni.com/pdf/vmmanual.pdf

I found that 2.5 turns out runs well with the Pinasco Symphony pipe and a K&N filter with no throttle body elbow (stock air box removed). Mikuni manual says any more than 3 turns out on the air screw and you could lose it since the spring isn't offering any resistance beyond 3 turns.

I think this air screw will work with the VM22 (Polini kit):

http://www.jpcycles.com/product/401-193 ... aQodicoC2w

[Cmarsh]

thank you ....

[jmer1234]

I think this air screw will work with the VM22 (Polini kit):

http://www.jpcycles.com/product/401-193 ... aQodicoC2w

In fact, this screw will not work. It is for a larger bore Mikuni carb; the carb in the Polini kit is a Mikuni VM22-133. I ordered this one out of Canada: http://www.minimobracing.com/store/p327 ... _info.html

The drilled holes are good because I still could't turn the screw once it was installed without fashioning a pushrod out of a coat hanger.

I ended up putting a Delorto 102 primary jet in it. I am in San Antonio at ~500 ft. At the moment, I have left the stock idle jet in and just opened the jet a little to enrich it. Stock air filter and exhaust, and the carb kit is a night and day difference for me.

[Johnny O]

Thanks for clearing that up.....I wasn't sure. Do you have the part number and a linky to where you ordered the 102 Main from? I'm looking for a simple winter project to do and that looks like a good one.

I'm also wondering how many turns out you think you have on that screw? If I recall, 2.5 turns out was my sweet spot. Thanks!

[jmer1234]

For the jetting, I wasn't sure which way it was going to go so I went ahead and bought 2 kits. http://www.sip-scootershop.com/en/produ ... +_40100000 and http://www.sip-scootershop.com/en/produ ... +_40100200

That gave me a full range from 75 - 120. The carb comes with a 100 primary.

The idle screw came with a default setting at 1 turn out. I am not sure where I settled in at, but if I had to guess, it is somewhere around 1.5 turns out.

One final note, about the choke. The spring supplied is very strong, and must be compressed quite a bit when the choke cable is installed. Every time I would pull the choke knob (which only has about 1/3 to 1/2 inch of travel compared to the generous 1+ inch of the stock carb) it would pul right back in. I ended cutting about 3 turns off of the spring, and now it is perfect.

[Johnny O]

Good call about the choke spring mine behaves the same......I didn't think to try that. Thanks for the info!