Mikuni VM28-418

[zingshoen]

this is good: http://www.mikuni-topham.de/DEUTSCHS.../VM28-418.html



as u can see, the carbie fits. i took out the nox reduction and used the bracket to support the carburettor. also cut open the airbox and stuck an angled unifilter on, using the original suction pipe to get past the monoshock. the blue goo is air filter oil.







the zongshen cable needs minor adjustments, shave the end bit on a piece of sandpaper to fit into the slider of the mikuni. i screwed the spacer on the top of the zs carbie onto the mikuni no problem. a close fit, but it works. mind you i also shortened the plastic intake piece between carb and cyl a little and widened it slightly.

the fuel intake on the carb is on the opposite side, so extra fuel line is needed. the choke stays clear of the petcock.



and i m pleased to report that the zs rocks. it is no surprise as it is a mod recommended on the tw200 website. it s a flat slide carbie and i am using a 230 mikuni main jet these days. i ve had this carbie for about 1500 ks now. of course you also need an unrestricted header pipe and muffler, but i had them already

[Weldangrind]

That's cool. 8) I've never played with a flat slide.

What kind of muffler are you running? Also, I see from your sig that you have an XL185; have you considered an XR200R cylinder and piston? As far as I can tell, the stroke is the same between the two engines and only the bore is different. As well, the R version has a 10:1 piston.

[FastDoc]

Spud is going to love this! :P

[SpudRider]

Originally Posted by FastDoc

Spud is going to love this! :P

Indeed! You did a very nice job, ZS. The TW200 forum is a wealth of information for all Zong owners; it is a very valuable resource for us!

Spud

[zingshoen]

i ve had the local exhaust guys make up a header pipe which does away with the u-curve and connected it to a chinese 250 racing muffler (60 A$ = mates' rates) which is completely unrestricted.

weldangrind: as for the xl, i'm considering having it bored up to 200 cc. there s just so many things to do...

off topic: she s a beauty, converted to single seater. btw: my zs is also a single seater, costs half the rego per year down here.

[Weldangrind]

I'd guess that a XR200R cylinder would bolt right on, rather than boring the 185 cylinder. Don't know for sure though. IF you like, I could measure on of our 200 cylinders. Let me know.

[SpudRider]

In the United States we can buy the Mikuni VM28-418 carburetor for less than $120.

http://www.powersportsuperstore.com/.../tr42-6090.htm

If you have time, please answer a few questions. Did you attach your remote choke cable to the Mikuni carburetor? Did you run the stock, Teikei MV28 carburetor with your unrestricted exhaust before you installed the Mikuni carburetor? How did you widen the carburetor boot next to the engine? Does the throttle cable route well to the carburetor?

If you have more photographs, we would love to see them!

Spud

[zingshoen]

yes, will do (as in post pictures, in a few days time). and i ll ask my xl buddy about the 200 cylinder, i think there s sth with the frame being in the way, the engine isn t the problem.

as for the choke cable, the zs here in oz don t have a choke cable.

yes, i ran the stock carbie and modified it substantially. with larger main and idle jets it can work quite well, but with the mikuni its a different bike!

an advantage of the mikuni is the ability to change main jets without disassembling the carbie (the mikuni bowl comes off with the carbie installed).

[katoranger]

That is interesting about the single seat. I removed my rear pegs since I never carried passengers. Just slides. :wink:

You XL looks really clean. I have a friend with two of them.

Allen

[SpudRider]

Originally Posted by zingshoen

...as for the choke cable, the zs here in oz don t have a choke cable...

I'm surprised. The Zong's imported into the United States have so much body plastic around the carburetor, you would never be able to reach a choke knob located on the carburetor, itself! 8O In fact, it is difficult to even reach the fuel petcock. :roll:

Originally Posted by zingshoen

...yes, i ran the stock carbie and modified it substantially. with larger main and idle jets it can work quite well, but with the mikuni its a different bike!...

That is good to know. My Zong has more power after I removed the highly restrictive, stock muffler, and installed an FMF Universal Spark Arrestor. If the Mikuni VM428-418 increases power even more, I will certainly consider getting one of these carburetors.

Thank you for your willingness to post more photos! We Zong owners would love to learn more about your installation of this Mikuni carburetor.

Spud

[zingshoen]

after trying a few things over the years i would like to report on the best jetting i ve achieved so far with the Mikuni VM 28-418 on my Zongshen GY 200 (the Yamaha clone fondly referred to a YamaZong by Spudrider)

Bear in mind that the bike has an unrestricted muffler, a unifilter, a half turn throttle and a 14/46 sprocket combo.
I ve changed the main jet, the needle jet and the needle.

main jet = 280
needle jet = Q - 0 of the 176 series
jet needle = J8-5J09 - 4th slot from the top

if you read the long post about trying to jet the Mikuni to work well on the TW200 forum you get the impression that it is a waste of time. But my experience is different. With the above jetting the bike is quick for what it is, and superbly responsive across the rpm range. The quirks of a flat slide (which doesn t handle sudden WOT and CT [closed throttle] as well as velocity carbs) are negligible, no stumbling or stalling.

[Weldangrind]

What is the top speed so far? Since that's a good indication of hp, it's a good measuring stick.

[zingshoen]

i do 80 km/h with a lot of headroom left, but vibration makes more than 90 km/h unpleasant. the power increase is very noticeable in acceleration.

[Weldangrind]

How are cold starts? What type of cold start device does it have? I've haven't looked closely enough at flat slides to determine if they have a choke or fuel enrichment circuit.

[zingshoen]

it has a choke, visible in the top photo as a brassy handle between carbie body and cylinder just to the left of the slide idle adjuster. i fire her up with the choke, but take it out after a few seconds.