Carb upgrade ( PZ30 to Mikuni VM3* )

Hi,

I have a Shineray XY250GY-2 SuperMoto. It comes with PZ30 carb which is very common in chinese bikes. I want to put a mikuni VM carburator. But I couldn't decide VM30, 32 or 34mm.

I think PZ30 has 100 main and 20 pilot(slow) jets (or close).

For Mikunies;

VM30: 250 main, 40 pilot
VM32: 200 main, 35 pilot
VM34: 260 main, 35 pilot jets...

Take a look;
http://www.motorcyclecarbs.com/About...etors_W143.cfm

I am confused with these numbers. I know carb. setting is not so simple but main jets are the biggest factor in performance. So in here, don't the main jets seem a little bit inconsistent ??

And another thing, when I checked the link above, VM32 has largest volume(acrd. to dimensions). It should be better for good fuel/air mixture IMO. Isn't it??

I can get a VM32 but not sure for jets...Do you have any suggestion for a jet combination? (There are jet kits for VM carbs.)

Merhaba.

Did you find out what kind of carbs and jets are on the engines with same displacement and similar construction (similar compression ratio, DOHC, 4V ...)? I would use someone else's successful formula to achive engine's optimum performance.

By the way, since you are the sole owner of the XY 250 GY-2 in this forum, could you make for us its detailed walkaround?

Selam,

Sorry for late reply. I am still searching...

It was a good idea. I searched the NX250 carb. Which I find is; #142 main and #38 pilot jet. And this a carb. rebuild kit for NX250 ; #138/38 main/pilot. The NX is known as a inconvenient bike to modify.

I also searched Yamaha TTR250, which has a similar DOHC+4Valve, ~25hp engine , and it uses #142/48 or #147/50 main/pilot jets. And for re-jet, users tried 138~152 main jet numbers. And I found a comparison for Mikuni-Yamaha jets. As we can see numbers are not same but very close for equivalent dyno power.

I forgot to look for KLR/KLX - 250.

Actually, a 30 or 32mm carb. is normal for a 250cc but Mıkuni's numbers are a bit weird. And I checked the link on my first mssg again, in the fist table;
"Dim A=40 mm(Intake Manif.)" for VM30,32,34 carbs. Does that mean it is a 40mm carb.? But I don't think Mikuni is fool enough to give a name VM30 for carb. which is actually 40mm. I think there is a big conflict on Mikuni numbering. I hope I will solve it...:confused1:

By the way, I am new in forum and I thougt XY-2 is well known here... I will make a good walkaround vid. when I get a good cam. from someone :thumbsup:

40 mm on a 1/4 of a liter, ~25 HP, engine - looks like overkill to me.

However, you see that the 40 mm refers to the diameter of a intake manfold. My experience with all kinds of Chinese two-wheelers says that carburetor diameter and manfold diameter does not have to be the same.

hi

the first problem is you cant fit a 40mm mikuni carb between the frame where it must be located in front of the intake manifold !!!!

some of VM series carb are for 2 stroke engines be aware cause the jet numbers are confusing and go for mikuni TM 33 or more

I realised that numbers on the jets can mean (at least) three things:
1. diameter of the jet orifice.
2. flow of fuel during a defined time and conditions
3. arbitrary number determined by carburetor/jet manufacturer

Why does have to be simple, when it can be complicated? :eek2:

Quote:

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Originally Posted by Nima Naderi

hi

the first problem is you cant fit a 40mm mikuni carb between the frame where it must be located in front of the intake manifold !!!!

some of VM series carb are for 2 stroke engines be aware cause the jet numbers are confusing and go for mikuni TM 33 or more

---

Thanks Nima. Actually we also not sure it(VM34mm) is a 40mm carb or not. But I know people do VM34 fit to this bike. I talked with them.

I checked the TM series. Commonly, they are claimed to give better perf. than VM's(also higher prices). And I saw TM33 (and TM36,TM40) has accelarator pump.
http://www.sudco.com/mikuni3.html and http://www.motorcyclecarbs.com/Mikun..._W138C1395.cfm

Other TM's don't use accl. pump like VM series.

TM33 uses #127,5/37,5 main/pilot jets but TM34(no pump) has #280/50 jetts as standart. So I think, accl. pump lets to use much smaller jetts bec. of different working characteristic. @Zorge this may be the reason of number confusing...I was thinking #280 or 260 is too much for a 250cc.

Now can we say, with the right jetting, TM33 is able to give better performance (also better fuel efficiency) than TM34 because of accl. pump ? I am comparing because TM33 is 50~70$ more expensive. I started to think It will be a good choice

Komşu, if you saw same bike as yours fitted with carb with accelerator pump, I think that yоur search is over. Buy it!

Quote:

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Originally Posted by Zorge

Komşu, if you saw same bike as yours fitted with carb with accelerator pump, I think that yоur search is over. Buy it!

---

:D The guys were from sweeden I talked(e-mailed) :lol8: They had fitted MV34 to their bike(which has no pump.) They had raced with the motocross model of this bike 2~3 years ago. And they made certain changes; cam shafts, Big bore kits, Exhaust modify etc....

I will measure the space for the carb. on my bike. If TM33 is OK, I will go with it. Otherwise I will get a MV34 which is smaller and cheaper.

Yes, the "search" seems almost over, but searching on forums never ends :clap: I like to talk with experienced people ;)

I like to talk with big breasted, preferably unexperienced, girls- it's more... informative. But it's only me...

By the way, the carburetor with acceleration pump is a wonderful thing. Perhaps classic design carburetor can give better overall performance, but the acceleration pump gives smoother ride without hiccups.

when the size of your main jet exceed 190(more or less) be sure, that carb wont respond on a 4 stroke engine nor designed to do so

all 4 stroke high performance carb from mikuni (as i use TM 33 pumper on my 200CC!!) use acc pump and flat side pistons

a guy fits the mikuni TM 40 by cutting the frame and rewelding it on the same shinery here ... the performance was great

@Nima :thumbsup: This is a brief & net info, thanks for that. I will go with the TM33.

I checked the space on my bike and yes, TM33 seems a little large for it.

I couldn't find any topic about it but you said "we cut the frame" at here; http://www.mychinamoto.com/forums/sh...ll=1#post39514

I would like to learn details (what part of the frame should be cutted and how did you handle with it...) if you can tell a little.

he cut the frame in exact location where top of the carb most fit and some how make some space there

and reweld the frame with keeping that space between .... but i think TM 33 + rejetting properly will do the same

if u have problem with the bracket that holds the throthle cables dont worry it can be redesigned ...sorry for bad dictation

Ok :thumbsup: "Cutting the frame" sounds scary but I will look at there again when I take of fuel tank and plastics.

Not the bracket but I hope I will not have problem with the rubber flange btw carb. and engine(intake manifold). I found some flanges for Mikuni-VM series but not sure to fit to TM33...

http://www.pic1.iran-forum.ir/images...5706511245.jpg
http://www.pic1.iran-forum.ir/images...4611483412.jpg

i found the guy and take these pretty much the same but not exactly the same lol ....TM 36 pumper by mikuni

That is great to see someone fitted a TM to these shinerays...:clap: Thanks...:thumbsup: I think he didn't neet to cut its frame or did he?

What does he say about perfomance(top end or acceleration or throttle resonse...) and fuel consnsumption change?? I wonder is there excessive fuel cons. increase...? If u can u ask when u see him again :bowdown: ;))

you can see such things only in IRAN ....lol

let's see : the frame was cutted and make sufficient room for the beast

The performance as far as i see was good he climbed a hill with third gear and i did the same with my 200 @first gear !!!

When it comes to tunning or changing a carb dont worry about consumption ... fuel will be burned much accurate and more power will be delivered ... so just reev it (in case u did the upgrade and adjustments right )

just a bit problem when the engine is getting so hot ...it seems that the fuel kinda exceed the need of engine and start to mallfunction a little

(i think there is something wrong with his jetting and adjustments .need some one expert to trouble shout )

cheers:)

Custom made intake manfold was not an option?

i think he use the same part from honda AX1....with little modifications

I've been working hard, couldn't write here for a while... :eek2:

Thanks Nima, nice pics. :thumbsup:

I ordered TM33 days ago, waiting now:rolleyes1:

I think I may not need to cut the frame, I have an idea. I'll try and tell here when mounting.

Our intake manifold is made combined with radiator connection rubber,,,, like this (pics. are from NX250);
http://i.ebayimg.com/t/HONDA-NX250-N...jRdyI!~~_1.JPG
http://i.ebayimg.com/t/88-90-Honda-N...KUBM4!~~_1.JPG

And my origianal, PZ30 carb is;
http://www.scooterparts4less.com/web...Choke_logo.jpg
There are bolt holes on it for mounting.


And the comming carb., TM33 ;
http://i.ebayimg.com/t/New-Mikuni-Fl...lKQrw~~0_1.JPG
http://www.motorcyclecarbs.com/image.../tm33-8012.jpg
No holes for bolt...No way to fit orginal manifold.


First of all, the new one has larger spigot(engine intake hole) and air intake diameters. So I'll need 2 new manifold, 1for engine mounting and the other is for air intake.

I found this mikuni engine intake manifold is for TM33, dimensions are ok;
http://i.ebayimg.com/t/NEW-RUBBER-IN...mSQsj!~~_1.JPG
But I can't remove the original one totaly bec. of radiator connection. May be I'll cut some part of it.


Now I'am looking for new carb. air intake manifold(plastic, rubber anythng...). Do you have any idea how I can make a custom one??

Quote:

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Originally Posted by Nima Naderi

just a bit problem when the engine is getting so hot ...it seems that the fuel kinda exceed the need of engine and start to mallfunction a little

---

Most probably this is because the TM36 is too "much" for this bike. Mikuni suggest the TM33 for 200~350 cc bikes, and TM36 for 325~500cc. So TM36 may really give excessive fuel...

Did your friend make any exhaust mod. ??

I do not know whether the intake manfold with this "thing" is necessary in a combination of your motorcycle and TM33, but if there is no curvature needed, new intake manfold could make any skilled turner.

yes ...there was a catalyst converter in the collector and some instruments in the muffler that are absent by now.

my TM 33 on 200 cc is lean even with 127 main jet and lifted needle clip, one up so consider a 134 main jet and may be one ,or more lifting in needle .... the suzuki dr 200 flang is perfect for this carb and i was lucky with this part of modification ...

I got the carb(TM33). Now waiting for the flange.

I will share the photos when I start to work ;)