Review: Gio 250cc Mikuni carb as a 200cc performance upgrade

suprf1y · 05-09-2009, 02:34 PM

Last week, we received the Gio 250cc Mikuni carb to use as an upgrade to our Giobeast 200 ATV.
The carb is a quality piece. Some say these Mikuni's are from China, but regardless of where they are made, this is my second one, and it works flawlessly.
Direct comparison to the stock carb on the beast, the Mikuni is substantially larger.

The Mikuni on the left has a 30mm opening which narrows down to 22.5 near the slide, while the stocker on the right measures 27, and 20.

Installation was a breeze, and everything bolted right up.

We elected to not install the choke cable, as it was just as easy, and more controllable using the lever on the carb. The Mikuni has 3 detents for choke off, halfway on, and full choke. We use full choke on the cooler mornings, and half choke all other times.

The inlet on the Mikuni is 42mm compared to 40mm on the old carb, but a little heat from a blow dryer, and it slid right on (don't tell my wife).

The results.
After installation, it fired on the first shot. After a bit of a learning curve (more on that later), performance is definitely improved. Power from idle, to the upper RPM is substantially increased. The difference between stock is like night and day. Having 2, its easy to do an A/B comparison. I would say that before it felt OK, but definitely not quick. For me, the stock machine has enough power for utility use, but my son rides much more aggressively, and is really able to take advantage of the extra power.
To quote him, he says 'it flies'.

Installation notes.
The first thing we did was to adjust the air/idle adjustment screw to 1.5 turns, to get a baseline setting. It started, idled, and ran so well, we left it at 1.5.
The Mikuni comes with a 100 main jet. It runs well enough that I don't get the feeling that its lean. I wouldn't say its rich, though, either. When we have time, a 105 main jet will go in. I don't think this is a bad idea.
The stock air breather is a serious restriction, and will NOT work with this carb. The elbow is too small, and along with the foam, anything out of the lower RPM regions and it will bog, and fall on its face. Take the breather off, and its a whole different story. For now, and untill we source a good, free flowing breather, we compromised by using the breather with only the coarse foam element. Its not ideal, but its better than nothing. Suffice to say we are staying out of dusty ares for now.

I have an accelerometer, and plan to do some A/B testing with that to put some numbers to the results.
Stay tuned, but for now, its 2 big thumbs up for the Mikuni carb.
I think a pipe, along with this carb, will turn the beast into a monster

pno420 · 05-10-2009, 06:33 PM

I put this carb on my SLA250 Sunl branded atv,(250cc liquid cooled cn250 motor) and couldnt get it to idle right, it was extremly high, and I checked everything. It seemed to me that the 27mm intake from my chinese keihin pz27 didnt fit it correctly and I was getting an air leak ? The intake manifold seems to be off and it is by 3mm, I even tried ordering another intake made for the carb off ebay (Mikuni 30mm carb intake for a ), but it was the same as my 27mm one !
Is yours the same way ? I might just have a bad carb?

pno420 · 05-10-2009, 06:38 PM

do you have a pic of your intake manifold ?

suprf1y · 05-10-2009, 06:58 PM

I don't have any pics, but the manifold id slightly offset. I forgot all about it, but I did open the phenolic spacer a bit, so there was a good transition between the carb, and the intake.
It idles absolutely perfect, in fact, we have it set lower than the other carb was, because its more stable.

pno420 · 05-10-2009, 07:50 PM

Great, Thanks so I guess I do have the right Intake, your is offset too, do you see the top of the oring on the carb when its screwed to the intake ?
yea it has me stumped, the mikuni seems like such a better quality carb to. I tried checking the throttle cable, Disconnected it, made sure the slide was in correct, even tried changing the pilot jet to a bigger jet, I thought maybe it was running lean causing it to not idle down . I put a 25, then 40 pilot, and a 120 main in it, I got it with a 20 pil and 100 MAIN. I do have a uni air intake and mrp exhaust so thats why I increased my Jetting.
The keihin runs ok but its a little lean and I cant find The odd pilot jet that was in that carb, so I tried the Mikuni but get that high idle situation and the idle air screws does nothing to change the idle at all.
I either need to find the odd 33mm long kehin pz27 pilot jet, or figure out why the Mikuni idles high? Anyone ever have that problem ? Maybe a bad Float ?

pno420 · 05-10-2009, 07:53 PM

nice to see someone else upgrading there chinese atv. What other mods have you done ?

pno420 · 05-10-2009, 08:00 PM

Is this your intake ? http://img.auctiva.com/imgdata/4/7/8...05504953_o.jpg

turnerburner94 · 05-25-2009, 10:31 AM

The carb is a good buy in my opinion. It makes my bike start better, it is more responsive, and has more power. It makes the motor into good from blah.

pno420 · 05-26-2009, 01:48 PM

Quote:

Originally Posted by turnerburner94

The carb is a good buy in my opinion. It makes my bike start better, it is more responsive, and has more power. It makes the motor into good from blah.

It made mine go from good to blah !! Just the opposite ! I wish I would have saved my money !

05-09-2009, 02:34 PM	#1
suprf1y Join Date: Oct 2007 Location: SW Ontario Posts: 408	Review: Gio 250cc Mikuni carb as a 200cc performance upgrade Last week, we received the Gio 250cc Mikuni carb to use as an upgrade to our Giobeast 200 ATV. The carb is a quality piece. Some say these Mikuni's are from China, but regardless of where they are made, this is my second one, and it works flawlessly. Direct comparison to the stock carb on the beast, the Mikuni is substantially larger. The Mikuni on the left has a 30mm opening which narrows down to 22.5 near the slide, while the stocker on the right measures 27, and 20. Installation was a breeze, and everything bolted right up. We elected to not install the choke cable, as it was just as easy, and more controllable using the lever on the carb. The Mikuni has 3 detents for choke off, halfway on, and full choke. We use full choke on the cooler mornings, and half choke all other times. The inlet on the Mikuni is 42mm compared to 40mm on the old carb, but a little heat from a blow dryer, and it slid right on (don't tell my wife). The results. After installation, it fired on the first shot. After a bit of a learning curve (more on that later), performance is definitely improved. Power from idle, to the upper RPM is substantially increased. The difference between stock is like night and day. Having 2, its easy to do an A/B comparison. I would say that before it felt OK, but definitely not quick. For me, the stock machine has enough power for utility use, but my son rides much more aggressively, and is really able to take advantage of the extra power. To quote him, he says 'it flies'. Installation notes. The first thing we did was to adjust the air/idle adjustment screw to 1.5 turns, to get a baseline setting. It started, idled, and ran so well, we left it at 1.5. The Mikuni comes with a 100 main jet. It runs well enough that I don't get the feeling that its lean. I wouldn't say its rich, though, either. When we have time, a 105 main jet will go in. I don't think this is a bad idea. The stock air breather is a serious restriction, and will NOT work with this carb. The elbow is too small, and along with the foam, anything out of the lower RPM regions and it will bog, and fall on its face. Take the breather off, and its a whole different story. For now, and untill we source a good, free flowing breather, we compromised by using the breather with only the coarse foam element. Its not ideal, but its better than nothing. Suffice to say we are staying out of dusty ares for now. I have an accelerometer, and plan to do some A/B testing with that to put some numbers to the results. Stay tuned, but for now, its 2 big thumbs up for the Mikuni carb. I think a pipe, along with this carb, will turn the beast into a monster
	0

05-25-2009, 10:31 AM	#8
turnerburner94 Join Date: May 2009 Location: Neepawa, MB, Canada Posts: 5	The carb is a good buy in my opinion. It makes my bike start better, it is more responsive, and has more power. It makes the motor into good from blah. __________________ <strong><em>Tyler Turner<br /></em></strong>
	0

05-10-2009, 06:33 PM	#2
pno420 Join Date: May 2009 Posts: 8	I put this carb on my SLA250 Sunl branded atv,(250cc liquid cooled cn250 motor) and couldnt get it to idle right, it was extremly high, and I checked everything. It seemed to me that the 27mm intake from my chinese keihin pz27 didnt fit it correctly and I was getting an air leak ? The intake manifold seems to be off and it is by 3mm, I even tried ordering another intake made for the carb off ebay (Mikuni 30mm carb intake for a ), but it was the same as my 27mm one ! Is yours the same way ? I might just have a bad carb?
	0

05-10-2009, 06:38 PM	#3
pno420 Join Date: May 2009 Posts: 8	do you have a pic of your intake manifold ?
	0

05-10-2009, 06:58 PM	#4
suprf1y Join Date: Oct 2007 Location: SW Ontario Posts: 408	I don't have any pics, but the manifold id slightly offset. I forgot all about it, but I did open the phenolic spacer a bit, so there was a good transition between the carb, and the intake. It idles absolutely perfect, in fact, we have it set lower than the other carb was, because its more stable.
	0

05-10-2009, 07:50 PM	#5
pno420 Join Date: May 2009 Posts: 8	Great, Thanks so I guess I do have the right Intake, your is offset too, do you see the top of the oring on the carb when its screwed to the intake ? yea it has me stumped, the mikuni seems like such a better quality carb to. I tried checking the throttle cable, Disconnected it, made sure the slide was in correct, even tried changing the pilot jet to a bigger jet, I thought maybe it was running lean causing it to not idle down . I put a 25, then 40 pilot, and a 120 main in it, I got it with a 20 pil and 100 MAIN. I do have a uni air intake and mrp exhaust so thats why I increased my Jetting. The keihin runs ok but its a little lean and I cant find The odd pilot jet that was in that carb, so I tried the Mikuni but get that high idle situation and the idle air screws does nothing to change the idle at all. I either need to find the odd 33mm long kehin pz27 pilot jet, or figure out why the Mikuni idles high? Anyone ever have that problem ? Maybe a bad Float ?
	0

05-10-2009, 07:53 PM	#6
pno420 Join Date: May 2009 Posts: 8	nice to see someone else upgrading there chinese atv. What other mods have you done ?
	0

05-10-2009, 08:00 PM	#7
pno420 Join Date: May 2009 Posts: 8	Is this your intake ? http://img.auctiva.com/imgdata/4/7/8...05504953_o.jpg
	0