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Author Topic: Like Carburetor 101 for the total Idiot?  (Read 59783 times)

Mike on the Rock

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Like Carburetor 101 for the total Idiot?
« on: December 24, 2005, 06:31:01 PM »

Was asked to explain how to richen the fuel mixture and about re-jetting the Gt250, this will cover the GV250 and is relevant to the GT/GV650 bikes as well, but I will use a GT250 for all the images unless marked with a deferent bike.

Wiki Link:
 http://www.korider.info/index.php?title=Re_Jetting_the_GT250_Engine


Image 1



MIKUNI BDS26 Type Double
Carburetor as used on the 2004 GT250 in the USA and Korea.

Idle r.p.m. 1,450 ~ 1,555 r.p.m.
Float height 17mm or 9.67in
Throttle cable play 0.5 ~ 1.0 mm

Main Jet (M.J.) Front 92.5 Rear 95

Main air jet (M.A.J.) Front and Rear 90
Jet Needle (J.N.) Front and Rear 2ND
Needle jet (N.J.) Front O-3 Rear O-4
Pilot jet (P.J.) Front and Rear 20
Throttle valve (TH.V) Front and Rear 130
By-pass (B.P.) #1-0.9 #2-0.9 #3- 0.8 #4- 0.8
Valve seat (V.S.) Front and Rear 1.2
Starter jet (G.S.) Front and Rear 22.5
Pilot outlet (P.O.) Front and Rear 0.75
PV Stroke (P.V.) Front and Rear STD



NOTE: The above data is from a printed Service Manual # 99000-94710, many of the terms are translated in several ways and some are swapped and do not correspond to the terms used elsewhere in the service manual or the parts book.

:bomb: TURN OFF THE FUEL :bomb:
:bomb: REMOVE THE BATTERY CABLES :bomb:


NOTE-2:
Safety, I assumed you have read all or at least some of the many safety notices and referenced section 1-1 of the above referenced service manual if you have not, it is at least funny to read and you just might not burn up your bike or hurt yourself.

------------------------------------------------------------------------------------

TOOLS and how to remove Metric Screws on the Comet bikes.


------------------------------------------------------------------------------------

Some images we will be referring to in this procedure, please do not do any of this unless you have read and understand all, this is a work in progress and we do not want to make expensive mistakes.

Image 2
Right side

Raising or lifting the needle, will mask or correct the [? lag/miss?] at the 3,600 r.p.m. spot. This is done by inserting some washers below the “C” clip on the needle. This will make the mixture richer.



Next

Image 3
Left side


:bomb: TURN OFF THE FUEL :bomb:

Image 4  Fuel Valve

This is the early Fuel valve, may not be the same on all bikes.

To remove the tank:

First turn off the fuel and remove the fuel valve if like the image # 4,this can be removed by removing the 10mm bolt (only one bolt), disconnect the fuel filter and plug the fuel line. You will also have to un-plug the electrical cable to the fuel gauge.

Then open the rear and pull the RED knob to relies the seat, remove the seat and you will see a 12mm bolt that holds the seat on, remove and lift the tank, if you are very careful you can turn the tank and rest it in the seat area to work on the engine.

Image 5

Carb removed for photographs, you can do this with the tank and carbs on the bike.

NOTE: The MSRP on a set of  MIKUNI BDS26 Type Double
Carburetors in the USA is $US 796.20 I am told, also it is not possible to get parts, only the set. So please do not brake or lose any parts, also as the needles are hard to tell apart so only work on one at a time.
The carburetors and most everything else on the bike is assembles with a permanent “Lock Tight” that must be broken to remove the screws, nuts and bolts, see the section on removing screws, nuts and bolts.

 
Image 6

Note this image does not agree with the Parts Book, but is from a factory installed Carb?
Imag 7

Shims and Jets

Imag 8

SHIM
Imag 9

More to come
Mike on the rock
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And above all, remember that this info is worth
exactly what you paid
for it.
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BeAR

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Like Carburetor 101 for the total Idiot?
« Reply #1 on: December 25, 2005, 01:01:04 AM »

Great Mike, thanks for doing this.
Have a Merry Christmas mate.
Cheers,
Gary.
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skadamo

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Like Carburetor 101 for the total Idiot?
« Reply #2 on: December 25, 2005, 06:39:04 PM »

:lurk:

Good info Mike, thanks!
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2007 GT250R

BeAR

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Like Carburetor 101 for the total Idiot?
« Reply #3 on: December 30, 2005, 11:04:42 AM »

Mike, is there a set jet size you would recomend for the GT250R?
Ive read that 2 X 100 jets are the go and a single shim under the needles to richen up the mixture a bit.   What would you recomend?
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Mike on the Rock

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Like Carburetor 101 for the total Idiot?
« Reply #4 on: December 30, 2005, 04:43:51 PM »

Hi BeAR

Most Bike tuners of carbureted bikes find that with a change to straight through muffler use two steps up as a starting point, this would be a 97.5 and a 100.

The 100 seem to be easer to get and experience indicates that 100/100 works very well.

I will post on changing the jets in the next section.

Ride safe
Mike on the rock
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BeAR

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Like Carburetor 101 for the total Idiot?
« Reply #5 on: January 07, 2006, 08:22:15 AM »

So if I go to 2 X 100 jets, is it necessary to shim the needle?   Will the larger jets by nature make the mixture ritcher?
Im getting popping on deceleration quite badly with the Zero/100 pipe and dont want to do any damage to the motor..... a bit more power wouldnt go astray either.
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Mike on the Rock

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Like Carburetor 101 for the total Idiot?
« Reply #6 on: January 07, 2006, 12:44:13 PM »

Hi BeAR

I think the new Bikes have a bigger plastic shim and you may not need to shim the needle with them to get rid of the flat spot at 3600 rpm.

As for the “crackling and all” when decelerating, I think the only way to really eliminate it is to keep the throttle part way open when decelerating, this is the cure that was used on several automobiles back in the days of Carburetion on them. I did not like that cure as it felt like you could not slow the car down.
I think that the noise does not have any effect on power being in the decelerating time so I had never thought of it as very important.

I think it might effect emissions but on my O2 readings, it does not seem to read high when this happens.

Maybe some one can post more information on this.

Hope this helps.
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BeAR

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Like Carburetor 101 for the total Idiot?
« Reply #7 on: January 07, 2006, 12:58:56 PM »

Thanks for your reply Mike.
This is kind of funny, The popping doesnt worry me at all, I figured it was just a way of telling that the bike was running too lean with the new muffler.   My only concern is not damaging the engine.   I think ill buy 2 100 jets and fit them.  Will this give more power and run a bit richer?
I figure it will but you would be the one to ask!!!!!
Please check your PM.
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Like Carburetor 101 for the total Idiot?
« Reply #8 on: January 09, 2006, 03:35:57 AM »

Gary,

I don't believe the popping will damage the engine - I've done 20,000km now with it, and had no ill effects as yet.

Have you managed to source 100 size jets?  

Paul
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BeAR

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Like Carburetor 101 for the total Idiot?
« Reply #9 on: January 09, 2006, 03:46:59 AM »

Yeah Paul, Mike sells them.  
I got the service done today and the 13T sprocket fitted, its like a new bike, I love it.   They didnt have 14T in stock tho.
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