Mikuni Problems...

[mx125c]

My bike is a 76 mx125c and I just recently got it a couple of weeks ago. After sealing the tank, getting a new petcock, finding a discontinued air filter,and general cleanup I have run in to a problem that I am sure one of you will be able to help me with.

Just a little background on me..it might help..I am no stranger to working on old cars or even new ones, I have enough mecanical skills to do motor swaps, but this little 2 stroke has me stumped.

First thing was while waiting for the new petcock we did a little cleanup on the bike(I am also rebuilding a 84 XT600 at the same time) and forgot to clean out the carb on the 125 (did it on the 600) after getting it all together tried to kick it over till we were blue in the face...no Luck!

A couple push starts...No Luck

Then remembered to clean out the carb.."oh ya"

Took it apart and cleaned all the sh@# out of it, reassembled, put back on the bike, opened the Petcock, all seems fine and then....

Fuel starts "pouring" out of the 2 vent hoses(side and bottom)

I am not familiar enough with repairing motorcycles to know why this is happening..Please Help!!!!

Sorry about the length and thanks in advance!

[Aus_Rider_22]

G'day and welcome to ATM!

It's a great place for off-roading enthusiasts!

To your problem. I don't have any experience with many older bikes so my opinion may be way off!

But, I would pull apart the carb and reset the float. It sounds like it's stuck and fuel is overflowing from this.

I am sure others will chime in with some better info!

[char393]

I'll second the welcome to ATM!

I'm certainly no expert either, but I agree with Geoff, sounds like your floats are stuck.

You might want to have a look at the following thread by Faded who does an excellent job of explaining it:

How To Set Your Motorcycle Carburetor Float Level

[gumby_55]

Ditto. That would be the first thing I would check.

[mx125c]

So after I posted the thread, I removed my head from my butt and started to think about why it we be pouring fuel....

So I removed everything again.....

Took it back apart.....again

Refered back to the pictures I took of the carb assembly(have to love digital cameras)

and noticed that the floats where holding the fuel inlet...wait for it.......OPEN

Duh....

The replys were dead on, reassembled, back on the bike, will try to start it today because it was a little late last night(1 am) would of really pissed my neighbors off...

I will let you guys know how it goes today...might have another proble you guys can help me with..

Thanks

[ossagp]

to get that old critter running it's sharpest (well worth doing) the float is really important. if that mikuni is the VM type, it should have two individual float "bulbs". Those ride up and down on thin shafts and can actuate the yoke that pushes the needle simultaneously or independently. this has been respected as a good design for a long time. Takes up lots of space though and is now considered obsolete designwise. Set the float by turning this one all the way upside down, and making sure the two legs of the yoke are even with eachother and set them level with the mating surface of the carburetor body and bowl. It is the easiest to set float I have seen.

Change the lower end seals (they take a set over time) jet for today's fuels and have a great time with your little piece of history.

[Aus_Rider_22]

Let us know how she goes.

[mx125c]

Okay so....

Step 1a. With carb on bike, tried to kick her over...nothing!
Step 1b. Noticed wet plug, and adjusted needle.
Step 2. Check Fire...Yeah, We have spark!
Step 3. Check Air...Yep, If I can breath so can she!
Step 4. Check Fuel supply...Nothing getting the carb...Damn!
Step 5. Removed carb (again), a bent float tab...Fixed!
Step 6. Reassemble, Back on bike!
Step 7. Legs are too tired to keep kicking...Push it down the driveway, Popped the clutch....VICTORY!

Popped the clutch and she ran like a dream. No hesitation, no stumble. Not bad for a 29 year old bike that has been sitting for almost 3 years.

Up and down the street she went...Wont hold idle though but that is easy to adjust.

Flush and Kreem tank....$32.00
New Petcock...$25.00
New Airfilter...$20.00
29 Year old Yamaha running like a dream....Priceless

Thanks all for the advice.

[Aus_Rider_22]

That's great to hear you got it going!

Older bikes are fun to ride.

I just got back from riding my neighbours older bikes.

Once was an XT500 from about 1979. It went well for an old bike!

Hard to kick over but we "got er done".

[mx125c]

I also got an 84 XT600 that I am rebuilding.

Its an 84 600 with a 83 XT550 motor that has been bored out to a 583, talk about an identity issue!

I got it as a basket...with motor and everything disassembled..almost done.

Just need a skid plate and seat for it(hint, hint if anyone knows someone who might have one lying around) and to finish "Kreeming" the tank and I should have that one ready to go..

Cant wait to have that giant 4 stroke up and going...weeeeeeeeeeeeeeeee

Again, Thanks for all the help...now, off to play with the toys!

[Dirtbikindad393]

Good job mx125c. You came to the right place also. Welcome to ATM hope you enjoy the bike.

[ossagp]

Mx
The thing you may not like the least about that XT engine are the carbs. Even then they were thinking low emissions. A set from the tt600 is lots easier to jet etc. PM, or email me at [Only registered and activated users can see links. ] if you want the name and contact phone number for a man who I know to have a pretty big stash of stuff for the tt600. He is a good source for any Yamaha information.