3MA-1 carburetor model

[14goods]

Hi
I got a 3MA-1. The bike runs fine. Once parked, the carbs leak slowly until the tank empties. I think it's the needle jet. This is not available with Yamaha Canada. I am trying to find out if this part is available in another Mitsumi carburetor that would be available. For example Sudco.com sells parts for Mitsumi carburetors, they cannot find my model. Does any one know the carburetor model?
Thanks
Dan

[paulyb]

Hi Dan

Carb on the 3ma-1 is Mikuni TM 32ss which is model specific although if you try a

mikuni stockist in your area they should be able to supply the parts u require i should think  and a fraction of the cost of yamaha

If you are unable to locate locally i sourced  needle valves,,main jets and needles for mine from motocarb here in the uk

Hope this helps

[14goods]

Thanks
At least I have a choice for supply. The fact that the whole tank empties through the carburetors, is this due only because of used nededle jets or do you think the problem lies elsewhere?
Dan

[Warwick]

You mean needle valves? The needle jet is a different thing entirely. It's the needle valve that controls fuel flow into the carb. If fuel is flooding the carbs then you probably have a couple of issues to address.

1. The seals and/or diaphragm in the fuel tap must be failing if fuel is flowing to the carbs when the motor isn't running as the tap is vacuum operated and should only flow fuel when the motor is turning over to create the vacuum (assuming you are not leaving the tap on the right of bike in the PRIme position? If so change this to the 'on' position for general use. This alone may reduce your problem substantially if you are currently in the habit of using the PRIme position for general use).

2. The needle valves and/or their sealing O rings must be worn/dirty/perished

or 3. the needle valve floats must be incorrectly set, punctured or sticking.

If you are confident that it's a job you can manage yourself, then strip, inspect and clean/replace the parts as needed. If not, take it to someone who can do that kind of stuff. It's all pretty straightforward so any general mechanic should be able to do the job for you.

Hope that helps

 



 

[14goods]

Hi
Sorry if I don't use the right vocabulary. Needle jet is what I meant.

You are right about fuel continuously flowing towards the carburetors. I did inspect the diaphragm and replaced an O ring inside it, I replaced the vacuum line, since the old one was cracked. This did not stop the flow of gas. I am not sure what else to do to repair the diaphragm to stop fuel from flowing without vacuum.

I tried adjusting the floaters. Still gas flows.

Now I noticed the O ring over the plastic, where the needle jet fits, is dried, so I will replace this too. The rubber over the needle jet feels soft and nice, should I replace this part too?

I am no mechanic but feel very close to fixing the problem, despite the number of hours spent on it.

Dan

[Warwick]

Needle VALVE or even float valve if you prefer, but not needle jet, OK? The needle jet lives on top of your emulsion tube on the 3MA, and along with the jet needle meters the amount of fuel/air the motor gets on part throttle. It has no bearing on fuel entering the carburettor at all.

The fuel tap should not flow any fuel at all when the motor isn't running, so replacing the seals and diaphragm in the tap (or fitting a new tap completely) will be necessary if your tap is flowing whilst in the 'on' position but no vacuum is being applied to the tap. Fixing this will reduce the pressure on the needle valve and substantially reduce your problem in itself. If the needle valve and seat themselves are in good condition, then replacing the needle valve seat sealing O rings as you've identified should stop the problem of any overflowing in use if your floats are in good condition, can move easily and are set correctly. Setting the floats to about 19.5mm should give you an ideal fuel height of around 5-7mm - and no pools of fuel on the garage floor  .

It would also be very well worth cleaning out the tank and flushing the fuel lines as quite often overflowing problems on older bikes are caused not by problems with seals per se, but by small tank rust particles wedging the float valves open slightly. Often simply cleaning the system, will solve the problem completely in itself so long as no damage has been caused to the seals.  Conversly, replacing the seals but not cleaning the fuel system will often fail to solve the problem if it's really being caused by bits of rusting fuel tank wedging things open.  It's all just basic maintenance stuff really, so if you are happy to get in and get your hands dirty you should have no problem fixing it yourself.  And that is very staisfying of course. Sounds like you're almost there, so good luck

[14goods]

Super
You are right about the rust. I've had to rub the inside of the tank with sand to remove the rust. I cleaned the inside of the fuel tap and parts of the carburetor.
After I had put it all together, fuel was leaking on the tap, below the tank and at the left of the bike. I was discouraged.
I was able to change both the O ring inside each fuel taps. Now they are fine.
Now replacing the fuel tap itself is another issue, since this part is not available here in Canada. Is it possible to replace the diaphragm? If so where do I get parts?

Thanks
Dan

[Warwick]

I've never had to replace them so can't help directly with that I'm afraid. I would think it would be possible to source or make a new diaphragm or fix the existing one if it turns out to be damaged though? Such travails are just part and parcel of living with an old grey import bike I'm afraid. New taps look to be still available though (just google the part number) if you need to go that route. 

[SP_BOTT]

There seem to be an increasing number of fuel tap repair kits now available on Fleabay, haven't seen one for a 3MA, but They have to be identical to another model, if not, can't you just turn of the auxillay tap under the tank, until it's fixed?