Vintage Dirt Bike Q & A

I am trying to repair a carburator on a Honda CR125M, 1975. The problem i am having is that it is always flooding with fuel. Put in new needle valve and it jams open when fuel enters the carby. The old one does exactly the same thing. Don't understand why the needle jams in the open position. Has anyone come across this problem or does anyone have any ideas on what can be the problem?

Did you replace the needle valve AND the screw-in valve seat? These should be replaced as a set, otherwise the new needle can cock and jam in the worn-out seat, or not make a good seal.

Also, are you using a fuel filter?

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Yes it is a new needle and seat and no it doesn't have a filter.

OK then, how about the following possibilities:

a) leaking float
b) incorrect float level
c) float snagging on something within the bowl area
d) binding float hinge or bent/sticking hinge pin
e) leaking valve seat (needle seat or threaded portion into boss)
f) cracked seat boss or carb body (I've seen cracked needle jet bosses)
g) dirt inside seat area
h) faulty needle spring and/or spring 'plunger'

etc.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Thanks Ray I will look in to them as I am ready to throw it over the fence.




Dave

Try this test:

Get a two foot long section of CLEAN fuel hose. Replace your stinky hose at the carb inlet with this clean one.

Take the carb off of the bike.

Remove the float bowl, and get rid of any gasoline.

Hold the carb at eye level, right side up.

Stick the end of the hose in your mouth and blow softly. Don't inhale through the hose.

With a finger, slowly move the float valve up to simulate fuel entering and raising the floats.

The air should stop flowing right when the float assembly support arm is parrallel with the float gasket mating surface. The float support arm will be way below that surface, but the two lines will be parrallel.

If you have to raise the floats much higher than that position to stop the air flow, then your float level is set too high. Bend the little actuator tab that hits the needle, and retest it.

If the air flow doesn't stop at all, then go through that other list of problems to check to see if the fuel is coming through the valve, around the valve, or ?? You might need to spray the area with some soapy water and look for bubbles to find the where the leakage is passing.

There are other ways to check the float level, but this one will help you find the trouble more directly, especially if the float level is not the problem. Besides, somebody just might take a picture of you doing this and post it here, and I'd love to see that!

Enjoy,
Jon

Thanks to all still playing with it


Dave