Re: [MV] M38 Carburetor acting up
Mon, 8 Dec 1997 22:29:27 -0500 (EST)

Alan wrote:

>The carb can probably benefit from a good cleaning anyway

There is no question of this, as past operation brought rust flakes and other
filth up into the carb. I don't think any further junk can get to the carb,
as I've added a high-quality inline filter.

> The mixture screw only affects idle mixture, not the mixture
> through the power circuit.

I didn't know that, altho the problem is most noticeable at idle.

> consider the relatively close clearance between a step-up
> piston and cylinder. If the piston gets stuck in a position
> where it is holding the metering rod up, it will allow an
> overly rich mixture under anything but the heaviest load

That sounds like a possibility...

> A leaking or stuck-open float valve can certainly cause an
> overly rich mixture as the bowl fills with fuel and overflows
> through the venting circuit into the throat. On some carbs,
> the higher fuel level may also prevent the air emulsion tube
> from introducing air when it needs to do so.

When I had the top off the carburetor earlier, I had some suspicions about
the free motion of the float valve.

6) A loose jet can create an overly rich mixture.

Does it screw into place, and can work loose with vibration?

>I assume you've checked this, but is your choke opening all
>the way?

Yes -- that's one thing I can be confident about. Choke action is normal.

> Ordering an overhaul kit is a good idea.
> It would help if you have the manual for the carb.

Anyone know where to find the manual on the Carter YS?

> Some tips: Cleanliness is imperative at all stages
> of an overhaul. Don't take apart throttle or choke plate
> assemblies unless you know your stuff.

I won't, as I don't really fall into that latter category. When I think about
the complexities of carburetors I find myself dreaming about designing a way
to do this electronically -- guess what technology I'm more comfortable with!

Thanks for all the good info, Alan.

Steve Johnston

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