Saturday, August 9, 2014

Tecumseh TVS90 Carburetor Teardown

Here's a view of a very grimy TVS90 carburetor just removed from its engine.

There's not a lot to it. As carburetors go, it's one of the less mystifying ones around. Proceed as follows:

a) Governor Link

Note the link's orientation, and which hole it hooks into at the throttle lever plate. It doesn't hurt to make a sketch of such details -- they can be surprisingly mystifying come reassembly time.

b) Fuel Supply Hose

Coax it off its nipple. A hose that's swollen or cracked ought to be replaced.

c) Primer Bulb

The primer bulb is held in place by a pushnut; it's not difficult to coax out the pushnut to free the bulb. See this post for more information.

A primer bulb that's no longer springy and supple should be replaced. Primer bulbs can be deceptive -- they can appear to be more-or-less ok, yet function poorly. If in doubt, replace it.

d) Float Bowl

The bowl's fastener is 1/2" hex. Unscrew it carefully so as not to damage its gasket. Pull off the float bowl and you'll have full access to the float chamber. Remove the float's pivot pin to remove the float and its valve needle. Remove the bowl's ring gasket.

That all brings you to here.

Still inside the carburetor's body is the resilient float-valve seat. Blowing compressed air into the fuel inlet will dislodge that item, but be careful not to launch the valve seat -- keep a thumb over the float-valve's opening to restrain the seat from leaving the carburetor entirely. I'm inclined to just leave the valve seat in place, unless I mean to replace it.

Clean all the parts in a parts washer, and blow out all the carburetor's passages. I never disturb a welch plug, or a throttle or choke butterfly, unless there's a pressing reason to. Should you need to dismantle a butterfly, be certain to note its orientation beforehand.

Adjustment -- Float Level

Float level is the only adjustment that can be made in this carburetor. It's easily gauged by eye with the carburetor upside down, so the float-valve is held closed by gravity.

In the above photo, note that the float is parallel to the bowl flange; that's correct float level. Float level is adjusted by bending the tang that presses on the end of the float-valve's needle.

Model Number

Should you need to obtain any replacement parts, you'll need the carburetor's model number. Typically, that will be stamped on the output flange of the carb's body casting, like so.

The model number may appear elsewhere, but it will be there somewhere. Even when you have the model number, it's not a bad idea to take the actual carburetor with you when you go to buy parts.


Lubricate the bowl fastener and its gasket with WD-40 prior to screwing it in and tightening it. Also lubricate the bowl's ring gasket. Here's the cleaned up carburetor back together.

Clean inside and out and ready to run.

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