Saturday, March 13, 2010

Rebuilding a Carburetor

Recently we inherited a lightly used lawn vacuum/shredder/chipper combo unit. It is an extremely well-built, high quality machine - I think its about $900 new. It will work great for chipping the branches that fall in our yard and picking up leaves in the fall - we are surrounded by hardwoods :)

When I filled it up, fuel immediately began leaking out of the primer bulb - a LOT of fuel. Sitting in storage for so long had deteriorated the carburetor badly enough to require a rebuild. I sent off for a rebuild kit which was about $20 including shipping.

I pulled off the air filter housing and the gas tank line and removed the carburetor. Gasoline in liquid form is not flammable, and air is not flammable either. The carburetor's job on an engine is to combine the fuel with air to form a combustible mixture.

When I took apart the carburetor the problem was obvious (thankfully) - The float in the fuel reservoir that meters gasoline into the carb was stuck in the bottom position, allowing fuel to freely flow and flood the entire unit. Clearly it had been left full of fuel for year or more, and the fuel had broken down and formed a sticky sludge inside. There is still some on the float in this picture, everything on the inside was coated with this.

I cleaned the inside of the fuel reservoir and the float of the scum using brake cleaner. I used a brass brush. It was time consuming but eventually I got it all off. The picture below is of it cleaned.

Something called a welch plug needed to be replaced and sealed with nail polish. The instructions were written for more than one engine, since my carb was missing a lot of the features described. I also ended up not using half the parts in the kit for this reason. My wife gave me some old polish she doesn't use anymore. While it dried I cleaned the rest of the unit.

I pulled the needle valve and seat off, and replaced them both with new. Here you can see the float reattached, and I am holding it in the "down" position. Its connected to the needle valve and opens or closes it based on the fuel level in that metal bulb reservoir.

Reattaching the reservoir with new grommets and seals.

Where the carb attaches to the engine.

Attaching the carb with a rubber o-ring.

Fuel line needs to be reattached. I thought about replacing it, but its actually in decent shape.

Its a pretty stiff line, and I just needed to be gentle with the gas tank side of the connection, since its plastic and could break if I got carried away.

Attaching the air-filter mount. This has a grommet that came with the carb kit which seals it to the carb housing.

I need to replace the air filter actually since it got soaked with fuel originally. But, the old one will work fine for testing.

Pops into place.


Done. I refilled the tank a little, checked for leaks, and then all the way up.

I gave the primer a few pushes and cranked it. It started up, then died. Tried twice more, and it started running good. I vacuumed some of the leaves in my yard and that works great, I also put a few branches through it and they turned into perfect mulch. This thing only effecitvely cost $20!! woohoo!

What this repair has taught me about seasonal maintenance is to be sure to run engines out of gas before storing it for the winter. Otherwise the carb gets gummed up and it won't run.


benthomasson said...

Now if it was just that easy for my car.

Glenn Hackleman said...

Oh I used to have pictures up of replacing my IACV valve, don't think I have them anymore though.

Mr. Porter said...

I did this two days ago. I wish I had come across you blog first.