DIY Network

Carburetor Overhaul Student mechanic Dillon Hryze overhauls a bike. From "Trade School" episode DTRS-210

Figure A

In this segment, Dillon moves beyond mowers to his first motorcycle repair. Instead of working on something state of the art, Dillon is assigned to a bike that is older than he is: a 1971 Honda Trail 90 (figure A). While this bike has a number of things wrong, Dillon's goal is simple—to get it started.

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	Figure B
	Figure C

Basic Tools:

compression test kit
leak down test kit
hose clamps
screwdrivers
wrenches
drain pan
carburetor cleaner
paint brush
ruler
air compressor
tap and die set

Dillon first runs a series of diagnostic checks hoping to determine the source of the problem. The oil level is normal and a spark plug test confirms that the plug is firing. A compression test (figure B) shows Dillon that the compression inside the cylinder is normal. A leak down test (figure C), which determines if unwanted air is leaking into the engine, comes up negative. With nothing abnormal on these tests, Dillon decides that fuel probably isn't reaching the cylinder. His next task is to perform a carburetor overhaul.

The carburetor controls the air to the fuel mixture in the engine. From choke to full open throttle, a carburetor is designed to operate under a number of different conditions and is a fairly complex component of the engine. After clamping off the fuel intake hoses, Dillon starts the overhaul by removing the carburetor (figure D), and then carefully disassembling (figure E). As he removes all the old gaskets for replacement, he keeps a careful eye on how the carburetor should be reassembled. He then puts the carburetor back together and soaks it overnight in a solvent bath to loosen any caked-on deposits. In the meantime, he drains and cleans out the gas tank (figure F).

Figure D

Figure E

Figure F

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