Engine Won't Start? Two Swapped Plug Wires on My 1966 Scout

Short answer: If an engine won't fire after new plugs or wire work, check that every plug wire is on the right cylinder and the engine's firing order. My 1966 International Scout 800 has the IH 152 four-cylinder, whose firing order is 1-3-4-2. Two of its plug wires were swapped. I put them back in the right order, and the engine fired.

The Scout and why it wouldn't start

This 1966 International Scout 800 had been parked since 1980. I set out to see whether it would run. The engine is IH's 4-152, a 152-cubic-inch four-cylinder. It had newer-looking wires and a newer distributor cap, so someone had worked on it at some point.

Before I got to the wires, I had already put lube in the cylinders so I wouldn't dry-start an engine that sat for decades. I had also installed new spark plugs and a new belt, and I had poured fuel down the carburetor and repaired a fuel line I had crimped while cutting it. Even so, the engine wouldn't fire.

Checking the firing order

The firing order on this engine is 1-3-4-2. I went through the plug wires against that order and found that two of them were swapped. Wires that look fine can still go to the wrong cylinders if they were changed at some point, and the spark has to reach each cylinder in order for the engine to fire.

I swapped the two wires back to the right order, and the Scout fired. In the full video, that's the moment I call "Dragon fire."

Common checks when an engine won't fire

These are standard checks, not a list of what I did on the Scout. On this Scout, the wires were the problem I found.

1. Plug wire order. Match each wire to its cylinder and the firing order for your engine. Find the order in a factory manual or a reliable engine-specific source.
2. Distributor cap and rotor. Confirm the cap is seated and each tower runs to the right wire, in the right direction around the cap.
3. Spark at the plugs. Pull a plug wire, use a spark tester or a grounded plug, and see whether you get spark while cranking.
4. Fuel. On an engine that has sat for years, confirm fuel is reaching the carburetor and the fuel line isn't crimped or leaking.
5. Compression and a free engine. Make sure the engine turns freely by hand before you spend more time on ignition.

What came next

Once the Scout would fire, the old carburetor wouldn't idle, so a $75 replacement carburetor went on, and the Scout started on it too. It still isn't driving, because the clutch Z-bar is disconnected and missing a piece. The whole story is on the 1966 International Scout 800 build page. If you're bringing back something that has sat, the free "Will It Run?" checklist covers what to check before you turn the key.