78 gs550 running on 3 cylinders

[Guest]

Last night I finally got my bike running but it seemed it was only running off of 3 cylinders. This morning I took the spark plug out of the cylinder in question and grounded it on the frame and got no spark. So my questions are, 1 did I do the right thing to check the plug for spark? And 2 It seems like the connection is very loose between the plug and wire, so can I replace just the boot on the factory wire or will I have to replace the whole coil?

[Nessism]

The plug caps screw onto the wires. It's common practice when performing maintenance to unscrew the cap from the wire, snip off 3/8" or so of the wire, then screw the cap back on. This assures you have good continuity between the parts. If the plug cap itself is broken internally, get a new one. NGK sells high quality equivalents that are easy to find and cheaper than the original Suzuki supplied parts.

Don't know if this is why you are not getting spark, but it's a good starting point regardless.

[tkent02]

Start with removing the spark plug boot, cutting the last 1/4 inch or so off the wire and reconnecting the boot. Look for cracks in the rubber insulation. Look at the engine while it's running in the dark, to see if sparks are coming off the wire anyplace. There shoudn't be any, but sometimes with old wires there are.

If the connections inside the boot are all corroded or if the boot itself is cracked or broken you may have to replace it.

Sounds like you tested it correctly, you grounded the plug, cranked the engine and got no spark. Each coil provides a spark to two spark plugs, 1 + 4 and 2 + 3. If the other plug in that pair has a spark the coil itself is probably good, and that half of the ignition system is working at least a little bit. Have you looked at the condition and adjustment of the points?

The spark plug could be bad too, swap it to another plug wire to check.

[akaerik21]

The spark plugs are really bad looking, they look very dry and almost burnt or melted, so I will try replacing them. The bike came with accel coils and wires but the coils weren't designed for that bike so I will hopefully be able to reuse the boot off of those wires. I am just wondering will in need any special tools to do this?

[eil]

This morning I took the spark plug out of the cylinder in question and grounded it on the frame and got no spark. So my questions are, 1 did I do the right thing to check the plug for spark?

Almost... the plug should be grounded to the engine because it's the other spark plug on the same coil that the current is coming from (or going to).

However, it should still technically work if the ground connection between the engine and frame is intact. It's just that grounding the plug against the engine removes one variable from the test.

Also, the plug cap can be disassembled and the parts inside cleaned. On my bike, all of the resistors were shot, which I replaced with equivalent lengths of metal and installed spark plugs with resistors in them instead. If that doesn't work, then perhaps spring for new caps and/or wires.

[Kiwi Canuck]

Maybe you have a GT550,

Couldn't resist.