cylinder 4 is not firing

[Idratherbehunting]

Im troubleshooting a 1988 classic 50. I hooked up a digital rpm meter to each spark plug wire and all the cylinders are about the same except #4 which is about half the rpm. Engine bogs down and i am suspecting this is the problem. Now not sure where to go from here.

 

[GA_Boater]

Have you looked at the plugs? #4 could be carboned up.

Also you can swap one of the other plugs with #4 and see if the problem follows the plug. I had a good looking bad plug and short of throwing in a new set, that's how I found it. She still got a set of new plugs

 

[JDusza]

If you can provide the engine serial number we can home in on the required parts. But, 'til then, we'll use what we have.

There are a few different ways for ignition to fail. The three main components we are interested in right now are (from #4) the spark plug, spark plug wire and magneto assembly. Just as you would swap the spark plug from one location to another, swap plug wires. Pull all your plugs so the engine cannot start, then swap wires from magneto outputs to plug inputs and see what fires.

p.s., please tell me the rpms of all cylinders is the same....if they're indeed different, you've found your problem. lol

 

[CharlieB]

If an ADI with separate ignition coils for switch cyl switch coils to see if the problem follows the coil.

 

[Idratherbehunting]

I used an inductive rpm gauge wrapped around the spark plug wires to determine rpm... however this actually only tell you the ignition/spark rate per minute. I cannot remember the actual rates but 1-3 were around 1400 rpm and #4 was around 800.

Can I move the coil from 4 to 1 and see if the problem remains?

I also got shocked when i touched the boot on #3, im guessing this also means i need a set of plug wires.

 

[Faztbullet]

You need to test it properly with a spark gap tester and it should jump a 3/8 gap with a "pop" and blue spark...