Backfiring when cranking

[plagrone]

I'm trying to get my bike cranked for the first time. Battery is good, compression is good, getting spark on both plugs, fuel is being delivered and the carbs were set up by our own crazypj.

I'm getting an occasional backfire/fire shooting out the header, strong smell of fuel. The plugs come out wet. Points are set, open right when they're supposed to. I don't have a timing light to confirm, but I am getting spark and I don't think being a degree or two off is going to keep me from idling?

HELP!

 

[Redliner]

I'm assuming it's a Vincent Black Shadow from your description. Feel free to clarify.

 

[HerrDeacon]

I don't have a timing light to confirm, but I am getting spark and I don't think being a degree or two off is going to keep me from idling?

Make sure you're not 180 degrees off though, spark may be happening at the wrong time.

 

[plagrone]

Ah sorry, it's a cb360. I checked timing, I built a timing light and I'm getting spark at the end of compression stroke on LF for left cylinder and at the next F for right.

 

[Redliner]

Remove both spark plug boots from the plugs.

Insert a clean plug in the left boot and place it on the head to ground it.

Remove the left exhaust tappet cover. Rotate the flywheel anti-clockwise and as you come to the LF mark, turn the ignition on.

As you continue rotating, do you see the exhaust tappet moving?

If so you should NOT hear the spark snap as you pass the LF mark.

Rotate another 360° at the flywheel.

Watch the exhaust tappet again. It should NOT move as you approach the LF mark and hear the plug fire.

If you hear the plug fire as the exhaust valve closes, you need to remove the points cam from the advancer weights and rotate it 180°.

As stated, it sounds like you are firing on the exhaust stroke.

 

[plagrone]

Followed these instructions and got spark when I'm supposed to be getting it. I have since found out my right cylinder has low compression. I was hoping to at least get it idling, but it's looking grim

 

[Redliner]

The left should at least burn if the compression is ok on that side. A cylinder may fire with low compression but it will almost never idle. The high piston velocity allows it to compress a bit of air before it can sneak out.

Ticking time bomb? Adjust cam chain, then tappets. Either of these can be bad for compression.

 

[plagrone]

Haha, the words "ticking time bomb" are not ones I wanna hear.

I'm just going to tear it down and figure out what's up.

 

[Redliner]

Have you checked compression after PROPER valve adjustment and chain tension?