Help. Popping from carbs and won't start.

[Barbermudge]

Hey everyone,
I recently picked up a 1978 Yamaha XS400 and I’m having trouble getting it started. Hoping someone here can help me diagnose what’s going on and possibly explain how to fix it. Here’s what I know so far:

The Situation:

• The bike was running before being parked about a year ago by the previous owner.
• It’s using pod filters, stock CV carbs (I believe), and has no airbox.
• I’ve never had it running myself.

What I’ve Checked So Far:

• Spark: Confirmed. I pulled the plugs and saw consistent spark on both cylinders.
• Compression: Haven’t done a formal test, but I feel strong resistance when kicking, and the engine pops with starting fluid.
• Carbs: Have cleaned them fully but they are all Frankensteined and I know they’re running pods. I suspect they weren’t rejetted properly.
• Starter: will turn over but the bike won’t start.
• Battery: Just fully charged, reading over 12.5V.
• Timing: Not confirmed yet, but I suspect it may be off. When I use starting fluid, I get loud popping through the carbs but no actual ignition or sustained firing.

Symptoms Right Now:

• Engine turns over with kickstarter and electric starter
• Spark is present
• Loud popping through the carbs when trying to start with starting fluid or without
• No ignition or running, just the occasional backfire

My Thoughts:

• Possibly timing is off?
• Lean condition from pod filters and stock jetting?
• May need to go through the carbs thoroughly and verify jet sizes.. will need a carb kit and every single fastener is stripped.

If anyone has dealt with similar symptoms — especially the popping through the carbs — or knows if I’m missing something obvious, I’d really appreciate the advice.
Thanks in advance!
—Colby

 

[CaptChrome]

Welcome! Before doing anything else, I would verify/set the timing up and make sure that the coil primary wires are not swapped.