Topic: 81' CB650C - Crank but no start

[anthograham]

Hey all,

Since getting the electrical sorted out, I've buttoned everything up and attempted to get this bike started. So far, this has been unsuccessful. I've checked over the "stupid simple" stuff to the best of my abilities. Here's what I can tell you:

Compression:

 - All cylinders are between 120-130psi dry. Confirmed via compression tester.
 - Adjusted all valves to their appropriate clearance per manual.
 - Tightened cam chain tension per manual.


Spark:

 - The ignition coils, plugs, wires, and caps have been replaced with new parts.
 - Each plug has spark. Confirmed via holding plug to block and observing spark.
 - With cylinder 4 in TDC, I verified that the timing mark was on the F and that the pulser was in alignment.

Fuel

 - FYI, the carbs are VM34's that I purchased from Murray's Carbs.
 - FWIW, I cleaned the carb internals and passages (including the pilot jet) with carb cleaner and compressed air.
 - I've have not adjusted the idle screw nor the air screw. 
 - New gas in the tank.

Other noteworthy items:

 - The exhaust system is the stock system. I cut off the muffler (do to severe rust) and am running it straight for the time being. A proper exhaust will be installed eventually but it should still run nevertheless.
 - I removed the plugs from cylinder 1 & 4 (since they were the easiest) and sprayed a little bit of starting fluid directly in them. I then attempted to start and this resulted in the most "action" I've had yet. Sounded like it was trying to go.
 - After a while of cranking, the smell of gas is present.
 - Also after a session of cranking, I removed the carbs (to clean them) to see a little bit of gas sitting in the insulator boot.
 - White smoke comes out of the exhaust while cranking. You can watch a video of that here:

That's everything I can think of right now. I've reached the end of the road for my knowledge so I'm hoping someone on here can help me get to the finish line. If you have any other questions, please ask. THANK YOU!

[caluser2000]

Are the coil connections reverse from what they should be?

[scottly]

 Each plug has spark. Confirmed via holding plug to block and observing spark.
 - With cylinder 4 in TDC, I verified that the timing mark was on the F and that the pulser was in alignment.


[/quote]
Have you verified timing with a timing light (strobe)? The 650 pulser or pick-ups are polarity sensitive: one of each pair of wires has a white band on it, and with the stock harness can't be reversed. If the wires are reversed, it will still make a spark, but at the wrong time.

[scottly]

Yes, a timing light would show the spark was not occurring at the F mark, but since you don't have one, you might try reversing the wires.

[scottly]

Something else came to mind: Should the blue/yellow wires at the coils only have power when timing is at F or should it have  key on 12v?

Don't over-think things.

[caluser2000]

Good stuff!

Well done.

[Pappy]

Gotta' love a good puzzle solving ! 

[Kevnz]

Many years ago I had a Jag with electronic ignition and I inadvertently broke the wires to the distributor. They were not colour coded and ( of course) when I reconnected them they were reversed. Nothing in any of the workshop manuals made any mention of this. Problem was, it didn't just put the timing out by 180 deg, it put it out by 270 deg. This meant that the timing varied from revolution to revolution, sometimes spitting back through the inlet, sometimes exhaust; all over the place. As the head had been off, I suspected issues with tight tappets or FI issues. ( Car was a non-runner when purchased) Eventually proved to be the simplest of things, as is often the case.