Topic: Backfire and flames on startup 76 cb750

[Cb^_^750]

I recently took my engine apart to re do the gearing in the lower case. But now it's seems that it doesn't want to start. When it cranks I get popping sounds and with the pods off I've seen flames come out the carbs. Is this a timing issue? I don't see any other possible reason I re assembled the bike exactly how I took it apart. Any idea on what it could be or possible fixes? It's feeling like I'm never going to see the light at the end of this tunnel

[goldarrow]

Ignition timing, try to swap the blue and yellow wires

[rb550four]

+1 on ignition timing. Check your points for gap, condition and firing time. Not everything went together the way it was.
Just need to back track and double check .

[PeWe]

+2 on ignition. If you have taken the advancer unit apart you might have mounted the rotor wrong so you must connect base plate wires with main harness, yellow wire with blue and vice versa to get it running.

Also possible if you have connected spark plug wires the other way. 1-4 to coil 2-3...... If you have changed coils+ wires. Std coils with wires still on not possible when 1-4 are much longer.

[Cb^_^750]

So you are saying the wiring coming from the advancer got mixed? The red goes to red and black to black. Then there is green but those go to the yellow and blue from the coils?

[flybox1]

Your points plate probably has shifted from where it was previously.
Set your points gap .014" when fully open

[Cb^_^750]

I had never touched my points or messed with them but I will double check when I get off work

[flybox1]

I had never touched my points or messed with them but I will double check when I get off work

you had to take the points plate and advancer unit off to do your bottom end work, right? 
it probably shifted from where it 'was' and has thrown your timing off...

[goldarrow]

So you are saying the wiring coming from the advancer got mixed? The red goes to red and black to black. Then there is green but those go to the yellow and blue from the coils?

I don't recall stock oem points have red and black wires

[Davez134]

So you are saying the wiring coming from the advancer got mixed? The red goes to red and black to black. Then there is green but those go to the yellow and blue from the coils?

I don't recall stock oem points have red and black wires

The red, black, green sounds like wiring from pamco ignition

[Cb^_^750]

Yeah looking at the wiring diagram my wire colors don't match up. Previous owner must've changed it but the bike was running before and I had wired it up just like it previously was. I'm about to take a look at the points right now.

[Cb^_^750]

I managed to get th bike fired up. Turns out two wires were crossed. But only after a minute of idling the bike was puttering and shut off. Checked plugs and there were darker than night. Assuming running to rich? Or timing is to far advanced?

[chewbacca5000]

I managed to get th bike fired up. Turns out two wires were crossed. But only after a minute of idling the bike was puttering and shut off. Checked plugs and there were darker than night. Assuming running to rich? Or timing is to far advanced?

Pull plug and clean with carb and blow off with compressed air and try again.  As for color they would be black after all that.  Have you done the 3,000 mile tune up?

[Cb^_^750]

No I have not I'm fairly new to the bike word. Enlighten me