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Project CB 750


A much better picture is being developed!

Can you believe it actually started?! ...after I turned my brain on!

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You know I could lie to you at this point and tell you that it started right up the first time, and you wouldn't be able to say anything, but I can't do that...

The moment I've been waiting for...I actually tried to start it...and...it cranked, and it cranked, but NOTHING. 

My Troubleshooting:

  1. Bikes pretty much just need two things to run: GAS and a SPARK.
  • How I checked for spark - Turn the bike off.  Take out one of the spark plugs.  Plug it into the plug wire and rest it against a metal part of the engine - don't rest it over the spark plug hole (if the fuel vapor is pushed out and the spark is in the right place...boom!).  Turn the lights in your garage off and close the garage door 90%.  Crank the engine for about 2 seconds.  Do you see a clean, blue spark? I did.
  • How I checked for gas - Turn the bike off.  Take a screwdriver and unscrew one of the drain plugs on the carbs about 1/4 turn.  Did I see any gas?  NO!  Unscrew it a bit more.  Still No. There was only about 4" of gas in the tank, which as it turns out, isn't enough to force the air bubbles in the fuel line through into the carbs!  So...all I did was to fill the gas tank about 1/2 full of gas and check the drain screws again.  3 of the 4 dribbled gas.

This 3 of 4 was enough to see if it ran.  So...I tried again...SUCCESS!  The bike started right up (but sounded a bit "lumpy" because only 3 of 4 cylinders were firing.  The first thing I checked was the oil pressure light - I wanted to be sure the oil pump and passageways were functioning.  The light went off after the obligatory 1 second - which meant at least that the oil was reaching the top of the engine.  I also glanced around to see if there were any leaks of any kind - I'm happy to report that there weren't.  I didn't want to leave it running on 3 of 4 for too long, so I revved it a bit to check that the throttle linkage and cables were functioning correctly.  The throttle had a little too much slack in it before it opened the carb, so I adjusted that out a bit to correctly set the free play (about 1/8").  I turned the bike off and approached carb 3, which wasn't getting any gas.

Figuring out Carb 3

So...no gas in carb 3.  I checked to make sure it should be getting gas (check to see that the fuel hose coming from the gas tank was hooked up correctly).  On this bike, there are 2 fuel lines - 1 going to in-between carbs 1 & 2, and the other between carbs 3 & 4.  If the hose was plugged, both 3 & 4 would be fuel-starved, which wasn't the case.  I know from working on small lawnmower/snowblower engines that sometimes the needle valve gets stuck closed.  So, I tapped carb 3's float bowl lightly with the butt end of a big screwdriver.  I was hoping that this might knock the needle out...it didn't.

I was nice that on these carbs, you can take the bowl off without taking the carbs off the bike.  After turning the fuel off, I was able to slide the bowl "clamp" off and gently remove the float.  In fact, the needle valve was stuck.  When I pulled it out, a bit of gas dribbled out.  I cleaned off the tip of the valve and slid it back in and made sure it didn't stick again, it didn't.  I carefully put the float back in (which is a trick on these older bikes...to hold the needle in without letting it fall, then put the float in place to hold the needle, all without dropping the needle into the endless supply of crevices on the bike!).  I put the bowl back on, turned the fuel back on and fired it up...again.  SUCCESS!  All 4 cylinders were now firing.


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Last Update: Wednesday, December 14, 2005 11:53 PM