Wont Start After Restoration 1979 CB750f

[jchimienti]

I am not a professional, but I am a very diligent person who performed a total rebuild of my 79cb750f. I used my Clymer guide and various YouTube videos on some of the harder spots. I had the carbs professionally rebuild and used OEM parts when restoring each system.

Everything works including upgrading my lighting to LED, new coils, plugs, spark generators, entire braking systems etc.

The only thing i did not do is remove the pistons and the lower engine assembly.

I've owned the bike since 1985, had the valves redone at 12k miles about 1 year before i stored it in my garage in 1998. It has 14.4K on it now, and its totally rebuild.

IT SIMPLY WILL NOT START. The timing is perfect, the spark is perfect, the carbs are perfect. It simply turns over repeatedly. I've tried switching the coils, putting drops of oil in the head, using starter fluid, putting gas directly in the cylinders. NOTHING works. I barely get a backfire. I have oil pressure and compression. It all checks out. I diligently placed the cams back according to the guide and took pictures.

Any ideas are welcome at this point. There are few professionals in my area who would work on it.

 

[Rod]

I would re check valve clearance, cam timing, and ignition timing.

 

[MickMick]

I am not a professional, but I am a very diligent person who performed a total rebuild of my 79cb750f. I used my Clymer guide and various YouTube videos on some of the harder spots. I had the carbs professionally rebuild and used OEM parts when restoring each system.

Everything works including upgrading my lighting to LED, new coils, plugs, spark generators, entire braking systems etc.

The only thing i did not do is remove the pistons and the lower engine assembly.

I've owned the bike since 1985, had the valves redone at 12k miles about 1 year before i stored it in my garage in 1998. It has 14.4K on it now, and its totally rebuild.

IT SIMPLY WILL NOT START. The timing is perfect, the spark is perfect, the carbs are perfect. It simply turns over repeatedly. I've tried switching the coils, putting drops of oil in the head, using starter fluid, putting gas directly in the cylinders. NOTHING works. I barely get a backfire. I have oil pressure and compression. It all checks out. I diligently placed the cams back according to the guide and took pictures.

Any ideas are welcome at this point. There are few professionals in my area who would work on it.

So, fuel, spark and air......
Fuel, instead of using the choke, try and put your hand over the airbox intake to try and increase the vacuum in the carb to pull the fuel through. Have you checked for vacuum strength? Also check for a blockage.
Spark, is it strong enough and firing at the right time.
Air, do you have an air leak between the carbs and head or a leak in the carbs such as missing felt seals in the throttle flap bar.

 

[Indydave]

Sounds like mine...and I had ZERO compression on 3 cylinders. I'm pretty sure the timing chain slipped (which caused it to instantly shut down on the road)...bending valves.

I'm TRYING to get a new head or all parts for a valve job. OR an engine, reasonable price. 79 cb750f