Help getting a CB77 to start after rebuild.

Dave!

Dave!

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I am getting very frustrated trying to get this CB77 to start and looking for some help. I am new to motorcycles but not mechanics so I am hoping I am missing something obvious. I inherited two 1965 Superhawks that were partially restored by the previous owner before he passed away. The engines were completed and I am assuming they were done properly as he had a lot of motorcycle knowledge and I am not eager to tear those apart if not necessary. I picked at them over the past 6 or so years and am determined to do something with them this summer instead of tripping over them in my garage. One was more assembled, so I am starting on it first. So far, I have done the following to try and make it run:
  • New carb kits. Rebuilt and set floats, idle, and mixture screws to datum points.
  • Fuel fills bowl.
  • New points. Set gap and static timing.
  • Coils. Tried an original set as well as a pair of Emgo ones that were with the parts included. New condenser, new plugs, new ignition wires.
  • Plugs will spark.
  • Adjusted tappets.
The starter will crank and the engine turns but absolutely no attempt at starting. Individual components seem to test OK but the engine will not even cough. I have a schematic and there is a reference to a stop switch. It appears to be just the switch to turn on the taillight but did this bike have a kill switch? Any help would be greatly appreciated. I would love to see this back on the road. Thanks. Dave
 
Just to confirm - you do get spark while cranking?

If so, that renders the kill switch piece irrelevant. All that switch does is stop power to the coil - if you've got spark, you've got power.

That brings us to Fuel, Air and Compression. If we take the leap of faith that compression is good, timing is correct, gap is correct and valves are correct, the next step is to check fuel. Remove a spark plug, clean it off, attach it back to the HT lead, then with the threads of the spark plug touching the cylinder head, crank the engine - make sure you've got a clean white/blue spark.

Place the plug back in the engine, crank again. Remove plug after about 2-3 attempts and take a look at the electrode - it should be wet with fuel. No fuel on the plug, then it's a matter of tracking fuel backwards through the equation.

If fuel is present, then we've got Air to tackle. Generally even with bad airflow you'd get some kind of popping or weak attempts at starts, but simply removing the filters/airbox for now not only makes it easier to see if the carbs are reacting properly to changes in throttle but also removes lack of airflow as a possible cause.
 
With everything set 'by the book' it should start easily, your going to have to re check the obvious as listed above.
One thing that used to be very common is assembling advance mechanism 180 degrees out.
I haven't worked on CB72/77 since I was about 14~15 though so can't be much help. (it was about 54 years ago)
 
Definitely get a spark while cranking. I am assuming it is a descent spark but never seen it in running condition. It is blue/white and about the same as what I would get on my snowblower which isn't much smaller of an engine. I had tested it the way you described.

I do not have the air box on so there really should be nothing impeding air flow.

I am going to look closer at the fuel the way you described. I tried a shot of starter fluid. On a car I have done that and it will attempt to start even if it is not getting fuel. Since it didn't try starting with the starter fluid I was focusing on spark. Any tip on how to determine if it is a good spark? I did give myself a pretty good shock while testing!
 
crazypj said:
With everything set 'by the book' it should start easily, your going to have to re check the obvious as listed above.
One thing that used to be very common is assembling advance mechanism 180 degrees out.
I haven't worked on CB72/77 since I was about 14~15 though so can't be much help. (it was about 54 years ago)
Click to expand...
That is what I am finding very frustrating. It is a very simple machine and really not many variables. I have started today by resetting everything and trying again. Thought I might not have set it on the compression stroke. Still no luck.
 
Dave! said:
Definitely get a spark while cranking. I am assuming it is a descent spark but never seen it in running condition. It is blue/white and about the same as what I would get on my snowblower which isn't much smaller of an engine. I had tested it the way you described.

I do not have the air box on so there really should be nothing impeding air flow.

I am going to look closer at the fuel the way you described. I tried a shot of starter fluid. On a car I have done that and it will attempt to start even if it is not getting fuel. Since it didn't try starting with the starter fluid I was focusing on spark. Any tip on how to determine if it is a good spark? I did give myself a pretty good shock while testing!
Click to expand...
If you've got that kind of spark you're in good shape there. Since starting fluid didn't yield even a pop, I'm doubting it's fuel - but check anyway.
As embarrassing as it is to admit, every single time I've encountered this after a rebuild it's been from having the coils flipped, and it's been more than a handful of times.
 
Something that can be a problem and is incredibly frustrating, the points plate has been loose in the housing at some time and points plate moves around too much (up/down/side/side) so setting gap becomes almost impossible.
You pretty much have to decide where it's going to be and make all adjustments with points plate held up or down.
Even if you don't have a groove, the plate is a pretty sloppy fit so getting gap correct both sides and timing marks lined up can take 'weeks' (or at least feel like it has)
If leads haven't been cut short over time they should reach opposite side without removing tank to get at wires and swapping there, much easier than pulling motor.
I guess you've watched the You Tube video on setting points/timing multiple times by now?
 
crazypj said:
Something that can be a problem and is incredibly frustrating, the points plate has been loose in the housing at some time and points plate moves around too much (up/down/side/side) so setting gap becomes almost impossible.
You pretty much have to decide where it's going to be and make all adjustments with points plate held up or down.
Even if you don't have a groove, the plate is a pretty sloppy fit so getting gap correct both sides and timing marks lined up can take 'weeks' (or at least feel like it has)
If leads haven't been cut short over time they should reach opposite side without removing tank to get at wires and swapping there, much easier than pulling motor.
I guess you've watched the You Tube video on setting points/timing multiple times by now?
Click to expand...
The plate seems to fit snugly and all retaining screws seem good. I had a hell of a time with using the light but finally figured out I was off by one rotation. I think I have things set using the compression stroke. That is right isn't it? Tappets too?

I think I will step away from it for this afternoon and try double checking settings in the morning. I will take out my frustrations chopping up a parts car that has been littering my driveway and haul it to the scrapyard. At least that will make my wife and neighbours happy!
 
Dave! said:
The plate seems to fit snugly and all retaining screws seem good. I had a hell of a time with using the light but finally figured out I was off by one rotation. I think I have things set using the compression stroke. That is right isn't it? Tappets too?
Click to expand...
Yes, timing and valve adjustments done on compression stroke. Valve adjustments done stone cold overnight.
 
A compression check wouldn't be a bad idea, just to ensure it has some and they are roughly equal

Regarding "new carb kits", I hope you didn't install brass from cheap carb kits. Main jets and jet needles are garbage in those kits and have caused much tuner hair loss. I always reuse the old brass, and never a problem
 
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