Help. 1978 CB750k not starting

[ratgoblin]

This is my first bike and I'm trying to fix it up so it'll run. I personally haven't worked on bikes or anything before but am being talked through a lot by my brother whos a mechanic and done this a few times just not with a CB. Yesterday it was starting with choke and idling with choke but wouldn't idle without it. We figured out one sparkplug was foul'd and I ended up replacing all of them but now the bike won't start at all. You can hear it trying to start up but it doesn't ignite I think. Again I am VERY new to this so any advice would be appreciated.

(My brother would help more but we live in different states)

 

[dirtdigger]

New points? Old points?, checked point gap? if old have you cleaned then adjusted? Check timing? How is the engine....is compression good? If engine isnt healthy it will never run well. you need to start with basic engine tune up first, more than likely the carbs need to be cleaned well. The idle jet is the first one to get plugged and easily done with todays gas.

 

[ratgoblin]

New points? Old points?, checked point gap? if old have you cleaned then adjusted? Check timing? How is the engine....is compression good? If engine isnt healthy it will never run well. you need to start with basic engine tune up first, more than likely the carbs need to be cleaned well. The idle jet is the first one to get plugged and easily done with todays gas.

I haven't done much due to long work hours and only having the bike for a week now. I was told the carbs were cleaned before I bought it along with a new battery (they sold it bc the intended rider was not tall enough and they couldn't figure out a work around they liked) I'm getting a timing lamp sometime this week in the mail so that's my next check. Problem is I'm not sure what I'm looking at for a lot of stuff. I'm good with tools but unknowledgeable in mechanics. I'm relying a lot on google and my brother on video call at the moment.

I'll take a look into what you mentioned with the points. they're probably the most confusing part of this for me so far so i need to do reaserch into them anyway.

 

[madmtnmotors]

You can determine whether the problem is fuel delivery by giving it a small shot of starter fluid. If it starts then fuel delivery is suspect.

 

[Snider1970]

YouTube my friend. Classic Octane is good source. The rabbit hole will open from there

 

[gunr]

Common Motor Collective shows exactly the right way.

 

[BAHNST]

Badly synch'ed carbs could make starting difficult as well as old fuel.
I would suspect the carbs are partially blocked if it wouldn't idle without choke....
You could always drain/refill/drain the carbs using the petcock and carb bowl drain screws to see if that gets it to fire.

 

[Scootch]

Sounds like you took a step backwards after you changed the plugs. Maybe there is an issue with plug wires or caps? Did you install correct plugs? I might go back to the old plugs, get it running and go from there.