Topic: 1 and 3 not firing on CB750SS, Advice?

[CBGBs]

My 1978 CB750SS will not idle. It seems to run pretty well above 3k rpm but the 1 and 3 pipes are cool. I have been through the carbs and replaced the points plate with a good used one which didn't help. Idle screws are 1 3/4 turn out. Any advice? I haven't had it out on the road because it dies so easily.

[Handlebar]

My advice would be to remove the carbs again,and make sure the pilot jet "slow jet" is clear. There are very small orfices on the ends of these jets. I use a small wire picked from a wire wheel. The jets are not screwed in they are pressed in,but a pair of plyers with some electric tape on them works good, pull and twist straight.
I fought the same issue a couple of months ago with the same bike.

Good luck.

[CBGBs]

OK. I think I can handle that but if its pressed in then won't I have issues getting it back in tightly?

[mrbreeze]

1-3 not firing indicates that coil isn't putting out. Check and make sure there's 12 volts going into coil (black/white stripe wire). If that's OK check the points for that coil. If you have a timing light check 1 and 3 plug wires for a flashing timing light. If none then you aren't getting fire on that coil.

[madmtnmotors]

1-3 not firing indicates that coil isn't putting out. Check and make sure there's 12 volts going into coil (black/white stripe wire). If that's OK check the points for that coil. If you have a timing light check 1 and 3 plug wires for a flashing timing light. If none then you aren't getting fire on that coil.

No, that's not right. Cylinders one and four fire from the same coil while cylinders two and three fire from the other coil. Both coils would have to fail to take out cylinders one and three which would also take out cylinders two and four so none would fire...

[madmtnmotors]

It would be a good idea to confirm spark at both the one and three spark plug though. Bad boots?

[CBGBs]

I did snip the end of the plug wire to freshen the connection up but I have spark. I'm going to try to pull the pressed jets out. Not sure if they will stay in afterward.

[Handlebar]

The pressed jets will re-seat. Just use a little caution when removing and replacing. I am not saying that this is your problem,but if you have good spark,fuel is where i would start. These jets have 4 small orfices that set in the bowl and a very small orfice that feeds the low throttle fuel supply. My 750ss did the same thing ran great above 3500 rpm but no idle.

[CBGBs]

I have pulled the jets. I slipped a piece of rubber fuel line over the brass jet and then used pliers to pull them and then tapped them in with a plastic mallet. I mounted the carbs in the boots but have run out of time for right now. One of them looked kind of plugged up but I could see through the rest. Hope this gets it. I'll let you know.

[qside]

dont forget to check your float height too. I have had needle pins stick a little and a slight tap with a rubber mallet may loosen them.

[CBGBs]

I was buttoning up the carbs and realized that I swapped 1 and 3 carb bowles So I pulled them off again and put them back on. I haven't started her up yet because it was pretty late when I got everything back together. I'll be firing the bike up soon. I have the idle screw set at 1 1/2 turn.

[mrbreeze]

1-3 not firing indicates that coil isn't putting out. Check and make sure there's 12 volts going into coil (black/white stripe wire). If that's OK check the points for that coil. If you have a timing light check 1 and 3 plug wires for a flashing timing light. If none then you aren't getting fire on that coil.

No, that's not right. Cylinders one and four fire from the same coil while cylinders two and three fire from the other coil. Both coils would have to fail to take out cylinders one and three which would also take out cylinders two and four so none would fire...

Right you are Wibur...my bad!!! Head up a$$ moment!! I had 2-3 go out a few years back and it was a power wire loose connection at the coil. I need to read more carefully before I post.

[madmtnmotors]

Head up a$$ moment!!

Pretty much describes me most of the time!     

[CBGBs]

I pulled all the idle jets and ran the bike. It seems a bit better. I actually took it around the block twice but it will not idle for anything. Pipe one was warm this time. I'm getting really tired of pulling this whole thing off and putting it back on. I must have done it 8 times in the last 6 weeks. I do feel like that was good advice though. Maybe the passage wasn't clean well. IDK. I did run a guitar wire up there. I'm running some Sea Foam in it. Maybe with some street time it will work out.

[CBGBs]

I rode around for 11 miles and it is getting better. This is the most this bike has seen the road in the last 12 years probably.
My mechanic suggested riding it for awhile and continue to use Sea Foam. It will nearly idle now.

[Handlebar]

They can be challenging. The pilot jets need to be very clean. Keep running it,it will get better.

[flybox1]

Clear tube test your fuel height to make sure your jets are not sitting in too little (or too much) fuel.
If you have the right carbs for your bike, this test is seconds.  Place the clear tube on the overflow pipe, and then turn open the drain screw.
Check the level is 3mm below bowl gasket seam.