1975 CB750K

[Bizz435]

Good afternoon group.
I was hooping to get some assistance. I inherited a 1975 CB 750 K from my father who has since passed away. This Bike means everything to me and has its original 10,200 miles. I remember when he was alive he fought and fought and fought to get this bike running back to its peak performance. Well the bike sat for some time after he couldn't get it right and spent a ton of money taking it to mechanics who "specialized" in fixing this kind of bike. We after all these years I am still in the same situation as where he left off.

I rebuilt the carbs and placed the clip on the 2nd ring on the main jet. I got the bike running and was told to leave the carb synch for last.

I've been driving the bike but its still not 100%.

It's tough to start at col and once it warms up it runs ok.

I checked the points gap and adjusted them to around. 15. The points look like they been replaced but not the entire plate. That looks original.

I checked the timing and noticed the timing is advanced. I loosened the 3 screws and tried to turn the plate to retard the timing and get the "F" to the line.

I noticed the plate will not move because the slots where the screws go are already at its max.

Once I try and raise the idle between 2000-3000 the motor sputters and a slight back fire comes out of the tail pipe.

I will be checking the compression tonight to see if that is an issue.

Can anyone tell me if this sounds like a carb problem or has anyone heard of a coil giving this problem?

Any help would be greatly appreciated.

PS Bizz (very frustrating)
 

[Re-run]

I have never had to adjust a points plate to its max. Honestly, I switched so long ago to an electronic ignition, I would have to see the plate and everything again. The plate though is for setting timing if I remember right.

I would download the service manual here, it is a big one so it will take a while.

My guess is your points are not set right and the timing is off. As for the plate age, unless it is warped, there is no reason to replace it. However, if your points and condensers are old, I would replace them. Fairly cheap to prevent a lot of headaches.

Also, with the manual, go through the initial carb settings. Get your air screws set right and the needle clip. Bench sync the carbs with a 1/8 inch drill bit, the smooth part, so all the openings are the same size.

If the plugs are old, might wanna replace those to, D8EA  NGK plugs. When you replace these, take the plug caps off the wires, they unscrew. Measure the resistance with an ohm meter, should be right around 5000 ohms. Take a wire cutter and clip half an inch off the end of each wire to present good wire to the caps, and then screw them back on. Watch the order you install them. Looking FROM the front of the bike, the right coil goes to  cylinders 2 & 3(the middle 2 cylinders), The left coil goes to 1 & 4. The order doesn't matter as both plugs fire at the same time on each coil, you just need the coils going to right set of plugs.

It will be somewhat hard to start when cold, not 20 seconds of cranking tough, but a couple.

Make sure the battery is charged well. A weak battery is bane to starting.

Also, when setting the points, closer together will make a stronger spark as the points will be closed slightly longer and allow the coils to saturate better. Closer to the minimum gap.

[Bizz435]

This is a picture of what I got I'm going to try to do the exhaust and intake valve adjustment and then see what else I can come up with and hopefully I'll be able to adjust the timing in the proper way. I appreciate your help and suggestions

On Apr 14, 2015 5:00 PM, "Re-run [via Honda CB750'S]" <[hidden email]> wrote:

I have never had to adjust a points plate to its max. Honestly, I switched so long ago to an electronic ignition, I would have to see the plate and everything again. The plate though is for setting timing if I remember right.

I would download the service manual here, it is a big one so it will take a while.

My guess is your points are not set right and the timing is off. As for the plate age, unless it is warped, there is no reason to replace it. However, if your points and condensers are old, I would replace them. Fairly cheap to prevent a lot of headaches.

Also, with the manual, go through the initial carb settings. Get your air screws set right and the needle clip. Bench sync the carbs with a 1/8 inch drill bit, the smooth part, so all the openings are the same size.

If the plugs are old, might wanna replace those to, D8EA  NGK plugs. When you replace these, take the plug caps off the wires, they unscrew. Measure the resistance with an ohm meter, should be right around 5000 ohms. Take a wire cutter and clip half an inch off the end of each wire to present good wire to the caps, and then screw them back on. Watch the order you install them. Looking FROM the front of the bike, the right coil goes to  cylinders 2 & 3(the middle 2 cylinders), The left coil goes to 1 & 4. The order doesn't matter as both plugs fire at the same time on each coil, you just need the coils going to right set of plugs.

It will be somewhat hard to start when cold, not 20 seconds of cranking tough, but a couple.

Make sure the battery is charged well. A weak battery is bane to starting.

Also, when setting the points, closer together will make a stronger spark as the points will be closed slightly longer and allow the coils to saturate better. Closer to the minimum gap.

The ride IS the adventure. The destination is just to get gas!

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