1981 CB750K Carb trouble.

[runabout879]

When first starting the bike, it will run a little rough, but smooth out as it warms up. Just as it's getting almost to the operating temperature, it will act like it's starving for fuel, choking back, with no power. If you're persistent with it, fuel will start leaking from the #2 carb. Given time and persistence, it will clear up and run for the rest of the trip. I remembered from cleaning them, that the vacuum pistons on the top were a little scored on the edges, so I removed them and used some 2000 grit sandpaper to smooth it out. I reassembled them, lubricated lightly. After reassembly, idle was better, but still had the same problem after it warmed up. Any thoughts on this matter would be greatly appreciated.

[Re-run]

Have you pulled out your spark plugs to see what they look like? If anything, they will tell you if your mix is lean or rich.

[runabout879]

I actually got to looking at the service manual, and it was mentioning the accelerator pump and air cut off. I tore it down again and found that all the diaphragms had holes. Some were worse than others. crc2onlinecatalog has all those parts for a reasonable price. Now I just have to wait to get them installed. My brother made me a deal I couldn't refuse. He'd trade his 2000 GS500 for my 81 CB750K plus some cash. He'll be joining this forum shortly. Thanks for all the help and suggestions!

[tabney]

runabout879 wrote

I actually got to looking at the service manual, and it was mentioning the
accelerator pump and air cut off. I tore it down again and found that all
the diaphragms had holes. Some were worse than others. crc2onlinecatalog has
all those parts for a reasonable price. Now I just have to wait to get them
installed. My brother made me a deal I couldn't refuse. He'd trade his 2000
GS500 for my 81 CB750K plus some cash. He'll be joining this forum shortly.
Thanks for all the help and suggestions!

And here I am. The parts have been ordered and hopefully this will solve the issue. Hopefully I'll be picking up a cb650 tomorrow as a parts bike...

[TOOLS1]

Welcome to the forum.
TOOLS

[Re-run]

Oh a cb650, what year? 79-82 are sohc bikes and so very few if any parts will cross over.
Welcome though and don't be afraid to ask anything!

[BoneyLiverThompkins]

Hi, just joined the forum. I have an 81 cb750k and im having the same problems. Please let me know if this work for you. Also im having trouble finding the correct valve replacements. Do you happen to remember what website you ordered them from.

[sgtslag]

Just an FYI, make sure you have the OEM air box, as pod filters will not work on the DOHC carbs (they depend on the vacuum generated by the air box, so without the air box, they will never work properly).  Cheers!