Jet Size for a '75 cb750k 5

[Niro]

I'm in the process of cleaning out, and rebuilding the carbs on my 1975 CB750 K5 and not sure if the jets in it now are correct. the bike has a velocity stack high flow air filter pods on it and it also has a 4 into 1 exhaust. once removed the main jet reads 115 and idle jet is 42. i know the stock should be 110 and 40. I was wondering if anyone could advise me on whether those are the appropriate size. Keeping in mind that i recently bought the and been having some fueling issues mainly fouled plugs every 3 weeks.

Some advice on where to purchase seals would be great too.
Thanks in advance for you help.

 

[brettp]

Your plugs tell the story of lean vs rich. Are you sure the fouled plugs are from fuel?

 

[Niro]

Yes too much fuel. I'll clean them and get. Few weeks of consistency, then fouled again.

 

[brettp]

Hard to tell what needs adjusting when reusing plugs. My suggestion, others may disagree, is to replace the plugs and only idle the engine for a minute or two, then check the plugs. When you know what you have to do with the idle circuit, get the bike to operating temp and rev the hell of of it for 15 seconds and kill the bike. Then check the plugs to see what they look like with the main jet involved.
Make adjustments based on the plugs' looks after these are done.

 

[barney905]

Pay attention to this guy Niro, Brett knows what he's talking about. My k5 sat in my shed for 22 years before my son shamed me into doing something with it. After getting it running and functioning I was also fouling plugs every time I'd ride it. I rebuilt, thoroughly cleaned the carburetors and re-synced them. The plugs still fouled every ride. I ended up pulling the engine, removing the top end and replaced the valve seals and anything rubber on the head. All of these rubber components were hard and cracking from lots of time and miles. That did the trick. No more fouling. Since I had it apart I lapped the valves also. New gaskets and a little love and I'm sure I'll get another 90k out of it.

 

[Niro]

Yep I plan to take his advice. Waiting on seal kit for the carb. Once I have it installed I plan to sync them and put new plugs and go from there.

I'm just not sure if the size of the jet is appropriate for my application. I hope I don't need to get I to the engine.

 

[barney905]

This is what 49 years and 97k miles looks like Niro. If the fouling problem is still there you might want to consider the valve seals. My 750 was well taken care of over the years with the exception of the storage time. When a friend was following on his bike he told me he was huffing gas fumes behind me. Too much fuel overwhelming the plugs. It ended up running on 2 cylinders before I got it home.

 

[barney905]

It's tough getting old but I do my best. My plugs were oil fouled not fuel fouled. Since the plugs weren't working it just pumped fuel out of the exhaust. Nasty.