Topic: Buds CB750 K4

[Don R]

 I've found myself the caretaker of my brothers one-owner K4, it hasn't run in a few years, it currently has a sunrise orange tank set and has sat indoors for quite a while. The oil pump leaks down and the output shaft lets the oil leak out. I have a pump kit and a seal set aside for it. I put on a NOS seat that came with a parts buy a few years ago.
  Yesterday I exchanged the loose swingarm for a rebuilt one, put original shocks and the stock chain guard back on it. I sprayed some Blaster on the chain to help soften the dry chain lube.
 Today, I removed the carbs and began cleaning them. So far, it's come apart like you would expect. Nothing broke and I was surprised to find a K&N filter and F1 type float valves on it with the screens on top. He always watched for an updated part that might be advantageous. Who knows, it might have been me that did it.
  I think I'll put a set of reproduction CMSNL 341 pipes on it. They are currently riding on a K0 and use a set of still in the box Busso 4-4 no-no pipes on the K0. I've already serviced the front brakes and re-adjusted the rear brake.

[Don R]

 I'm also re-installing the stock front fender, right now it has one taken from an early gl1000 with the built-in mud flap mounted to the 750 bracket, it looks like a CB750A fender. The handlebar setbacks, windjammer wiring and top mounted start switch all have to go too.

[HondaMan]

That oil pump issue might be a stuck bypass valve: this is pretty common on the K4-5 era engines when Honda changed their molds. This also wasn't the first time: the 'new factory' K1 bikes also started out with the first of these leakers I remember seeing. What happened with the K1 bikes was: the hole where the little piston moves in-out with pump pressure, to hold oil in the pump and in the oil filter separate when shut off, would warp oval-ish in the sand-mold pump bodies, making the piston just barely stick open. In the K4-5 situation it happened near the transition from the K4 to the K5 engines when something must have happened to one (or more?) of the pump molds, which left a small ridge inside the tunnel where the piston's seal rests (these were not bored to finish). After some years of use, these will distort slightly and then the O-ring sticks, holding it slightly open and lowering the oil PSI about 15 (to 30-ish PSI at 4000 RPM with hot 20w50 oil). The 'cure' for the latter one is to remove the piston, gently file the ridge away with a round-profile file (it's on the top of the tunnel) and install a new O-ring. The K1 pumps usually just had to be changed out, or the hole rebored (tedious) to round and a new O-ring installed.

[Don R]

Thanks Mark, I'll check the pump closely when I take it apart.

[BenelliSEI]

Don…. I have a pair of nice, clean oil pumps that came with all the K7-8 stuff I bought a few months back. Do you know if all the cb750 oil pumps are interchangeable? You’re welcome to one if you need it.

[Don R]

 I believe they are the same, this one is a low miler, it just sat for a spell and decided to leak down but I do appreciate the offer and will keep it in mind when I get back to the k4.   
   I'm thrashing on a long-neglected (by a PO) pit bike for my daughter so she can take it home, today I noticed it had a North American type spark plug under an NGK resistor cap. It was an NGK so I just unscrewed the nub off of it and put the cap back on the threaded stud. I'm wondering how toasty the cap is inside after a long spell of double sparking. 

[MauiK3]

My K3 750 is draining back, I need to look into this.

[scottly]

They all leak down some over time.

[Don R]

They all leak down some over time.

The leaking down isn't as bad as the leaking out. Two issues.

[Don R]

 I find myself with the K4 in my race trailer ahead of the golf cart and pit bike Yamahopper. It needs some work and is in the way of setting up the Dragster for next month's opening day.
   Today it's going to be in the high 50's so I'm headed out to get the K4 out of the big white box and begin to unmodify the little things that my brother did over the years. Remove the windjammer brackets, hondlebar setbacks, top mount key switch, GL front fender, chrome chain guard, aftermarket rusty shocks. etc.
  I also have a K0 with a 341 CMSNL reproduction exhaust that is better suited to the K4, it needs to get that move and my remaining Busso set can go onto the K0.

[Don R]

 I got started on the K4 tonight, it's out of the trailer and on the lift. Bud had a failure of a Scotchlock leading to riding in a group in the dark using my headlight to see. He went wild in the headlight bucket cutting and soldering the Vetter harness in. It's gone now but I have repairs to make.
 Next up is the aftermarket faded red brake light/turn rear signals and wide eye turn signals. I'm not a fan of the look. I have a sweet set of early turn signal stems both front and rear that I'm thinking it needs.
 The once plentiful early turn signal box-o-stuff is looking pretty shabby after the bikes I've prettied up. I did find one more sweet set of chrome bodies and lenses. It's down to rust, pitts and faded lenses, I may do a fresh start and toss it. Even my Ratty Bike needs good lenses and chrome. L0L!

[newday777]

I got started on the K4 tonight, it's out of the trailer and on the lift. Bud had a failure of a Scotchlock leading to riding in a group in the dark using my headlight to see. He went wild in the headlight bucket cutting and soldering the Vetter harness in. It's gone now but I have repairs to make.
 Next up is the aftermarket faded red brake light/turn rear signals and wide eye turn signals. I'm not a fan of the look. I have a sweet set of early turn signal stems both front and rear that I'm thinking it needs.
 The once plentiful early turn signal box-o-stuff is looking pretty shabby after the bikes I've prettied up. I did find one more sweet set of chrome bodies and lenses. It's down to rust, pitts and faded lenses, I may do a fresh start and toss it. Even my Ratty Bike needs good lenses and chrome. L0L!

Ah yes, Scotchlocks..... I've put a large bag full of new of them in the yard sale bin and lots more removed and circular bin filed. I wonder if Lucus had his hand in designing them?
Have fun bringing the K4 back up to snuff.