Purchased this Cb750k7 in late July of 2019. Just want to share the story so as to involve myself a little more on the forum. This bike could do much better than I but since I've been lurking here the site has helped me much in doing right by this old ride.
Let me preface this by saying I learn things by doing them. Didn't have anyone in my life who rode so I taught myself what i know by putting together an old Yam dt175 from spare parts in someone's garage when I was in highschool. It ran for a month. Couldn't figure out what was wrong and sold it. Almost 10 years later I got the itch to ride again, at this point my mechanic knowledge have developed nicely. Im no expert but my skills are relied upon by those close to me, and i am beginning a transition from DIYer to a hobbyist. Needless to say I now enjoy collecting tools.
With around a month of riding experience (10 years ago) under my belt I set my eyes on my first cb750. Traveled an hour away to see it and found it didn't run with the choke off but I reckoned I could clean and tweak the carb and it'd be alright. It also was showing beginning signs of a head gasket leak because I could see tiny drops of oil developing around that area. The tank wasn't right for the year causing the petcock to be on the wrong side and there was no seat just a bundle of towels. I signed the title before I could think about it.
I clumsily rode to an empty nearby training course to practice a bit before making the trip home. About 45 minutes later the bike died. I was bummed. I thought to call the PO and ask if there were any tricks to getting started again. He brought me a spare battery and explained that the charge on these old bikes drain in the lower rpm range. But I felt it might be more than that.
At this point it was dark and I decided I needed to make the trip now. I rode home with my jacket open, getting slapped by the zipper constantly and forgetting I'd stuffed the title into the inside jacket pocket. It fell out on the ride.
I researched the battery draining issue and the titling laws of my area. Upon testing I concluded the stator was bad. I bought a replacement and the charging problem was solved for now. I contacted the PO and with his cooperation received a title 2 months later (he took his time getting a new title). In that time a friend had given me pretty cool seat which is what you see in the pictures.
While on a ride a couple months after that my headlight and taillight stopped working but my brake light still did. I found the fuse busted, and 3 more replacement fuses busted as soon as I flipped the switch. The stator cover also leaked a lot of oil. I decided now would be a good time to tackle the carburetor as well.
I took a while to clean the pd41a carbs. I found some of the seals busted so I had to become familiar with parts suppliers. Then the carbs weeped gas from the intake, I adjusted the floats and changed the float needles. I went for a ride and it now could idle with choke off. But it still ran rough, taking a lot of throttle to take off. I also knocked the tank off a table, and while trying to catch the tank knocked the bike over. Dented tank, dented stator cover...
It took a lot of tries to get the stator cover to not leak and i blame the whole ordeal on the delicate rubber grommet where the wires come out. I finally got that sealed just to notice a small leak from the head.
I rode it like that a couple months, only during the day of course. When I was ready again, i dove in to trying to fix it up again.
After reading about other forum members set ups I ended up going back into the carb to check the jets. 120 mains and 42 slow. I check the slide needle, its on the last notch (lowest notch, highest fuel flow setting). I didn't mess with any of that. Then I realized the holes in my accelerator pump plunger were sealed up! Replaced with new.
At this point I had the bright idea to pop the dents in the tank out by igniting a tiny bit of gas inside of it and having the pressure do the work. I added 3 tbsp of gasoline, and fired away.
The new tank is the correct year tank for it and I like it much better. Although it doesn't have a funky design.
Installed new tank and also upgraded the cheap pods with uni filters and l went for a ride. It ran great! Leapt off the line and accelerated much better throughout the throttle, but I think I still percieved some weakness in the mid range.
I also sat down and made a wiring diagram and with much testing tracked the headlight issue down to a short in the taillight. I seem to be accident prone because the red plastic on the taillight fell out while on a ride and I had to rig up a solution for the time being. Also the kerker badge fell off the exhaust.
Everything was good for a couple weeks. After that. The new tank had a little rust in it so I cleaned it out with some phosphoric acid, drained it. Rinsed with a gallon of gasoline and a tiny bit of 2 stroke oil to keep flash rust off. Then I filled the tank back up. Ordered and installed a fuel filter.
Battery died the other day but might've been cause of all the riding in town. I rode in the rain for the first time on it also and the engine kept losing power and dying. I limped it home at its max speed of 40 miles an hour with it dying constantly and lots backfiring when decelerating. I was able to get the bike started up the next day so I thought all was normal again. Must've been the rain I thought...
I was coming home from completing a motorcycle safety course (100% on both tests!) When the engine suddenly let out a huge bang. Then another. I started losing power so I made my way over to the shoulder of the highway. The engine would turn over and rev up but would lose power again quickly and die.
I decided to call a tow and had a feeling the engine had finally lost compression through the head gasket. I really shouldn't have been riding it as much as I was but I though I could wait to work on the engine until winter. The next day I started the bike and it idled rough. I also found that cylinder 2 and 3 plug holes were getting worn out. I shut it off and decided it was time to take the engine out. I got a frame kit from scotly so when I received that I cut the frame. Only I pulled a bonehead move and cut it wrong...
Starting to think my brain needs an overhaul. I stil think im doing more good than harm. Anyway, that's where I'm at as of today.
If anyone has tips throughout the project feel free to chime in.
