1979 KZ750 twin(s)

[Yoflaco]

I recently acquired TWO identical 1979 KZ750 twins... now I'm starting to do some troubleshooting, tearing down and cleaning of components on one of them, the other is strong running right now and fun for daily rides.
Technical questions for any knowing folks out there; best method for removing flywheel without flywheel puller tool available? Going to diagnose and check out starter clutches on both. Heard these are notorious for issues. I have tried using the rear axle trick, but maybe I'm missing something as it isn't working.
Also, sprocket nut to replace 16 tooth front WILL NOT come off. tried heat, tried Kano Kroil penetrating, tried it again and again, tried impact gun, big *** breaker bar and tried most everything. Insight from anyone on frozen socket nut removal?

Any folks knowing or working on this era KZ750 twins still? Any common shared knowledge is appreciated. Looking for slip on exhaust recommendations, performance swap mods, tire and chain recommendations, etc... also looking for parts, parts swapping, etc





David
Marfa TX
PS BOTH bikes look like the blue one... well certainly because one is the pictured bike. Identical twins?! fun!

 

[Yoflaco]

Ok, so Im going to treat this thread as a running notebook for this KZtwin twin project. Ignore if you don’t care what im doing. Maybe it'll help someone else.
I got the frozen sprocket nut off. Pretty big nut was truly on there! Took four days of penetrating oils and lots of breaker bar action to loosen. A little heat gun action likely helped, but be careful with that and oils and solutions all around. Had the tank removed to be safe. Have now ordered 17 tooth front sunstar sprocket , stock 38 tooth rear also made by sunstar. going with 530 x-ring chain, about $95. Dropped oil pan, dropped oil pump, cleaning those now, luckily not much issue there, no metal. Still struggling with flywheel removal to get to starter clutch. Also, ordered new tubes and tires. I’ve been liking the Michelin pilot activs, stock sized. Will have whole new rear end as the swingarm has been removed and repacked with new grease. Cleaning up electrical contacts is slow going, but have rear master cylinder rehabilitation done, just need new rear brake hoses and new rear pads.
Btw.
These two twins, once Im done with the cleaning and going through, will become rental bikes for visitors wanting to tour around streets of west TX ... anyone using Twisted Road app and have advice or ideas how to do that rental idea best?

 

[Fordf350]

Love the old bikes, I have a 76 Honda cb 750. Will be following your progress.

 

[Yoflaco]

Thanks for the support. I too love the old bikes. All I’ve ever owned as for bikes- nothing more modern than 1999 (if that’s considered old I dont really know.)
They are simple enough when you think about it compared to nearly everything with a computer nowadays. I like that, but also like them to be reliable.

Weekend update- got some parts in and always more to order.
Both front and rear stock sized tires/tubes/rim strips, golden spectro 20w50 semi synthetic oil (I love this oil, but expensive!) , oil filters, front and rear sprocket, new 530 xring chain, and some carb rebuild kit. Need to get rear master cylinder mounted (has a broken bolt in the lower mounting hole...hm)
Rear caliper had some ripped dust seals on the mounting bolts, brake pads are getting low so going to order new ebc pads. Need new brake hose and banjo bolts, and bleeders. Total rear brake overhaul needed, basically. Even that piston was pretty scratched and corroded...Anywhere to get a replacement?

10mm x 1.25 on these rear banjo bolts
Rear Brake hose about 23” long eye to eye
Bleeder valves rusted and missing cap
Still havent remounted oil pan- need to get that done soon. Going to order some gaskets. Cleaned up oil pan sealing surfaces with light razor blade action and mineral spirits. Looks pretty good, not entirely clear of old gunk.
Will get into carbs and boots and etc likely next week.
Looking forward to wrapping these up to refocus on my 1984 R80RT thats been sitting for over 12 years by PO. Not in bad shape however, just ignored for a bit in the garage. Still serviced and checked yearly by him, just needs some love.

 

[Yoflaco]

Old dirty tank and gunky petcock clean up next.
Doing the vinegar soak for 48 hours, any ideas or advice best tank cleaning steps?
My thoughts were whte Vinegar soak and flush with h2o, rinse with acetone , air dry and blow dry in sun to dry out...

 

[Fordf350]

Pretty much how I have done some of mine. Then coated inside with some light machine oil if it was going to be some time before I was ready to use it.

 

[Yoflaco]

Before and after pics of my gas tank rehab.
Its taken me a bit more time than imagined, but happy with results now. Heres what I did, and this tank was pretty bad yall... 3-4 days total.
Removed petcock, put a cork bung in bottom hole. Filled with 3 gallons white vinegar , slosh around on occasion for about 24-48 hours, drain into 5 gal bucket you wont need for anything impt, rinse with good high pressure water hose spray nozzle, do it all over again with fresh vinegar another 24-48 hours. H20 Flush, rinsed with a little with acetone and air pressure hose. Nasty crap comes out of this tank! Then I used a new cork bung, replug hole, filled with about 1qt orthophosphoric acid rust remover (green liquid stuff) shake around careful not to spill or leaks on yourself or tank...let that sit about 10-30 minutes did a rinse after w h20 to remove some more gunk, and another .5 qt phosphoric rinse sloshed around, drained, air dry...
If spills anywehre outside tank use tshirt rag w soap and h20...

Here the pics...
before with little vinegar action just starting.

Nasty stuff rinsed out


After !

 

[Tim Scholz]

Id have never guessed you could get one that clean

 

[Texas T]

Wow!

That's a huge difference.

 

[Yoflaco]

Certainly have to dump the nasty tank rinse water/vinegar waste somewhere safely... in my case a giant bonfire pile I have going seemed fairly appropriate. Was pretty nasty stuff for a good few days in that tank and in the rinse water draining out of it. I like to protect the environment and our waters, and this stuff looked so nasty and had me worried!

Wasn’t until about day 4 that I felt happy enough to start in with the orthophospho (phosphoric acid) stages... that stuff also makes a bit more ‘gunk’ as it works its action, so rinse and repeat with that seemed appropriate as well in my case. A bit did dribble out and get on the tank paint which I didnt see or wipe up in time, and now it does appear it left a small acid ‘drip stain’ on the paint. Bummer. But, for a bike that came to me very affordably and essentially a project, felt good seeing clean metal inside. I shone a bright light in there and its not 100%, but about 80-90%, and will certainly be ready for my next steps. Waiting on aftermarket Harley petcock which fits these bikes, and new fuel lines (with in-line filters just in case ).
This bike came without an airbox, so might run pod filters. However, if anyone has an extra airbox let me know. Likely needs carb intake boots and etc too. Carbs look rebuilt already, so might just throw them on and hope its the right move.

 

[Yoflaco]

Where does the time go?

Since last update on this KZ750 twin, met a young man that broke down (had electrical issues) in Alpine TX riding an old 1980 CB650 from South Carolina to San Diego for the Diablo run put on by Biltwell. BTW in Alpine, look up and spend money at Big Bend Cycles... good helpful peeps and nice location if ever within 100 miles of this area. I then allowed him to rent/borrow a bike to cruise around Big Bend NP on. Well he somehow managed to break the turn light off. Likely tied gear to the light stems is my guess and that is the end of that light. He did manage to put 350+ miles on the bike in under 48 hours too, which is just TOO **** EASY to do while living out here in West Texas. Sounds like he had a blast and gazed lovingly at the mountains of Mexico south of Boquillas, so that is good...

Since that episode, I started tearing into the front end of the project KZ last weekend. Got 90% of the rear end put back together, new chain riveted, am just debating about new shocks.
ANY SHOCK RECOMMENDATIONS FOR KZ750 twin? I am looking at Hagon, or maybe YSS, but also leaning toward cheaper options if anyone has advice on this. ?

I did remov front wheel which has a speedometer gear unit attached to the hub, then removed master cylinder which will need EXTENSIVE love, will now be replacing original 1978 brake hoses, banjos, etc. I've removed the speedometer cable, removed turn/light switch, and will likely get into forks soon. Upgrading weight of fork oil and likely springs is all I am hoping to do there. Not sure what I will be getting into exactly as I've never worked on forks before. Thoughts, advice or helpful links?

 

[Jeff S]

Love the progress reports! And thanks for the note on Big Bend Cycles - I'm part-timer in Alpine and have seen that develop, but have never been in.