Topic: First build: CB750 K3 cafe

[-JP-]

Hello everybody.

I`ve been debaiting with myself should I open this build thread or not. I`ve been reading here a lot of extremely well written and documented build threads that are very entertaining and more importantly very helpful. It takes time and effort to write a good one. I hope I can meet the standards and maybe my story even helps somebody. More importantly this will help to keep me motivated with my project. Hope you enjoy.

So, last month me & my father bought a CB750 k5. My Father has always been into bikes so it was an easy desicion to buy it together. Plus I get to spend more time with the old man. We are no mechanics so we will have a lot of questions and this forum have so far been very helpful. I also bought Hondamans book and printed the workshop manual. So I think we are good to go to get this project underway.

Bike is documented k5, but after research we found out it has k3 engine, k2 frame and those 69-72 forks. It has 85 000 km (53 000ml) on the clock. Unclear is this true or not. When we bought the bike it was rideable, started right up which was somewhat a miracle. It was last ridden almost two years ago if I remember correctly. Not sure was it smart to start it, but it ran fine. Previous owner mentioned that it eats spark plugs when cold starting. Have to look in to that one asap. Regardless the starting point is not as bad as those rusty nightmares I`ve seen here.

First plan is to rebuild the forks & front brake. Also I will try to figure out that spark plug problem. Cleaning the fuel tank is on the list too. So we are not going to disassemble the whole bike right now. Summer is coming and we are trying to get on the road. Plan is to rebuild the engine next winter. What comes to looks of the bike I would like to keep it vintage. Everything else is still open and might and probably will change. Project will go on when the budget allows so this is going to be a long one.

Couple of photos:

(Sorry for the phone picture quality. I will take better ones from now on.)

Previous owners photo:



From my garage. Starting point:



And it begins:





Disassembled the forks.





These popped out:



Oil in the tubes were black and dirty as you can expect. I cleaned all the parts and ordered new fork tubes and seals. I will first use old springs because I want to know how they perform on the street. Springs were in factory specs.

Looking forward to post again. Thanks and nice to meet you all.

-JP-

[riffman12]

are those sockets the guy was using as spacers in the forks?? 

[70CB750]

Welcome, JP!

Good plan, get it on the road and maybe there will be no need to rebuild the engine.  53 000 miles is not that much for Honda.

[754]

 nothing wrong with your writing or pics... nice bike... i suspect the sockets were used to preload the springs ..

[-JP-]

Thanks! Yes, the sockets were used for preload. Common thing as I later discovered. Bought some hard plastic rod to use instead when I put the forks back together.

I removed the tank and disassembled the petcock. I have to order new seals for it. And those two screws were quite rusty so I think I`m going to replace them too. The tank was in relatively good condition. It has rust inside, but I didn`t find huge wear or holes at a quick glimpse. Bikes original paint scheme had been candy gold as I discovered when I flipped the tank over.

I also removed the triple tree for painting. I tried to remove the old paint with a paint remover, but I didn`t have much luck. So I have to soda plast them. One thing that can cause a little problem is the indicator light panel. I have to remove that decal from it to be able to paint it. Maybe I should apply some heat on it and try to carefully remove it with a knife. If there`s a better way please feel free to tell.






-JP-

[pmanning]

With pod filters and aftermarket exhaust carburetor jetting could be an issue with your spark plug situation.  Also with the bike sitting for a long time carbs will need a close look.

[70CB750]

I took the decal of mine and as far as i remember I just carefully pried it off.  Heat would probably work too.  I stripped and polished my dash and glued the decal back on.

[Stev-o]

Nice project...subscribed.

[SOHC4 Cafe Racer Fan]

Get under it with a razor blade and work it gently off. It should give and pop loose.
Replacements are available if you botch it. 

[-JP-]

Previous owner mentioned that he put bigger jets in, but I`m not sure what size so I have to contact the guy. This carburator thing is a bit dark zone to me. I have to look in to that after I got the front end sorted out.

I spent the last day soda blasting the triple tree. Worked like a charm. That decal in the instrument panel was an easy task. Some heat and carpet knife and a little patience did the job. About the paint: Is the original paint gloss black or something else? What do you guys prefer for the factory look? I`m going to send the parts for powder coating next week.












-JP-

[Stev-o]

Nice job on the blast.  Semi gloss black is a close match to stock. 

[SOHC4 Cafe Racer Fan]

Good work on the blasting.  The powder/paint has some sheen but not a high gloss.  Semi would work well.

[-JP-]

Trying to figure out should I keep the pods or not. I like the looks of them. I have also read that pods can be very difficult to tune. And tuning is something I`m not familiar at all. Yet. I just watched last episode of Hackaweek where Dino told his opinion about this so I decided to use the stock airbox. After all it fits my plans and more likely it will hopefully be easier to tune and there should be less running issues. So I took a look inside the airbox:





Velocity stack on the left is hard and deformed. It is possible to revive these, but how? Or should I just replace it?





I certainly need to order new airfilter and maybe velocity stacks if I can`t revive them. Airbox rubber seal was also broken. Is k&n the only way to go or are you running oem filters. I`m going to rebuild the carbs so does the k&n perform well with stock setup? I also have 4 K&L carb rebuild kits. Are these any good? What I`ve read many prefer oem Honda (hard to find). What about Yamiya kits?

-JP-

[SOHC4 Cafe Racer Fan]

If you have the stock airbox and you are running a stock engine, use it.  You can try rejuvenating the rubber velocity stacks using wintergreen oil (do a search on the forum), or buy new ones.

Also, buy a K&N aftermarket filter to replace the stock filter.

[przjohn]

Great pics and best of luck with your build. Personally I would just replace the rubber stacks if you have it in the budget. There is enough going on already with getting the carbs, aligned, air box mounted, etc. that you don't want those things making it more of a PITA.

[Stev-o]

+1...replace the rubbers and get a K&N...

[-JP-]

I spent the last evening trying to figure out that spark plug problem. I tried to test the coils with multimeter. Primary sides were ok. About 4,7 ohms both. But I didn`t get any readings from the secondary side. So I quess I have to order new coils too and plug wires. I have to figure out which ones to get. 3 ohm or 5 ohm Dyna coils.

I also pulled the plugs out. What do you guys think? (Order 4-3-2-1)




Things are building up. I`m still waiting last parts for my front end. Should be arriving shortly. I decided to paint the triple tree instead of powdercoating so I have to get some semi gloss black paint and primer. I also have to order the parts for the carbs and for the airbox.

-JP-

[calj737]

5 Ohm coils for best results.

[SOHC4 Cafe Racer Fan]

Regardless of whether they appeared in spec, I would replace the old stock fork springs with some inexpensive progressive springs. You'll get an improvement over 40 plus year old springs.

[-JP-]

Received some parts today. Fork gaiters and headlamp ears. Both of them are top quality. That`s nice. I also found something during the weekend from my girlfriends farm. Or shes dads farm. Anyway, I was looking in these old warehouse/barn type buildings and I found an old drill press. It was dusty and rusty and had spider webs all over and it had probably been sitting in that corner for ages. I asked can I buy it. Well he gave it to me. So now I have a drill press in my garage. Maybe it will come in handy in this project. I cleaned it up the best I could and greased everything. Happy with the result.

I ordered progressive springs for my forks today. When those arrive (hopefully in 2 weeks) I can finally build the forks.



Headlamp ears and Ariete fork gaiters:



-JP-

[-JP-]

Took the carbs off today. I have to replace all the rubber hoses. Hoses were hard and brittle and broke when I took them off. Inlet manifold rubbers were quite hard too. Are they supposed to be soft?







I will receive a package from yamiya tomorrow so I can start the rebuild of these things. Nice to put something together for a while.

-JP-

[Davez134]

Yes, the intake manifold rubbers should be soft. They can be rejuvenated, or buy new if budget allows. Hard ones can cause all kinds of tuning nightmares if leaking.

[Stev-o]

+1 ... buy new carb boots...

[-JP-]

Got the parts from Yamiya today. Bleeder screw that I ordered is bigger than the old one that I had. Size difference is quite huge. New one is same diameter but longer. My caliper is in painting so I don`t have it to test fit. I have to contact Yamiya if nobody can`t point some light on this matter. Parts listing on Yamiyas website has only this bigger size bleeder screw.

Finally got that caliper bracket pin out. I had to use a press to get it moving. WD-40, hammering and heat didn`t work at all.







-JP-

[Stev-o]

That pin looks badly corroded, I'd be shopping for a replacement.