Topic: First Bike, First Build: 81' CB650

[dmable44]

Hey all, my names Derek. I bought an 81' CB650 with 9700 miles on it back in the fall and have plans to build it into a Brat/Cafe style bike. This is my first bike and I have a lot of questions and need a lot of help with it. It is cosmetically rough but starts and runs great. Its a project, which is what I wanted, and for the price I paid, I can't be happier.

 I have torn it down to the frame already, taking pictures and labeling everything and have done some modifications to the frame already but it needs a lot of parts and a lot of work yet. The plan is to get some clip ons, a 4-1 header with a cone muffler on it and a custom seat that I already have an idea for. Other than that, I already got a CB750 tank for it as the original one was shot. I'll need a chain, sprockets, tires, turn signals, tail light, headlight, an electronics pan, brake master cylinder, brake components and some other odds and ends like exhaust studs. I snapped a few removing the pipes. I also want to find a set of 82' CB650 carbs to get away from the pressed in main jet issue. I'm in college so I'll be working on a college budget but the goal is to get the bike road worthy by spring time.

Here is the bike the night I picked it up:




Here is the frame as it sits now:




And the tank:

[scunny]

Welcome Derek, you have come to the right place. just a thought looking at your frame, that round bar you welded at the back will likely come into contact with the rear tyre when shocks are compressed.
cheers Scunny

[dmable44]

Scunny, thank you! That's a rather good point that I obviously didn't think about. How do people do the frame loops then and not have that issue?

[SOHC4 Cafe Racer Fan]

You can get a great 4-2-1 Hindle exhaust from Ripple Rock. http://www.ripplerockracers.com/product/honda-cb650-hindle-stainless-steel-exhaust-fits-1979-82/
It's much better than a Mac header.

Rebuild/service your front shocks and brakes. The stock 650 uses air assist forks which really do not maintain pressure. You might want to replace the valve-top fork caps with non-valve caps. You can also replace the 40-year old springs with some progressives.

The brake calipers are an improvement over the 550 brakes.  You can further improve them by cross-drilling for less unsprung weight.

[dmable44]

I am really looking for a 4-1 unfortunately. Thanks for the info! My buddy has a 550 4-1 that we are going to look at modifying to work on the 650. I know they are slightly different.

Yes the shocks will get overhauled. I plan on doing front and rear. At the very minimum, new seals and fluid. I was also throwing around the idea of a fork swap to get a lower stance and get away from the air assist.

[SOHC4 Cafe Racer Fan]

I am really looking for a 4-1 unfortunately. Thanks for the info! My buddy has a 550 4-1 that we are going to look at modifying to work on the 650. I know they are slightly different.

Yes the shocks will get overhauled. I plan on doing front and rear. At the very minimum, new seals and fluid. I was also throwing around the idea of a fork swap to get a lower stance and get away from the air assist.

You could use standard non-valve caps and shorter tubes. Or 1975-76 GL1000 direct bolt in swap.

[dmable44]

Thanks for the info! Is it possible to clamp the triple tree farther down on the fork tubes to lower the front end?

Also, I am on the hunt for carbs. I have read that my 81' carbs have pressed in jets and cannot be rejetted; people usually swap 82' or later CB650 carbs to avoid the pressed in jets. Doing some further research, I have VB44A carbs and I am looking for VB44B or VB44C carbs. Is this correct?

[SOHC4 Cafe Racer Fan]

Thanks for the info! Is it possible to clamp the triple tree farther down on the fork tubes to lower the front end?

Yes. Make sure to examine the geometry (rake and trail) to make sure you do not make the bike unstable.

[dmable44]

I'll be sure to give that method a try and see how it handles then before I do a fork swap or anything. I will rebuild them regardless.

I am also looking for a brat/cafe style seat. I started to make one out of an old skateboard but the deck is not wide enough. Any ideas?

[SOHC4 Cafe Racer Fan]

I'll be sure to give that method a try and see how it handles then before I do a fork swap or anything. I will rebuild them regardless.

I am also looking for a brat/cafe style seat. I started to make one out of an old skateboard but the deck is not wide enough. Any ideas?

I would suggest not making it too flat. That style of seat does NOT lend itself to riding more than a couple of miles at a time. You also may want to keep your modification reversible.

[dmable44]

It will have an upsweep in the rear and be on the thicker side of seats for sure and it will be reversible.

As far as the for nuts, will 750 regular fork nuts work? I want to replace the air assist nuts with regular ones and run 15W fork oil.

I also need some help with mounting the tank. The 750 tank sits farther back but luckily the tab and the threaded hole on the frame match up, I just can't get to it from the top. I'll grab a picture shortly.

[SOHC4 Cafe Racer Fan]

It will have an upsweep in the rear and be on the thicker side of seats for sure and it will be reversible.

As far as the for nuts, will 750 regular fork nuts work? I want to replace the air assist nuts with regular ones and run 15W fork oil.

I also need some help with mounting the tank. The 750 tank sits farther back but luckily the tab and the threaded hole on the frame match up, I just can't get to it from the top. I'll grab a picture shortly.

I believe they are both 35mm tubes so the 750 or 550 caps should work.

[dmable44]

Here is the tank. I need to come up with something that comes up from underneath.

[dmable44]

Ordered a rear upswept frame loop which will be here tomorrow. Once I have that welded on I'm going to get some aluminum sheet metal and for a pan. My idea is to over cut the pan and hammer down the edges over the frame for a snug fit. Then I'll bolt a piece of wood to the aluminum. That will be my base for the seat, I'll put foam and other support on the wood and cover that. Still trying to figure out a mount for the tank.

[DohcBikes]

Wood has no place on a motorcycle.

Lowering a UJM will decrease performance almost every single time.

Congrats on your first build!

[dmable44]

Thanks! I need all the help and tips I can get.

Well I need something to staple the fabric and foam into and I wouldn't think the thin aluminum alone would be suitable for that and hold my weight.

I may get some taller/stiffer shocks in the rear to raise that then. I'm trying to get a straighter line on the bike if that makes sense.

[SOHC4 Cafe Racer Fan]

The 1980-82 CB650s are more cruiser than standard.  I am not sure as to the fork length, but it may be longer than a 550/750. 

Lowering the forks to the triple may or may not improve/worsen the performance.  You should look into the stock rake/trail measurements and see how lowering the stock forks will affect those numbers.

[dmable44]

I'll play around with it. Definitely don't want to go to any extremes and throw it out of that much whack.

Small update, I got a frame loop and welded it on today. Next step is to get some aluminum sheet metal for a seat pan.

[dmable44]

Got some steel sheet metal and made a seat pan and welded it to the frame. I need to invest in a better welder.

Also figured out the tank mount and its finalized.

Next step is to figure out a seat base, put the foam on it and cover it. Also need to stop by Honda and get some fork nuts, oil, oil filter, chain, sprockets, fork seals, fork oil, exhaust studs, and some other odds and ends I am probably forgetting.

[dmable44]

I also need to figure out some sort of electronics tray or area for the battery and connections. Any ideas/tips/opinions?

[SOHC4 Cafe Racer Fan]

Take a look at Cognitomoto's electronic tray pans -- that mount in the frame rails.  You may be able to fabricate something similar to mount underneath your seat.  One of the problems you may have is that it appears you have welded your seat pan directly onto the frame rails, making removal difficult or impossible.  If that's what you have done, you may want to rethink that idea - and instead weld tabs to mount a new seat onto the frame rails which you can remove to access electronics below.

[dmable44]

I rethought what I did after reading your post and I decided I screwed myself. So I looked at it and came up with an idea. I cut some of the pan out up front for top access and I'm gonna use existing bolt holes to hold the battery tray to the frame. Next step is a cardboard mockup of the tray and go from there.

I also scooped a great condition 17" rear wire wheel with a good tire on it from an 82' 650 last night. Waiting for that to come in the mail. Plan was to stop at the dealership to get some parts but with this incoming snow on the East Coast, I doubt they will be open.

[dmable44]

Was able to get to the Honda dealer in hopes of rebuilding the front forks today but had to order the seals and fork oil in. I did get all new exhaust studs, oil and oil filter for when the motor goes back in though. Where is the best place to buy a chain and set of sprockets? Still working out a battery tray design.

[dmable44]

I've been keeping up with my thread over on DTT if any of you really are interested.

So far I've changed directions and will be putting my money and time into making the bike fully operation, roadworthy, and safe for this season. I'll tear it all down next winter and do the aesthetic mods and powder the frame and make it look nice.

For now I picked up NOS sprockets, found an exhaust and carb rack, built a seat, mocked up a temporary battery tray to run the regular old battery for now, got a new rear wire wheel and tire, and some other odds and ends. Like I said, check out my thread on DTT, it has pictures and more info.

[irish44395]

Thanks for mentioning the TTD fourm. I like following 650 threads hopping I can learn as much as I can about these bikes .
Pete