Topic: 1973 CB750 build - Toronto Canada

[drumandbass75]

How's it going everybody!
There is a lot of great information on these forums and I am glad to be apart of this site as of now! I recently got into the cafe racer scene as I really like the overall style and heritage of the older jap bikes.

I picked up a 1973 CB750 in December that has had some work done to it by the previous owner. It has a custom rear seat, the frame was done in an interesting way in order to cover up the previous oil tank brackets..custom front headlights, forks apparently off a suzuki.
Also: new points, new spark plugs and wires, new ignition coils, new gaskets on the interior, valves had been gapped (lashed), fully rewired, stainless breakline, rebuilt front master cylinder and front break, new dunlop tires, new spedometer. He said he rebuilt the engine but I don't believe anything serious was done other than replaced gaskets.
This is how I bough the bike from the owner for 2500.00 off kijiji.

16733486610_1d68a7885e_o by fpi_tactics, on Flickr

Decent looking bike. I drove it around, it was pretty damn cold around -20 but me an my buddies were excited to get it off the trailer and start it up. The bike started up without any problems when I went to go see the bike. It did so again however died a couple times (because of the cold I guess) and after warming up it did seem to bog a bit in the higher rpms. Anyway warmed up the bike again the next week and took it for a spin, no bogging this time worked pretty good had a healthy idle (a little backfiring).

*First problem, the custom rearsets were attached to some piece of aluminum and the welded onto the frame, these flew off while riding (I guess after using the kick start a couple times. The rearsets did not have enough clearance and interfered with the kick start).

DSC_0229 by fpi_tactics, on Flickr

Second problem, I noticed quite a bit of oil or unburned gas in the left tailpipe (its a 4-2 exhaust) after warming it up the second time for about 20 minutes. I had pulled off the exhaust (to repaint) and removed the spark plugs. Looks like its coming from cylinder 1 (if im not getting it backwards). Plugs also seem to be fouled, so it's running a bit rich I assume.

Here you can see the unburned fuel or oil
DSC_0024 by fpi_tactics, on Flickr

There was about triple this amount in the exhaust tip
DSC_0026 by fpi_tactics, on Flickr

The inside of the corresponding headers
DSC_0053 by fpi_tactics, on Flickr
DSC_0052 by fpi_tactics, on Flickr


Here are the spark plugs, the plug from the leaky cylinder is black and a bit wet as you can tell by the first photo. All of the other plugs are sort of dusty black, (second photo)
DSC_0039 by fpi_tactics, on Flickr
DSC_0038 by fpi_tactics, on Flickr

Anyway they're Champions so first thing I did was buy Some NGKS's. Will be gapping and installing them soon. Anyone know what the gap is on these??
DSC_0071 by fpi_tactics, on Flickr

I also bought some new pod filters (old square breadbox filter) for the carbs which seem to be in decent shape. Im going to have them cleaned, and also replacing all the fuel lines and filters (i broke one as you can see)
DSC_0054 by fpi_tactics, on Flickr
DSC_0065 by fpi_tactics, on Flickr
DSC_0029 by fpi_tactics, on Flickr
DSC_0075 by fpi_tactics, on Flickr

Also got rid of these chrome grips and bought something nicer
DSC_0068 by fpi_tactics, on Flickr
DSC_0083 by fpi_tactics, on Flickr


Anyways, in order to address the first problem I started off by buying these custom CNC'D rearset brackets from CognitoMoto.
Very happy with the part, although it was a bit expensive to ship, especially with the Canadian dollar being so low (not the best time to be buying stuff from the states on a regular basis) I had some friends help me out grinding down and cleaning up the old tig welding marks. I have a airbrush coming in the mail so I will paint over that nicely as well.
DSC_0019 by fpi_tactics, on Flickr
DSC_0021 by fpi_tactics, on Flickr

These are the custom cb750 rearsets from CognitoMoto, and some photos of the workspace 
Also bought some plastidip as I plan on painting the bike flat black! and still retain the copper orange paintjob for the future
DSC_0093 by fpi_tactics, on Flickr
DSC_0078 by fpi_tactics, on Flickr
DSC_0082 by fpi_tactics, on Flickr
DSC_0070 by fpi_tactics, on Flickr
DSC_0055 by fpi_tactics, on Flickr
DSC_0076 by fpi_tactics, on Flickr



ALSO, I decided to take off the tank as there was a bit of rust inside. After 2 days of it being taken off the bike, and filled with 18LITERS of APPLE CIDER VINIGAR, it was completely spotless. Magic. I didn't put bolts and washers in or or anything, I just let it sit for a couple days. The rust came back kind of quickly at the cap, but I shall clean it again quickly after painting it and fill it with gasoline. Also bought a new rear mounted licence plate bracket off of ebay for 40.00, which included the break light.
Guess what, the petcock was also cracked when I took it out so I'm getting a new one along with some other miscellaneous from vintage0cb750.
DSC_0098 by fpi_tactics, on Flickr
DSC_0016 by fpi_tactics, on Flickr
DSC_0088 by fpi_tactics, on Flickr

Probably my biggest worry/ problem with the bike right now is at the fork and headtube. Looks like it was hacked at with a flathead in order for the fork to properly clear.
I dont think its a big issue although Im not quite sure about this. It does however not look too great. Probably the worst part about the bike I think.
DSC_0056 by fpi_tactics, on Flickr
DSC_0060 by fpi_tactics, on Flickr




More to come!! Thanks for reading! If you guys have any advice in regards to the Oil please let me know! It could be the piston rings however I dont want to pull the engine out just yet, as Im thinking of selling the bike.

I am going to put in the new park plugs, get the carbs cleaned, get the thing tuned and ignition coils timed, install other parts I have ordered (mechanical and aesthetic) and take her around for a couple rides as the weather here is finally starting to warm up. And Ill be taking it from there!

[calj737]

Backfiring is likely due to a lean condition. That is contributed to by the exhausts being so short and apparently non-baffled. Best to get your carbs tuned for the configuration of exhaust and induction setup.

The wet soot in the exhaust chambers is probably fuel mixing with the carbon. Does it have an odor of fuel or consistency of oil?

[Retro Rocket]

You might want to look at using the breadbox filter mate, your bike will be far easier to tune using it. The breadbox relies on the stock style velocity stacks to work properly, the little pod filters are just a problem and NEVER work as well as the stock airbox or the breadbox.......

[drumandbass75]

Finally took he carbs off, they look pretty clea
except for these deposits, they look like fish eggs??!

I'm joking, my bet guess is that its rust accumulated from the tank? Any ideas?
I was going to get the carbs ultrasonically cleaned however I think I'll be able to manage this one myself it seems

DSC_0117[1] by fpi_tactics,

DSC_0118[1] by fpi_tactics,
DSC_0123[1] by fpi_tactics,

[drumandbass75]

calj737,

I will definitely get the bike tuned once I finish everything up, might need some different jets. The black stuff was more viscous and had less of a smell I found.

[calj737]

Do get them cleaned Ultrasonically. Cant beat that. But that won't be enough cleaning anyway. Those dudes need a full disassembly. Thats varnished gas (dehydrated and left sitting). By the way, the inline fuel filter looks backwards in that picture. Best to remove it anyway...

If your carbs look like that, your tank is probably as bad. Drain it. Inspect it thoroughly. You want shiny, shiny, shiny inside and under the cap.

[drumandbass75]

I was actually speaking to a local shop which fully disassembles the carb, then cleans the components ultrasonically and then assembles everything back for 130.00. I could take the carbs apart, but feel nervous about setting everything right back together; rater have it done right the first time.

Tank was drained, got most of the rust out, however Im going to repeat my apple cider vinegar process once i finish painting. Was thinking of just pressure washing the inside too after.

[calj737]

The vinegar soak should be all you need. Rinse with soapy water followed promptly by some fuel with a little 2-stroke oil mixed in. Slosh around well, set aside until ready to use.

Drain before using and fill with fresh gas.

[drumandbass75]

Awesome thanks for your help!

[SOHC4 Cafe Racer Fan]

$130 for complete disassembly, clean and rebuild is dirt cheap.  I assume parts (rebuild kit, jets, etc.), will be extra.  Still a good deal.

[drumandbass75]

$130 for complete disassembly, clean and rebuild is dirt cheap.  I assume parts (rebuild kit, jets, etc.), will be extra.  Still a good deal.

Indeed. My thoughts the same. I'm a bit tight right now so hopefully I won;t require additional components and make due with what is there.

[drumandbass75]

Carbs are back from cleaning. The gentleman did a great job, recommend it! Pannon Sports if your located in the GTA region.
Also plastidipped and clearcoated the fairing and tank black for now too see if I like it.
DSC_0897 by fpi_tactics
DSC_0901 by fpi_tactics, on Flickr