1982 CB750C Project

[LuckyB50]

New to the forum, new to classic bikes. I got a good idea to build a cafe racer and spent a few long weeks looking for old hondas to satisfy that need. Unfortunately every bike I could see in NoVa that ran was already either built up, or extremely overpriced. So I took the leap and bought a non-running '82 Custom with 16k miles off a guy in WV for $750 bucks. He said it ran when parked (fingers crossed) and I have a new battery on the way. So far the tank is rusty so I cleaned it out, and have a new battery and ignition coil / spark wire pair coming to replace the dead battery and dry rotted cables. I did jumper-cable a different sized motorcycle battery to the bike and it does whump and chug over so the motor isn't seized, but the old spark plugs were black and a little wet, and I'm just hoping the piston rings aren't smoked. Either way, I'm excited to build on it over the winter and have a new bike by spring!

 

[amc49]

Do a compression test first and then run the valves, nobody ever does it and how most of them die. Probably why the plugs are black, no compression. Set all valves at .004"-.006" rather than what the service manual says.

Rare for the rings to be bad, will be valve seals if anything.

 

[LuckyB50]

While I'm waiting for some time and some parts to come in, can anyone identify the type of rear rim on this build?

https://www.pipeburn.com/honda-cb750-cafe-racer-7/

Thats the general size and look I'm looking for, it looks like a maybe 19" rim like the front but I can't find any info on a 19" comstar rear, so I must be off.

 

[amc49]

Could easily be a euro bike and they have access to things we don't. There is no 19" comstar here US at all for back, only 18" or 16". Pic shows a '79 18" spoke wheel, which reversed (convex to concave spoke profile) in '80 to not be the same. The front compared to back appears to be a 19", I measured it on screen like 3 times.

I understand the wanting the 'look' but when you guys go to those fat but tall profile front and rear Harley tires like that pic shows you get bad handling, the tires due to the tread pattern which is 100 years old absolutely loathe rain grooved pavement and complaints about it once you do it. The bike will hunt all over the place. Then look at the CORNERS on the back tire, corners on a modern roadbike tire??!! You lose all ability to ease and lean into a corner with that and bike is ruined as far as handling goes. What good is a hot looking bike if it sucks driving it? That square corner tire design was made for 700 pound motorcycles that never lean hardly at all.

Of course yours and do as you will..............you as well have picked the spoke that goes with the narrowest rear wheel made (2.15"), the '81 is somewhat wider (2.50") but still not enough for that tire size wanted.

 

[LuckyB50]

So getting into it, the tank is a bit of a dud. There is a dent near the fill cap that lets it leak, the petcock leaks, the inside appears to have been poorly lined in the past, there is still a ton of rust in it and there seems to be a few pinholes in the bottom near the petcock itself.

Does anyone know compatible tanks for these 1982 Customs? Anybody use any of the repro tanks or the ebay tanks, or do you all mostly just stick to hunting for OEM tanks?

 

[LuckyB50]

Well got all the slime cleaned out of the carbs, junk out of the jets and got it back together, (i think the kit came with 72 for the main jet and 102 for the secondary main) I tried to start it turns over, I got one huge backfire through the carb and then nothing but a little smoke. Just starter turning it over. Now I did try it with the carbs wide open, no filter/airbox on whatsoever. Would this completely stop it from starting? I've started old trucks with their filters off by spraying some starter fluid down the carb and its worked, and i know some bikes run things like velocity stacks, so i wouldn't think running wide open would stop it. I replaced the spark plugs, wires and ingition coils, I guess I need to go back through the wires and check for a break or check sparkulation on each plug before digging any deeper?

 

[fg1972]

Have you checked the coils are connected to the correct cdi igniter modules?