Topic: New CB rider from Alabama

[yitzac1990]

Hello everyone!  Just picked up a 1978 CB750K.  It definitely needs some work, but i look forward to spending some time on it.  This is my third bike; my first was a 2007 Yamaha YZF600R (NOT an R6..), and my second bike was a Honda CBR600RR.  I have always liked the old school bikes and especially cafe racers, so now its time to build one!  Im sure I will have lots of questions, but hopefully I can make good use of the search feature...

Here's a pic when I got it last night:



and here is a pic as it sits in my shop today:



When I bought it, the electric start wouldn't work, but the seller started it via kick, and it started on the second try.  When I got home, I tried to start it, but it wouldn't go.  I think maybe the clutch switch wires came disconnected?  either way, I checked to see if there was gas and found out the entire inside of the tank had rusted.  I am guessing this is what was causing the seller problems with running the bike, because when he started it, it died as soon as he gave it any throttle.  My guess is he used the last bit of fuel left in the lines to get it to kick over, and it had been running bad for him because rust was clogging the lines/filter.

Going to order carb rebuild kits, pod filters, jets, full 4-1 exhaust, redo the wiring, and some other stuff, and get it put back together and running.  It will also need a new chain and sprockets.

First question actually.....would it be worth it to try and remove the rust in the tank with (whatever chamicals)?  or should I go ahead and just find a new tank that is not as bad?  I bought a gallon of acetone today in case I wanted to try and clean it out, but I am wondering if its worth it to attempt...

[dhall57]

Welcome from North Carolina. The Works toilet bowl cleaner does a great job on rusty tanks. Get you 5 or 6 bottles,it's cheap $1.25 or so a bottle.

[calj737]

Do not replace the brass internals in your carbs with aftermarket jet kits. The stock jets and needles and tubes clean up and are far better quality and spec than most new junk.

The Works is the bomb for de-rusting. Just treat the tank promptly afterwards with a dose of Prep N Etch to prevent flash rusting.

[70CB750]

Welcome!

[yitzac1990]

Thanks for the info.  I actually found a tank on ebay today for $135 shipped, in pretty good condition, and looking super clean and shiny, like new, on the inside.  so ive got that on order, as well as a bnch of other parts.

Also, i thought i had to rejet the carbs in order to make up for the 4-1 exhaust system as well as pod filters?  I looked for Honda OEM part numbers of the jet sizes I needed specifically.

[scottly]

Welcome Yitz! There are some non K8 parts on your bike; the front fork and brake caliper appear to be from a K2 or earlier model, the exhaust is from an earlier model, although I can't identify the year, and the rear wheel is also from an earlier bike. Regarding pods, it's best to get the bike running properly with the stock airbox, if you have it, then re-tune for pods; otherwise you will be chasing your tail.  

[754]

Forks look right, and wheel...caliper is earlier. Is the chain 530 or 630.? Check the alignment.
 Welcome aboard. 

[grcamna2]

Welcome to the forum

[yitzac1990]

Thanks everyone, sorry for the slow replies, I have been working non-stop on this and other projects.

I currently have the carbs fully disassembled, and the bodies soaking to get them clean.  the previous owner did not take care of this thing one bit it seems, as every carb bowl was filled with nasty orange goo from the rusted tank.  I know its best to get things running good all stock, but that stock exhaust had to go as well, rust holes all over and whatnot.  and I figured while I am rebuilding the carbs let me go ahead and calculate the jets I need for the filters and exhaust and do it all.  I found a "calculator" on another forum that explained a "general" guideline with what jets to use for these mods.  once I get it running okay, I will bring it to a pro and have them look at it, tune it further, change out the chain and sprockets (current are a bit rusty and super loose), possibly rebuild the forks, etc.  bunch of maintenance items like that.

Also, oes anyone have a good in-depth instruction on re-assembling the carbs all back together?  when I was taking them apart, there were a few things that were real loose, springs hanging off, etc....would like to assemble them correctly without having to guess at anything!  I tried searching, but honestly couldn't find much on re-assembling the bank of carbs back together.

[yitzac1990]

also, to give you guys an idea of what I am going for, I really like the style of this bike here:



the only thing different from this i want to do, is some aftermarket rearsets with the Cognito rearset brackets to set them further back and a bit higher.

https://cognitomoto.com/collections/rearsets/products/cb550k-cb750k-rearset-brackets-keep-linkage?variant=668018161