tell me about 70's honda bikes

[kunar]

my dad's got a 72 (ish) honda cb750 (or cbr750?) thats been sitting for years. the last time it was registered was sometime in the 90's and its been sitting in a garage ever since. he got it in trade probably 5 years ago and hasn't done much with. im thinking about trying to get it from him and working on it myself. i dont know a thing about bikes, so i'm looking for help here. i know that the exhaust needs replaced. if i remember right, theres an issue in the carbs as well. not sure if it was the rubber boots or the carbs them selves. whats to look out for on these bikes, whats the common issues? any rough guess on what it could/would take to replace the exhaust and get the carbs straightened out?

 

[chrwilkins30]

I actually just got a 81 cb750f.

The carbs are probably your problem. They gum up the jets causing a poorly running bike. What is wrong with the exhaust btw.

 

[93 4x4]

cop a header for it and take the carbs off look in side the bowls see if gas was left in it to gum up check the tank see if it's clean , check the plugs ect. very dependable and reliable bikes of course get it running first, there not as fast as todays 750's but they fun to tinker with. start with the basics and go from there this is my bike i've had since 1973 a 65 honda cb160

 

[backwoods]

Restore what you can and keep original as much as possible. Those bikes are collectors items now. The value has started to skyrocket recently. A friend just sold an '83 cb1000 parts bike for 5k.

 

[kryptonitecb]

Easy to work on, Randaaks is a good source of carb rebuild kits and tech.

Sent from the road while ignoring traffic

 

[JibbaJibba56]

Someone might be referring to the setting each carb to get all cylinders running well. I had experience with one briefly and though it was clearly abused the engine still ran like a top. Really smooth good first bike for anyone that is curious and handy IMO. Have a go at it and I am sure you will get hooked on how advanced that motor was for that era.

 

[dhinch279]

Here's a short checklist of general problems and what to look out for.
My experience is with my 1982 Honda CB750F, it is a dual overhead cam engine and yours is a single overhead cam.
So they are not exactly the same but both are old none the less.

These instructions are mainly just to get the bike running to see if it's worth putting any money and time into:

Check the oil and make sure it hasn't leaked out. I would change the oil since it has been sitting for so long, but before changing the oil I would make sure that it turns over using the kick start. If plenty of oil is in there, its up to you if you want to change it, but I definitely wouldn't run that old oil in there for more than 15 seconds if it starts and runs. IMHO

Check the gas tank with a flashlight for alot of rust.
Cleaning the carbs won't do any good if rust clogs them up as soon as you put fresh gas through them.

If the tank is ok, you will definitely at least need to pull the bowls off the carbs and check them out and
clean them while you have them off. Spray carb cleaner up into the jets as best you can.
Normally, I recommend just taking the carbs off, but with a bike that old the carb boots are most likely dryer
than a 90 year old Nuns you know what, and they may crumble when you remove the carbs.
Eventually, you may have to replace them or make custom boots like I did out of radiator hose and aluminum inserts.

If it has a kick start (which a 72 should), you may not need a battery.
I would recommend you get a battery anyway because the electronics on these bikes are finicky and,
at least with my bike, it starts easier and runs better with a fully charged battery.

Check the Spark plugs to make sure they aren't fouled out.
Clean if necessary, and make sure the plug wires are securely attached to the coils and spark plugs.

After you do these things you should be able to at least crank it over and see what happens.
If it doesn't start after that, then it will be trouble shooting time.

Having said all this if it does start, FOR THE LOVE OF ALL THAT IS HOLY, I don't recommend driving
it any farther than 5 feet and only do that just to see if the clutch works and first gear works.
The front master cylinder is most likely seized and the brakes themselves need to be checked
before a ride around the block.
The last time I failed to heed that warning the front brakes locked up on me and I dumped the bike. Not cool.
The rear brakes on that bike are drum so they should work ok since it is all mechanical,
so if you do drive it a few feet I would use the rear brake to stop as long as it works.

Also, after/if you do get it running, their may be issues with the charging system,
and I can pretty much guarantee you that there will be some idle issues or carb issues of some sort,
but you may be able to get a riding season out of it before it bothers you enough to do something about it.

Also, don't let any of this scare you. If you are handy with some tools and can read a forum or Haynes manual you will be fine. Motorcycles are tons of fun to work on and in most cases way easier than working on cars.

Here is what I have:

I started with a bone stock bike that ran, but not very well. Now I have GSXR carbs, CBR600 coils, Yamaha R1 Master cylinder, and plenty of other parts waiting to be installed. At the end of the day I have about $1300 in this bike including the purchase price. They really are cheap and easy to work on, not to mention a blast to ride!

PM me if you get the bike and have any questions, or just reply to this thread and I will answer what I can.

 

[kunar]

i've got no worries about my mechanical abilities. not proclaiming im an expert but ive done engine swaps and axle swaps etc. the carbs worry me though, ive never done anything with carbs other than lawn mowers. i do know that when my dad got this bike a few years back, he did have it running. it didnt run well but it did run. he didnt put too much into it after that before it got pushed back into the corner and stuff started piling in front of it. as for the exhaust, somebody's done some work to it. long story short, it has car mufflers on it. how big of an impact does exhaust play on these engines? i mean, i know they need to be replaced but would it be an issue to leave it that way for now?

btw, thank you all for the info so far. i dont have the bike here and wont be able to even look at it till at least the weekend, but there's lots of good info here and its a good start.

 

[Tominator]

I'd check the cold compression after squirting Marvel Mystery oil in the spark plug holes and turning it over with the kick starter a bunch of times.

Check if it has spark. The points may need replaced.

The Mikuni carbs are pretty strait forward and easy to rebuild. Getting them synchronized can be trying, but you are not worried about that yet.

Finding a set of exhaust pipes shouldn't be too hard. Many were turned into 'choppers' and I've seen many with the pipes just sawed off at various locations. It'll be ear drum popping loud but won't hurt the motor at all.

This was Honda's first try at a 4cyl design. They made them in 350, 400, 650 and 750. They have nothing in common with the later 'F' models except both were Honda!

Good luck and let us know how it goes.

 

[adsm08]

I hear the 70's bikes run better if you drop a pot leaf in the tank and let it soak in there.

 

[88_Eddie]

i'd reckon that at least 99% of them were built in the 70's.....sorry, that's all i got

 

[85_Ranger4x4]

Replacing the exhaust is also a good idea. You also need to check the gas tank if it hasn't leak. You can also get a new battery for it to run well. And also consider repainting your bike for it to look good.

You can check the gas tank if it doesn't leak?

It is possible to buy a battery for it to run better?

Paint makes things look good?

Will the wonders ever cease...