Is this CB750F a Good Buy?

[excessivedemon]

Hey Guys, I am looking into getting a CB750 soon - I'm no expert so I'm hoping you could help me out. I'm going to check this bike on Saturday and I wanted to know what you guys think



Bike currently has a mileage of 37035, been sitting for over 2 1/2 years now. It was running before it was left sitting, bike rolls on neutral, owner wants $700 for it. Transport would add to the cost. Does this bike look complete and in one piece? I'd really like to get this one but I wanted to know your thoughts. Thanks in advance.

[Half-Caf]

From what I've seen, the price depends largely on the market in your area. I live in Chicago and bikes are average to slightly more expensive here and my 750f was $750 (running very rough, and not charging).
It's pretty much a guarantee you could get it running, but its a gamble guessing how much you would have to do to get it there. Personally, I wouldn't want to pay over 5 for it, but then again, the engine does look nice in black
The crappy flame job should take off about $250 right there

[Half-Caf]

By the way, welcome to the forum

[motogrady]

They take a lot of work.
Pretty much a given the carbs will need work.
And a battery.
37,000 is a good bit on the clock.
But it's all there.
Myself, I'm kinda diggin' the flames

Good luck with whatever you do guy, and like Hafcalf said,
welcome to thew site.

[excessivedemon]

Thanks Half-Calf Prices in my area are quite high - one of the CB750s posted here (1976 SOHC) without papers, in a rusty condition, and mostly appears incomplete is about $970. Good running condition CB750s (advertised as nothing to fix and with complete papers) of the same year and model as the one I'm looking at (1980) goes for around $3000 so I'm really thinking it's a good bargain if I can get this one running.

Another plus side of this bike (aside from it being the cheapest in the market) is that according to the owner the top end of the engine has been replaced with one from a CB900F I'm not really sure if that makes getting the engine running more complicated but I'm very much happy with that upgrade.

It's hard to tell how much is involved getting this bike to run and how much harder I have to source for parts. In my city alone, I haven't seen anyone riding this kind of bike - I actually have to travel to another city about 5 hours drive just to reach the seller's place. There might not be any mechanics in my area as well that specializes in this kind of bike

Will this kind of setup (CB900F topend on a CB750F case) make rebuilding the engine more complicated for me? There does not seem to be a way for me to verify if the topend indeed came from a CB900F until I have the engine opened so I guess I'll just have to trust the owner on that. I might also have to learn doing things on my own with this bike since I don't think there are good mechanics for this bike around here. I would appreciate any other inputs you may have. Thanks again in advance.

[Half-Caf]

excessivedemon wrote

<p>Another plus side of this bike (aside from it being the cheapest in the market) is that according to the owner the top end of the engine has been replaced with one from a CB900F  I'm not really sure if that makes getting the engine running more complicated but I'm very much happy with that upgrade. </p>

I'd be willing to bet that the "top-end swap" is referring to swapping out the 750 cams for 900 ones. This is a common mod and is supposed to add a nice performance boost.
I've never seen anyone swap just the heads -the cylinder size, piston doming, and valve size/travel would all be different. And you can't "plop" the 900 cylinders and head on the 750 crankcase without replacing everything down to the crankshaft and boring out the holes to accept the larger cylinder sleeves.
What I'm really trying to say is that he's more than likely just referring to a cam swap  

[Half-Caf]

If you would like to read more about these things, check out this thread.

[excessivedemon]

@Half-Calf - Thanks for the link and info. I'm guessing that 900 cam swap is supposed to add some "good value" to it? So you're saying $500 should be fair price? The owner did advertise it as a "1981 Honda CB900F SuperSport" - along with the following details: I have for sale this 1981 750F SuperSport converted to a CB900F (The top end replaced)

@motogrady - Battery is indeed dead I'm hoping the carbs are not that bad

I'm thinking first thing that needs to be done when I get it home (if we do close the deal) would be to drain the oil, put some new one, plugin a new battery, and try to start it? Or are there other things I should do prior?

I'd really really like to get this one, but please let me know if you think otherwise. I'm a noob, I'm in a dilema, I know for sure I may not get a chance to get another CB750 in the future if I pass this chance (there are not that many around here, and if ever there are, prices are too steep, or the task of restoring is too difficult). On the other hand, I'm not sure how much cost I will end up with to get it to atleast get it to road worthy condition - I don't want this project to drain my bank account

[motogrady]

If you have the patience, and stick-to-itness, and access to some hand tools, 500 isn't a bad price.
The battery, you might be able to save it.
Check the water level in it, add if it needs it, and give it a slow charge on a charger.
It might take the charge.
The carbs, if they're just gunked up, all one needs is a guitar string, some ether, some compressed air,
and a lot of patience.
Or buy a set for 800.

Thing is tho, as a noob to mechanics on general, it can be a steep hill to climb.
You can do it, especially with this site as a reference pool.
There's some good guys here that know what's up.
And you might luck out, bop a battery in it, check the oil, put some fresh gas in it and see whats up.
But.
Is it, or will it be a money pit that gives nothing but grief?

Only the guy that buys it will ever know.

[shultz_1978]

Well put, You take chance all the time. This could be the best or one the worst.

[excessivedemon]

Thanks for the advice Motogrady. I think I can invest in some tools, but I only have very very minimal automotive mechanics experience - I have only tried working with an old old car (73 VW Beetle) - some maintenance work like carb cleaning using carb cleaner, adjusting A/F mixture, doing some small valve adjustments, adjusting brakes, changing tires, but that's it, nothing near engine rebuilding at all - but I am very very much willing to learn. I've read somewhere though not to use carb cleaner on the CB750's carbs as it will eat up some of the parts - is this true?

You're right, I guess I'll just have to try my luck, there's no sure way to know unless I try, sometimes you win some, sometimes you lose some, just the way things are. Wish me luck

[seestheday]

Welcome to the forum.

I had basically zero mechanical experience prior to getting my cb750 3 years ago.  With the help of this form (and others) I just completed a top-end rebuild (lapped valves, cleaned pistons, installed 900 cams, etc...).

You can do it if you have the time and are willing to invest in some tools.  I bought my bike for $750 running and I thought it was a fantastic deal given where I live.  It sounds like prices where you live are similar to here.  $3K for a running SOHC or DOHC is pretty standard.

You can use carb cleaner on the carbs, but don't soak them in it unless you are fully breaking them down.  If you have questions about carbs just ask.  There are great resources here.

[excessivedemon]

Thanks seestheday, wow, I really hope I can someday do a complete engine rebuild on my own like you. That's really cool

Thanks for the info about cleaning the carbs, will dig out other resources in the site. It's really good to have this nice community where people share their knowledge and help each other out. Thanks guys

[excessivedemon]

Just wanted to thank everybody's help with this - I got the bike for $700, plus about $100 transport, and almost 12 hours total travel time and loading / unloading the bike.

Battery is totally dead and won't charge anymore. I tried plugging in a newly charged car battery to test things out - won't start after pushing the electric starter.. so I connected the positive cable directly to that thick wire leading to the starter and I can hear the starter turning very slowly, it can't crank the / run the engine though. I realized the fuel tank was set to off so I turned it on but gas started pouring out of the carbs. I tried tapping the carbs a few times and they started leaking less.

I'm thinking bad solenoid since starter turns when the battery's positive cable goes directly to that thick wire - but what about the starter? It still can't turn the engine - I also think it's worse now because after a number of tries trying to start the engine, this time, it won't turn the starter anymore, it just makes a click sound

[motogrady]

Sounds like you ran the battery dead.
Try recharging it.

Avoid cranking till it won't anymore.
If it doesn't start after 2 or 3 tries, there's a reason.

Get a cheap 12volt test light.
When you hit the button, you should get juice to the solenoid,
which should close and let juice go thru to the big thick wire going to the starter.

Recharge the battery.
Pull the carbs and clean them.
Figure out what's happening with the starter.
When you hit the button, the light should go on anywhere along the big wire to the starter.
If you're getting juice to the starter, and it has a good battery, it's either a bad connection
or wire, or the starter needs rebuilding/replacing.
You get that figured out, and clean the carbs, it's time to try starting again.

Then it's basics.
Pull the plugs to see if they're wet with gas, if so, check for spark, if you do and still no start check compression.

And quit laying on the button till you kill it.
Wishing ain't gonna do it, you gotta figure it out.  

Good luck guy, keep us informed, even if it is you just thrownin wrenches across the room

[excessivedemon]

Hey Motogrady - how do I clean the carbs using a guitar string and ether? I managed to remove the carbs and the starter today - the carbs look ok from outside except for some moulds and was hoping to clean everything up - I want to thoroughly clean the carbs (but not rebuild yet since I don't have access to a carb rebuild kit where I am).

Starter's teeth / gears look ok so I guess I'll have to open it up tomorrow to check the carbon and stuff

[motogrady]

First off take the starter and put it on the workbench.
Charge that 12v battery up.
Take a set of jumper cables, black to neg on the battery and the body of the starter.
Red to the hot side of the battery, then just touch the lug on the starter where the big wire goes with the other red end..
This gives you strong 12 volts right to the starter, bypassing all the wiring and components
that might be bad.  If it turns good like this, somethings up in the wiring harness, a connector
or the relays that let the juice thru.
If it''s still cranking slow, or siezed up like this, it's toast imo.  Take it apart and try to clean and
lube anything you see that might be binding things up.  You have nothing to lose at this point,
and you might fix it.

Cleaning the carbs, check the stickies at the bottom of the front page, there's a few way's
to clean them.  Remove all the jets you can, keep everything in order and seperated, and just spray
the starting fluid thru all the passages you can.  Some of the passages are real small where they dump into the opening of the carb, like the size of a sewing needle small.  Mine dump right around the
choke butterflys, there's 3 of them.  The small, thin guitar string, work that sucker as far back in the holes you can, then spray some more, work it some more.  3 or 4 times.  Then blow everything out with
100 pounds of compressed air, both ways (back to the jets, then from the jets to the throttle opening.)

I think it was Lucky or Rerun that have a thread here on how to get some of the jets out for
different years if all is clogged, it's good, just be patient with this part.  You mess up 1 carb, it's gonna be real hard to find that part, if not impossible, which means a new set, which new go for about 800 bucks.

Take your time, be methodical, don't worry about riding right now, there's plenty of time this season,
it's still early.  The bike needs your help, give it to her.

And by the way guy, congrats of taking the plunge, and welcome to the club.  
Keep in touch.  

[shinyribs]

Excessive,it looks like your in good hands with Motogrady taking care of you. I just stepped in to say congrats on your new bike.Have fun bud!

[excessivedemon]

Hey Motogrady, thanks so much for all the help and patience.. I realized I did something stupid - I thought starter was dead, turns out, body is not grounding properly due to all the rust / molds that built up, I tried sanding one side of starter's body and connecting negative of battery there and starter spins really strong with a big spark (same battery, did not have to recharge).

I'm still doing more reading on the carb cleaning process since I'm still not confident of my skills (how I wish it was as easy as pouring pine sol on a bucket and soaking the carbs there without disassembling them overnight LOL )

In the mean time I tried testing if engine is stuck up.. I pulled crankshaft flywheel cover, placed a wrench on the end of the crank and tried turning it while transmission is in neutral.. it turns both clockwise and counterclockwise.. thing is after about 180 degree turn on one direction it stops there and can no longer be turned.. it would turn fine if you try reversing the direction but again just until about 180 degrees and stops there - does this mean engine is stuck? How come it only turns till 180 degrees?

Thanks again for all the help and patience guys

[TOOLS1]

That is not a good sign. You could do a leak down test to find out which, or if it is a cylinder, or crank problem. However that engine is going to have to come apart. The good news is that you can remove the top end without removing the engine from the frame.
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