Topic: 1970 CB750 K0... My first bike

[cmoses]

Hello all!  This thread should have been started a while ago but I am a busy student and haven't had the time. So here we go.  I have a 1970 Honda CB750 K0... candy red... semi stock.

I bought this 750 a few months ago from a friend who needed the $.  It didn't run and had been modified a little bit to fit the PO personality.  I had originally intended on just getting it started and selling.  I figured it would be a good way to get introduced to a new hobby (I had been a car guy before) and make a few dollars.  But after I did a little work and research I quickly realized that I actually enjoyed this much more than I anticipated, and the bike wasn't just some "dime a dozen" bike.

I have since flip flopped back and forth on what to do with it, while doing little things to see if I could get it started.  After a month and a half of tinkering I finally kick started it and heard it roar (no mufflers) for the first time.  It was awesome... and loud... so loud it actually scared me haha. I still didn't trust it so I quickly turned it off and have since not been able to get it started again.

The things I have done:
-new plugs
-new boots
-tested coils... replaced 2/3 with a used one from my local bike shop.
-replaced both points sets and one condensor (idk why but they only ordered me 1)
-new petcock (old one prob just needed rebuilt but I wanted the piece of mind that it was good)
-rebuilt/cleaned carbs (some new hardware, soaked bodies and jets in chem dip over-night, one at a time)
-purchased used throttle cable (4 to 1) off of ebay.  It works great... and 120 cheaper than a brand new one.
-soaked the tank in evaporust for days... rinsed with water... immediately filled with gas.
-changed the oil and filter

After I did all of this I got the bike to fire (kicked a few times with a closed choke, then opened the choke and it fired right up).  It sounded like I had the throttle wide open.  I didnt have any airbox or pod filters on at the time and the choke was open so that might have been why.  The throttle was not stuck, it is operating smoothly. Once I shut it off I was unable to get it started again.  The battery was weak so I replaced it with a new, sealed battery. Once I did this I realized that the bike was not in neutral (I had the clutch in when I started it) so after a little fidgetting I figured out the way it worked and got it in neutral... the light works!  Also the oil light goes off everytime I kick it but then comes back on?  I still have had no luck getting it started.  I have started the hunt for a box and my buddy gave me an old set of K&N pods to try while tries to save my stock box.  So I will see if this helps.  I am thinking that maybe the plugs are getting fouled? Not sure... maybe the air to gas ratio is screwed up since it is wide open on the back end.

Anyways here are some pictures!  Any help would be appreciated.... I will post more tomorrow in terms of problems I am having (one point wont close! argghhh).  Thanks for reading please follow along!!








Here is the airbox... a buddy is trying to fix it for me and should have it back the next couple days.

[SOHC4 Cafe Racer Fan]

That's a pretty decent bike.  You could get it in reliable rideable condition and ride the pants off of it through the summer, upgrade gradually to improve safety and reliability, and decide IF you want to restore it or do something else once the weather turns again.

[cmoses]

Thats what I am hoping for.  I did have a few safety issues I HAD to address like the triple tree being broke.  I am buying on from a forum member tomorrow... along with a stock k0 seat.... which has nothing to do with safety.... it just looks cooler haha.

[754]

Head has been changed.. What is the motor number?

[cmoses]

Here is the motor



Here is the frame

[Greggo]

Head has been changed.. What is the motor number?

Think it's a later head Frank?  They had the extra bolt added before 20xxx.



Very nice project cmoses!  If you do it up right, you'll have a $10K+ bike

[754]

Look at the three bars visible from end of head, and the leading edge of top front fin.

[Old Scrambler]

Good eyes Frank...............Also has a later set of turn-signals and ears. Be sure to get the correct triple-clamp. That box is from a K1 or later.............it will work but not worth saving or repairing.........K0 replacements are available but a K1-K6 box is an easy replacement.

Regarding starting.............study how to bench-synch the carbs............be sure the slides are all in the down position. If they are not, look for the 'cut-out' at the rear edge of the slides.............its common for beginners to install the slides backwards.  If you want to restore the bike, the early heads are available........somewhat scarce for K0 but outwardly look the same for K1-early K3. 

You have a good start to a worthwhile project.  Look for an aftermarket exhaust system to get you on the street. Original pipes and mufflers are in very tight supply from the aftermarket people........and very pricey. 

[cmoses]

I have been made aware of the signals and ears... I am little confused about the head? Not sure what you are refferring to? 

UPDATE:  I have now got the bike to start with basically every kick.  I ended up cleaning the old points I had and putting them back on the bike (Since I couldn't get the new replacements to close) after I adjusted the gaps (.014) and this worked. with a little fidgetting with the carbs I got it going steady, with no air pods or box.  It would run but as soon as I put it in gear and gave it some gas it would die.  I toyed with it for a while and found that the pipes coming from 1 and 2 were scolding hot (burnt myself) but 3 and 4 were not hot (could grip them with my hands, they were a little warm but I chalked that up to heat radiating from the other pipes.

SO, I check 3 and 4 for spark and found that both were getting spark (Im not sure how this is normally done but I just took the plug out attached it to the wire and held it on the exhaust while I kicked the bike.  Sparked every time)  After trying for a while I gave up.  I felt like they were trying to fire but just wouldn't get there.  This doesnt make much sense to me I was hoping one of you gurus could help me out?

Scrambler... I used a bare wire twisty tie to synch them... it seemed to work well, I could be wrong tho. 

Another thing I noticed was the overflow lines from the bottom of the carbs were dripping gas?  And a little gas (maybe oil mixed) was coming out of the spot where the exhaust mounts up to number 3.  Aghhhhh at least it starts up every time now!!  Baby steps!... OH and the tach works!! woohoo

this is the triple clamp I am purchasing is this right ? (Minus the gauges)

[Stev-o]

The dripping gas out of the carbs could be a sticky float.  Unburnt gas out the exhaust means that cylinder isnt firing.
Don't let this get you down, that bike needs a proper full 3000 mi tune up and a carb rebuild.

[cmoses]

Steve-o is that the right triple tree?

I have rebuilt the carbs... I will post pictures of what was replaced and what was not.  The only difference between the build kit and what was in there was one piece.  Whatever the float needle sits in... the old one had 2.5 stamped on the top and the new ones had 2.0 stamped on it.  And there was an O-ring the I never saw come off the carbs and what looks to be a gasket that might be for a spring seat or something??

The kit I ordered was for a 1971 since thats what I was under the impression I owned at the time.  Problems there maybe?  I am lost as to why its not firing... I have spark and fuel....

[Stev-o]

Yes, that the correct triple. Does it have the D washers?

Have you changed your spark plugs and plug caps?

http://www.ebay.com/itm/HONDA-SOHC-CB750-CB750K-CB750F-CB750A-NGK-SPARK-PLUG-WIRE-RESISTOR-CAPS-/251472383120?pt=Motorcycles_Parts_Accessories&hash=item3a8cec0c90&vxp=mtr

[cmoses]

I replaced the plugs and caps with NGK brand.

I have been reading and some people say the coils are wired wrong??  I too them to my local shop to get wires and plugs and found out the wires couldnt be changed and the one that goes to 2/3 had bad wires.... luckily they had a used one that was good so I left it there and they put them together for me and after testing they sent me home.  I guess this could be the culprit?

And great... seat and tree are hopefully on the way!

[cmoses]

So today I am going to open up the carbs and clean out the jets again... I am thinking that maybe the idle jets got plugged up on 3/4 and not 1/2... which would make sense seeing as how 1/2 share a fuel line and 3/4 do.  Hopefully it works.

Also in the market for a center stand if anyone has one laying around!

[Johnie]

Pay attention to what Stev-o says about the D washers or you will have another broke triple there.

[cmoses]

Johnie... I def will not haha I asked the seller if they came with and he said yes but he was not sure how they go together.  I will make sure to check with you all first.... he also asked if I was replacing the bearings.... any suggestions on that??

Sorry guys... I feel like a total idiot posting on here sometimes and I appreciate you all keeping the chuckles to behind your respective computer screens haha.  I am very aware some of these questions are probably.... elementary at best.

Also 754... are you talking about the head on motor... how can you tell?    thats me blushing because I should probably already know all this....

[754]

You could not already know this, some owners that have owned for decades still don't know..
 I will try to take pics to explain, may take a few days.

Simply put, view the cylinder Head from the end only..look what is between the fins, then compare to the others.  There will be oblong bars, or round rods.
 Plus the top fin edge is different.

[cmoses]

754 I will check it out... thank you!

Update:  Figured out my problem with 3 and 4... an friend of mine, who always has worked on autos with me, assisted me in installing the top half of the carb (where the throttle cable connects.  He installed the shiny cylinder  (again, should probably already know the name) backwards... so it was never closing.  I discovered this after I cleaned the idle jets, didn't work, so I went to take the carbs off.... choke was open... and I saw that it was wide open... BINGO... luckily Adam (my friend) was there so I got to have a little fun with it.

I know... I know...

So she lives! I am now in need of an airbox... big time...

I really don't care if it is an original smooth side, I know they are pricey and hard to come by. Any box that fits will do.

Guess I will head over to the parts wanted forums!

[Johnie]

The D washer goes in the slit on the top clamp of the triple where the top of the fork goes. The flat spot goes towards the fork tube. You should have 2 D washers as one goes in top left and the other top right. The purpose is so you do not overtighten that clamp which will break it like the one you have there. The pics will give you a good visual.
Regarding the bearings you mentioned, he must be asking if you are going to use the original ball bearings that came in the top and bottom of the triple or if you are going to install tapered ones like in the pics.

[cmoses]

Thank you Johnnie!  It is nice to get a visual. And thats exactly what he was asking, he didnt seem to like the original ball bearings... do you suggest switching to the tapered ones? If so what are good ones to get?

Also, I think I found a good 18 inch rear rim here:
http://cleveland.craigslist.org/mcy/4394990381.html

I could be wrong but it looks right to my rookie eye... thinking $50 sounds like a decent deal

[Stev-o]

Thank you Johnnie!  It is nice to get a visual. And thats exactly what he was asking, he didnt seem to like the original ball bearings... do you suggest switching to the tapered ones? If so what are good ones to get?

Also, I think I found a good 18 inch rear rim here:
http://cleveland.craigslist.org/mcy/4394990381.html

I could be wrong but it looks right to my rookie eye... thinking $50 sounds like a decent deal

Tapered bearing are highly recommended, I like All Balls:

http://www.amazon.com/All-Balls-Steering-Bearing-22-1011/dp/B000GU3Y5C/ref=sr_1_1?s=automotive&ie=UTF8&qid=1396041048&sr=1-1&keywords=steering+stem+cb750+1970


That rear wheel appears to be a good deal as long as not too rusted and spins straight.

[Johnie]

Once you get those tapered bearings take a look at this nice thread with pics regarding installation of the lower bearing especially. It will help you out a lot:

http://forums.sohc4.net/index.php?topic=1516.msg1522357#msg1522357

[cmoses]

So as of now I am waiting on the tree, seat, and pipes to get here.  The suspense is killing me    I found this stuff the other day and was curious if it would fit my k0... I know it is not original but I have been looking for a center stand and well... just a K0 center stand on ebay is 110 bucks and all of this is only 100 total.  It would be cool if it works

http://forums.sohc4.net/index.php?topic=135291.0

Thank you!  I also need a tail light lense.... my pops hit my bike the other day.... broke the lense and dent the fender a bit.  Will have to pop that out somehow.... probably just use a body hammer i guess

[754]

You can use any centerstand... Dont get analysis on the parts right now..pricey..
 Be careful with fender, i would not use a steel hammer..might be better get an expert to fix it.
Fender I think has 2 types 3 hole and 2 hole..one is harder to find....be carefull.

[Johnie]

When it comes time to install your center stand here is how she looks. Do you have the half moon bracket yet?