Topic: New to me 750K7! Few issues to address

[SierraCB]

Hey Guys!!

Just picked up the bike i've always wanted, a SOHC 750!! Really stoked to add into my stable of bikes.

It runs, but not too well.  Here are my issues maybe you all can help me with

1. Idle, off idle response is awful and constantly stalls the bike unless totally warm.  The motor sounds really tappy and clanky when it's idling also.  Maybe cam chain and valve noise combined?  Once it's above idle it seems better.  Power is pretty damn awesome.

2. I'm sure a carb rebuild and balance is needed.  Any good write ups on this?  This is my first 4 carb bike and it seems overwhelming.

3.  The front brake caliper is sticking and makes the bike really hard to move around.  Do I need to just bleed the brake and mess with the piston or should I look into other things??

4.  I switched to some street bike bars and now my cables are too long.  Does anyone make a clutch and a pull cable that just take 2-3 inches off stock size??  That's all I need.

Thanks in advance everyone!!

[Stev-o]

Welcome from Texas.

1.  Carbs prolly need to be cleaned, if the bike has been sitting for any length of time. Your bike has an accelerator pump on carb #2, I'd bet this needs attention [maybe a new diaphragm] When was the full 3000 mile given to it? If you dont know, it is time. These motors are noisier than modern bikes, a good carb sync may help quiet it.

2. See #1. And see the Carb FAQ...   http://forums.sohc4.net/index.php/topic,5410.0.html

3. The front caliper needs to be taken apart, cleaned and a new seal replaced. Pretty basic, I'm confident you can do it! 
Tip:  do NOT disconnect the brake line until the piston is totally out of the caliper.

4. Yes.  Locate Honda clutch cable # 22870-426-610, it will fit perfect [I just installed one on my K4] Motion Pro may have the throttle cables.

Your bike looks good, enjoy it!

[HondaMan]

Hey Guys!!

Just picked up the bike i've always wanted, a SOHC 750!! Really stoked to add into my stable of bikes.

It runs, but not too well.  Here are my issues maybe you all can help me with

1. Idle, off idle response is awful and constantly stalls the bike unless totally warm.  The motor sounds really tappy and clanky when it's idling also.  Maybe cam chain and valve noise combined?  Once it's above idle it seems better.  Power is pretty damn awesome.

2. I'm sure a carb rebuild and balance is needed.  Any good write ups on this?  This is my first 4 carb bike and it seems overwhelming.

3.  The front brake caliper is sticking and makes the bike really hard to move around.  Do I need to just bleed the brake and mess with the piston or should I look into other things??

4.  I switched to some street bike bars and now my cables are too long.  Does anyone make a clutch and a pull cable that just take 2-3 inches off stock size??  That's all I need.

Thanks in advance everyone!!

Welcome to the fun!

1. The carbs and likely their rubber hoses need some help. You can get new hoses at PartsNmore.com, among other places. Make sure to get the right year! There are early and late types, with 1975-6 being the division for the novice. The accelerator pump in the carbs is probably very hard and stiff after years of age and sitting, and MTBE gas we used to have. PartsNmore sells carb kits and the accelerator pump, too. When these engines run unevenly due to misbalanced carbs or out-of-tolerance points timing, they sound like a bucket of bolts: if properly tuned up they sound like a Porsche!
2. See #1...
3. If the bike sat a long time, the rubber seal in the front brake caliper probably got hard and now it makes the caliper stick. You'll have to take the caliper apart, replace the (square-section) O-ring inside, and reinstall and bleed the brake.  It's not hard, just mysterious if you haven't done it before - like those carbs?
4. Check with Motion-Pro for cables, they make them in stock, +3 and +6 and -3 inch sizes.

[scottly]

While you have the caliper apart, make sure you clean all the varnish and oxidation out of the piston bore and the O-ring groove; in many cases this is enough even with the old O-ring. When cleaning the bore, avoid using a wire brush in a dremel tool.

[SierraCB]

Awesome this is all very helpful!! I will pull the caliper tomorrow and do some cleaning.

as far as carb rebuild/tune/syncing goes... Any good write ups? I love just doing it myself but also love a little help!

I also noticed my head tube seems to catch in dead center when I turn the bars.  Almost like a groove is in it so that it sticks straight... This seems very strange to me.  Normal or not?

[Wobbly]

[Wobbly]

[Wobbly]

[Wobbly]

[Wobbly]

The Honda clutch cable for the European K7 model would be my choice (David Silver Spares, Honda). Part number:  22870-405-610. Same goes for the throttle cables--Honda, European model. I be happy to post the pages from the manual regarding the front brake. Brake fluid, fork oil ought to be replaced too. The reflectors for the headlight are still available from Honda (just saying). I prefer to stay with genuine Honda parts since they actually work the first time. Some aftermarket stuff is outright crap. And there is a lot more available from Honda than some people think. I could make a fortune buying new parts from Honda and putting them out on EBay. But, I guess, I am drifting off topic...

[brewsky]

Suggest you pump the piston out of the front brake with the hand lever before dis-connecting the lines.

Also, when cleaning the carbs, DO pull the slow jet out for cleaning, even though the book says not to remove.

[brewsky]

I also noticed my head tube seems to catch in dead center when I turn the bars.  Almost like a groove is in it so that it sticks straight... This seems very strange to me.  Normal or not?

You will need to replace the steering stem bearings, as the races wear and cause this symptom.

Here is what many people use:
http://www.amazon.com/All-Balls-Steering-Bearing-22-1011/dp/B000GZQ3XW/ref=au_as_r?ie=UTF8&Make=Honda%7C59&Model=CB750K%7C17058&Year=1977%7C1977&n=15684181&newVehicle=1&s=automotive&vehicleId=1&vehicleType=motorcycle

[brewsky]

Awesome this is all very helpful!! I will pull the caliper tomorrow and do some cleaning.

as far as carb rebuild/tune/syncing goes... Any good write ups? I love just doing it myself but also love a little help!

 

Here is a thread on bench syncing which has some pics as well as entertainment value!
http://forums.sohc4.net/index.php/topic,113931.msg1282383.html#msg1282383

[Wobbly]

Here is what many people use:
http://www.amazon.com/All-Balls-Steering-Bearing-22-1011/dp/B000GZQ3XW/ref=au_as_r?ie=UTF8&Make=Honda%7C59&Model=CB750K%7C17058&Year=1977%7C1977&n=15684181&newVehicle=1&s=automotive&vehicleId=1&vehicleType=motorcycle

I am happy with these:

[SierraCB]

Bearings ordered!

Can I just do a static sync and be okay or do I need to a do a dynamic sync off the bench?? I'm sure a carb clean will get this thing going so much better anyway.

Do you have that piston brake diagram??

[Wobbly]

[SierraCB]

Front brake all fixed!

Bearings come in tomorrow

I pulled the carbs last night, (what a total pain in the a)... I can't pull the pilot out with pliers like people say to do. Also I removed all the rubber in the float bowl area and I took off the top caps of the carbs also. Are these good to soak in cleaner now? Don't want to mess up any rubbers etc.

[flybox1]

Front brake all fixed!

Bearings come in tomorrow

I pulled the carbs last night, (what a total pain in the a)... I can't pull the pilot out with pliers like people say to do. Also I removed all the rubber in the float bowl area and I took off the top caps of the carbs also. Are these good to soak in cleaner now? Don't want to mess up any rubbers etc.

Pilot jets - gentle twist and pull, straight out, and they will follow.
unscrew the main jets and clean the emulsion tubes and its holes.
PD carbs - be sure to know which are the fuel delivery tubes and which are the accel pump tubes.
the accel tubes have tiny brass inserts, which help to take up volume in the accel pump circuit.  dont loose these.
be sure to clean and clear the accel pump circuit. learn how it functions. this really helps with getting off the line when functioning properly

[SierraCB]

Front brake all fixed!

Bearings come in tomorrow

I pulled the carbs last night, (what a total pain in the a)... I can't pull the pilot out with pliers like people say to do. Also I removed all the rubber in the float bowl area and I took off the top caps of the carbs also. Are these good to soak in cleaner now? Don't want to mess up any rubbers etc.

Pilot jets - gentle twist and pull, straight out, and they will follow.
unscrew the main jets and clean the emulsion tubes and its holes.
PD carbs - be sure to know which are the fuel delivery tubes and which are the accel pump tubes.
the accel tubes have tiny brass inserts, which help to take up volume in the accel pump circuit.  dont loose these.
be sure to clean and clear the accel pump circuit. learn how it functions. this really helps with getting off the line when functioning properly

Got them all torn apart for the most part.  The pilot screws had tons of crap under them.  Also my throttle linkage is very greasy and makes it hard to turn.  I want to just soak the whole carb bank but I'm worried about the rubber getting messed up.

Also my pilot jets, the press in ones, are kind of bent.  Very weird...  I'm going to use a caliper to do a bench sync also.

Where can I get new pilot jet and slow jets??

[flybox1]

dont soak it.
simple green, carb cleaner, and some compressed air are all you need.

http://www.jetsrus.com/a_jet_kit_street/honda_750_CB750K_1977_1978.htm

[SierraCB]

dont soak it.
simple green, carb cleaner, and some compressed air are all you need.

http://www.jetsrus.com/a_jet_kit_street/honda_750_CB750K_1977_1978.htm

Alright, guess I need to get at with more elbow grease...

What about pilot air screws?? I'd like the replace those also

[flybox1]

why? 
unless stripped out or missing a part (spring, flat washer and o-ring) just clean out their resting place and reuse

[SierraCB]

One of the O-rings wasn't even in there...

[brewsky]

One of the O-rings wasn't even in there...

Are you sure? They are very good at hiding in there!

[SierraCB]

One of the O-rings wasn't even in there...

Are you sure? They are very good at hiding in there!

Yes...