Topic: First post, resurrection of CB750K2

[Artfrombama]

Hey, it was a freebie....

Previous owner said he rode it home, tore it down for a restoration then had heart surgery. Sadly he couldn't finish it.

The plan is fire the motor, check the clutch, alternator, transmission. (EDIT-Should have included pull the sprocket cover and make sure a broken chain hadn't busted the transmission case )If everything checks out OK, then buy a few parts and de-chopperize it. The forks and the king/queen seat have to go!
After all, this is the 90's, right?
I must say, after lurking on this site this week, I'm quite intrigued with the cafe' racer look.

Picked the bike up as a rolling frame, engine out, fenders off. Had been sitting outside a couple of years. The frame was in the open, at least the engine and parts were under a tarp. It looks 85% there.

Swung the engine back in the frame, waiting on two 6 x 75mm machine bolts that were missing for the valve cover before I can really bolt the engine in.



Electrical system was horrible. I've been repairing wiring today that basically was OK to begin with. Carburetors were as bad as you could imagine. A little Gumout spray, dipped the small parts, hopefully it'll start and run with this B/Y overhaul.


If the motor won't fire or has serious problems, gonna whore it out on ebay.

Any comments, suggestions are greatly appreciated.

[mattcb350f]

If the motor won't fire or has serious problems, gonna whore it out on ebay.

Oh don't do that 


......sell the parts here silly 

Actually it looks to be in good shape to me.

Make sure all the lil' jets are clear in the carbs before you button them up.

Beware too, that the clutch plates may be stuck together from sitting...... so point it down the driveway when you get er' going.

 Matt.

[Artfrombama]

If the motor won't fire or has serious problems, gonna whore it out on ebay.

Oh don't do that 


......sell the parts here silly 

I hope the thing runs well and doesn't hemorrhage oil, I want to keep this bike. I will give the forum first crack if it comes down to that.

Actually it looks to be in good shape to me.

I'm itching to tear it down for a repaint, shorter fork tubes, add road race bars, etc., etc., etc.,

Make sure all the lil' jets are clear in the carbs before you button them up.
Beware too, that the clutch plates may be stuck together from sitting...... so point it down the driveway when you get er' going.

 Matt.

Good idea, thanks

[Artfrombama]

Have dealt with several little issues to get the bike where it is today, points plate, "ghetto" wiring repairs, carburetor leaks, etc. Now it starts easy and idles nicely. Lights work, controls work (starter button relocated to handlebar clamp), alternator puts out 13.5V idling, life is good!

I wasn't going to buy any parts until the engine and transmission were proven to be good, well I'm at that point. Found a NOS loaded points plate on sleazebay, good fork tubes and a decent seat.

It's amazing what a little cleaner and some 000 steel wool will do.



See the fuel stains under the carburetors? Gas had to be dripping back there long before I got the thing, discovered 3 of the 4 carbs had this problem;

Now it's on to front brake repair, the caliper is salvageable but I'm afraid the master cylinder is toast. I'm going to have to make a tool tomorrow to remove the MC snap ring to survey the damage. If it's too badly pitted I'll probably use a MC from a later model Honda like a GL1200. I like the idea of using a master cylinder with a built-in brake light switch, eliminates the need for the junction block under the headlight and will allow me to use a 1 piece steel braided -3 brake line.

As always, comments and suggestions are welcome.

[greenjeans]

Glad to see it runs.  These things are remarkably tough.  Mine (72 CB750K) had sat for over 15 years and was as filthy as
your run of the mill pirate hooker.  Steel wool, & simple green are an amazing combo.

Carb bowl gaskets are relatively cheap, so grab som of those.  Might as well take those carbs back out and really, really clean them
thoroughly.  I had to clean mine twice before they were really clean.  Double check your float levels while you're at it - they can
cause alot of grief if not set accurately.

As for your caliper, mine looked pretty bad.  But after a rebuild with a fresh seal and a phenolic caliper (will last forever) from ebay,
they are great.    Good luck.

Looks like you have a great start.

[MJL]

I think I spent about $45 on the rebuild for my master.  The hard part was getting the snap rig out, but that was because I hadn't taken the circlip out first. After everything came out the bore looked good, so I lubed my new parts with brake fluid (Don't use WD-40, it swells the rubber) made sure both holes in the bottom of the master were clear and put it back together.

[Tim in Ohio]

Looking good Art.  Keep the progress reports coming.

[captaincrash80]

You should let me know if you're lookin to get that king/queen off your hands  Lookin good so far.

[Artfrombama]

After everything came out the bore looked good, so I lubed my new parts with brake fluid (Don't use WD-40, it swells the rubber) made sure both holes in the bottom of the master were clear and put it back together.

I was afraid my front brake master would be bad, the years of sitting outside took it's toll. The reservoir was corroded and so was the bore, so much that it'll never hold a seal.

You should let me know if you're lookin to get that king/queen off your hands  Lookin good so far.

$20. + shipping?

[Artfrombama]

First ride today, woo-hoo!
Still feel like the slow speed jets are clogged, idles on 3-4, 1-2 start firing after 4K rpm.
Anyway, looks are 100% better;


Work in progress

[Artfrombama]

Things I've noticed that aren't exactly right;

Clutch grabs at the end of the travel, suspect cooked clutch

Bad flat spot/hesitation just off idle, have to rev the motor and slip the clutch to get underway. Move the needles up a notch?

Damn stiff throttle spring, is this normal?

Jumps out of gear, mostly noticed this in 1st and 2nd. Worn shift forks?

Any suggestions?

[TwoTired]

In what country were H2s sold in?

[Artfrombama]

In what country were H2s sold in?

Sorry
K2

[Artfrombama]

In what country were H2s sold in?

Now that I've got your attention;
What's the solution for cracked overflow tubes. J.B. Weld ain't it!

[tonycb650]

Solder.

[TwoTired]

I've soldered up a few.  Must use acid core solder to "tin" the crack and the surrounding area properly.  Check your work with a couple lbs of air pressure inside and fuel or water in the bowl.  Bubbles mean you haven't succeeded yet.

Cheers,

[Artfrombama]

I've soldered up a few.  Must use acid core solder to "tin" the crack and the surrounding area properly.  Check your work with a couple lbs of air pressure inside and fuel or water in the bowl.  Bubbles mean you haven't succeeded yet.

Cheers,

Thanks pal
I really "gooked" up the inside of those carbs with J.B. Weld. I'm surprised it ran as good as it did....
But it does RUN!

After riding a XR650L for years it's amazing how smooth and torquey the CB750 is.

[Artfrombama]

engine flares if I gas it in high gear.
Clutch time.

[HondaMan]

Things I've noticed that aren't exactly right;

Clutch grabs at the end of the travel, suspect cooked clutch

This can happen from long sitting. It's also a characteristic of the K3-and-earlier bikes. Chamfering the oil holes in the center clutch hub, followed by adding 4-6 additional, similar holes, will solve it 100%. Don't make the holes bigger, it will weaken the rib in the hub at that point, causing aluminum migration later.

Bad flat spot/hesitation just off idle, have to rev the motor and slip the clutch to get underway. Move the needles up a notch?

Needles belong in 2nd notch from bottom on K2, put them there and leave them. Main jets should be 100 to 110 size, depending on altitude. If you are outside this range, something else is wrong in the carbs. Most likely culprit: there is a hard-to-clean air passage in the carbs: it runs from the air horn to the mainjet holder (the threaded casting in the middle of the bowl). Unfortunately, it starts out in a right-angle turn, right after the tiny brass port at the air horn (you can see the even tinier brass cap that blocks the drilled passageway, below the inlet port), so use a soft mechanic's wire to run it thru and solvent to clean it: mine took 4 passes to clean out. With those individual air filters, these holes plug quickly: a stock airbox, with its built-in velocity stacks, helps prevent recurrence. I have a post about this somewhere here, may try to find it for you.
[/quote]

Damn stiff throttle spring, is this normal?

Yes, especially if the rubber tube around the spring is gone. I usually stretch out the first 2 coils a little bit more, so getting off idle isn't so dicey. The K2 has a sudden throttle at low end, like the K0 and K1.

Jumps out of gear, mostly noticed this in 1st and 2nd. Worn shift forks?

Not likely. More likely: see comment about clutch, above. Chances are, it's not going fully home to the gear, because the clutch is not fully disengaging during shifts. Also, use 20w50 petroleum type or 15w50 Mobil 1 (NOT the 'V-Twin' oil version, though!) on these engines, it really improves their performance and shifting.

[Artfrombama]

Things I've noticed that aren't exactly right;

Clutch grabs at the end of the travel, suspect cooked clutch

This can happen from long sitting. It's also a characteristic of the K3-and-earlier bikes. Chamfering the oil holes in the center clutch hub, followed by adding 4-6 additional, similar holes, will solve it 100%. Don't make the holes bigger, it will weaken the rib in the hub at that point, causing aluminum migration later.

I will do this, I think it's something I can adapt to but for now it's a pain in the ass.

Bad flat spot/hesitation just off idle, have to rev the motor and slip the clutch to get underway. Move the needles up a notch?

Needles belong in 2nd notch from bottom on K2,

Mine were in the lowest notch. I noticed when I would rev the motor I would get a puff of black smoke. I read where the "default" setting was the middle notch, that's where I put them.

put them there and leave them. Main jets should be 100 to 110 size, depending on altitude. If you are outside this range, something else is wrong in the carbs.

These are 125 mains and 41 idle jets but I have K&N's and a 4-1 header. I haven't done any WOT plug reads, but crusing (4-5K RPM) the plugs are colored perfect.

Most likely culprit: there is a hard-to-clean air passage in the carbs: it runs from the air horn to the mainjet holder (the threaded casting in the middle of the bowl). Unfortunately, it starts out in a right-angle turn, right after the tiny brass port at the air horn (you can see the even tinier brass cap that blocks the drilled passageway, below the inlet port), so use a soft mechanic's wire to run it thru and solvent to clean it: mine took 4 passes to clean out. With those individual air filters, these holes plug quickly: a stock airbox, with its built-in velocity stacks, helps prevent recurrence. I have a post about this somewhere here, may try to find it for you.

I know the passage you're speaking of, I used lots of compressed air and carburetor cleaner but didn't try to use a small wire.

Damn stiff throttle spring, is this normal?

Yes, especially if the rubber tube around the spring is gone. I usually stretch out the first 2 coils a little bit more, so getting off idle isn't so dicey. The K2 has a sudden throttle at low end, like the K0 and K1.

Jumps out of gear, mostly noticed this in 1st and 2nd. Worn shift forks?

Not likely. More likely: see comment about clutch, above. Chances are, it's not going fully home to the gear, because the clutch is not fully disengaging during shifts. Also, use 20w50 petroleum type or 15w50 Mobil 1 (NOT the 'V-Twin' oil version, though!) on these engines, it really improves their performance and shifting.

I'm an long-time user of Castrol 20W50 in Honda engines, will do this. Thanks for the response HondaMan!

[754]

I am thinking you may have a wheel trade underway, but if not, run the 16 in rear a while..some prefer them.


Honda man suggests 110, but your combination is known to run well with 115 oe 120 jets.. cant hurt to try..


Do you still have lathe access?.. i bet you could work most of them dents out of the pipes, if you make a set of balls with a hole drilled thru for a cable.. get them down into the pipe with something flexible or curved. Then work up to a bigger ball a bit at a time.

[Artfrombama]

I am thinking you may have a wheel trade underway, but if not, run the 16 in rear a while..some prefer them.


Honda man suggests 110, but your combination is known to run well with 115 oe 120 jets.. cant hurt to try..

I'm going to keep the 125 jet in there until I can do some WOT plug readings... But not with the present tires.

Do you still have lathe access?.. i bet you could work most of them dents out of the pipes, if you make a set of balls with a hole drilled thru for a cable.. get them down into the pipe with something flexible or curved. Then work up to a bigger ball a bit at a time.

Funny you mentioned that. I did work the two most noticeable dents out of #1 and #4 head pipes. Tapped them out with a blunt 1/2" bar then gas fill welded/ground/filed the area smooth. I couldn't replicate the surrounding area rust pits though.
Later I would like to buy a set of the 4-2 Mac headers.

BTW, noticed a lot of white, crusty deposits in the sediment bowl/screen and the main jet holder/well that weren't there last month... WTF could it be?

[754]

If the bike sat for a long time, & if the underside of the gas cap was corroded, and if the gas washed that off...

 That is what the filter would look like..jmo..

[Artfrombama]

A little accident today;
Still have the "twisted iron" long chopper side stand, had to go to town to do some errands.... Parked and got off the bike.

WHAM!

Bike fell over, broke the clutch lever, bent my new handlebars, cracked the generator cover. #%&*@

Rode home, immediately pulled the side stand, shortened it 1.5" and blasted the remainder of the crappy Taiwan chrome off and Kryloned it semi-flat black.
Pulled the generator cover, pecked the dent out as best I could then J.B. Weld in the crack.
Pulled the L.S. grip and straightened the handlebars, ordered a new clutch lever (and some other odds-n-ends) from Honda Direct.

Finished in time to make the "Bike night" at the local coffee shop...Only after I was delayed when the + battery terminal decided to break.

One day soon this will be a dependable bike, I'm narrowing down on it!

[fastbroshi]

Looks like your little pocket coke container