Topic: First Motorcylce 1978 CB750K. Cafe Build

[Retro Rocket]

I sure wish you would tell me about those shocks.

I have spoken at length about these shocks Lucky, and answered a similar question in another thread you were in. I had a link thats now dead about a guy that "fixed" these cheap shocks so they worked properly, unless you have a lathe and really know what you are doing then i wouldn't bother at all. They have cheap crappy seals, poor quality oil and the alloy clevis and shaft on the bottom have been known to break because its cheap alloy. I have a set right in front of me now, i bought them before i read the blog i referred to, after seeing them first hand, the first thing i noticed was the cheap alloy parts on them, i only use them for mocking up and have no intention of using them on any bike i ride. There is plenty of info on this site about them..  You pay peanuts you get monkeys.....

[TommyT]

The shocks seem to be working OK.  I did tear them down and actually fill them all the way up with oil and actually charged them to 100psi.  So far so good. a bit on the stiff side but overall much better than my old sagging blown out shocks.

Not back to the accelerator pump dilemma.  Do your diaphragm has holes in both the little ears?  my check ball seems to be working fine, when I filled it up with bowl off I could pump the accel with my hand and it would push gas out the hole but not back into the bowl.

[Kev Nemo]

Just remove the little rubber tube between the carbs that flow to the spray nozzles and spray some carb cleaner through till you see it spray out the nozzle. Protect your eyes!!!

The top edge of the float bowl as a little hole with a brass square thing in the hole.
That is where the "O ring goes. under that brass thing is the spring and check ball.
That keeps the gas from draining back down into the float bowl.

Now in the very bottom piece is another little square brass piece with spring and check ball.'This is the critical one. If it does not work right your motorcycle will NEVER run right. A new bottom plate with check ball is $85.00 and IS available. After I tried to clean mine 3 times with no success I bought a new one and now it works perfect.
I think what happened is the check ball gets corrosion and leaks or does not seal.

I have a spare diaphram and bottom plate but the check ball is no good. If you want it and try to find a new check ball the right size I can give it to you. My ADVICE, bite the bullet and buy a new one before they are no longer available.

OK, pretty sure I'm having the same issue. I cleaned out my 78 CB750 PD41A last night, opened up the accel pump and noticed a small tear in the diaphragm,the ribbed grommet that keeps out moisture from the top is gone, and the top of the plunger is rusty. It now runs like it's starved for fuel/ boggy. Do you think that's the culprit? I'm ordering a new one from Parts N More (along with a float needle, since #4 looks corroded)

[TommyT]

OK I got my bike runnign great but it was only running good for about 1-2 miles before it would die.  Traced that back to a clogged vent on the gas cap.  Cleaned out the hole and it's been running great ever since.  New update.  Gas tank developed a small weep out of a spot weld on the bottom of the tank.  I am going to just clean it out and coat the inside of the tank.

I know it's been covered a bunch but I can't seem to find a definite answer.  Which coating should I use and will it mess up the nice paint if I do it?  I'm planning on masking off the top of the tank to protect it but I know some chemicals used to clean them out could eat through paint in no time.

Now to the carbs.  I removed each carb from the plate and cleaned out the passages for the accel pump to squirt through, re assembled and it works great now.  Rejetted to 130 and even with the pods and 4-1 almost no stumble through the rpm range.  I did have to punch out the feed hole in the diaphragm since it just super small and accel pump wouldn't squirt after 2nd or 3rd twist of the throttle.

My accel pump was still good just a little rusted on the shaft, just buffed it off and applied some oil onto it.  So far so good until the leaking tank now. 

[Killer Canary]

Are those the $85 rearsets from China? If so, I have a set and just the weight of my legs was enough to bend the carriers down. I cut sheetmetal reinforcements to shape and installed them on the mounting bolts between the rearsets and the mounts for strength. Nice job making a K8 tank look good!

[TommyT]

Yes they are the $85.00 rearsets.  They are flexing when I put all my weight on them.  On my "to-Do" list are making my own rearsets and moving them up about 2" and forward another 1" but these are working for now.

On the brake side I welded a new longer arm onto the pivot above the peg to work the rear brake lever.  Works but I feel the lever move as suspension cycles a bit so I know that's not perfect either.

[Killer Canary]

The brake side is tricky.

[lucky]

With the carbs off and on the bench when I hook up the fuel it's leaking on the #2 carb between the body and the bowl.  I cleaned off all the silicone #$%* the PO had put on there and cleaned it all out but still leaking a bit.  Floats/needle and seats all look good. Float levels are spot on and everything was running great when tore down.  Just sitting for the last 3 months without fuel i think the carb gasket dried out a bit letting it leak out.

There should be NO Silicone on the carb float bowl or any other parts.
The #2 carb is supposed to have a small "O" ring where the accellerator pump pushes the fuel up to the spray nozzles. The "O" ring sits on the lip of the #2 float bowl, in a recess.

[TommyT]

yeah PO had no o ring.  got everything cleaned up and o ring installed.  doesn't leak a drop now.

[Kev Nemo]

Since you cut the cross underseat brace, where is that plastic inner fender bolted to now?

Just an suggestion, but with the color scheme and stripe, you should slap a number plate on this side to cover your electrics:

[TommyT]

The plastic inner fender is cliped in the bottom and I welded a couple tabs that the top corners push into.  It's kinda just wedged in there, not bolted at all.

[TommyT]

Well I've been riding it off and on for a while now without any problems except the very bottom rear of the gas tank has a small weeping hole making the paint start to bubble.  I'll clean it out and coat the inside of the tank.  So far put about 700 miles on it and the rear shocks are working ok but a bit stiff even for my 6'2" 230lbs. 

[TommyT]

OK so been riding bike off an on for last year.  Havn't been riding it much at all lately though.  Probably gonna put it up for sale.  Any idea on what I should ask for the bike.  Pricing seems to be all over the place on these things.  some deals at $1000 and some guys asking $5K

Thanks

[JerseyHonda]

Are you going to list it on Craigslist or eBay?
I've had bikes that I've sold on eBay that went for more than I
thought they would.

[TommyT]

Was going to list on craigslist but sounds like I'll be looking into ebay.  Luck has it went out to ride the bike last night and rear corner of the tank has a nice bubble.  it appears gas is seeping through a small pinhole and f-ed the paint.  Looks like i'll get to solder the hole. doa  little bodywork and repaint the gas tank this weekend.

[TommyT]

Well decided not to sell the bike but bought another one too.