Topic: 1973 CB750 Rescue

[j343my]

Coming along nicely.  Go for the helmet mount but get good documentation! Pictures are a must have!

Thanks!

When I was taking apart the front fender, one of the fender stay grommets completely disintegrated.  I dug through my box of wire grommets and found one that was pretty much the exact size.  The outer diameter is a little smaller, and I had to sand it down a bit to make it thinner.  I'll probably replace all 4 at some point but for the time being it worked perfectly:

FYI...... I’ve noticed that vintagecb750.com is selling fender mounting hardware now. Looks like they have yours.

I did see that.  I don't really want to buy the hardware too just to get the grommets.  Also, interestingly my fender stays have shoulder bolts and flat washers, as opposed to the regular bolt and shoulder washers.

[Gamma]

Following with interest.  Coming on well 

[Stev-o]

Making good progress, looks good too!  Hope that 3.5" tire doesnt rub, is the fender on yet?

What is that other bike in your garage, a Kawasaki? The grab bar looks familiar.

[j343my]

Following with interest.  Coming on well 

Thanks!

Making good progress, looks good too!  Hope that 3.5" tire doesnt rub, is the fender on yet?

What is that other bike in your garage, a Kawasaki? The grab bar looks familiar.

Thanks!  The fender is on now and there is plenty of clearance for the 3.5" tire.  The bike with the grab bar in the background is an '84 XS650.  I also have a '74.

[j343my]

Got a bit more done this week. 

I cleaned up the rear fender, grab bar, turn signals, and tail light.  I wasn't planning on doing that just yet, but I have been cleaning up the chrome on other parts as I went along and they looked so bad in comparison.

Also the bolts that hold the front turn signals to the stalks were mismatched and it was really bothering me.  As an added bonus I found the turn signal bolt had been swapped with one of the rear fender bolts.

Before with turn signal bolt circled in red:


After with matching bolts:


Next I went back to the gas tank which is becoming the bane of my existence. I have managed to remove most of the rust, but I'm still dealing with some varnish/rust sludge at the bottom of the tank.  I wanted to remove the petcock before resorting to more drastic measures. 

The petcock screws absolutely would not budge, even with an impact driver.  I decided to drill off the screw heads and just pull the petcock off.  After drilling off the heads, it still would not budge. I drilled a tiny bit further and realized the screw threads were completely packed with varnish.  Gluing the petcock to the screws:


I added a few drops of acetone to the screws and picked away at it with a pin.  I repeated the process for about an hour and finally...

Success:


Luckily the screws came out pretty easily after that with some channel locks.


The game plan now is to add some acetone or lacquer thinner to the tank with an old bike chain and see how that goes. 

[RAFster122s]

Acetone will destroy your paint, so if you are not planning on repainting be very careful...

Warm up the lacquer thinner and see if a warm batch softens the junk in the tank...

[Stev-o]

Thank your lucky stars that you were able to remove the petcock screws!

Hows the inside of the tank look? If rusted, EvapoRust may be a better option.

[j343my]

Thank your lucky stars that you were able to remove the petcock screws!

Hows the inside of the tank look? If rusted, EvapoRust may be a better option.

The inside of the tank is pretty bad.  I tried EvapoRust initially after I rinsed it out.  That did a very good job on all the rust.  What I didn't realize was how much varnish was at the bottom of the tank.  I have lacquer thinner in it right now which seems to be doing a pretty good job of dissolving the varnish.  I'll probably put the EvapoRust back in once I take out the lacquer thinner.

[RAFster122s]

Warm evaporust works best... So, keeping the tank warm while derusting is always a good idea.

[RAFster122s]

A black painted cardboard backstop if a tank is sitting in the sun will gain radiator effect...

People living in the desert quickly realize how dark clothing and the heat of summer do not mix well. I tend to reserve my dark colored clothing for wintertime.

[j343my]

Warm evaporust works best... So, keeping the tank warm while derusting is always a good idea.

I had the tank with EvapoRust in the house.  Best I could do being in Canada in the winter.

[j343my]

Lots more progress recently.

Cleaned up the exhaust.  Other than the surface rust it is actually in pretty good shape. No holes anywhere.

Before:


After:


Also did a full engine tune up.

- Cleaned and lubed the advancer
- Set the points gap
- did static timing
- set cam chain tension and valve tappet clearances

Checked the spark plug caps next.  The cap on cylinder one basically just fell off when I took off the rubber boot.

3 of the caps were around 9-10 kΩ, but this one was the winner:


So I replaced them along with the spark plugs.  It had D7EA plugs.  I replaced them with D8EA.

Then I fired her up, set the idle, did the timing, and synced the carbs:


Also my sluggish tach seems to have righted itself.  I guess it just needed to shake off the cobwebs.  Its now moving as it should.

Made a bit more progress with the tank also.  The lacquer thinner appears to have done a good job dissolving the varnish.  I can actually see the bottom of the tank now.  After rinsing thoroughly, I put the EvapoRust back in to hopefully finish the job.

[grcamna2]

Those pipes turned out Excellent 

[BenelliSEI]

Moving right along! Nice work.

[denward17]

How did you get all the rust off the exhaust pipes?

[RAFster122s]

Brasso and 0000 steel wool can work as can phosphoric acid...


Nice Jardines exhaust...

[j343my]

Those pipes turned out Excellent 

Moving right along! Nice work.

Thanks guys!

How did you get all the rust off the exhaust pipes?

A damp blue scrubbing pad got the majority of the rust off.  I used some wadded up tinfoil to get the more stubborn areas.  Then I just gave it a good polish.

[j343my]

So my gas tank struggles continued.  I finally got the varnish and rust out, and back on the bike.  I filled the tank with gas, and when I came back a little later I was greeted with a small puddle of gas on the ground.  It turned out there was a pin hole in the side of the tank.  I drained it, and ordered the POR-15 kit.  In order to do the degreasing and acid etching I super glued the hole from the outside:



Thankfully that worked and I was able to get the tank lined:



and with that done, I had a rideable bike:



She turns 50 this month, so my goal was to get her out on a ride to celebrate.  The weather cooperated yesterday so we went out for a quick spin.  She shifts through all the gears and runs pretty good for a bike that hasn't stretched its legs in over three decades.

A few challenges remain:

- doesn't really like to idle around 900 rpm.  It will idle fine a little over 1000, but below it sounds like its really struggling and eventually stalls.
- the clutch is still rattling quite a bit.  The carbs have been sync'd but that didn't fix the problem.
- the petcock is leaking and carb no. 4's float needle doesn't seem to seal completely so about once a day it spits fuel out the overflow.  I tightened the petcock screws a bit more, and that seems to have solved the petcock leaking.

[denward17]

It's great you were able to get a ride in, looking good.

[BenelliSEI]

That has turned into a fine looking ride! Did you use the fibre washers under the heads of the petcock screws? Without them it will drool forever. I always let my bikes idle where the rattle disappears. The tach is not that accurate. If it likes 1,000 rpm, just leave it there. All my 750’s creep higher as they really warm up. You’ll get good at just setting it up or down with a glove, from the seat! Congrats.

[bek1966]

Great looking results. Nice work!

[grcamna2]

I like the look of the inside of your fuel tank: Sweet 

[willbird]

So my gas tank struggles continued.  I finally got the varnish and rust out, and back on the bike.  I filled the tank with gas, and when I came back a little later I was greeted with a small puddle of gas on the ground.  It turned out there was a pin hole in the side of the tank.  I drained it, and ordered the POR-15 kit.  In order to do the degreasing and acid etching I super glued the hole from the outside:



Thankfully that worked and I was able to get the tank lined:



and with that done, I had a rideable bike:



She turns 50 this month, so my goal was to get her out on a ride to celebrate.  The weather cooperated yesterday so we went out for a quick spin.  She shifts through all the gears and runs pretty good for a bike that hasn't stretched its legs in over three decades.

A few challenges remain:

- doesn't really like to idle around 900 rpm.  It will idle fine a little over 1000, but below it sounds like its really struggling and eventually stalls.
- the clutch is still rattling quite a bit.  The carbs have been sync'd but that didn't fix the problem.
- the petcock is leaking and carb no. 4's float needle doesn't seem to seal completely so about once a day it spits fuel out the overflow.  I tightened the petcock screws a bit more, and that seems to have solved the petcock leaking.

In the 1970's somebody stole my bike when it was my dads (he bought it new in 72). They took it down the street to a car dealer and stole tank and side covers. He bought a used tank from the "trading post" weekly newspaper. It was the color your bike is. He never did find new side covers. My bike went that color for a decade :-). It is one of the 3 colors my bike has been LOL.

[MauiK3]

green is good!

[j343my]

It's great you were able to get a ride in, looking good.

Thank you!

That has turned into a fine looking ride! Did you use the fibre washers under the heads of the petcock screws? Without them it will drool forever. I always let my bikes idle where the rattle disappears. The tach is not that accurate. If it likes 1,000 rpm, just leave it there. All my 750’s creep higher as they really warm up. You’ll get good at just setting it up or down with a glove, from the seat! Congrats.

Thanks!  I used new fibre washers.  It turns out I just didn't tighten the screws enough.  I opened up the petcock and cranked them down harder and it stopped leaking.  Thanks for the idle tips.  I'm going to have to play around with that a bit more.

Great looking results. Nice work!

Thanks!

I like the look of the inside of your fuel tank: Sweet 

Thanks.  The tank was my biggest struggle with this bike.  Hopefully that's the end of my tank problems.