Topic: New Project - 1972 Honda CB750

[God of Thunder]

I do have a clean title for the 1972. I do not have one for the 1971.

[God of Thunder]

Well I'm tired. Rebuilt the carbs tonight. Took about 4 hours. Those puppies were solid and didn't want to let anything go without a fight. I didn't realize it at first, but the throttle would barely even open. Now...? They'll open with pride. The inside was terrible. Black, Brown, and everything was just like glue.

Lots of cleaner, lots of elbow grease, but I think we're in good shape. I didn't have the ability to take photos throughout the process as I was covered in grime. I will take some tomorrow for sure though.

I did however break a pilot jet. I was convinced that the clog was "that" bad - and might have gave the needle I was using to free it up a little tap.....caused that sucker to break. So I need to get one new pilot jet. Additionally, 2 of the pins holding the floats were real buggers to come out, so they are rather mangled. They went back in okay, but I don't trust them to allow to float to work freely, so I will likely be replacing those as well. Surprisingly, the gaskets looked in very good shape.

Tomorrow - my new bars and starting controls come in! In a perfect world, i would be able to hook them up and see if she starts - but I NEED to do the gas tank first, or I'll create the same problem as its very rusty. So tomorrow, the gas tank will be removed, and I'll start using vinegar to clean it up. Fortunately, I leave town on Thursday, so it'll have tomorrow through Sunday to sit - and my father will come by on Saturday to shake the can! I'll have pics of the carb soon!

[God of Thunder]

Picture time! Much to my surprise, all the way from Canada came the new handlebars and switch. The handlebars throw me off quite a bit as they look so different than the last set - which I felt was correct. Maybe 71 and 72 have different handlebars?! Either way, I got them mounted mostly with no issues. The wires were ran through the bars. The brake wires will still need to be ran, but I installed it anyway. Does it look correct to you?!







Look at how the brake line goes over the RPM gauge.


By comparison - I thought "these' were the correct ones....



Additionally, I am having a devil of a time getting this switch to seat properly.....



Oh yeah! And the carbs. The local Honda store did not have any of the pilot jets, so I will have to order one online, but here's how the look now!



I leave town tomorrow afternoon, so today I plan to get the gas tank pulled and soaking in vinegar while I am gone. Also - the underside of the gas tank, its gold.

[God of Thunder]

I love the easy jobs. Too bad it seems there never is one. I got the gas tank pulled tonight, drained the terrible gas that was in there and filled it with distilled white vinegar. For some reason, my petcock determined this was a good time to start leaking a lot. I did everything I could - adjusting all the gaskets, disassembling and reassembling, and nothing would cause it to stop leaking. So currently, its filled with vinegar and sitting on its side - at a slight angle no less so it can be filled with vinegar and nuts and bolts for the weekend. I'll have to order a new petcock I guess......drat.

[Alan F.]

You probably don't want to leave the petcock on the tank while it's full of vinegar. There are petcock rebuild kits available.

[God of Thunder]

You probably don't want to leave the petcock on the tank while it's full of vinegar. There are petcock rebuild kits available.

Wouldn't it clean out the petcock?

[newday777]

You probably don't want to leave the petcock on the tank while it's full of vinegar. There are petcock rebuild kits available.

Wouldn't it clean out the petcock?

The vinegar(acid!) will probably eat the pot metal of the petcock.

Make a flat metal plate the size of the petcock with holes drilled to screw it on the tank and use a sheet of rubber to make a gasket to seal the tank at the petcock mount.
Get a large plastic container to put the tank in while doing the tank de-rust to contain any leaks. Use blocks under the tank of 2x4s to keep the tank out of any leakage.

Get an aux fuel tank to test and tune the carbs (protects from rust getting in the carbs too)
https://4into1.com/motion-pro-auxiliary-tank/

[newday777]

As to the handlebars.....
1972 did have shorter bars than the 71 had.

[Stev-o]

Resist the temptation of buying a cheap aftermarket petcock. You will regret it...

[MauiK3]

+1 on petcock

[Don R]

 The guy that bought my brothers xs1100 cleaned the tank with works toilet bowl cleaner and left the petcock on. It blew up. He had not heard of a works bomb until then.

[God of Thunder]

Fantastic stuff - late last night around 1am, I read that the vinegar can eat the brass and that shocked me. So I did remove it late last night and have a make-shift plug in the hole! This wasn't planned very well on my part! I did order a new petcock just to be safe from (Sorry if I can't name names) cb750supply.com - hopefully its a decent one! If not, perhaps I can cancel it.

[Don R]

  You can take the old petcock apart to inspect it. Often, it's the washers on the mounting screws leaking through or the 4 hole washer inside has gotten hard. They usually need cleaned and inspected anyway.

[God of Thunder]

  You can take the old petcock apart to inspect it. Often, it's the washers on the mounting screws leaking through or the 4 hole washer inside has gotten hard. They usually need cleaned and inspected anyway.

I took it off a few times - and found a seal near the tank that looked suspect. But when I watched where the leak was coming from, it made that gasket with the 4 holes in it look like IT was the culprit. I don't know why it suddenly started leaking when its been fine the hole time, unless it was gummed up, but when I turned the petcock to ON, fuel would flow out of it and not leak. Makes me think I just don't have something right.

[Alan F.]

There was a thread a while back where someone was rebuilding or disassembling their leaky petcock and noticed grooves worn into the back of the 'handle' part...back of which seals against the 4-hole rubber & should be flat. He cleaned the part well, then applied a smear of JB weld, next day placed sandpaper on a flat sheet of glass and dressed the surface of the part with 220, 400 & 600 grit paper, then greased up the parts and reassembled.
I remember it working but can't find the thread now.

[God of Thunder]

Here are some photos of my petcock. If you see anything suspect, let me know. We're here in Branson, MO for the wife's 40th tomorrow, and here I am thinking of motorcycles!

I assume the round seal with 4 holes only goes one way....

[Kelly E]

I lightly sand the surface of the selector switch and replace the four hole gasket. I have both riveted and used screws for reassembley, both ways work.
We use EvapoRust to de-rust gas tanks. It won't hurt metal, paint or pot metal petcocks. We rinse with diesel instead of water. I just can't pour water into a freshly de-rusted gas tank. After you dump the diesel out into a jug let it settle, pour the diesel back in for another round and dump the sludge in the trash. We've done many gas tanks this way with great results.

[God of Thunder]

Today, Tuesday April 5th - the THUNDER rolled!

Armed with a new petcock, new pilot jet, and everything else. I was able to finish cleaning the gas tank, get everything installed and said "LETS GO"

And it STARTED! My grandpa came over and decided he wanted to help get it running, so it made it even better when it finally did.

It did not however, enjoy it much. There was a definitely fuel issue going on, like it wasn't getting enough gas. Moving the lines around caused it to help - some. Then I opened the gas tank lid and that caused the RPM's to speed up immensely. Then it would be tough to start, but if you held you hand over the intakes, that would cause it to catch. It didn't want to be consistent. There were times it would idle well for 5 minutes or so, and then slowly sputter out. Either way, today is a WIN and I'll just have to iron out the carbs. I DO (booooo!) have a float that likes to stick and pour gas. They were all pretty free the other day, but obviously the one isn't having a great time. I probably should pull it out and do the full rebuild instead of just a clean.

Additionally, the electric start likes to make a "chunk" sound every so often. It doesn't sound good. Either the teeth miss a lot, or perhaps one is missing, so we'll have to take that apart and see what we've got in there.

[Alan F.]

Good progress!

[God of Thunder]

Alright - I make no bones about it that I am as much of a novice as can be....and now I need to ask a stupid question.

As I mentioned, the starter makes an odd 'chunk' sound - it almost sounds like metal on metal. I'll try to get a video of it. Anyways, I got the bright idea to take the cover off and see if the gear had a tooth missing or anything. What I didn't anticipate, was that this cover - or at least behind it - would be immersed in oil. So I started to take the screws out - and then had to dremel several of them because they were stripped. So once I got it free - well it started to leak oil everywhere. So I quickly got it back together, and its no longer leaking, but what I need to know is.....is IS that the same oil that you pour into the main oil tank? It was very dark - and I have a fresh oil change in there, but considering how long it sat, it might be expected that it would dirty up that fast. But I don't want to risk starting it again until I know thats a shared oil....I checked the dipstick and the level was still good - which is why I felt the need to make the post.





Lastly - this outer cover, I am unsure of its purpose, but the top screw it stripped out. Any tips for removing this one?

[newday777]

Alright - I make no bones about it that I am as much of a novice as can be....and now I need to ask a stupid question.

As I mentioned, the starter makes an odd 'chunk' sound - it almost sounds like metal on metal. I'll try to get a video of it. Anyways, I got the bright idea to take the cover off and see if the gear had a tooth missing or anything. What I didn't anticipate, was that this cover - or at least behind it - would be immersed in oil. So I started to take the screws out - and then had to dremel several of them because they were stripped. So once I got it free - well it started to leak oil everywhere. So I quickly got it back together, and its no longer leaking, but what I need to know is.....is IS that the same oil that you pour into the main oil tank? It was very dark - and I have a fresh oil change in there, but considering how long it sat, it might be expected that it would dirty up that fast. But I don't want to risk starting it again until I know thats a shared oil....I checked the dipstick and the level was still good - which is why I felt the need to make the post.





Lastly - this outer cover, I am unsure of its purpose, but the top screw it stripped out. Any tips for removing this one?

That is the stator cover and yes there is oil in there.
The 3 bolts in the center hold the windings of the stator in place. You'll need to remove the cover anyhow to replace the gasket so drill the head off that screw then remove the other 2 screws to drop out the windings, then you can put visegrips on the screw stud to remove it. Clean up the inside of the cover(good time to polish the stator cover while it's off), reinstall the windings and then the cover.

[God of Thunder]

Newday - just to confirm, that’s the same oil that’s filled from the side cover yes?

[Stev-o]

It's the same engine oil.   Do you have an impact driver?  Guessing no, hence the stripped screw.  They are essential...

https://www.amazon.com/CRAFTSMAN-Impact-Driver-8-Inch-CMMT14104/dp/B07R96M9VW/ref=pd_lpo_3?pd_rd_i=B07R96M9VW&psc=1

[God of Thunder]

It's the same engine oil.   Do you have an impact driver?  Guessing no, hence the stripped screw.  They are essential...

https://www.amazon.com/CRAFTSMAN-Impact-Driver-8-Inch-CMMT14104/dp/B07R96M9VW/ref=pd_lpo_3?pd_rd_i=B07R96M9VW&psc=1

I'll be ordering that puppy right now! Thanks for confirming its the same - I didn't want any potential to risk damage, so figured I needed to check.

[newday777]

Newday - just to confirm, that’s the same oil that’s filled from the side cover yes?

Yes same oil