Topic: Came across 1974 cb 750 that is near mint, sitting 30 yrs

[Hinomaru]

Your wrong battery install is a real bummer.

My stock battery replacement choice is the Yuasa brand for the Honda CB750K FOUR 1969-82.

Yuasa website: http://www.yuasabatteries.com/motorcycle.php

If you decide to go with the Yuasa brand, there are 3 different types of (stock replacement) batteries that have the correct fit  +/- terminals and electrical function for your 750 K4:

1. Conventional Battery Type:  12N14-3A

2. YuMicron Battery Type:  YB14L-A2

3. High Performance, Maintenance Free Battery Type: YTX14AHL-BS

How to read Yuasa battery numbers:

[Sniper X]

I would make that dude buy you a new wring harness, and install it without giving a battery.

[Spanner 1]

I wudda had a meltdown over the meltdown....... About the meltdown, remember the rectifier is the one thing on the bike that is connected directly to the battery, ignition on or off doesn't matter.  No fuse. If connected reverse polarity then the results are exactly as the pics. show. All the rectifier wires and the ground wire melted   
BTW.... Whichever battery wire he connected last would have produced a flash/spark as the battery would be directly shorted-out. Should have stopped there to investigate before attaching/tightening the terminal bolt  .

[Johnie]

Seems to me the person helping you was in a hurry to say, "I got it started." So few miles on this survivor and to have this happen is really not acceptable. He owes you something. Look forward to when you actually get it up and running and you are riding down the road for the first time. You will get plenty of envious looks on that bike. Good luck and let us know how it comes out.

[Trevdawg]

Thanks for all your advice on the battery.

Here are current pics of the tank. I dont know if this is better than what it was or worse. 

[Trevdawg]

I don't like it, I would rather do another dip. Vinegar and water maybe...

[Stev-o]

Looks bad

[Johnie]

YUK...that has a ways to go for sure. Gas in there will just close up the carb jets and you will have more issues. Has to be a lot better than that. It looks like a candidate for a liner if that is the best it can be. And I am not a fan of liners if they are not needed.

[Tews19]

How long has it been soaking and soaking in what??

I did Evaporust on a much worse looking tank and had results within hours. Of course you need to drain the tank out, rinse with water then use evaporust

[James T Kirk]

phew!

i had a similar problem when i entrusted my carbs for cleaning to a 'carb guru' on another forum. i was at the same stage as you, just trying to work out the bugs and get her going. he's got a great reputation and, most of the time, does great work.

carbs are nice and clean, but, he neglected to tighten the screws on the choke butterfly plates. one screw got sucked into the #1 cylinder! i hadn't even put one mile on that thing and i had to pull the head and clean the bits out of the cylinder.

at least i was able to really get familiar with the engine and replace the valve seals while i was in there.

oh and about the tank rust, i'm sure youve seen this thread? http://forums.sohc4.net/index.php?topic=109066.0

Kirk Out

[Spanner 1]

DOHC4, 4 valve head..... head removes with motor in frame... easy 

[BeSeeingYou]

    Something is not right if it looks like that after the Evapo Rust.  I have not used that but I have used phosphoric acid (Prep and Etch).  The acids will not remove gas residue/varnish and I wonder if some of that is what we are seeing. 
   This is a photo of a battery box from my XS650 that was covered 30% by corrosion, some surface but much of it was also was pitting corrosion from battery acid.  I actually thought of throwing it out at first.  I wish I had taken a before picture.  This is what it looked like after about 3 hours of treatment.   The bits of black is just paint still adhered and the zinc like coloring is the phosphate coating the acid leaves behind to protect the metal.  I did not rinse this but left the Prep and Etch to dry on the metal.

Another post mentioned muriatic acid.  This stuff is effective and quick but very nasty fumes  to catch a whiff of and they will cause flash rust on any unprotected metal nearby.  Need to neutralize this stuff right away before moving on to any next step.  I do use it on deeper corrosion as it is much quicker but always finish with phosphoric acid to avoid any flash rust or drying issues.  You just have to be careful with it.

[Tews19]

Look at the first tank pic on page 2.... That tank has gotten worse.

[Trevdawg]

The tank was drained.
Then we put the evaporust in there. My negligence, I only bought one container of it. I did this for 2 reasons, one it was the only thing they had and like you guys said "expensive." Two, there was only one container on the shelf.
So then I put it in the tank and was like ".....". We needed more. By this time it was already later at night and any auto shop was closed. I figured 2 things. One, it covered the part where the old gas was and I assumed this was good because the rest of the tank wasn't that bad. Two, we could let it sit over night and then just rotate the tank every few hours the next day.
That plan didn't work out. It appears whatever wasn't initially covered overnight only got worse.

Do you guys think the vinagar and water  might help this?

[Trevdawg]

I also forgot to add the second day I went to the auto parts store and they had another jug of it. So I bought it and put it in the tank as well. I asked if the store had more in the back and they said no, I bought them.

[Tews19]

I am not saying someone is messing with you, but how close are you and your friend? You state the bike is in his possession. Honestly, within an hour your tank should have looked a lot better. Even if you had only one gallon, the amount in the tank would not have made the middle hump get rusty. It wouldn't have touched the area minus putting it in. Just looking out for a new CB go'er. I would get that bike back ASAP.... Even if it sits.

[Trevdawg]

I have grown up with him. But I poured it in, then we worked on the bike for a bit  It worked great on the area that it covered but yes. The next day I was shocked to see how what wasn't covered got worse.

[Tews19]

Ahhhh eff it dude! I trade you my 75 550 supersport that is done up for your 750. Running and road ready!

[Stev-o]

Ahhhh eff it dude! I trade you my 75 550 supersport that is done up for your 750. Running and road ready!

Dawg - take that deal!

[Trevdawg]

I'll consider... But I'm on vacation. So it needs to wait.

He really wants this thing

[750K]

Fill the tank full of straight white vinegar, no water. Let it sit for a week, dump it into a bucket and rinse really well with water. Strain the vinegar through a nylon or t-shirt to get all the rust flake out and fill the tank back up for another week.

This is the part where you have to be quick, empty the tank and rinse with water. Get out all the final rust flake quickly. To neutralize the vinegar you need to dump a box or two of baking soda in and fill back up with warm water, it's an alkali and neutralizes the acid of the vinegar. Slosh it all around and dump and rinse get as much water out as you can. Then pour in a bottle of methyl hydrate or aceton and slosh around and dump, that gets rid of left over water. Blow dry with compressed air or hair dryer, I pour 2 stroke oil in to coat the inside till I'm ready to use.

If you do it quick you should have little to no flash rust, here's a link with some pics of the kz1000 tank I did. It was pretty rusty, I've done another tank since with similar results but it was not as rusted.

http://forums.sohc4.net/index.php?topic=64952.msg1169072#msg1169072

[apehanger 550]

Bad idea to use evaporust and not full the whole tank with it!! It works well for what was submerged under the fluid. But anything higher than the fluid got worse. I'm gunna buy 2 more containers of that stuff tomorrow and put it in the tank.

  I was excited reading this thread and at the same time, I hoped that I would get to post this before you had added anything to your tank to clean it.
  Old gas that turns to varnish can change the varnish to stuff that can be just varnish, or rust combined with varnish. If the varnish is really a lot from having started out with a full tank of gas,,the various caustic cleaners may have a hard time removing it. Those same cleaners are not very friendly to the pot metal in the petcock assembly.
  What I do is go ahead and buy enough lacquer thinner to fill the tank. Two days of soaking in it will almost assuredly dissolve all the varnish in the tank. It will not hurt the metal in the petcock,so leave it in there and use the petcock to carefully drain the tank. Use care in keeping it off the nice paint on this bike!
  Another bonus about lacquer thinner is that it does displace some of the water that may be mixed with the gasoline. I do save my used lacquer thinner and skim off the top and then filter it as necessary.
  After the lacquer thinner has done its thing, rest assured that any further treatment with rust conversion products will work in a more uniform manner. Expect to pay $15 a gallon for the thinner
 

[754]

 Juat a note. I tried vinegar in a Z 50 tank..left it in too long.. looked like crap and I did not fill it up. Looked sorta like the pic..
 BUT.. and this is important.. what looked like  worse corrosion easily brushed off you can scratch it off with a finger nail.
 So I am thinking, it may easily come off rinsing with  bolts or tumbling media.
 Hope it just looks worse than it is.

[James T Kirk]

DOHC4, 4 valve head..... head removes with motor in frame... easy 

no, you can't remove the head while the motor is in the frame. however, honda finally got a clue and redesigned the frame starting with the '79 model. you can remove a section of the bottom of the frame, soooooo much easier!

[Spanner 1]

Nice pic. !.... well I should have said rocker cover comes off in the frame rather than head  , right?