Advice for N00B on Restoration of Family CB750

[jglawrence]

Hello all,

For the time being, I have a 1974 CB750 in my basement ready for restoration. It is my grandfather's bike that has been passed down to my father and we will be doing the restoration. We don't need to restore it to original stock condition, it has a few non-oem mods, but we do want it to look and run like new.

We are fairly competent with doing our own engine work but have a few questions to get started.
I should note that the bike has been sitting for at least a decade.

1. Is a Clymer manual worth buying?
2. What are some good parts retailers for this bike?
3. What is the opion of the memebers on doing a full engine rebuild?

-The bike has ~14k miles and when we pulled the plugs they looked perfect. My grandfather is certain the engine doesn't need any work, but while we're at it do you think it's worth just doing a full teardown and rebuild?​

Pics coming soon!

 

[tommycarl]

If the engine runs, has decent power, doesn't leak oil, doesn't smoke excessively, and doesn't have any signs of another issue, I'd certainly just leave it alone.

 

[jglawrence]

We're not quite sure how it runs yet. The plugs tell a good story, but it hasn't been run in quite some time.

Our main concern is that one of the oil passages could be blocked and ruin the motor.

 

[tommycarl]

If it was me, I'd make sure it has oil, fresh gas, and no critters have been living in the airbox. Be sure the gas tank is clean inside and put an inline fuel filter on. Remove the valve adjustment caps from the valve cover and put some oil on the rockers. Put a fan on the engine and start the bike... and look at the rockers to be sure you see oil flowing.If you don't have an oil pressure gauge on the engine you might want to consider getting one since they aren't really expensive.

If the bike runs halfway decent I'd make sure the brakes work and the steering is fine, put half a can of Seafoam in the gas tank... and see what you get. Be careful and don't get silly with those 10 year-old tires, they need replaced before you do any fast riding, but I personally wouldn't worry much at low speeds.

I'm betting that the most you'll need to do is clean the carbs and the bike is going to run just fine... I hope I'm right and you can get to riding or cleaning or whatever it is you want to focus on.

 

[jglawrence]

I agree, my bet would be that it is fine also. It is a Honda after-all!

By the way, does fuel with ethanol muck up these carbs?
How big of a fan is needed to keep the engine cool for a test run?

 

[tommycarl]

It's my opinion that ethanol won't mess things up unless it's been sitting awhile... keep it fresh and things will be fine.

I suggested a fan just in case you start it and let it sit running... and if it's sitting I'd use the biggest fan I could find. A large box-type fan is what I'd use because I have one. Most of all, just be aware that the bike is air cooled and needs a decent amount of air flow to keep it cool. Kind of a "dance-around-the-question" response, but the best I can do. I have no idea how much CFM it takes to be safe.

 

[jglawrence]

Thanks for the advice! I started by removing the front wheel and fender and will be replacing the brake caliper soon as well.

My plan is to basically work front to back, disassemble it all, and put it back together once everything is in good shape cosmetically.

 

[jglawrence]

Any recommendations on worthwhile upgrades? Or fixes to common problems I can take care of during the restoration?

Electronic ignition comes to mind first and foremost, but if the points are working I don't know if it's worth the cost...

 

[tommycarl]

I really can't say a lot about upgrades since I've never felt the need to do much of that, but I did change some things on my first 750... a new '71 when I was in the army at Fort Bragg... bike came from Meridian Honda in Fayetteville, North Carolina. After I got back home and rode like 15,000 miles a year, I did make changes to that bike.

At various times I had drag pipes, 4-2 Jardines, and the stock pipes. Stock was best for that bike. I put a dual row chain on and that saved me from a new chain every 4,000 miles, but I rode it really hard, so really don't think you'd want to go that route if you're a reasonable rider (unlike I was at 21). I put in a Barnett Clutch and heavy duty springs, and there was a noticeable difference and worth doing... but again, I rode really hard back then.

These days, probably the best upgrade I would consider is Dyna coils and wires. I wouldn't personally go with electronic ignition because I've never had any real issue with points, and I adjusted them pretty regularly when I was riding "in the day". I have,, however, considered trying the transistor ignition that still uses the points, but eliminates the burning because it just uses them as a switch of sorts. If I remember correctly, it costs about $75 and is available through a fella named Mark Paris in Colorado. It's been awhile since I looked at his stuff that is described on the SOHC4 forum... he goes by Hondaman. You might contact him about what coils, wires, plug caps, and whatever else he might recommend using, and at a much lower price than electronic ignition. Here;s a link to his post with contact information: http://forums.sohc4.net/index.php?topic=67543.0

 

[dirtdigger]

Ethanol will cause issues in the carbs. It will cause corrosion "white death" over time because of the fact ethanol is alcohol and it absorbs moisture. If you run it often and drain the carbs over extended periods of sitting then you more than likely wont have an issue. Problem with ethanol besides absorbing moisture, it will boil and vapor lock easier then regular fuel. Running up to 10% is as high as I would go. More than that and you will start to lose performance without some major rejetting and carb work. Ethanol isn't as efficient as gas and needs more fuel the higher the percentage you go.

As far as a rebuild... go through all the tuneup parts, plugs, valve clearance adjust, timing chain adjust, check point gap/dwell, carb sync. Change oil and get it running to see how it does run. After you run it for a while I would then do a compression check to see how balanced they are.

An ignition upgrade will make a noticable difference how the motor runs. Yes you can get by with the stock points but they do take regular adjustments for correct performance. I have installed several dyna electonic ignitions and they do make the idle smoother and you can feel the difference in throttle response, plus you never have to check and adjust points again. A less expensive alternative is the Hondaman ignition. He is a great guy to deal with and he was a mechanic on these things when they were new so he has a wealth of information. He has his own book that is the cb750 bible and I do highly recommend it.