New Member, New to bike's

[MHluv2ride]

Hey all,
I'm new to the forum and new to bikes. I recently bought a, near complete, 1981 cb750k and am already in love! Since I am new to the bike world, I am learning with every turn of the wrench. When I bought my bike, it had been in dry storage for ten years (original owner won the lottery...sold 10-15 bikes to his neighbor, who then, years later, sold about 10 bikes to the man I purchased from.) The bike was nearly complete when I purchased it, only missing the headlight and ignition components, as far as I know and fairly priced, so I went for it. I have been warned about purchasing a bike without being able to run it, but I planned on completly tearing her apart, to restore and declutter into a cafe racer.

Since the purchase (a week ago) I have become obsessed, and all i want to do is work on it and learn about it. Ive stripped her down so that all that remains on the frame is the engine and wheels/tires. I didnt really know what to do first so I decided to tackle the carbs as project #1. I, being a novice mechanic, have enlisted the help of my pops to disassemble, replace, and reassemble the carburetor this coming weekend. I have a Clymer, repair manual on its way. I was hoping someone could help with a few questions I have before we begin.

Question 1: Should I replace all the rubber in and on the carburetor, and do most carb rebuild kits come with what I will need?

Question 2: Is a carb rebuild kit, something that can be purchased from my local Honda dealership or is that something that has to be ordered online?

Question 3: What else do I need to know when rebuilding a carburetor?

Anything will help, and be very much appreciated, for I know very very little thus far. I wish I had more time to elaborate on my questions but Im at work and have used up way too much time looking at cb750 porn! Thanks everyone!

[shinyribs]

Welcome to the forum and welcome to bikes! They're a blast! Sorry I cant help you with your questions,but there are plenty of guys with DOHC bikes like yours that will help you out. Good luck and have fun

[MarkPBG]

Welcome to the addiction! Nice bike.
To answer your questions, I got an old one too that had been sitting a long time, here are my personal recommendations,

1. Carb kits come in two types, gaskets and seals only (good for cleanup jobs) and complete carb kits (gaskets and seals, plus float needle and seat, main jet, pilot jet, adjusting screw and spring.) you'll have to buy floats separately if you end up needing them. If it's been sitting a year or more, yes, take it apart and clean them, gaskets and seals kit should be all that's needed if your luck is good. :)

2. Some Honda dealerships do have the older kits, most don't. Sorry, but you'll have to make the call to them to see if they have them. If they're special order, check the price. Often they are cheaper at the places listed on this site here....http://honda-cb750-s.456789.n3.nabble.com/Parts-sources-for-our-cb750s-Updated-with-a-little-dohc-and-electrical-6-3-10-td462672.html

3. Not a lot, just common sense and the right information. Start by downloading the big manual here on this site, you may need a carb synch gauge set and float level measure tool, both can be found through links on this site with a search. These carbs are fairly simple, I did my rebuild and got it close enough to ride. I did end up bringing it to a pro to have it tuned right, but he said I was very close, and it was my first motorcycle carb rebuild.

Have fun, and welcome!

[Piute]

http://search.yahoo.com/search?p=1981+cb750k+carb+kit&b=&fr=ie8

[seestheday]

Welcome to the forum

I have the exact same bike as you, and I'm currently going through the carbs a 2nd time (first time helped a lot, but I wanted to do a complete teardown/clean).

First question - why do you think you need to clean the carbs?  Have you confirmed that you have spark, compression and gas yet?  (suck, squeeze, bang, blow).  You may have other issues that you need to address first.  Often carbs are one of the last things to do in order to get the bike running right.

Also, word of warning about making a cafe racer from a DOHC CB750 - the CV carbs that these have are notoriously hard to tune to work with pods.  Not saying it isn't possible, but everything I've read is that it is much harder to.  I haven't done it myself yet, but I'll likely try it this winter.

Now, for the carbs there are many kits.  If you want to get one comes with absolutely everything I'd recommend the Randakk's one.  It's pricey, but it comes with everything.  If you buy a cheaper one, then stuff will be missing and you'll need to buy separately if you end up needing to replace them.

It all depends on your budget and what shape your carbs are in as to what route you want to take.  The first time I cleaned mine I didn't buy a kit at all.  I just re-used all of the old rubber/gaskets and it worked great.  The 2nd time around I'm sourcing my own o-rings etc, and it's much cheaper than the randakk's kit.  I'm also going to bypass my air-cutoff valves, so I don't need those (saving myself about $80).

Search this forum for the "DOHC carb cleaning" thread for lots of information on how to clean these carbs.

Enjoy

[MHluv2ride]

I appreciate what you've all done to help me out, with the links and answers to my questions. I have been doing a lot of reading on this subject, within this forum, and other sources on the web. It has certainly provided me with a little more knowledge about these carbs, as well as, DOHC airbox modifications/pods, but it has also made me start second guessing myself and decision. I understand that pods are not the best option for the DOHC's because of their need for constant vaccum and filtering, that the stock airbox provides...? Soo, i've decided to put that decision off untill the bike is back together and i really need to start thinking about the airbox mods.

Seestheday, As mentioned in the original post, I know basically nothing about bikes. I chose to start with the carbs first because it was one of the first things to come off the frame, kinda random decision. That being said, my plan to rebuild the carbs was pretty much based off me thinking that it couldnt hurt to have everything be as fresh and new as possible, and that I want to know my bike inside and out. After reading a lot of different forums, I dont know what to do now. My girlfriend told me her dad only cleaned her carbs and that it seemed to be enough and she thinks im going to spend way more money than I need. A concern I have, since I was unable to start the bike when purchased and really go through and find out what was working, what needed repaired, or what need replaced, is that I really didnt know where I should begin. Any tips? I also realized, from compairing rebuild kit prices, that each kit does ONE carb (duhh) so I would obviously need 4 kits, If i so choose to fully rebuild. I dont know, I just dont know...

*Question: Is it the just cb750 stock carbs that dont do well with DOHC engines and pods, or all the CB series stock carbs?? Could I put cb900 carbs on and run pods or does that run into the same issue. (novice question but I just dont know and researching has been taking me all over the place.)

Thanks all!!

[seestheday]

Randakk's kit comes with everything you need for all four carbs: http://www.randakks.com/DOHC%20Four%20Page.htm

If you're on a budget though, I would start with just a soak/clean.  Don't break the carb bank apart, just do as good a clean as you can with the bank together.  You will need to invest in some tools and cleaning stuff if you don't have it though.  A carb sync tool was a wise purchase for me.  There is a great thread on here called DOHC carb cleaning procedure that you can find via the search box.

Interesting thought - I was literally exactly where you are now 1 year ago.  I knew almost zero about bikes bike, and was preparing to tackle my first job (cleaning the carbs).  That DOHC carb cleaning thread has a lot of posts from me in it from when I was going through it.

I did have a running bike though.  I just wanted to make it better.

How would you rate your technical aptitude?  Given that you are planning on taking this on, I'm guess it's pretty good.  You should be fine.  Just take your time and ask here or the other forums if you have questions.

The reason I asked about the carbs, is that there may not even be a problem with them.  There could be another issue that is easier to fix that would get you on the road faster.

At a high level, what you really need to remember is that an engine needs to do 4 things to work.
Suck: pull fuel/air into the combustion chamber
Squeeze: Compress the fuel/air
Bang: spark to ignite the fuel/air
Blow: push out the exhaust gas

If you have all of these your engine will run.

Here is what I would check first:
0: Oil - make sure your engine isn't dry and not seized
1. battery (bang) - do you have any power at all - it is likely that the battery is totally shot and that you need a new one.  If you think its in good shape make sure you get it tested (most places where you can buy batteries do this for free).  There is a high likelihood you'll need a new one.
2. spark (bang) - lots of videos on youtube on how to do this, methods don't really vary by engine, just make sure you wear a glove or hold the plug with pliers (shocks hurt).  It's one of the first things you do because it's free and quick.
3. Check for gas flow (suck): now that you know your battery is good and that you have spark, are you getting gas.  Run the starter for a few seconds and then pull a plug.  Is it wet?  Does it smell like gas? If it's completely dry then there are a bunch of things to hunt down (carbs are one of them, but it could be as simple as a turned off fuel valve).
4. Compression test (squeeze): ok, now you know that you are getting at least some gas and spark.  You should check your compression level.  Any motorcycle will need a minimum of 100psi to run at all.  Factory spec is 170 +/- 14 psi.  I run around 135 for all 4 cylinders and it runs fine.  You need a special tool to check this, but they run about $30, less if you can get one on sale.

Check all of this and if you haven't figured it out, come ask more questions

After you get the bike engine running, make sure you get NEW tires.  If the ones that are on there are over 3 years old you need to replace them.  This is probably the most important safety consideration.  If you can't afford new tires, you can't afford to ride your bike.  A blowout at high speed could easily = death or severe injury.

[seestheday]

Also, it looks like that bike doesn't have any exhaust on it, just straight headers.  That beast is going to be LOUD when you get it running.