Topic: cb 750 wont start

[nwern2010]

just picked up a bike last week. Nothing major missing from the bike just a couple odds and ends. I changed the oil, put a new battery in and tried starting it the other day. The tank wasn't on  but it started up for a couple seconds, blew out some black smoke and then died. I figured it just needed some gas. I tried starting it again and got nothing. After about 10 minutes of trying to start it and the battery just about dead, it backfired and shot a flame out of the pipe. Wonder if anybody has had a similar experience and could help me out. I'm not familiar with these motors and what problems they often have.  The only thing i checked was the plugs, and they didn't look too bad. Thanks

[greenjeans]

When I find one that's been sitting, I:

1.  Get a 6 pack.  Open 1
2.  Drain the gas out of the tank.  clean it out as best you can. 
3.  Remove the carbs and clean the snot out of them - not as bad as you think it might be. 
4.  check the valve tappets & set them  -  put a few drops of oil in each of the openings while you are there.  (engine cold)
     http://www.salocal.com/sohc/tech/vlvadj/vlv.htm
5.  check/set  the cam chain tensioner   (engine cold)
6.  take a points file to the points - set the gap and ignition timing (you can use a cheap test light - about 5-7 bucks - you don't need a timing light/gun)
7.  change the oil.  drop the oil pan and clean out the screen on the oil pump.  New filter
8.  put some new spark plugs in there - trim off 1/2" of the ends plug wires and put the caps back on there.  Put a couple drops of oil down there.
     (It fired - so you can assume you're getting spark - you'll want to check each plug individually for spark)
9.  grab another beer, cross your fingers and fire it up.

All of the procedures are in the FAQ section or do a search.   

You'll likely have to use the choke until it warms up a bit.  Might run a bit ragged for a bit until everything gets nice and hot.
Don't let it idle for too long (they are air-cooled)     Lube the chain up and take it around the block. 

These old Hondas are darn near bullet proof.    All the above will only cost you about $25 bucks including the beer, so you're not out much.
It won't take that long either - maybe a half a day to a day if your new to them.  Have fun


While you're at it, download a pdf of the manual or buy one if you don't have one.   A must have for old bikes. 
 http://forums.sohc4.net/index.php?topic=426.0

[kerryb]

+1...and by the time it does run, which it will, you will be hopelessly smitten with it and start wondering whether to do a restoration, a cafe, or just make it look as good as you can and ride the &*%$#@ out of it.

just for fun.

[poboy]

+1...and by the time it does run, which it will, you will be hopelessly smitten with it and start wondering whether to do a restoration, a cafe, or just make it look as good as you can and ride the &*%$#@ out of it.

just for fun.

Yep! I vote for the third option. You will buy at least one more to do the restoration or cafe route

[TwoTired]

I'd look in the carb bowls before committing to a total rebuild.  You didn't give any bike history or care, though.

If it looks like a sewer inside, then yes, total clean. If it was put away last month.  Maybe not. 
 If the floats don't swing freely, you probably just found out why the exhaust spit flame.
Look in the tank, too.  Should only find gas inside there, nothing else.

Anyway, the entire 3000 mile tuneup schedule is now due.  Plugs, points(gap and timing), air filter, tappets and cam chain tension adjust, etc.

Lot's of people here like beer.  But, if it makes you witless, even though you feel the genius, it is not recommended for solving mental puzzles of what's wrong and what is safe for a motorcycle, imo.

Cheers,

[Lars]

A few tip here:

http://www.hondahobby.no/website.aspx?displayid=1736

[nwern2010]

How do you check the cam chain tension and the gap and ignition timing? Should that be in my Manuel? . And Green jeans what is the purpose of cutting the plug wires? I don't know really anything about the bike. The guy that i bought if off of was really just using it as a doner bike. It does have 28,000 miles on it . Sorry for the probably stupid questions, but i am new to this 4 cylinder thing. Thanks guys! And green jeans good way to start off the list with number 1. That's always a must.

[Johnie]

Welcome to the forum. Sounds like you could use a service manual. It on this board and you can download it. The service manual is your repair bible and will help you learn tons. To answer your questions, yes, the owner's manual (not to be confused with service manual) should tell how to adjust the cam chain, points gap and timing. Many of us cut a small part of the front of the plug wire and install a new plug cap on the end of that wire. The reason is the end of an old wire usually shows corrosion and will rob that plug of a good spark. When you get a chance post a pic or 2 of the bike. We like pics here... And by the way, what bike you got there?

[bollingball]

If the tank was not on what were you using for a fuel supply? What year is the bike? Is it a K or F model?

[albertaboy]

I'd look in the carb bowls before committing to a total rebuild.  You didn't give any bike history or care, though.

If it looks like a sewer inside, then yes, total clean. If it was put away last month.  Maybe not. 
 If the floats don't swing freely, you probably just found out why the exhaust spit flame.
Look in the tank, too.  Should only find gas inside there, nothing else.

Anyway, the entire 3000 mile tuneup schedule is now due.  Plugs, points(gap and timing), air filter, tappets and cam chain tension adjust, etc.

Lot's of people here like beer.  But, if it makes you witless, even though you feel the genius, it is not recommended for solving mental puzzles of what's wrong and what is safe for a motorcycle, imo.

Cheers,

Lmao.  Hey I really seen the humor in your beer comment and I get your intended message but I had a hearty belly laugh as a result.

[TwoTired]

Lmao.  Hey I really seen the humor in your beer comment and I get your intended message but I had a hearty belly laugh as a result.

Well good!

In the 70's I was a stoner.  Preferred it while playing music and appreciated the lack of hangover.  I also worked on cars fixing their problems.  The wife and I would smoke up and usually watch TV.  But sometimes, I had a car to fix.  So, telling her it was about an hour job (it really was normally), I would meander out to the car with the tool box, drag up a stool and then sit and plan what had to be done for the repair.  The "planing" was my standard process, developed in my early teens, sans any mind altering additives.  When the TV program ended, the wife would come out to see how I was doing.  Usually, I had some superficial components removed, just to get a better look at what was to be done.  Often I was still planning on the stool (about an hour away from finishing).  But, other times I was watching an ant trail or a caterpillar saunter across the drive way (almost there!).  When it became clear that there wasn't enough time left to finish the job, the superficial parts would go back on, and the rest of the evening was in front of the TV.  Alcohol had a mostly similar effect, except in the morning, I'd feel like sh!t.  But, there were rare occasions that I actually did muddle through the entire repair.  Of course, the next day I had to do the job again to put it right.

It usually doesn't matter if you hit a wrong note or go off on tangents while playing rock and roll (it all sounds good).  But leaving screws and bolts out, that belong, and getting gaskets a little crooked, aren't really tolerated well by most machinery.  Electronics is similar, and it sometime gives you the way wrong kind of smoke under the wrong influence.  It took me about five years.  But, I eventually learned to make repairs and figure out problems sans alcohol or other substances.

I think I'll go play some music, now.

Cheers,

[Duke McDukiedook]

Download a copy of the manual in the FAQ section for your model and start reading before you proceed with anything further, please.