Results 1 to 10 of 10
  1. #1
    CB750 Member shadowmoses42's Avatar
    Join Date
    May 2014
    Location
    Pennsylvania
    Posts
    24

    I have a 1980 CB750C Custom that hasn't run since 1998. Need help on where to start.

    Hello,

    I'm new to this forum and am looking to get my CB750C in working order. The bike was given to my dad in 1997 in perfect physical and running condition. I'm sad to say that after a few months he never rode it again and said it would be mine when I was old enough to ride. It was never properly stored. About a year later gas leaked out (through somewhere, I don't really know) and then we moved it outside where it sat for years. About 5 years ago we moved it into my shed. Not too much rust anywhere really and looks in surprisingly decent shape.

    I desperately want to revive this bike and ride it. It has 18,000 miles on it. What I need to know is where to start. I plan on changing all fluids, cables, and lines, as well as, repainting it and replacing the rear shocks and front brake pads. I know I'll need to clean the carbs (but I don't know where to begin there). Also, what sort of things should I be looking out for in regards to the engine, since it has been sitting for so long?

    My brother and I opened up the gas tank yesterday and saw a decent amount of rust inside (likely due to being stored with gas). I've looked online and had trouble finding a replacement gas tank for my exact model. I did, however, see a thread on this forum showing a way to eliminate rust inside a gas tank by using electricity. Is this a legitimate method that could help me not have to replace the tank entirely?

    Does fixing this sound like a lost cause or should I embark on this journey???

    Sorry for the long-winded post, I just really want to gain the knowledge to be able to fix this and I figured this site would be a great starting point. Any help would be appreciated.

    I can post pictures if needed, but the bike is in one piece at the moment so I don't know how well that could assist someone.

  2. #2
    CB750 Addict motogtp's Avatar
    Join Date
    Dec 2013
    Location
    Des Moines
    Posts
    294
    First get a Clymer or Hayes manual that covers the C model. Carbs - get them ultrasonic cleaned if you can. Check the condition of the slides, needles, jets, idle screws, and accelerator pump. Drop the floats in a little can of gas and make sure they float. Let them sit a while to make sure. Once back together set the vacuum level and sync the carbs.
    Is the engine free? Does it kick over? If not, this forum can offer some suggestions to free it up or do a search, lots of good old posts here. A squirt of oil in each cylinder probably wouldn't hurt given the amount of time sitting. If you can get the front end elevated so the oil lubricates the entire circumference of the rings it would help. Pull the oil pan to make sure the pump screen is free of sludge and debris.
    The rust reversing method is legit but it has to be done right. I have also heard of people dropping a handful of dry wall screws in the tank and shaking it lot to knock off the rust scale but it obviously has to be evacuated of all fumes. If it is severe rust you can use a liquid liner, I am sure there are posts about that as well.
    Then set your points gap and dwell, put a filter on your gas line, pop in a new set of plugs and see what happens. 18,000 miles is not a lot. If it is otherwise good shape it's probably worth the journey. Good luck.

  3. #3
    Moderator dirtdigger's Avatar
    Join Date
    Feb 2012
    Location
    Black Hawk SD
    Posts
    3,018
    First thing with the tank is to make sure it is actually rust and not gasoline varnish. A lot of times people think they have a rusty flaky tank but it is actually a build up of varnish from old evaporated gas. Get a gallon of acetone and fill the tank and slosh around for a while and let it set then slosh again. Drain it and see if the tank is coming clean...if it is it is varnish and you can keep cleaning. I am not saying it isn't rusted but I have seen a lot more heavily varnished tanks then rusted tanks.

    Get a book so you have it for reference. Change the oil before you try to start it.

  4. #4
    CB750 Member shadowmoses42's Avatar
    Join Date
    May 2014
    Location
    Pennsylvania
    Posts
    24
    Thanks a lot, I was definitively looking into getting the Clymer manual on eBay. What does the engine being free or kicking over mean exactly? Yea, I feel terrible that such a low mileage bike was given to me in such good shape and I let it go a little. I was in 2nd or 3rd grade back then. My brother's 2003 r6 has more than that so I'm hoping all is well with the engine and it just needs proper lubricants, spark plugs, and filters to run properly. I'm super excited so I hope this isn't a fail.

  5. #5
    CB750 Member shadowmoses42's Avatar
    Join Date
    May 2014
    Location
    Pennsylvania
    Posts
    24
    Quote Originally Posted by dirtdigger View Post
    First thing with the tank is to make sure it is actually rust and not gasoline varnish. A lot of times people think they have a rusty flaky tank but it is actually a build up of varnish from old evaporated gas. Get a gallon of acetone and fill the tank and slosh around for a while and let it set then slosh again. Drain it and see if the tank is coming clean...if it is it is varnish and you can keep cleaning. I am not saying it isn't rusted but I have seen a lot more heavily varnished tanks then rusted tanks.

    Get a book so you have it for reference. Change the oil before you try to start it.
    Will acetone damage the metal in the tank that isn't rusty looking? I just don't want to weaken it or anything. Curious.

  6. #6
    Moderator dirtdigger's Avatar
    Join Date
    Feb 2012
    Location
    Black Hawk SD
    Posts
    3,018
    Acetone is just a strong paint thinner, cleaner....it doesn't hurt metal.

  7. #7
    CB750 Member shadowmoses42's Avatar
    Join Date
    May 2014
    Location
    Pennsylvania
    Posts
    24
    Quote Originally Posted by dirtdigger View Post
    Acetone is just a strong paint thinner, cleaner....it doesn't hurt metal.
    Ok cool, i'll try that first. The tank was never opened during the years it sat but the gas was left in there and eventually leaked out through a fuel line. I guess it's likely the rust looking stuff can be varnish and residue. I hope.

  8. #8
    CB750 Addict motogtp's Avatar
    Join Date
    Dec 2013
    Location
    Des Moines
    Posts
    294
    Quote Originally Posted by shadowmoses42 View Post
    Thanks a lot, I was definitively looking into getting the Clymer manual on eBay. What does the engine being free or kicking over mean exactly? Yea, I feel terrible that such a low mileage bike was given to me in such good shape and I let it go a little. I was in 2nd or 3rd grade back then. My brother's 2003 r6 has more than that so I'm hoping all is well with the engine and it just needs proper lubricants, spark plugs, and filters to run properly. I'm super excited so I hope this isn't a fail.
    Free just means, does the engine turn over freely. Sometimes motors that have sat for long periods have pistons or other internals that get stuck. They can be unstuck but it's usually a lot more work.

  9. #9
    CB750 Member shadowmoses42's Avatar
    Join Date
    May 2014
    Location
    Pennsylvania
    Posts
    24
    Quote Originally Posted by motogtp View Post
    Free just means, does the engine turn over freely. Sometimes motors that have sat for long periods have pistons or other internals that get stuck. They can be unstuck but it's usually a lot more work.
    So I'm guessing that once I remove the carbs I'll be able to see the piston or something and then see if it moves how it should be? Also, I put in an order for an ultrasonic cleaner. Did some research and it looks like they're a very good method of cleaning carbs. This is the one I got: http://www.ebay.com/itm/120998200230...84.m1497.l2649
    Think it'll do the trick? If not I can return it or cancel payment and get a different one.

  10. #10
    CB750 Addict motogtp's Avatar
    Join Date
    Dec 2013
    Location
    Des Moines
    Posts
    294
    If you can turn over the motor with the kick starter it if free. You might want to ask around about the ultrasonic cleaner. A lot of hobbyists have them and it is probably cheaper to have them clean the carbs than buying the cleaner yourself.

Similar Threads

  1. 1982 CB750C Where to Start? Need suggestions
    By phillip142 in forum Builds
    Replies: 3
    Last Post: 09-05-2015, 09:21 PM
  2. For Sale - FOR SALE: 1980 CB750C Excellent Shape
    By Christopher Scesny in forum Classifieds
    Replies: 0
    Last Post: 03-20-2014, 10:30 AM
  3. Replies: 1
    Last Post: 11-18-2013, 07:38 PM
  4. Aftermarket levers for 1980 CB750c
    By narclark in forum The CB750 Garage
    Replies: 0
    Last Post: 06-11-2013, 12:31 PM
  5. Replies: 2
    Last Post: 12-07-2012, 08:51 AM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •