Topic: cb750a, nasty carbs, and other questions.

[merc2dogs]

 Picked up the 750a from Terry sunday, got it home and tore into it, and just as Terry said it had sat for a long time, pulled carbs and set them to soaking,  soaked over night and up till about 5pm this afternoon,  question is on the best way to free up the slides?
 They are locked right in place, can't budge them no matter what I've tried.

  never had the slides frozen on all the bikes I've pulled from barns and fields so this is a new one on me.
pic after soaking nearly 24 hours in the carb album here:

http://pg.photos.yahoo.com/ph/merc2dogs/my_photos
 
   Tried a different soaking solution this time, don't like it! Though the carbs are a lot cleaner then when they went in. Think I'll go back to my kerosene mix for the aluminum, and ruby fluid for the brass bits.

 Also, anyone know where I could find some 750a specific information? a shop manual or other I could download?
 And a source for a muffler to fit the stock pipes?
 
 Ken.
 
 
 
 
 

[cleveland]

I have not heard of a CB750A.  The F, the E, and the K are the only ones I knew about.  If the carbs from a K will work for you, I am sure I have an extra set.  What year is it?

[eurban]

The CB750 automatics use smaller carbs than the Ks and Fs.   Those carbs will need some serious cleaning . . . .You may want to consider replacing them although the auto parts are a bit harder to find. 

[cleveland]

Douh, automatic.  I guess that makes sense.

[tomkimberly]

 Picked up the 750a from Terry sunday, got it home and tore into it, and just as Terry said it had sat for a long time, pulled carbs and set them to soaking,  soaked over night and up till about 5pm this afternoon,  question is on the best way to free up the slides?
 They are locked right in place, can't budge them no matter what I've tried.

  never had the slides frozen on all the bikes I've pulled from barns and fields so this is a new one on me.
pic after soaking nearly 24 hours in the carb album here:

http://pg.photos.yahoo.com/ph/merc2dogs/my_photos
 
 Ken.
 
  

You are going to need a large metal tub and some serious carb cleaner unless you plan (and I would recommed you do) to seperate these carbs from each other for a proper cleaning. If you cannot locate any carb dip, then go to your local Yamaha shop and purchase their cleaner. Us it in conjuction with a hot plate, there are a few threads on this board.

Tom

[kettlesd]

Ugh - those are some seriously ugly carbs!

I would definitely separate the carbs to give them a super-thorough cleaning. Pour carb-soak into the slides, then set the whole works on top of the dryer (while the wifes out), or something similar. The vibrations of the motor running helps the stuff to creep. If it is still stuck, you can GENTLY heat the carb body with a propane torch, and then IMMEDIATELY try to work the slide a bit. The aluminum body will expand faster than the harder metal of the slide and should help to work things free.

However, if you heat too long then the slide itself expand too and you are right back where you started - so only heat and free one carb at a time. As soon as you get the slightest bit of movement in the slides they'll come free.

[merc2dogs]

   
 Cleveland,
  it's automatic, but you figured that out eh?, I had the same reaction when I first heard about them,  that was back in the 70's though, late 74, early 75, was cruising around walla-walla and ran into some canadians on tour and one of them had a 750a.
   May want to get a hold of you about those carbs, need to figure out a couple things with the auto first though.

 Eurban,
  I noticed they were smaller,  and looks like slightly closer. Any idea if the spigots in the head are smaller too or is it just a stepped boot?  so if I'm not able to get the slides out without a hammer, would the boots from a K work on them ? (not home right now, so can't look)

 Tom, 
 Have them, soaking in some crap I picked up at an auto supply, not too good. Doesn't even work as well as plain old kerosene
   normally I'll tear them down, and toss the bodies slides etc in kerosene (sometimes mixed with gas) and drop the brass bits in ruby fluid which makes the jets come out looking like new in a couple hours normally. I'll get some better solvent, or Kero and try it warm.


 Kettlesd,
  I couldn't get them to come apart  So decided to soak them a while complete hoping it would free them up, hasn't worked yet!
    I'll try the torch, as for the dryer, weeelll, she turns green and grows when she's mad, so I try to stay on her good side!   Figure I could chuck something in the lathe off center and let it run at low speed for a short while and get some shaking going.
 
    I've got acetone, lacquer thinner, and a few other less friendly chemicals in the garage, so I may give them a try too.
     So far I've tried a spreader vise, but I'm afraid I'll break the castings if I get too excited with them, so soaking is it for now.
  Never had this kind of problems with carbs, normally the problems don't show up till the carbs are torn down, and you start seeing all the dried varnish in the jets etc.

  Plan to let them soak for a while longer, while I get the bike started and chase down any other issues (brake master is realy nasty for one!

Thanks all,
Ken.

[cleveland]

I just got off the phone with a guy that has a 1977 750a.  I might be getting the bike for parts, but any auto specific parts are no good to me.  Depending on how cheap I get the bike I could probably ship you a bunch of parts for just over cost.  I don't want to give any quotes till I know for sure. 

 What year is your bike?

[merc2dogs]

  Sounds like a winner, It's a 76, the one that was listed here:

http://www.sohc4.us/forums/index.php?topic=15463.0

  Have to go play with it and get it into the garage, it's starting to rain.

 Thanks
Ken.
 

[eurban]

The aluminum body will expand faster than the harder metal of the slide and should help to work things free.

Not sure what metal the carb bodies are but it is not aluminum. Pot metal??

[kettlesd]

There non-ferrous, so I'm assuming an aluminum alloy.

[eurban]

The bodies are definitely not a typical aluminum alloy.  Here's a desription of the somewhat generic term Pot Metal.  I think thats what they are , , , , , http://en.wikipedia.org/wiki/Pot_metal

[kettlesd]

Sounds right - as evident from the number of cracked jetholders out there! 

[csendker]

These guys --> http://www.crotchrocket.com/fiche_section_detail.asp?category=Motorcycles&make=Honda&year=1976&fveh=2977 list the '76 750A specific  on their parts fiche.  I've downloaded each diagram & parts list for my own reference (at least the ones for my bikes).  Both saved the large format .gif and printed to Adobe.