1978 cb750 carb swap

[shultz_1978]

Kool thanks Rerun I thought so I just wanted some one else to say so too.

[Piute]

  I only painted the outside carbs 1 n 4 ,was due to time ,but glad I did cause all the pulling in and out off bike would of scratched the  out of them,
  You can check for leaks, float level,accelerator,outside the bike on a bucket(yet hooked to gas tank).
 The look is great and different,I used the same low gloss Rustoleum engine paint used thru out my bike ,But Engine haven't painted it.
     Read your curring time or gas will just eat off ,I waxed mine with tooth brush also after cure a few times.

                                                                #4
                                                  polished cap/paint bowl

                         AND YES #2 WILL ONLY WORK ON #2 (accelerator diaphragm)

[Lucky 1]

If the carbs are 1977-78 the #2 bowl is very different.

I do not know what you meant by needles run off?

[shultz_1978]

Thanks for the info Piute. I will have to use the buck and check them out befor I install them.

Lucky what I meant is that I know I had adjustable needles befor I started trying the bike shops out to get it running better and some where some one changed them out.

They must have thought it will run better with new needles. who knows

I went a head and ordered all new rubber seals, floats, float needles, and a used #3.4 bowl.

For the next few days I will be cleaning, painting, and polishing while the part are on the way.

[shinyribs]

*edit*  Sorry,nevermind. I leaped before I looked.

[shultz_1978]

I finally getting the new carbs put together. I am starting with all stock jets and needles. I do have a set of adjustable needles out of what I think are 77 carbs. I also have some shims just in case I need to try that route. right now I only have #35 idle jets but I can get bigger ones if need be. No more drillingalthough I am running the bike with the jets Idrill out and it is not running to bad just a bit rich on the low end.

Hope to have the new carbs on in the next day or two. I will post the out come. I should really look into a sync gauge.I will see what happens

[Lucky 1]

I recently found out that the 1976 needles ARE the SAME as the 1978 needle profile.

Still would cost $100.00 unless you can get used 77's or used 76's.

[shultz_1978]

Will got the carbs on and running. I think I need to get a set of sync gauges. I am running The stock jets #35 idle and stock main needle. I have been playing with the mixing screws alittle and right now they are at 2-1/8 to 2-1/4 turns. Its not running to bad but I think I should sync them before I go any further with them. I am still running pod filters with drag pipes.

O this is how I checked for leaks.

[Re-run]

Nothing wrong with checking them like that really. Gravity is still in effect.

[shultz_1978]

Question!!! What do any of you guys thing it would do if I left the #35 idle in, but changed out the mains for the 77 neddles?I have the mix turned out to 2-1/8 - 2-1/4. If I went with the 77 needles and raised the needle a little shouldn"t I be able to get the mix back down to around 1 to 1-1/2?

[Re-run]

The needles control the mix as it transitions from the idle jets to the mains. It wouldn't do anything to control your idle mix.
Easy way to say it is they control how rich the mains are and when. Picture it like this, visualize the needle in the main all the way down. Now see the fuel going through the jet as the needle is raised, the more it goes up, the more fuel the needle allows. Now, imagine changing the clip location, see how it raises or lowers the needle in the jet and thus how much more or less fuel is coming at the same throttle position. For example, at half throttle, if you lower the clip it raises the needle thus allowing more fuel in at half throttle.
I hope I was clear enough on that.
It still does not change your over all slide position and thus throttle position. It changes the amount of fuel coming in the mains so you can lean it out or richen it up. Remember, raising the needle makes it richer, lower is leaner.

[shultz_1978]

Thanks Rerun that been say. Would it let more fuel in at idle as will as half and full throttle?

What I am thinking is by using the 77 adjustable needles would I be able to richin the idle with out changing my idle jet. Buy just rising the main.

If you change the idle jet to richin at idles. Is it wrong to try to richin the main to get a even increase throught the throttle range? Sorry maybe I am thinking to much.

[Piute]

http://honda-cb750-s.456789.n3.nabble.com/Carb-Sync-tool-59-00-Cycle-X-TECH-TIPS-also-being-added-td3963996.html#a3966301

[shultz_1978]

Thanks Piute that is pretty clear how the needles work with the fuel supply.

[rrgunslinger]

I found this interesting, May try it tomorrow since I have my carbs off again.  :( 

http://www.hondachopper.com/garage/carb_info/bench_sync/bench_sync.html
 

On Sat, Jun 16, 2012 at 4:02 PM, shultz_1978 [via Honda CB750'S] <[hidden email]> wrote:

Thanks Piute that is pretty clear how the needles work with the fuel supply.

Jamie

---

If you reply to this email, your message will be added to the discussion below:

http://honda-cb750-s.456789.n3.nabble.com/1978-cb750-carb-swap-tp3911046p4023097.html

To start a new topic under Honda CB750'S, email [hidden email]
To unsubscribe from Honda CB750'S, click here.
NAML

[Lucky 1]

I would be upset if I had adjustable needles and then they were gone. Those are $100.+

The 1976 needles are the same. But like I said $100.00 for the set.

[Re-run]

Yup typical bench sync for slide or piston carbs, CV carbs bench sync differently though, you sync the opening of the butterfly valves.

[shultz_1978]

I am starting to think this post took a 180 from swapping 78 carbs for 80 carbs

First thanks rrgunslinger and Re-Run for the tip on bench syncing the slides. I pulled the carbs back off and did it today. They were off not alot but they were off. I also liked how it was running with the idle jets I drilled out, so Iputtheminthenewcarbs and then I put the adjustable needles in with the clip on the third notch down from the top. My mixing screws are at 3/4 of a turn and it is running good. no stumbles pops or anything. If I jump on the throttle it is right there with no hesitation at all.

I will run it like this for a day or two to see if I need any adjustments. Then change to new plugs.

How the bike looks with the new carbs.

[shinyribs]

That bike is just sharp.I mean it.The white walls and those wild pipes.Real nice,bud.Real nice!

oh,new carbs look good,too!

[rrgunslinger]

Really nice looking bike ya got there!!!

On Wed, Jun 20, 2012 at 11:23 PM, shinyribs [via Honda CB750'S] <[hidden email]> wrote:

That bike is just sharp.I mean it.The white walls and those wild pipes.Real nice,bud.Real nice!

oh,new carbs look good,too!

Montvale,Virginia
 Piute said it best:  "wheres my 10mm?"
Hellbilly-"that is a great way to tell if you have come to your senses, when you start drilling random holes in things... "

LukeM-"Scooters rock, especially when they're in posse formation. "

Those who are too smart to engage in politics are punished by being governed by those who are dumber. ~Plato

---

If you reply to this email, your message will be added to the discussion below:

http://honda-cb750-s.456789.n3.nabble.com/1978-cb750-carb-swap-tp3911046p4023329.html

To start a new topic under Honda CB750'S, email [hidden email]
To unsubscribe from Honda CB750'S, click here.
NAML