Topic: 1978 cb750 carb adj.

[grwmotocycles]

Just fired up the 750 from a year resto.  runs good better with a little choke and will not hold an idle, have to flutter to keep running.  Any secrets to adjust carb. before I go through the manual.   

            thanks Geno

[TwoTired]

The secret is to pull the idle jets for cleaning.

[joeb]

I secound that.

[cafe2be]

i have the same problem. I am running a 77 750f with pods and a pipe. I was told i need to raise the needle height

[Bill K]

I can third that. PULLING and cleaning those idle jets made a bigger difference in the way my bike than everything else combined.

[shoemanII]

after the idle jets are pulled for cleaning, how are the internal passageways/slow speed circuits cleaned.  carb clean sprayed into the jet side, or something?  i'd like to avoid separating the individual carbs for soaking if possible.  bike takes a 3-4miles to warm up then runs great.  just trying to improve this a little.  thanks,
bobp     

[Sd455]

My 77 F takes forever to warm up, I think they're cold blooded. I took them apart soaked them in Chem tool (be very carefull with that) sprayed them with carb cleaner and blew them out. Then synced them. Did you take out the pressed in jets?

Oh, and it wouldn't run right w/o the air box on. Seemed too lean.

[shoemanII]

stock pipes and airbox, K engine.  took out and checked the idle jets (were clean).  no air compressor, maybe a can of compressed air for computers?
bobp 

[grwmotocycles]

Thanks for the heads up, I will clean and let you know the results.

[alis]

Is the idle jet the same as the slow jet?  Im having the same problem on my 78 750k and am suspecting thats what it is?  What is the name that is used in the manual?

[grwmotocycles]

dissembled the carbs. cleaned all jets.  Engine still will not idle under 2/2200 rpm.  The center pipes (both ) are discoloring.  checked the plugs and they are very white (Lean) on both center cylinders.  Restarted the bike and used a piece of cardboard to cover each carb. one at a time to see the reaction and the two outer carbs. when slightly covered will raise Rpm I am sure it is pulling more fuel.  The two center carbs. when covered will not raise rpm just push fuel out of the intake and soak the cover.  ?  Idle circuits still plugged??? Need some other thoughts on this matter.  Thanks Geno

[TwoTired]

When checking the idle/slow/pilot circuits you have to make sure the passageway in the carbs are open between four exit hole from the carb body.
1. The idle/slow/pilot jet
2. The  idle/slow/pilot AIR jet
3. the adjust screw recepacle
4. the exit hole into the carb throat.

You also MUST be able to see light through the  idle/slow/pilot jet itself.

Cheers,

[grwmotocycles]

TwoTired;  I may have many questions for you.  I will check the items you said,  be patient I am not real familiar with these carbs,    Thanks Geno

[BobbyR]

I have the same bike and it took me three tries to get them right. I finally rodded out everything with a high E guitar string and strands of copper wire. You can also be running lean due to hardened carb boots. These bikes are a bit cold blooded at startup, but not to your extent.

[grwmotocycles]

I hear Ya! Cold blooded is not even the word for it.  I am sure I will figure it out with a little time.  Just wanted to be on the right track

[eldar]

Maybe this winter I will do a write up for these carbs. They are actually pretty simple really. Cleanliness is the top priority.

[medic09]

There are several past threads on this, as well.  If you search, they may help.  Or at least entertain you. 

Cafe2Be, if you have the 77-78 carbs, there is no adjustment for needle height like the earlier carbs have.

Eldar, that's a great idea.  Get to work! 

[eldar]

Actually the 77 does have needle height adjustment.

[grwmotocycles]

Maybe this winter I will do a write up for these carbs. They are actually pretty simple really. Cleanliness is the top priority.

Why wait its Snowing in OHIO!!!

Thanks Geno

[eldar]

I have to winterize my house first! AND clean up my workbench!

[upperlake04]

Maybe this winter I will do a write up for these carbs. They are actually pretty simple really.

Eldar, that's a great idea.  Get to work! 

I have to winterize my house first! AND clean up my workbench!

 You're wiggling Eldar 

[medic09]

Actually the 77 does have needle height adjustment.

 

My bad!  I thought the 77 and 78 carbs are identical?  ...

[78CB750CAFE]

um, 78's have adjustable needles as well, you just have to separate the carbs fully to do it.

[medic09]

I have stripped and rebuilt 78 carbs twice.  Those needle do not have clips.  They're fixed on my bike.  Of that, I am certain.

 

[Porscheguy912]

I have stripped and rebuilt 78 carbs twice.  Those needle do not have clips.  They're fixed on my bike.  Of that, I am certain.

 

+1 on that. No clips on 78 carbs. 100% sure.
Unless someone rebuilt them before and used the wrong kit.