CB750 A2 / Hondamatic two-speed with 4 into 2 exhaust

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CB750 A2 / Hondamatic two-speed with 4 into 2 exhaust

jwdenos
All Stock.

I am the lucky owner of a bike that has been sitting for twelve years I have cleaned it up nicely.

I have cleaned the carbs.

I've gone over the wiring harness and purchased the coil that was missing (right side).

I am using the same plugs (seemed ok) with adjustments.

I've filed the points and cleaned with card, adjust gap set timing..

I changed the oil/filter. replaced the hoses on the carb and gas tank.

---------------------------------------

I do not have a breather hose for the manifold to the breather box right now.

On the carb there is a hose attached to a nipple next to where the fuel line hooks up; I am unsure where this goes.

the choke plates are fairly close to matching except for the number four plate. (guitar string check)

-----

I have  a crack in the number one boot and have taped it with several turns of electrical tape and clamped it tight on both sides. seems to be good for now. however a can discern that there is a possibility that air will still leak from the crack.

^^^^^^
Major Problem: With the choke activated the bike will start and idle,... not without the choke. [hmmm maybe it's the boot leak] yea,.. it just wont do anything without the choke engaged.

So, I'm thinking a carb rebuild kit and some new boots. Also checking the pump arm to rod distance etc.

Any help will be greatly appreciated.

Thank You.

-John

1978 CB750 A2

California Dreamer
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Re: CB750 A2 / Hondamatic two-speed with 4 into 2 exhaust

jwdenos
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Re: CB750 A2 / Hondamatic two-speed with 4 into 2 exhaust

jwdenos
In reply to this post by jwdenos
back view
1978 CB750 A2

California Dreamer
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Re: CB750 A2 / Hondamatic two-speed with 4 into 2 exhaust

TOOLS1
Administrator
In reply to this post by jwdenos
Nice bike. I have one it that color also. That hose you are asking about is a vacuum hose for the throttle kick-up. When you put the bike in gear it will increase the idle speed. However I run my bikes with the system disconnected. On the boot being cracked, yes it will cause a vacuum leak. Those must be sealed. No one makes boots for the matic. When mine went bad I switched over to K model carbs which boots are still available for. However I might have the "one" you need, which one is it? That is if the rest of yours are good. As for the not running without the choke on, it could be just the cracked boot, but I doubt it. These carbs a notorious for plugging up, especially the pilot jets. I have a write-up in the repairs section on "how to remove the pressed in pilot jets". Also the accelerator pump circuit is often clogged. You should have fuel squirting out of the four brass nipples in the throats of the carbs when you give it throttle. These can be cleaned, but are a pain in the butt as they have two tiny, and I do mean tiny check balls, and a even tinier spring that likes to fly.
TOOLS
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1976 CB 750-A X 2
1977 CB 750-A X 4
1977 CB 750-K
1976 CB 750 F
1981 CB 750
1966 Kawasaki SG 250
1981 KZ 750 LTD
1973 CB 350
1979 CM 185 Twinstar
1982 Honda XL 80
South of Eden (Kansas City MO)
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Re: CB750 A2 / Hondamatic two-speed with 4 into 2 exhaust

rich
In reply to this post by jwdenos
I really like that color. Only being able to run with the choke is a classic example of plugged idle jets.
This is what the jets look like after you pull them. You can't see the gunk without removing them.


Bike looks to be in good shape. I watched your video on facebook, it sounds a little "clanky". But that's probably because the carbs need to be synchronized once you get them clean and fix the air leaks.

89 VN 750A
79 CB 750K
78 CB 750K
77 CB 750K
77 GL 1000 x 2
77 CB 550F
Holton, KS, US
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Re: CB750 A2 / Hondamatic two-speed with 4 into 2 exhaust

kandrtech
+1 on the pilots being plugged.

Also just in case your asking about a different carb nipple:

The three hose connections (on carb 2) are (from front to back - or from head towards rear tire) are: solenoid connection; carb vent; and fuel supply
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Re: CB750 A2 / Hondamatic two-speed with 4 into 2 exhaust

jwdenos
In reply to this post by TOOLS1
Thank You.

The crack is on boot #1, actually.

I will take the carbs apart again. I have noticed that fuel only squirts from carb three. [the fuel squirts out of the carb towards the back of the bike with air box off].
1978 CB750 A2

California Dreamer
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Re: CB750 A2 / Hondamatic two-speed with 4 into 2 exhaust

jwdenos
In reply to this post by rich
Thank You.

I will be sure to check those.

http://youtu.be/YZoOp9Zwq8U

this video is interesting about the noise from the engine,.. my bike has 34,000 miles on it.
1978 CB750 A2

California Dreamer
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Re: CB750 A2 / Hondamatic two-speed with 4 into 2 exhaust

jwdenos
In reply to this post by kandrtech
Excellent. Thank You, very much.

-John
1978 CB750 A2

California Dreamer
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Re: CB750 A2 / Hondamatic two-speed with 4 into 2 exhaust

jwdenos
In reply to this post by kandrtech
wow,.. i took the float bowls off and the pilots slipped right out. They were not screwed in...

1978 CB750 A2

California Dreamer
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Re: CB750 A2 / Hondamatic two-speed with 4 into 2 exhaust

jwdenos
Made a world of difference. Now I will actually tune the carbs by ear best that I can.

As for the boot: I was thinking of using some muffler repair gunk stuff under the tape to seal the crack from the inside. Any recommendations on heat resistant adhesive that is ok with gas>?
1978 CB750 A2

California Dreamer
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Re: CB750 A2 / Hondamatic two-speed with 4 into 2 exhaust

jwdenos
In reply to this post by jwdenos
I am noticing that the exhaust feels stronger on the left pipe. The bike was extra dirty on the right side in front... cylinder 3 at the exhaust manifold. I have intuitively set the carbs 3 and four leaner than the others.

.. I will obtain a manometer.
1978 CB750 A2

California Dreamer
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Re: CB750 A2 / Hondamatic two-speed with 4 into 2 exhaust

kandrtech
If you haven't done so, make sure that you have adjusted your valves - and set the timing BEFORE you try to sync the carbs (using your manometer).

Also - one of the most often neglected items is the oil pickup screen (which is supposed to be cleaned every 6,000 miles).  You'll have to drop the pan - and replace the gasket - but your transmission will love you for it.
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Re: CB750 A2 / Hondamatic two-speed with 4 into 2 exhaust

jwdenos
Thank You for the epic suggestions. Will do.

1978 CB750 A2

California Dreamer