1977 Honda cb750k Carburetor

[unmovabletitan1]

I just bought my first bike and it's a 1977 Honda cb750k four. I need Carbs for it and can't seem to find them. If you know where I can find some or have some to sell yourself please post. Thanks!

[TOOLS1]

Welcome to the forum. I would suggest e-bay. If, you are not concerned about originality I would suggest switching to the 70-76 round top carbs.
TOOLS

[shinyribs]

Welcome! Tools is right.The round top carburetors are awesome. Very easy to understand and tune.Especially if you are new to it. Good luck on your search

[Re-run]

I LIKE my 78 carbs. They work great and are more tunable than the round tops before replacing jets.
The fuel screws allow much more flexibility than the older air screws. This is why people can run pods with 836 kits without having to replace the idle jet like you would have to on the round tops.

[unmovabletitan1]

Thanks for the welcome!! I'll continue my search, if you all happen to hear about some available it would be much appreciated to pass on the word. Thanks again!!

[shinyribs]

Rerun,does your bike have the CV carbs?

[Re-run]

Nope, stock piston carbs. CV might be nice but I'm not spending 700+!

[shinyribs]

OK.Are the piston carbs the ones called keyholes,or is there yet another type I dont know of?

I swear,I cannot keep up with you guys!

[Lucky 1]

Sorry double post.

[Lucky 1]

You are right,the earlier carbs were simpler and better as far as less parts to go wrong.

The 1977-78 (so called keyhole) carbs have a main difference.
The difference is that the #2 carb on those carbs has a accelerator pump connected to the other 3 carbs and  also spray nozzles in the venturi. The earlier styles do not have that feature. EXPLANATION: If you look downwards on the carb of the 77-78, the top of the carb cover is the shape of a old fashioned keyhole in the door of a house built in the 1930-40's-50's

The 1977-78 models have three screws that hold the float bowls on.

The 1976 model does not have the accelerator pump or spray nozzles.
The 1976 carbs have clips to hold the float bowls on.

The 1979 models went to double overhead cams and have the vacuum controlled slide.
Opening the throttle butterfly would control vacuum to the slide vacuum piston.

I would go for the 1976 carbs. Simple.

[Re-run]

The carbs are called piston for the operational design. The slide is the piston.
I still prefer the 77/78 carbs but then I know how to make them work, they are more complicated than the earlier ones but not that much. I still say they are much more flexible in their operation than the earlier carbs.

[Lucky 1]

Re-Run...
I am interested in what you are saying.

QUOTE."The carbs are called piston for the operational design. The slide is the piston.
I still prefer the 77/78 carbs but then I know how to make them work, they are more complicated than the earlier ones but not that much. I still say they are much more flexible in their operation than the earlier carbs. "

Can you tell us more about what YOU did, and what intake and exhaust you have on your 77-78 engine?

If we all share this info on these 77-78 carbs I think all of the 77-78 owners will benefit. Thanks.

[TOOLS1]

The best way I have found to make keyhole carbs work is to set them on top of papers to keep them from blowing away.
TOOLS

[Lucky 1]

At least the return spring on the carbs on the 77 is much more sensible than the 78.
It seems like as time went by the engineers at Honda got more unsensible.
The 78 carbs had a coil spring wound around the throttle shaft. A real finger mangler.

Now all they have is computer geeks that drive cars making tranformer toy motorcycles
with lousy cheap aluminum frames. Lots of graphics on the computer screen instruments though,
like a computer game.

BTW today I saw some repair kits to fix steel bolts getting corroded into the aluminum frames.
The chain adjustment slots.
Also saw parts to bolt onto aluminum swing arms to keep the rear axle plates from breaking off.

[Re-run]

I have done nothing special to my carbs. I have run with and without a air filter and straight piped it for a bit. A simple tweak of the idle mix is all I needed to do. Otherwise shimming the needle a little helped mid a bit.
I know people who have also dropped in a K&N, with head porting, and an 836 kit and the only thing sometimes needed was upping the mains as you would do with the old ones.
The fuel screw is much more adjustable than the older air screw is, then you get to add the accel pump and you have a much more adjustable carb for low speed adjustments. When I frequented the other sohc site, I talked to a number of others about this and while most people liked the older carbs, once people actually see how flexible the 77/78 carbs are, they never went back.
Ultimately there are only 3 differences between the carbs. The fuel screw, accel pump, and press in jet. I do not count the shimmed needles as washer solve that easy.
The press in is a bit of a pain but if ultimately is of little issue. The carb CAN be tapped to allow screw in jets. An old sohc member named Buffo, did it. There goes that restraint. It is acknowledged that the accel pump is nice to have and the fuel screw allows more adjustment.
I think what throws people is the touchyness of any sort of crud, but you know, the CV carbs are just as touchy.

[shinyribs]

Ok,so lets see. Up to '76 all bikes used the round tops. '77 & '78 used keyholes and '79 and up used CV's.

Is that right?

[shinyribs]

TOOLS1 wrote

The best way I have found to make keyhole carbs work is to set them on top of papers to keep them from blowing away.
TOOLS

LOL