Topic: A little help from you carb gurus out there.

[jrrobertsjr]

Any idea what year these carbs might be? I know they need a rebuild but I am not sure what kits to buy.

I bought them separate from my 78 engine and don't have any background info on them.

Any recommendations on which kit and where to get it from?

This is my first carb rebuild...ever. So I am open to any and all suggestions.

Thanks,

Johnny

[upperlake04]

can't tell you what they are, but they're not from a 78

[scondon]

What year did they change from brass floats to rubber floats?     Anyway, those look like 750K carbs. 74-76?   There should be letters and #'s stamped into the carb body which will help identify them.

[tazzmann]

I am working on a 1970 CB750 that has carbs that look like those. That might be what they are from.

[jrrobertsjr]

I will give them another look but I couldn't find any identification on them last night when I was taking pics for this post.

Thanks for the info. A friend of mine says he bets they are a 75 set.

Johnny

[liaudio]

i'd place a bet that they're 75 750k's

[scondon]

The #'s are stamped into each carb body. They are up top, just behind the main plate that holds all four carbs together.

   There is a Old Fart who lurks this site. He has some great info on his own site. Hope he doesn't mind me linking to his carb ID page.....

http://www.motorcycleproject.com/motorcycle/text/specs.html

[oldfart]

Someone mention my name?  It really won't matter what year, except that as upperlake04 has said, they aint 77/78 carbs.  Thems 70-76 units.  No accelerator pump.  Removable idle jets.  The number on the casting near the engine will id them, as well as tell you what main jets and whatnot go in them (once you look up the id number in a Honda spec book).  As scondon has pointed out, the short cut is to visit my site, where there is a spec table.   

[jrrobertsjr]

Alright... PROGRESS! Thanks guys and nice info there oldfart.

I'll call my dad that right before he whoops my butt.

Anyway, any suggestions on carb kit manufacturers?

Who makes the best?

[dusterdude]

they`re just like mine,except mine has brass floats

[Jonesy]

Honda makes the best parts.

Many of us have had problems with the "Keyster" carbs kits widely found on the net. The two main issues are a different taper on the jet needle and different spring loading of the needle valve. Aside from these problems, they are OK.

[oldfart]

I agree, and would add that the only real wearing part in these carbs is the float valve needle and the needle jet (the part the jet [slide] needle pokes into).  The classic symptom of a worn jet needle is a sudden richening when coming to a stop, that makes the engine rpm either dip really low or even to stall. 

I am always hesitant to recommend the use of carb rebuild kits. The reason Honda and other manufacturers do not sell carb rebuild kits is because they are not needed. They sell carb gasket kits. Those are needed. But rarely does someone need a handful of jets when overhauling carburetors. The good thing Keyster and other kits do is provide relatively inexpensive sources for hard-to get o-rings and similar parts. The worst thing about the kits however is that the hard parts (jets etc.) just aren't up to factory quality. You have no idea what you're getting, and worse, you don't need to replace that stuff anyway. The only time I have ever replaced a standard jet was when the carbs had green moss or gray corrosion in them from severe sitting disease.

[Jonesy]

The only time I have ever replaced a standard jet was when the carbs had green moss or gray corrosion in them from severe sitting disease.

Or, as in my case, the PO decided the bike needed to run richer and got out the drill bits. The idle jet (normally a #40) was drilled out to at least 130! I say at least because my jet wires don't go any bigger and the 130 wire had plenty of room to slop around.

[Bob Wessner]

The only time I have ever replaced a standard jet was when the carbs had green moss or gray corrosion in them from severe sitting disease.

Or, as in my case, the PO decided the bike needed to run richer and got out the drill bits. The idle jet (normally a #40) was drilled out to at least 130! I say at least because my jet wires don't go any bigger and the 130 wire had plenty of room to slop around.

Yipes! That sounds more like a syphon than an idle jet.

[m00ntan]

They are 72 to 76, looking at the lifter arms and adjuster nuts.  The K1 had a different lifter shape and the k7 used the diaphram.

[Jonesy]

Yipes! That sounds more like a syphon than an idle jet.

It practically was! I didn't need the choke to start it cold and the offending carb's cylinder would drip raw gasoline from the exhaust joint at the head. I chased what I thought were spark and carb float issues for 2 months and rebuilt the carbs twice before I finally discovered the problem! A new idle jet and it idled great after that.

Of course, I still ponder why they put in 130 main jets, when all they did was put on a 4-to-1 exhaust with no other changes...

[jerimiah797]

By the way, I just went through this last week - putting earlier carbs on a 78 engine/bike. It worked out all right, just remember you'll need the matching year range (70-76) intake boots and throttle cables for the '75 carbs - and if you are using the 78 tank, then there's some custom fuel line routing involved. The carbs were designed for a double-outlet petcock on the right side, and the '78 tank has a single outlet one on the left side. I took a single 1/4" fuel line straight across the top/front of the carbs, then curved it around the right side and down into carbs 3 and 4. Right before that, is where I put a t-connector, to feed the 1 and 2 carbs.  Fuel filter is smack in the middle of the curve on the right side, just under the right side of the tank. I'll try and get you a picture. Good luck with the carb rebuild!

-Jerimiah