Author Topic: 750k0 Aftermarket carbs (Read 5077 times)

martini · « **on:** July 16, 2005, 09:07:40 PM »

I've just been told that the carbs on my newly purchased cb750k0 are shot. I'm trying to pick up a good used set but I'm also wondering if its possible to get a new aftermarket set?

Bob Wessner · « **Reply #1 on:** July 17, 2005, 02:48:40 AM »

What exactly to you mean by "shot." I have a K0 also, and there is not much to these things that can be described that way unless you are talking about wasted floats, dinged slides, or dented bodies and cracked bowls. Come back with more details about their current condition and what you see.

Clyde · « **Reply #2 on:** July 17, 2005, 05:29:15 PM »

I have a K0 with the original set of carbs still in good condition, together with a spare set of carbs that I made up out of two and a half damaged sets. The only reason I could only make one set was that the bodies were damaged from handling/dropping etc, (not wear) and some parts were missing.
I agree with Bob- the slides hardly wear at all. The floats do get damaged, but it is better to replace the floats with later ones anyway. If the bodies and float chambers are visually OK, then what exactly is the problem?

martini · « **Reply #3 on:** July 17, 2005, 08:44:49 PM »

Thanks Bob and Clyde,

First of all let me start by admitting I am not a techy. I'm relatively new to the motorcyle game. I recently bought this K0 because I fell in love with it the moment I saw it. The bike has been completly restored (save for the carbs, obviously) and looks awesome. The guy I bought it from told me it would need carb work so I don't begrudge him. Anyway, I took it to the shop, it was running poor, firing on only two cylinders, stalling out, etc. They had a look at the crabs and apparently they are a mess. They are not damaged physically, but they have the wrong needles, the floats are mismatched, etc, etc. They advised me that it would likely be cheaper for me to get a new set then for them to put in the work necessary to fix them. They of course cannot get me a new set, so here I am. Any ideas?

Clyde · « **Reply #4 on:** July 17, 2005, 09:58:44 PM »

If they are not damaged I would try to get the correct parts. The only alternative is to look on eBay for a second hand set, but they are not cheap and there is no guarantee they will be any better than the ones you already have.
If you are comfortable doing the work your self, it is not hard to rebuild thaese carbs, then get the shop to tune/balance them.
You can buy kits for them, but even that might not solve all your problems, but would give you new gaskets, float valves and seats.
In the case of the floats, I would use the later plastic ones rather than the older brass/soft soldered floats. Less to worry about.
I would try David Silver Spares or CSM for the needles. Better to use Honda ones than aftermarket types.
I would also replace the O-rings on the fuel line t-pieces. The K0 had only two o-rings per T-piece whereas the later ones(K1 onwards) had 4 per T-piece.
You may find if you check the part books that the needles are interchangeable with later carbs. If you do not have the info, email me and I will look it up.
Funnily enough when I bought my K0 from a shop in Farmington NM, they told me that the carbs needed work, but when I pulled them apart, the only things needed were these o-rings and just setting up the float heights

Clyde · « **Reply #5 on:** July 17, 2005, 10:49:59 PM »

Check this out on eBay
HONDA CB750 SANDCAST K0 ? CARBS Item number: 4561985055

Bob Wessner · « **Reply #6 on:** July 18, 2005, 02:26:37 AM »

martini,

You mention the K0 is "completely restored" save for the condition of the carbs. If this is an accurate restoration, keeping the orig. carbs may be important, down to the floats, if keeping the bike orig. is a goal. If the floats are not holed or dented, there should be no reason not to continue using them. Clyde's right, but keep in mind those eBay carbs are an unknown also and just looking at them, they need a good cleaning inside and out at the very least also.

I was certianly no expert on carbs (still not, but am now more knowledgeable of them), but if you take it slow and carefully, they are quite simple really, to remove, disassemble and clean. There are many posts and FAQ's on this site regarding carb cleaning and rebuilding.

The one drawback to the K0 carbs will come after you have cleaned them. They have four separate cables leading from a junction under the tank which makes syncing them something of a pain. If an accurate restoration is not necessarily a goal, you have an option to fit a set of later Honda carbs. After the K0, Honda redesigned them so the individual carbs are linked via a bar rather than individually.

phylo101 · « **Reply #7 on:** July 18, 2005, 05:35:35 AM »

whoa - hold on WHICH two cylinders?

We wouldn't by any chance have an electrical/ignition problem masquerading as a carb issue again?

Could of course be bad points or coil, rather than the cabrs...but a LOT of shops nowadays will not touch old-style points ignition with a ten foot pole, and I HAVE heard of people being shoo'd out the door by being told it needs a part...which they dont have lol lol

Phylo

martini · « **Reply #8 on:** July 18, 2005, 08:44:35 AM »

Thanks again for the replies.

Bob, I agree with you about keeping the original carbs. If they in fact cannot be restored I intend on putting them in a box and should I ever decide to sell the bike they will go along with as the originals. I am not as concerned myself with keeping everything original as I am with having a good runner. You mention the possibility of using later model carbs. Will these later model carbs work with the K0 given the different throttle on later model 750's? As you know the K0 model used only one throttle cable whereas later models had the push/pull throttle set up with two cables. I am probably showing my ignorance here, I would think the carbs themselves shoud be interchangable but that the cable system would have to be changed.

Thanks again for the replies, very helpful to a newbie like myself.

Bob Wessner · « **Reply #9 on:** July 18, 2005, 09:13:31 AM »

I don't have any direct experience with later carbs/throttles, so perhaps someone more knowledgeable could chime-in. It seems like you could just use the one cable for opening the throttle. The second is a back-up/assist to close things down, but still the springs in the carb body should be doing the real work of closing the slides down.

kghost · « **Reply #10 on:** July 18, 2005, 11:22:02 AM »

On the later carbs all the work is done by the rack that holds the carbs. The rack has arms that pivot about a shaft which opens and closes the slides.

The slides have no springs on them. The slides are closed by a single spring which controls the arms on the rack. If you can get a complete rack you will only need the two cables.

I see complete carbs/rack on E-bay all the time.

Bob Wessner · « **Reply #11 on:** July 18, 2005, 11:26:21 AM »

Thanks for clarifying. Guess I'm still partial to the K0 carbs since he already has them.

martini · « **Reply #12 on:** July 18, 2005, 12:44:32 PM »

Thanks kghost,

I'm not sure I follow when you say that I will only need the two cables. On the K0 there is only one cable from the throttle which in turn is connected to single cables coming from each of the carbs. Again probably my ignorance showing but I don't see how two cables would work with the K0 throttle setup.

Thanks for the help.

eldar · « **Reply #13 on:** July 18, 2005, 02:04:58 PM »

The k0 only had 1 cable. A second was added later for better throttle response and safety. The later carbs have springs to close the carbs but as springs are not always reliable, a second cable was added to close the carbs. It is a pull-pull system. Either way you turn the gas, a cable is pulling.

Bob Wessner · « **Reply #14 on:** July 18, 2005, 02:07:46 PM »

Just had a thought, wouldn't changing to later carbs and two cables necessitate a change up on the right grip assembly?

kghost · « **Reply #15 on:** July 18, 2005, 02:09:31 PM »

Ok, I'm not sure if the early throttle housing on the handle bar has provisions for two cables or not. You can look where the cable comes out, if there are two holes in the housing on the handle bars your in business.

If there is only one you could still run the later carbs your just not going to have a cable to close the carbs. The later carbs are closed by a single spring and the second cable is a back up.

If you feel like you need the second cable as a back up (Notice I am refraining from comment one way or the other). You will need a switch/Housing on the handle bars.

On the later carbs like the K2 the two cables go to a bellcrank which is connected to a common shaft. The shaft has arms which open and close the carb slides. There is a spring on the bellcrank which pulls and closes the arms as well.

I am including a picture. Blow it up and look at number 20. The arms, bellcrank, and spring will then make more sense.

Bob Wessner · « **Reply #16 on:** July 18, 2005, 02:13:14 PM »

Actually, my K0 grip housing has provisions for a second cable, but of course, no cable, but I have no idea if this is an original part as far as my bike goes. Martini will have to take a look under there on his to see what he has.

eldar · « **Reply #17 on:** July 18, 2005, 02:14:34 PM »

Boy I dont think it is original. Why put on a housing for 2 cables but only have a system which uses 1.

Bob Wessner · « **Reply #18 on:** July 18, 2005, 02:16:06 PM »

My thoughts exactly. There are more than a few "mutt" parts on my bike.

eldar · « **Reply #19 on:** July 18, 2005, 02:16:56 PM »

Ok now imagine how I felt trying to use a clymer on my 78k!

kghost · « **Reply #20 on:** July 18, 2005, 02:17:30 PM »

Well, Parts bin engineering of course.

Why design, tool, and make a little rinkydink part like a throttle/switch housing when you have a perfectly good part already in production that will work.

Lots of the throttle/switch housing on the different make/year will interchange. The switch/throttle om my 750 and 350 are the same.

eldar · « **Reply #21 on:** July 18, 2005, 02:23:51 PM »

Thats true but the original k0 only had 1 cable with no provisions for a second. This and the carb setup is why the throttle and rack were redesigned.

One cable must have proven to be incapable by certain standards and the 4 cable carb set up was a real pain to work with and may not have maintained adjustment properly.

Thus a redesign that was then used for the next 8 years.

kghost · « **Reply #22 on:** July 18, 2005, 02:29:11 PM »

Yeah I've seen the original setup, what a pain in the ass to work on.

Bob Wessner · « **Reply #23 on:** July 18, 2005, 02:30:30 PM »

Hey, guys, you're talking about my carbs. You're going to hurt their feelings.

kghost · « **Reply #24 on:** July 18, 2005, 02:34:59 PM »

Bob,

You'd better run out to the garage right now!!!

Say soothing thinks to them, maybe burn money as an offering. Else they'll break.

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Author Topic: 750k0 Aftermarket carbs (Read 5077 times)

phylo101

eldar

eldar

eldar

eldar