Topic: '78 CB750K Carb Questions

[rundogdave]

My carbs are in pieces. Got them with the bike. And like the bike, they were partially disassembled. It appears all the major parts are there. Trying to complete the disassembly. Having difficulty removing one of the pilot jets. Stripped out the screw head. Getting frustrated.
Question 1. Can someone recommend a place to send the carbs for rebuild? Approx. cost?
Question 2. If I decide to continue trying to do the rebuilds myself, it sounds like OE rebuild kits are the best choice. Where is the best source for OE rebuild kits?
Question 3. Didn't realize there was a felt seal around the throttle shaft on a couple of the carbs. There appear to be destroyed by the carb cleaner soak.  Do these felt seals come in the rebuild kits?
Question 4. How would one remove the pilot jet after the screw head has been stripped out?
Please forgive my ignorance.
Thank you for the help!

[newday777]

#1. Check with HondaMan if he has time to do them.
#2. South Sound Honda in Washington state usually have the best prices for OEM parts.
#3. Felt are not in the kits. Get them off ebay. Measure the OD and ID to order correct size.
#4. Sounds like you have to easy easyout or left hand drill bit if you can't use a screwdriver to get the pilot jet out and get a replacement Keihin pilot jet(don't use any aftermarket jets!)

Here's a rebuild thread on PD42A carbs

http://forums.sohc4.net/index.php/topic,146893.0.html

[newday777]

#1 gasket set

You need to order 4 sets

https://www.southsoundhonda.com/--xpartsstream#/Honda_Powersports/CB750KA_(78)_750_FOUR_K%2c_JPN%2c_VIN%23_CB750-2800001/CARBURETOR_COMPONENTS/14cf52cd-d282-42e1-9a4b-99870811a8c4/5991abff-2229-487b-90d3-38db9cd20889/y

[rundogdave]

Thank you Newday777! I have the thread on PD42A carbs, and I'm reading through it now. I'll be concentrating on that fouled up pilot jet today. I'll try HondaMan if things don't progress to my liking.

[madmtnmotors]

I’ve linked a couple other posts about the later model PD carbs in my signature below.

[rundogdave]

#1. Check with HondaMan if he has time to do them.
#2. South Sound Honda in Washington state usually have the best prices for OEM parts.
#3. Felt are not in the kits. Get them off ebay. Measure the OD and ID to order correct size.
#4. Sounds like you have to easy easyout or left hand drill bit if you can't use a screwdriver to get the pilot jet out and get a replacement Keihin pilot jet(don't use any aftermarket jets!)

Here's a rebuild thread on PD42A carbs

http://forums.sohc4.net/index.php/topic,146893.0.html

Where does one acquire the socket head screw kit in the rebuild thread above?

[newday777]

Don't know as I haven't used the socket head screws.

[rundogdave]

Ok, so I've got them all assembled and connected together. However, there is a problem. The choke rods do not rotate freely. When assembled as pairs, Carbs 1 & 2 and 3 & 4, they seem to rotate freely. I assembled them by following the instructions in the links posted previously. Outstanding instructions! But something doesn't look right where the two choke rods interact. See attached photos. The rods are straight per a machinist straight edge. Any thoughts?? Also, how does one tell whether these carbs are from a K or an F?

[denward17]

Did you remove/loosen the choke plates?  If so, you may have to loosen all the screws on the carb bracket (the bracket where each carb body screws into), just to see if the choke plates will open and close.  One or more of the choke plates could be binding.


Here is a pic of my K8 spring, not sure if it helps at all.

[Alan F.]

Here are the 2 photos zoomed in for easy  comparison.

[starf]

The second photo shows what looks like the piece on the end of the left choke shaft is bent. It should sit under the choke lever cam.

Added some lines to your photo as it's difficult to describe. The top lever (red line) should pop under where the arrow is.

[madmtnmotors]

starf is right, see attached picts from one of my other threads.

[rundogdave]

Ok, I've got that tab bent back in to place under the choke lever arm. Again, forgive my ignorance as the carbs were removed and mostly disassembled when I got this project. I assume that when the choke knob is pulled, the choke lever rotates, and the choke rods are rotated closed by the springs? My chokes still do not rotate freely, even with the choke plates loosened. I have new felt washers installed, and lubed with a little penetrating oil.

[rundogdave]

Sorry to be a PITA, but still having an issue with the choke rods. I've got it assembled correctly, as far as I can tell. But when I pull on the choke linkage, the choke rods stay in the open position. The choke rods seem to move freely before assembly. Could the spring that attaches the two choke rods together loose tension? I'm kinda grabbing at straws here. The second photo shows what it looks like with the choke linkage pulled and tied off.

[madmtnmotors]

I assume that when the choke knob is pulled, the choke lever rotates, and the choke rods are rotated closed by the springs?

You are correct, spring tension actuates the choke rods, there is no direct link to the choke rods, only the indirect connection of the springs. Something is in a bind. These springs don't see much use so I seriously doubt they would lose any appreciable tension. Without the carbs mounted to the "fixing plate" your carbs are all out of alignment. You need to bolt the carbs to the fixing plate on the intake discharge (head) side in order to hold the carbs in alignment. The slightest misalignment will bind the choke rods.

EZPZ