• Enter the March CB750 Supply gift certificate giveaway! It's easy... Click here, post something, and you're entered into the drawing!

New Guy Here, Needing some help....

Is there supposed to be a tool kit under the seat???

Yeah, in the little tray next to the battery.

Capture.JPG
 
I found the tool kit. On this CB750F2 it is in a box at the rear of the seat,
a deep box. I overlooked it the first time around.
 
Things are looking up, started the bike today on starting fluid, will now start on gasoline
as soon as I get a carb to settle down and quit flooding. How do these carbs come off??
I have never worked on a set of 4 carbs, will be an experience. Was hoping to avoid that chore,
guess not. It looks like remove the air box, loosen the clamps and remove carbs, just like
a twin but more clamps.
 
They come off a hell of a lot easier then they go on ;) Make sure you really need to take them off.

Sound like you got a stuck float needle. Try banging it with a screwdriver handle? It works more often then you might think.

Each bowl has a drain screw you can try that, and if your hands aren't too big and you have the right screwdriver, you can actually remove the float bowls and the floats while the carbs are still on the bike.

Take a look at this thread while your at it. http://www.cb750.com/threads/4710-Induction-Boots
 
Banging on the carbs helped some but still flooding through the drain tubes.
The bike sat for about 5 years so I probably at least need to clean out the jets.
I will try to remove the float bowls with the carbs on the bike if that fails, pull them off.
The bike ran today but not very well with all the leaking. What is the float setting height??
I need to check my boots, that could be a problem. I suppose these are JIS screws???
Is there a down loadable manual on the site??? I have nothing in the way of a manual.
Is the air box easy to remove??
My Honda twins have a flange on the boots that bolts to the head. I never try to force the carbs
out of the boots, I unbolt them, some work but they go back on easily. I cleaned the carbs
3 times on the CB400T but it finally ran right when I replaced the coil.
 
Last edited:
As advised, I am doing what I can with the carbs without removing them from the engine.
Pulled 2 float bowls and cleaned jets as best as I could. Bowls were not that bad but I could
not remove the floats, the pins are stuck and the posts are breakable, soooo. Will do the other
2 carbs tomorrow and start her again. Using fine wires, carb cleaner and compressed air for the jets,
hope it works. I can't wait for this beast to run. Got 3 park plugs out, still soaking 1 with penetrant.
I am not able to download the manual??? Does not like my browser, Firefox??
 
I am not able to download the manual??? Does not like my browser, Firefox??

Link works for me on Edge. On Firefox too but, I use the NoScript addon (plus Trace, Cookie AutoDelete, Privacy Badger, and AdBlockPlus) on FF and I have to trust or temp trust mega.nz in Noscript for it to work. Maybe you have an addon that blocks JavaScript?

If you can't get it to work you can always go sign up at http://www.sohc4.net/ they have online manuals as well.
 
Last edited:
I now have access to the shop manuals I need. Is it OK to continue this thread for my questions/problems??
2 things....I have worked on the carbs as much as I can with them on the bike and number 4 still floods.
Will have another look tomorrow. The other thing, the headlight does not work. The light itself checks good
but will not light on the bike. Tested with a multi-meter I have less that battery voltage at the headlight plug but I do have some current. Is there a relay for the headlight??? The high/low light does not work. Dismantle the switch?? Fuse??? But I have some current??? Bike starts and runs but the muffler( 4 into 1) rattles like hell. Probably rusted out inside. Another thing to fix.
 
Of course it is ok. By the time you finish that bike you should be ready to start some answering questions too ;)

You mentioned the float pivot shafts won't slide out. Your correct about those 2 castings they slide through being fragile. If they are really stuck the safest way is destructive! ;)

First, not all carb kits come with floats and float shafts. You may need to buy them separately.

So, you mangle the floats by unwrapping the metal from the shafts. Then grab the center of the shaft with some pliers and twist it free. Once freed by twisting, cut a piece out of the center of the shaft (assuming you have a zip disk) so you have enough room to twist and pull the remaining pieces out inward so you don't do any damage to the castings. Unless of course you have a mill in your garage then you can fabricate your own special tool to press the pin out while supporting both castings equally ;)

The only place the headlamp should get any voltage from is the dimmer switch. Myself, I take apart any switch I can, clean it, sand the contacts if needed, and apply new grease instead of just buying new ones.

CB750 Wiring.JPG
 
Last edited:
I did manage to remove the float from #4, the only one I am having trouble with.
As far as the head light dimmer switch, I repair everything if I possibly can. I
have about 10 years experience with old Hondas, CX and GL and 1 CB400 and
now this CB750. Other Hondas have been easy, this CB750 is challenging me.
I have 3 fuses in a panel but I only find 1 on the diagram. Also I see breaker points,
do these bikes have breaker points??? Thanks for the response.
 
Oh yeah, dual point with mechanical advancer.

Replacing it with an electronic unit is some of the best money you could put into it.

The wiring diagram is generic.
 
Tell me more about the electronic ignition for this bike. I have not had a bike with points ignition since the 1963 CB77. How primitive for these nice bikes. She starts and runs, some but does not take throttle well. If I gently speedup the engine it is OK but if I open the throttle quickly she hisses at me and tries to die. Not sure the accelerator pump is working, will check that today. Throttle cables are sticky, got to lube them, removed the baffle from the 4 into 1 exhaust, it rattled but that is fixable. I suppose if the advance does not work that could cause this type of problem. Soon as I get this thing running I will put new brakes and tires on it and send her home.
 
The 750 came out in 69 so points was the standard for the day. The stock point system works very well as long as you keep up on the maintenance. If you dont have the timing, point gap and dwell set you will lose performance quickly. Point adjustments and timing are critical to how well the bike runs. Even with electronic ignition you will still have the mechanical advance so you will still need to check that it is working. Over time the springs lose a bit of tension and if not maintained the advancer mechanism it self can easily get stuck...either at base timing or at full advance. Little dab of grease at point change keeps them working and dont forget a dap of point rub block lube...most people never do it and 30 years later the lobes for the points get worn/ You need to start and go through all the basic tuneup items i you are having running issues...beings you didnt know it had points I assume you havent checked any of it. Point condition, gap, dwell, advancer function, compression test, valve clearances, timing chain adjust, running carb sync are at the top of the list.
 
Progress is slow but there is progress. Starts and runs, fair but seems like the throttle is hanging a little.
I have lubed the cables and the linkage, hope that helps. The accelerator pump may not be working.
Can that be repaired with the carbs on the bike, looks accessible. Looking at the points and advance
tomorrow. That will be a new experience. Seems like the choke pulls out too far, adjustable???
Do I need to take the tops off the carbs and lube the linkage under the tops???
 
No lube under the tops. The accel pump is built into the float bowl but the diaphragm is replaceable. There is a checkball that sticks in the bottom cover from junk that settles out of the fuel...main cause for the pump to not work besides a hole in the diaphram
 
Guess I got lucky, this bike has electronic ignition, already. A little black donut where the points once were.
I checked the advancer, it moves freely. What spark plugs?? It has NGK D8EAs in it gapped at about .030.
It will get new plugs. Got to do the accel pump, set the valves, adjust cam chain and sync the carbs. My
vacuum tool only has 2 gauges. Can I make this work for the 4 cylinder bike?? She runs better with each
little thing I do to her. Looking for a big breakthrough when she begins to run well. My CB400 has CDI ignition.
A common mod for the CB400 is to replace the stock coil with a coil for GM distributor-less ignition.
Any mods for the CB750 coils. The GM coil fires both cylinders simultaneously but one cylinder is on exhaust so it
doesnt really see the spark. The spark went from stock to 40,000 volts or so and the bike starts instantly and runs really well.
 
Stay with D8EA plugs .024 to .028 is spec. Really need 4 gauges for best accuracy, adjusting one carb can affect the others and you want to be able to watch what all 4 are doing when its running as you adjust. 750 coils work fine on a stock motor.
 
Always one more thing....how are the cylinders numbered?? the plug wires are numbered with 4 on the left
side of the bike, looking from the rider position. A place in the manual says the opposite, I think. So which is it???
With electronic ignition module I do not find the marks for timing and setting the tappets??? Could this thing run
if plug wires are reversed??? It does start and run, poorly. Then is the accelerator pump in carb 2 or 3??
Also, what activates the accelerator pump and how to sync carbs, what do I adjust???
 
cylinder 1 in on the left. Cylinders 1 and 4 share a coil and 2 and 3 share a coil. What kind of ignition?, there has to marks somewhere. The accel pump is pretty straight forward if you just study it for a bit...all of this should be in the manual as far as syncing the carbs, if its not then get a good honda manual.
 
Back
Top