CB 750 carbs checklist before install

Maritime

Over 10,000 Posts
the carbs can oxidize and you really don't see it but you can feel it with your fingers and a cleaning with fine sandpaper can make a big difference. I had a slide that was fouling on a CX carb that I couldn't figure out until I felt the sides of the slide chamber and they were ever so slightly rough. quick sand with 2000 and a polish with aluminum polish and all was well.
 

chickenStripCharlie

Been Around the Block
I did verify that it wasnt the binding, because I had the flaps on there very loose and only tightened them up when everything was properly aligned.

Yes, they were 100% disassembled to clean.
I'm still thinking it might be the way I have the springs hooked up on there. So hard to find pictures online that show details clearly
 

Jimbonaut

Over 1,000 Posts
DTT SUPPORTER
Here's a photo I lifted from my Rhonda thread. Of course the old photobucket watermark is exactly where we don't want it, but it hopefully helps -



This is how the spring and linkage should look with the choke in the relaxed (off) position - you can see the choke butterflies are open. I'll take another photo of the linkage on the carbs on my current build too and will send it over later today.
 

chickenStripCharlie

Been Around the Block
Thanks jim! I asked around a bit more and the consensus is that the spring is on correctly and that likely the plates are binding somewhere a tiny little bit still.

So, going to look into that tonight and see if I can spot it.
 

chickenStripCharlie

Been Around the Block
Smooth out all the throats and yoj may find them just fine
Upon closer inspection the plates do seem to bind a tiny bit. Perhaps because I used the plates from another (but same!) Set of carbs?

I cant really be sanding the carbs because then I gotta clean everything again. And I am NOT taking those apart any time soon unless I get a leak.

What I did was take off one end of the spring and carefully wind it around once more and hook it back up. They still dont close 100% but close enough I think. Much better than before.

I dont know how I didnt catch this before everything and before I put loctite on those screws holding the plates. Ughhhhh
 

chickenStripCharlie

Been Around the Block
How much resistance should there when you pull the throttle cables out by hand? I'm definitely getting some and lubing them is a giant pain in the azz. The lube just won't go down the cable.
Might have to get new ones now.

I thought the carbs spring would be strong enough to work the cables, but throttle closes too sloooooowwwwwllllyyyy now. ugh.
 

Maritime

Over 10,000 Posts
Motion pro makes a cable lube tool that might work. It pulls the cable over and allows the lube to go down the sleeve. I've not used one but came close to buying one a few times. I use a silicone spray and make a mess but can usually get them free and working by spraying from both ends and working the cables back and forth a lot.
 

chickenStripCharlie

Been Around the Block
Motion pro makes a cable lube tool that might work. It pulls the cable over and allows the lube to go down the sleeve. I've not used one but came close to buying one a few times. I use a silicone spray and make a mess but can usually get them free and working by spraying from both ends and working the cables back and forth a lot.
just ordered new ones. $33 CAD for both from a local shop. Who knows how old the ones on this bike are. Probably too old to salvage anyways.
Considering what a pain in the butt connecting those cables is once the carbs are on i might as well do it before they go on.
 

Jimbonaut

Over 1,000 Posts
DTT SUPPORTER
Forget trying to install the throttle cables once the carbs are on the bike. If it's even possible there's a special circle of hell reserved for the job. Sit on the left hand side of the bike with the carbs on your knees, so that they're at the same height as they will be once they're installed. Get as close to the bike as possible, then hook up the throttle cables to the carbs - you should have enough free play in the cables to hook them into place. I find some right angled mechanics picks are useful for the job. Also - a pair of rubber-handled small pliers (rubber handled so you don't damage the plates) positioned under two open throttle plates keeps the throttle assembly on the carb rack much easier to access with the cables. Easier that way.
 

chickenStripCharlie

Been Around the Block
Got new cables. Throttle works perfectly.

Installed the carbs. Wasnt too bad with a little heat gun on the boots.

But trying to install an inline filter is an absolute nightmare! The distance is too damn short and any way I route it the line is getting a kink in it.

I gotta try a fuel filter with a 90* offset next. Of course no one here carries one so I gotta order one and wait some more. Ugh

At least my stainless Norma clamps arrived and are looking really good!
 

Attachments

pidjones

Over 1,000 Posts
Get some reinforced fuel lines to prevent collapsing and make a large bend after the filter. At least that's what I had to do.
 

chickenStripCharlie

Been Around the Block
Get some reinforced fuel lines to prevent collapsing and make a large bend after the filter. At least that's what I had to do.
I did but the size at the petcock (and fuel filter) is different than the size at the fuel rail. There is absolutely NO way to slide reinforced 1/4" line onto the fuel rail at the carb. And if you get one that fits there, then it would be loose at the petcock/filter side would it not?. (Yes I tried heating it up).

What size worked for you given the two different sizes??
 

pidjones

Over 1,000 Posts
Gee, I can't remember. Seems that it was 1/4". Maybe the '79 CB750F had a different size fuel inlet.
 

chickenStripCharlie

Been Around the Block
Gee, I can't remember. Seems that it was 1/4". Maybe the '79 CB750F had a different size fuel inlet.
Yeah the answers I got so far are 5.5mm. Theres no way to fit that on the fuel rail of my 83

In any case, I did what you said, use 5/16 downstream of the filter with a big loop. No kinks. Used a hose clamp at the filter outlet so hopefully it wont leak there. seems tight enough.

Will revisit if it starts to leak. Lol. Hoping to have some electrical out of the way this week and get it fired up after 1+ years
 

chickenStripCharlie

Been Around the Block
Might slip short thin tube over filter and the 5/16 over that.
I did the clear plastic tube upstream of filter and 5/16 downstream. Seems to fit. No leaks. However I'm noticing my inline filter isnt filling up with fuel. It's like half full.

Got the bike started and she seems to run well, but as it's not insured I just did a couple loops around the house in 1st and 2nd gear. No chance to open it up.


I think she sounds pretty good for just a bench sync and no carb balancing at all. Thoughts??

 

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