1977 CB750F Super Sport Carburetor rebuild

[Floshenbarnical]

Hi there friends, new to the forum. Tried a quick search, couldn't find an existing topic.

I bought a Super Sport a week ago for very little money, and it starts first time (kick) but runs fairly rough. It only really runs on choke, even when warmed up. I'm pretty sure the guy left gas in it over the winter, so I took the carbs off to check them out and my suspicions were confirmed that the float bowls were fairly grimy and one of the floats was stuck. I have a brand new carb rebuild kit from CB750supply, new jets, etc.

What I really want to do is completely disassemble the carbs and run them through my friend's ultrasonic cleaner and then blast out all the passageways etc, and then install new gaskets, jets, floats, etc. This is pretty easy - I took Carb #1 off the stack and disassembled it, they're pretty simple. However, I am perplexed and intimidated by the idea of unracking the whole assembly because the spring-loaded assembly for the choke and throttle looks extremely complex and I'm concerned that if I do actually manage to take it apart I won't be able to put it back together properly.

The bike is ready to go otherwise - the timing is spot-on, everything works, oil pressure is good, tappets/ cam chain/ etc are all spot on.

I guess my question is as follows:

Does anyone have a link to a video or step-by-step guide for disassembling these particular carburetors?

Every guide I've found so far has been for a very slightly different bike with slightly different carbs, and the one video I did find for these carbs skipped over the spring-loaded stuff much to my disgust.

I'm very tempted to do a quick and easy clean on the lower halves of the carbs and call it a day for the season. Clean the bowls, blast out the passages and crevices, reinstall jets etc and get riding. The top halves of the carbs look pretty damn clean to be honest.

 

[madmtnmotors]

Yep:

http://forums.sohc4.net/index.php/topic,48858.msg515204.html#msg515204

 

[Floshenbarnical]

Thank for you for a frankly life-changing response.

 

[madmtnmotors]

 

[hinksy]

this guy does a good vid

 

[Floshenbarnical]

Thanks again folks. Due to time constraints, I've been thinking about giving them to a local Honda shop to clean them but the rubber hoses joining them together at the bowl end are all hard and cracked a little. Does anyone know what kind of tubing this is?

 

[madmtnmotors]

It depends. Some of the later PD carbs had two sets of rubber crossover tubes, one for a common bowl vent and one for the accelerator crossover tubes. The accelerator crossover tubes have little brass restrictors inside that should be removed and inserted into the new rubber crossover tubes when these rubber tubes are replaced. Make sure you use a knowledgeable/reputable shop.

 

[Floshenbarnical]

Thanks again. I think this is the earlier kind, as there's only one line of connective tubing. I took the brass restrictors out already and saved them.

 

[Floshenbarnical]

Ok, I've been busy so I've only just started putting them all back together again. The local shop changed their minds about wanting to work on them. Oh well. Going very well so far, however when I was trying to put in the accelerator check ball (I believe that's what it's called, it's a tiny ball bearing that sits under a spring and a bung in the bowl on carb #2) it flew out of my fingers and disappeared forever.

Does anyone know what exact size that ball is? I've seen some replacements for other bikes online but I don't want to cram something in there and have it get stuck because it's too large. Thanks for your patience.

 

[madmtnmotors]

You should be able to find a replacement accel pump bowl, someone on here might even have one.

 

[Floshenbarnical]

Update: the correct ball sizing is 3.5mm

Carbs are fully cleaned, rebuilt, bench-synced, and on the bike. The bike runs pretty well, kind of bubbly in the low end (pod filters) but it absolutely screams and flies when you open it up. I have K&N pod filters on there because the previous owner sold the stock airbox and installed velocity stacks. After a lot of internet research I have gotten the jet/ needle tuning pretty damn close to make it run properly with the pods, but if it's not 100% dialed in in a month or so I'm just going to bite the bullet and buy an airbox from eBay and recondition it. I prefer the look of pods but I'm not willing to sacrifice regular street performance just for the ability to strip the paint off merging onto the highway.

I was quite pleased that I managed to bench-sync the carbs almost perfectly first time, having never done it before. Once I connected the vacuum synchronizer, the only slide that needed adjusting was #1 by a small fraction. Ok, boasting over.

 

[Floshenbarnical]

Update: fuck pods on CV carbs, I have an OEM airbox ready to install

 

[dirtdigger]

77 doesnt have CV carbs.

 

[Floshenbarnical]

77 doesnt have CV carbs.

You're quite right, I got confused last month.

I hope you're all pleased to know that having rejetted with OEM brass a whole bunch and raised the needle one notch, perfected timing and tappet clearance etc, the bike runs beautifully with K&N pods. Thanks to everyone here for the help. I have had to helicoil every single float bowl bolt hole, replace all the felt o-rings, replace a busted emulsion tube, and replace the bowl gaskets twice.

However, the other night a tappet nut flew off and disappeared somewhere under the valve cover, presumably into the cam chain tunnel but may have made it into my bottom end. So tonight I shall be employing a mini flexible camera with a magnet superglued to it, and going fishing. Wish me luck - can't turn the bike over until I find it, because doing so could cause catastrophic damage.