'77 CB750 Overhaul (HELP A NEWBIE OUT!!!)

[KCOMoto]

Hey gentleman,

Great to e-meet you all. Just wanted to introduce myself and say I'm looking forward to sharing my project with everyone and learning what I can from the community.

I recently came across a few custom cafe builds on old Honda's (i.e. - Seaweed & Gravel builds) that caught my eye and then I wasn't the same after that. I decided to take the leap and take on a project. The challenge is that I have zero mechanical training other than helping out family members and friends here and there.

I found a 1977 CB750k at the end of last fall to use as my victim. The previous owner had started doing various things to it but I believe him to be of questionable skill and intentions. I also joined a local community garage called MotoGuild which stores the bike for me and let's me use the lifts and tools as much as I want to (awesome!).

I'm looking forward to hosting the project here on DTT and really looking forward to connecting with many of you.

I don't have a ton of photos yet but I've posted one below just to get a quick glance at it and also posted a photo of a rough inspiration of the direction I'd like to go. **DISCLAIMER** While I like the aesthetic of the attached bike my intentions are to take care of engine and suspension first and pretty second.

I like the brat style seats because I want my wife to be able to hop on for a quick jaunt when possible. I also would like a very stripped down minimalist bike with good performance (not race performance but good). I do like the relatively lower handlebars but the clip ons that this previous owner put on are WAY too low in relation to how wide this stock tank is IMO.

From what I can surmise the previous owner has done (and not done) the following:
+ Banged in the gas tank with a hammer in a very DIY fashion
+ Installed clip-on bars
+ Installed a 4-1 Kerker exhaust
+ Removed the front and back fenders (which luckily I still have if needed)
+ Cut the rear loop off and put this sloppy seat on (which isn't even bolted on)
+ Ripped off all the gauges up front and took off all the turn signals (left me with pretty shitty wiring setup)
+ Relocated the license plate in a way that is illegal in Illinois
+ Completely disconnected the rear drum brake (we'll find out why)
+ He DID clean out and coat the inside of the gas tank...
+ Removed the stock airbox and installed pods

So now what I REALLY need is helping building a framework and checklist of what all I need to do to this rig to overhaul it. I've been able to determine a few things that I know I want to do based on aesthetics but I also want to make sure we consider bringing the performance up to a level that will be worthy as well.

The local moto-dalai lama at the garage I joined suggested I start by simply getting the engine running as well as possible so I can have a baseline of performance prior to taking the entire bike apart. He suggested starting relatively simply (since I'm trying to learn anyways) and going through my Clymers, Haynes and factory Honda manuals.

As it sits now here are some blaring problems the bike has:

+ rear brakes lock up if you engage them
+ throttle is hard to pull (snaps back but just really stiff)
+ If I take it on the road it has a hard time getting up into the RPM range where the charging system would even activate so my battery keeps dying.
+ It can't get into the mid to high RPM range because it just bogs down and wants to stall out. Really anything beyond 1/4 throttle and it dies out.

There will more issues that come up but since the goal from the beginning was to go through the entire bike I figured what the hell...

What I know that I want:
+ brat style seat
+ minimalist styling
+ hidden electronics from someone like Devin at Cognito Moto for controls, turn signals and rear LED
+ super clean and advanced electronic/wiring like the MotoGadget M Unit
+ Mostly black color scheme
+ As many performance adjustments/upgrades that I can fit into the budget w/o looking like a putz.

PS - I'm going to need a lot of advice so feel free to suggest any starting points!! I'll post more photos of it on that thread as well.

- Josh (K+CO Moto)

 

[jnorman]

Re: New to DTT - '78 CB750 Overhaul (NEED ADVICE!!!)

Welcome to the forum.

I'm sure people much more experienced than me will weigh in shortly. However, I'll pass on a couple things I've picked up.

- Put those two manuals in a nice little pile and start a warm fire...then find the factory service manual and go by that. Most are available online.
- Those Firestone tires on that Seaweed and Gravel build look pretty but will probably kill you from what I've read.
- I echo getting the bike running and operating safely and well before doing more mods. Also, understand that many mods will change the operating or handling characteristics of the bike. For instance, you'll probably need to install rear sets along with those clip ons to make the bike comfortable for any length of time.

Also, knowing the intricacies of the styles will be useful to know. In general, brat style refers to a bike that sacrifices performance and safety for aesthetics, where as (if done right) Cafe bikes have increased performance and a minimalist styling.

I'm also from Michigan. Long live the mitten.

 

[davedogg]

Re: New to DTT - '78 CB750 Overhaul (NEED ADVICE!!!)

Pretty ambitious project from your starting point. There is plenty of great information on this site especially for CB750's. Do some research. I will point out the obvious with your project. You have a choice to make. Form or Function. What you described you would like to do with your bike and what you want it to look like are polar opposites. The bike will never run correctly with pod filters but it does "look cool". The picture of your inspiration bike is in my opinion a death trap. Terrible suspension, awful tires, exhaust wrap, and clip ons with no rear sets. You couldn't pay me to ride that bike. My advice: take your time, do your research, and find out WHY people do the mods they do. Not simply aesthetics. Good luck.

-Dave

 

[coyote13]

Re: New to DTT - '78 CB750 Overhaul (NEED ADVICE!!!)

That's a pretty nice looking start, and I'll be happy to add my $.02 on top of what's already been said. You need some sort of brace on your forks, whether the stock fender/brace unit, or some other. Your forks being slid up that high will cause you to bottom out your front tire on the bottom triple tree/yoke. Slide them back up where they're supposed to be. If you have 2 cylinders not firing, it's likely a dead coil. One coil fires cylinders 1/4 and the other fires 2/3. If that is not the case, you probably need to go through the full tuneup procedure, found in the owners manual below (this link is the factory manual in PDF's and free to download). IF you MUST have one of those silly looking board flat "brat" seats and a looped tail, please please please check rear tire clearance at FULL COMPRESSION before you weld anything in place. There is a very high likelihood that you'll destroy your rear fender/tail light/tire if you don't check this. Pods are difficult to tune, but not impossible. Do your homework on what works and what doesn't with your specific bike and carb rack, and get very familiar with plug chops. The forum at sohc4.net are a great resource for performance tuning and real upgrades to this bike which are not simply aesthetic. Your throttle stiffness is a common symptom of old cables, I would replace throttle and clutch cables, they are cheap and available.

Word of advice: spend money on things that matter first. Simple maintenance items such as cables, chain, sprockets, oil and filter, etc. add up fast. Just getting the bike in good running shape can take a chunk out of your budget. You have an aesthetically clean looking bike for now, focus on the important stuff first, ride it to see what you like about it and what you don't, and THEN start plotting changes. I ride my '78 K model in a nearly stock configuration except for exhaust, suspension, and ignition. Those were all upgraded to perform better than stock, not just to look good.

Link to service manuals:

http://forums.sohc4.net/?topic=17788.0

 

[J-Rod10]

Re: New to DTT - '78 CB750 Overhaul (NEED ADVICE!!!)

Welcome to the forum.

I'm sure people much more experienced than me will weigh in shortly. However, I'll pass on a couple things I've picked up.

- Put those two manuals in a nice little pile and start a warm fire...then find the factory service manual and go by that. Most are available online.
- Those Firestone tires on that Seaweed and Gravel build look pretty but will probably kill you from what I've read.
- I echo getting the bike running and operating safely and well before doing more mods. Also, understand that many mods will change the operating or handling characteristics of the bike. For instance, you'll probably need to install rear sets along with those clip ons to make the bike comfortable for any length of time.

Also, knowing the intricacies of the styles will be useful to know. In general, brat style refers to a bike that sacrifices performance and safety for aesthetics, where as (if done right) Cafe bikes have increased performance and a minimalist styling.

I'm also from Michigan. Long live the mitten.

Those manuals are perfectly fine.

If you are dead set on a brat, don't set up the front end where it has no travel. MAKE SURE YOU HAVE CLEARANCE IN THE BACK FOR THE SEAT.

 

[canyoncarver]

Re: New to DTT - '78 CB750 Overhaul (NEED ADVICE!!!)

My .02: The seaweed and gravel bikes are only made for instagram selfies and internet art bike fluffery. When you build yours, make sure you have suspension especially because you plan for two up riding. The SG bikes have no real suspension and both of you would "dislike" the feel of the ride for more than a few minutes. Now imagine hitting a bump and your passengers bottom is right above where the tire hits the seat pan. Just saying, your bike, make it cool but make it ride correctly.

 

[KCOMoto]

Re: New to DTT - '78 CB750 Overhaul (NEED ADVICE!!!)

Welcome to the forum.

I'm sure people much more experienced than me will weigh in shortly. However, I'll pass on a couple things I've picked up.

- Put those two manuals in a nice little pile and start a warm fire...then find the factory service manual and go by that. Most are available online.
- Those Firestone tires on that Seaweed and Gravel build look pretty but will probably kill you from what I've read.
- I echo getting the bike running and operating safely and well before doing more mods. Also, understand that many mods will change the operating or handling characteristics of the bike. For instance, you'll probably need to install rear sets along with those clip ons to make the bike comfortable for any length of time.

Also, knowing the intricacies of the styles will be useful to know. In general, brat style refers to a bike that sacrifices performance and safety for aesthetics, where as (if done right) Cafe bikes have increased performance and a minimalist styling.

I'm also from Michigan. Long live the mitten.

My .02: The seaweed and gravel bikes are only made for instagram selfies and internet art bike fluffery. When you build yours, make sure you have suspension especially because you plan for two up riding. The SG bikes have no real suspension and both of you would "dislike" the feel of the ride for more than a few minutes. Now imagine hitting a bump and your passengers bottom is right above where the tire hits the seat pan. Just saying, your bike, make it cool but make it ride correctly.

Those manuals are perfectly fine.

If you are dead set on a brat, don't set up the front end where it has no travel. MAKE SURE YOU HAVE CLEARANCE IN THE BACK FOR THE SEAT.

Thank you for the advice here guys. I actually do have the factory service manual and intend on having all 3 of these side by side throughout the build so I can take in as much info as possible.

Also the community garage I joined has a member that they say is the Honda Dalai Lama, lol, so hopefully I can get some insights from him as well.

I agree that I want to keep the initial focus on engine performance as well as getting the suspension setup properly.

Aesthetic bikes are bound to get attention because they are very visual, yes, but I'll certainly be conscious about not dismissing the importance of safety.

 

[KCOMoto]

Re: New to DTT - '78 CB750 Overhaul (NEED ADVICE!!!)

All being said, with regards to suspension and wheels, what are some great examples of setups that I should consider? I've read a lot about people tweaking suspension from upgraded components to entirely different front ends to wheel swaps...

Is there a good way I could keep my existing setup (assuming functioning well) while getting wheels that are the same size on the fronts and rears? I see those bikes all over but I'm not familiar with what wheels they are using for it.

Alternatively, if there is a overall suspension setup that is incredibly popular for these bikes in general that I'd definitely consider that (considering what I want the bike to look like).

 

[canyoncarver]

Re: New to DTT - '78 CB750 Overhaul (NEED ADVICE!!!)

All being said, with regards to suspension and wheels, what are some great examples of setups that I should consider? I've read a lot about people tweaking suspension from upgraded components to entirely different front ends to wheel swaps...

Is there a good way I could keep my existing setup (assuming functioning well) while getting wheels that are the same size on the fronts and rears? I see those bikes all over but I'm not familiar with what wheels they are using for it.

Alternatively, if there is a overall suspension setup that is incredibly popular for these bikes in general that I'd definitely consider that (considering what I want the bike to look like).

Your bike (SOHC CB750) is one of the more customized bikes around. Lots of guys here do amazing stuff with them. Search the forum here and you'll find numerous examples with sometimes hilarious commentary. There is no "one" setup that rules them all unless you are looking to do a 70's superbike style (highly recommended).


Remember that a correctly setup suspension is a safety and performance goal. Yes, you can lower the bike for looks but know that you reduce an already 40+ year old motorcycles' ability to deal with the road. Lowering/changing from stock also changes the steering geometry such that it handles differently, sometimes in a scary bad way, sometimes acceptably depending of course on the how. Consult with your "Honda Guru" for further info. Lots of guys will tell you want to hear, some will tell you what you need.

 

[KCOMoto]

Re: New to DTT - '78 CB750 Overhaul (NEED ADVICE!!!)

Your bike (SOHC CB750) is one of the more customized bikes around. Lots of guys here do amazing stuff with them. Search the forum here and you'll find numerous examples with sometimes hilarious commentary. There is no "one" setup that rules them all unless you are looking to do a 70's superbike style (highly recommended).


Remember that a correctly setup suspension is a safety and performance goal. Yes, you can lower the bike for looks but know that you reduce an already 40+ year old motorcycles' ability to deal with the road. Lowering/changing from stock also changes the steering geometry such that it handles differently, sometimes in a scary bad way, sometimes acceptably depending of course on the how. Consult with your "Honda Guru" for further info. Lots of guys will tell you want to hear, some will tell you what you need.

You're right. One of the beautiful things about this is actually that there is so much creative freedom. Being a noob I'll just do my best to make sure my creative expression doesn't result in a creative injury!


Heading to change oil for first time ever now. Baby steps!

Will snag additional photos while I'm at it so further conversations can ensue!!

 

[coyote13]

Re: New to DTT - '78 CB750 Overhaul (NEED ADVICE!!!)

Google google google! Most of what you want to do has been done, including the right ways, the wrong ways, and every way in between! Good luck out there

And check out some other build threads on here, like Yozzer's, for REAL inspiration. None of that froo froo art bike bs.
http://www.dotheton.com/forum/index.php?topic=64613.0;topicseen

 

[Tune-A-Fish]

Re: New to DTT - '78 CB750 Overhaul (NEED ADVICE!!!)

LOL... Just gonna be Wilde

 

[coyote13]

Re: New to DTT - '78 CB750 Overhaul (NEED ADVICE!!!)

LOL... Just gonna be Wilde

He does have that long winded and....shall we say....spirited? attitude doesn't he :-X

 

[Tune-A-Fish]

Re: New to DTT - '78 CB750 Overhaul (NEED ADVICE!!!)

He does have that long winded and....shall we say....spirited? attitude doesn't he :-X

Wut? :-X

 

[hillsy]

Re: New to DTT - '78 CB750 Overhaul (NEED ADVICE!!!)

Your 750 has an oil tank sitting in the triangle so unless you are willing to pay out for a custom gas tank with a built in oil tank you aren't going to get that Seaweed and Gravel "aesthetic".


If it were me I'd track down a stock airbox and get things back to "normal" so you can at least get the thing running properly and have a baseline to evaluate if the changes you make improve things or suck.

 

[irk miller]

Re: New to DTT - '78 CB750 Overhaul (NEED ADVICE!!!)

As it sits now here are some blaring problems the bike has:

+ rear brakes aren't working

Need more information. Is it pads, or an adjustment. You say disconnected, so I bet the pads are shot.

+ throttle is hard to pull (snaps back but just really stiff)

This may be a routing issue. Cables don't like to bend sharply. Could also just need some greasing in a few places.

+ starts, idles and revs however cylinder 2 seems to NOT be firing
+ If I take it on the road it has a hard time getting up into the RPM range where the charging system would even activate so my battery keeps dying.
+ It can't get into the mid to high RPM range because it just bogs down and wants to stall out. Too rich I think (cylinder 2 cause?)

#2 is your pump carb. This could be a host of issues, but I would start with the pump. The idle circuit on these notoriously gives novice builders the fits. They think they have them cleaned and rebuilt, but then the idle circuit ends up being a mess. Float height is another issue that needs to be checked. Then syncing. I'd consider getting these carbs cleaned and bench synced and the gaskets replaced. Unless the stock jets are effed up, or if the needles are broken (another issue that would cause problems with #2) then stick with the stock components. If you're not comfortable cleaning the carbs yourself get the guru to help, or we can walk you through anything that a manual doesn't give you.

 

[KCOMoto]

Re: New to DTT - '78 CB750 Overhaul (NEED ADVICE!!!)

Morning guys,

Several folks in my "community" garage had a few opinions on what to look at on my bike but the most common was an improper air/fuel mixture and thus the carbs are off so we can take a look.

Photos below show they were very clean to begin with. No broken needles and jets were very clean and clear as well. A few of the o rings and gaskets were pretty dry but not broken.

Prior to pulling the carbs we got the 2nd cylinder working by simply cleaning the plug off. It was really wet with gas. Took it out on the road however and as soon as I tried to give it anything more than about 1/4 throttle you could hear it just huffing air in and then power dies out. A couple more times of doing that and it stalls out. Had to walk it back to the shop.

Here are a few key questions for you guys:

1. In all of the carb rebuild kits sold online they have the rubber gasket that goes into the float bowl but no one seems to sell the composite type gasket that is actually on the body of each of my carburetors. Photos attached. So where the heck do I buy these things???

2. Given how the bike is performing is it possible that I could need to adjust the slide needle position in each carb? Currently they are all set as the highest notch of each (again shown in photo).

3. What is the majority opinion on using silicon grease or similar when reassembling carbs? Specifically around gaskets and o rings?

Thanks for any input fellas.

 

[Tune-A-Fish]

Re: New to DTT - '78 CB750 Overhaul (NEED ADVICE!!!)

The needles dropped all the way in may be bouncing off her cervix Move to the three G spot ;D

 

[KCOMoto]

@deviant

I attached a photo of the pump from carb 2 below. How do I know if it looks bad? Not sure how you check the performance of that once it's taken apart.

@tuneafish

Yeah, happy to try whatever combo of positions on the slide needles will work.


Really wondering about these gaskets too. Strange that I can't find them anywhere for sale unless I'm not searching for the right stuff.

 

[irk miller]

Pump rubber should be pliable and without cracks or pinholes. You can hold it to the light to check. The rod should be smooth and clean. I light emory or scotch bright to polish it up. Also, make sure that whole circuit is free and clear. Gaskets can be bought through 4-into-1---> http://4into1.com/carburetor-parts/