1980 CB750F Project

Discussion in 'Old's Cool' started by henrymartin, Jun 12, 2011.

  1. henrymartin

    henrymartin Mr. Tourguide

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    First off, apologies to those who started reading parts of this in my post about the value of this CB (started before I bought it). From now the project will be chronicled here (and on my blog) only.

    So, without further ado, a little intro and the results of the first day working on her.

    CB750F Project: part I


    I found her sitting in the front lawn of a house next town over. Neglected by her previous master, the old man who put her in front of his house took her home two weeks earlier. Maybe things between them did not work out as he had imagined they would...maybe it was a matter of personality. I'll never know. Either way, he thought she was too much for him. I knew there and then that I had to save her.

    Friday, after lunch, I brought her home. Dust covered, she sat on the trailer, strapped down in a way no self-respecting old lady would ever want to be seen in public. Still, she did not complain.

    As I walked around her running my fingers along her once smooth lines, I felt the wrinkles age engraves in everything in this world. She stunk of old rubber and bad gas, but her allure was still there...just under the surface, begging to be discovered. Yet, bastardly as it was of me, I left her there waiting for me until the evening.

    Little did I know I was going to pay for my selfish attitude. Perhaps she got jealous of the younger ones she saw in the garage, or perhaps she just didn't care for me leaving her there all day. Either way, she gave me a nasty gash when I was trying to bring her down from the trailer. I sat on top of her and untied the first strap. Suddenly, she bucked to the side and threw me off. I had just enough time to jump to the side before she could land on me. Seeing this, she fells faster and landed on my ankle, pinning me down against the trailer. Full of adrenaline, I wiggled my foot free, grabbed her, and stood her upright. She hasn't tried to do that since.

    So, let me introduce you to her, a 1980 CB750F Super Sport.
    [​IMG]

    [​IMG]

    [​IMG]
    The motor ran, but only on three cylinders. My initial thought was to save this project for the long winter ahead, but the mysterious running issue kept bothering me. I knew I had to dive in and work on it.
    [​IMG]
    I checked spark, fuel, and all seemed to be there. So I took the carbs and the airbox out, and proceeded to clean the carburetors.
    [​IMG]
    It turns out that someone installed one float upside down. Still, while at it, I cleaned all jets and passages, tightened all screw, and soaked gaskets in brake fluid. Then I put it all back together (except the airbox which had the wrong filter element inside).
    Upon starting, all four cylinders came alive. I'll have to wait for a full adjustment until I get a new air filter, but for now the faulty cylinder issue has been solved.

    There are a couple of things on this bike that are just plain wrong. namely the seat and the handlebars, but there are many more issues I'll need to work on.

    I took the seat off, stripped the upholstery and foam, and discovered that I don't like the shape of the pan. Since this bike is not exactly a cafe-racer (although it can be made that way), I decided against the traditional cafe seat in place of a comfortable, low seat. My initial thought was to make my own pan (here is another first one), but after seeing the lines, bends, and curves in the fender and seat area, I decided to try something else. Since my KLR250 Project, I've had a spare KLR seat sitting on the shelf. I took the foam off and tried fitting it. Yup, with a little modification it could be made to work. I like the way the KLR seat comes up against the tank, and follows through. The pan has to be bend a little, curved a little, and cut a little, but it should work. For the fitting, I bolted the pan thought to the battery box up front, and the fender bracket in the rear.
    [​IMG]
    [​IMG]
    There is a little shaping involved to follow the lines of the battery covers.
    [​IMG]
    And I still have to figure out what to do with the rear section. I'm thinking fiberglass, and a lots of shaping.
    [​IMG]
    For now though, I'm excited even about the possibility of having a custom-made seat from an old KLR seat. Who would have thought.

    This project may take some time. After all, the summer is here and I have two bikes that need to get out every now and then. But I'll keep you posted.
    #1
  2. henrymartin

    henrymartin Mr. Tourguide

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    I see, I must have offended the purists by trying to fit a KLR seat in there:lol3
    #2
  3. jeffs900s

    jeffs900s Prophet of Doom

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    Well, I'll be watching - KLR seat or no KLR seat. It actually looks pretty promising, and anything has to be better than the goofy seat that was on there before.

    I've got an '80 CB750 project going as well, so it's good to see someone else make progress while I sit around waiting for parts :D.
    #3
  4. henrymartin

    henrymartin Mr. Tourguide

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    Yeah, I hear you. I'm waiting for an air filter (a week out), to see how she runs with full setup. I'm also waiting on bars. Decided against clubman as the internal wiring has its own risks with crappy inside welds, and the drag bars I thought would work (with 4" pullback) are too narrow to accommodate the controls. So, I decided on trying superbike bars instead. We'll see how it looks and feels.

    Still trying to decided on turn signals. The stock ones are way too big and fugly. Unfortunately, the only dealer left around here would fail me with non-DOT signals, so I'm trying to locate some sleek DOT approved signals, which is proving to be somewhat of a challenge.
    The dealer failed my KLR because it had small aftermarket signals. Well, I got tired of snapping the stock ones off on the trails. It took three inspection stations to find one that let me pass. Lights are lights, so what's the big deal.

    Anyway, what are you doing with yours? Restoration or modifications?

    I chopped the rear part of the KLR seat last night. Now I'm trying to decide whether to chop the rear fender short, or whether to keep it stock and fiberglass some sort of a cowl that will compliment the lines.

    For the record, I'm not building a cafe bike, just a fun bike that will perform well and look good (in my eyes).
    #4
  5. Brad Felmey

    Brad Felmey Long timer

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    I'm watching this. I can't wait to see what that seat turns out like.
    #5
  6. JLeather

    JLeather Bike Butcherer

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    My buddy Matt put together a decent cafe out of a 1980 CB750 earlier this year. Check it out:

    Before:
    [​IMG]


    After:
    [​IMG]
    #6
  7. jeffs900s

    jeffs900s Prophet of Doom

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    I guess I'd call it a refresh. It was in pretty good shape really. Just catching up on maintenance, replacing fork seals, brake line, seat cover, stuff like that. It's mostly stock and will probably stay that way for a while (though the cafe JLeather just posted makes me want to change my mind). I did change out the handlebars for some Wee-Strom bars, which I liked the position of better.

    Bummer to hear about the hassles with turn signals. I didn't even consider that. I think eBay and stock signals from other bikes may be the way to go. Some of the newer sport bikes have pretty sleek looking little signals which are DOT approved.
    #7
  8. henrymartin

    henrymartin Mr. Tourguide

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    Nice. The CB750F has different wheels and dual disc up front, plus disc in the rear. How does your buddy's run without the airbox?

    I thought about pods, but decided against them after reading too many horror stories online. I'll keep mine almost stock except a few changes.
    #8
  9. henrymartin

    henrymartin Mr. Tourguide

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    I put Harley bullets on my last restoration project. the lines were just fine for the VT750 Shadow.

    I really dislike the stock taillight and there is no pretty way to fit it in any modified cowl I'll end up having. I may go round.

    Honestly, I never had a problem with any cop or inspection station until this year. But, if this is the sign of times, then better be safe then sorry.

    I never had an code-enforcement call me about anything in my house either, but I got two calls already this year. One for something really stupid, such as a vehicle parked on lawn instead of the paved lot. There is an ordinance against it? Whatever. It's not in my town, but in the next town over (rental). I guess all the cash-needy entities are looking for a way to make money.
    #9
  10. JLeather

    JLeather Bike Butcherer

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    Honestly, I was concerned about tuning it without the airbox too but it runs great on the v-stacks. Pods are actually worse than stacks, unless you get the more expensive ones with internal runners. Eventually you can tune the CV carbs to run in any configuration, but it requires a lot of work (different slide springs, changing the vacuum port sizes, jets and needles, etc). I'll stick to the earlier CB's, I know them better.

    As for your signals, wire up the stockers to get it through inspection and then put on whatever you want. As long as it can be seen relatively well in daylight no cop is gonna pull you over to look for the DOT marks on your signal lenses.
    #10
  11. henrymartin

    henrymartin Mr. Tourguide

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    Ran into a first glitch today with the seat/cowl combo.

    I sprayed some foam insulation onto the rear fender, covering the entire area behind the seat. once it cured, I took a knife and a rasp, and started hacking away until I created what I thought was a reasonably close image of what i wanted. Yeah, sculpting foam into something is fun :eek1(much less fun than what it sounds like)

    Anyway, I thought I would give it a try and went ahead with resin and cloth. And this is where things went wrong. My resin never set, even after 30 minutes, and just continued dripping through the cloth, soaking into the foam which took me hours to sculpt. Pissed off, I ripped the whole thing off (luckily I used plenty of car wax underneath the foam as a release agent). So, back to square one.

    The reason why I'm doing this instead of buying a cafe seat pan, is that there aren't a whole lot of choices for the F model (long chassis), and the ones I found are rather square in the rear.
    #11
  12. henrymartin

    henrymartin Mr. Tourguide

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    CB750F Project: part II


    I spent the past two evenings attempting to sculpt the new tail section on the bike. When it comes to designing, I'm more of a visual person, so I need to see things in place. Forget about using Photoshop! So, armed with several cans of expanding foam insulation, a discarded kitchen knife, a rasp, and some sand paper, I went to work. Needless to say, things never go as they should, but here is an update nonetheless.

    Tail number one. This first attempt started life as a block of cured foam
    [​IMG]
    After much hacking, rasping, and sanding, I got to a point where I sort of liked it, and decides to try my hand at fiberglass. Hmm...never done that before, although I used plenty of body fillers with success. How hard could it be? Well, it's pretty weird. I spread the cloth, stapled it to the foam, mixed my resin, and started spreading it with an old paint brush. The resin flows like molasses and sticks worse than honey. Within minutes I was in trouble and so was my foam. I ripped the mat off, but it was too late. Unfortunately, I don't have any pictures of the mold before it got eaten away by the resin, but here is one just before it got real nasty. You can still get an idea of what shape I was going for.
    [​IMG]

    After I ripped the foam off and cleaned all the sticky mess, I started building up a new block for attempt number 2.
    [​IMG]
    While the foam was curing (overnight), I thought about the tailsection. The more I thought the less I liked the cafe style tail on this bike. Don't get me wrong, I like the simple, round tails, but something about this bike makes it not flow. Maybe it is the seat I'm trying to make, maybe it is the long chassis. Either way, with attempt number two, I decided to try something that will flow with the bike's lines better. Just remember: this is very subjective opinion.
    So, tail number two looks nothing like a cafe.
    [​IMG]

    This is likely not the final shape, but here is a semi-frontal view:
    [​IMG]
    And the rear view, with mocked up taillight I had laying around. I even think that the round light will go well with the bike.
    [​IMG]

    Of course, the stock fender is only there to support the foam and to get the inside lines right. It will be eliminated as I progress. And yes, I know the light is off-center in this pic.
    #12
  13. henrymartin

    henrymartin Mr. Tourguide

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    Guys,

    Did my first mockup from 2 layers of cloth and resin, based on the foam setup number 2. Now I'm not sure about the shape. What are your sentiments?

    Oh, and I just ordered these from Lockhart Phillips. I think they will go well with the round taillight and are big enough not to cause any inspection issues. Sort of a retro look. [​IMG]
    #13
  14. Tbone

    Tbone off-ramp slayer

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    Looks good to me.
    #14
  15. MayerMR

    MayerMR Been here awhile

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    I dunno, before I read this sentence I saw that and it kind of looked a little vintage Ducati Single-ish to me. Look up a couple of the 70's Ducati Desmo singles...that could be a cool look.
    #15
  16. Sniper X

    Sniper X De Oppresso Liber

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    Personally, I love the whale tail look on these F's. So a cafe seat on one looks wrong. BUT to each their own!
    #16
  17. Kurt V

    Kurt V Been here awhile

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    I owned that exact year/model/color 750 back in the mid-80's. Was the first real "high-performance" motorcycle I had ever owned. A great bike.
    #17
  18. Sniper X

    Sniper X De Oppresso Liber

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    Here's what I mean.

    [​IMG]
    #18
  19. henrymartin

    henrymartin Mr. Tourguide

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    yeah, I'm not digging the whole cafe seat concept on this either, hence making my own crap instead of buying an airtech (which I can get locally for a reasonable price). The whole square spot before the tank makes it look all wrong.

    But, I don't really care for the square stock tail either. Something round would be good. And a round taillight. :D

    Now, yours looks sooooo much lifted in the rear.
    #19
  20. AfricaWim

    AfricaWim Been here awhile

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    That Spencer look one if saweeet!!!
    #20