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1980 Honda CB750F Cafe Build

This is a discussion on 1980 Honda CB750F Cafe Build within the Project Builds forums, part of the Caferacer.net Forums category; decided on a STDThermo Straight Oil Cooler with adapters. plan to replace the oil pan on the 750 with one from a 900F of the ...

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Thread: 1980 Honda CB750F Cafe Build

  1. #101
    Senior Member tjurek51's Avatar
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    decided on a STDThermo Straight Oil Cooler with adapters. plan to replace the oil pan on the 750 with one from a 900F of the same year. the oil cooler kit comes with adapters for the hoses, etc... also decided on a 3/4 fairing and box style café seat from Airtech products. Question for this group; anyone know of a good place to buy the mounting frame for a 3/4 fairing. I need some options as I went with a ducati Pantha 600 style and it has dual headlights. my fabricator can make one, but wanted to see if I can just find one. online, so far, has yielded limited results.

  2. #102
    Senior Member Geeto67's Avatar
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    Quote Originally Posted by tjurek51 View Post
    Lastly, do I really need to do something with my oil pump? if so, what's the recommendation? thanks.
    I believe you can use the 900F oil pump in the 750 if you can find a good working one. The 750 oil pump will not push enough oil to even support the oil cooler and you run the risk of top end oil starvation.

    If you feel like spending money this company in japan offers an upgraded pump: https://japan.webike.net/products/21151771.html
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  3. #103
    Senior Member CaTacL1sm's Avatar
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    FYI, the airtech glass is thin so you're going to want to have adequate bracing/mounting for the fairing.... as far as mounting, your best bet is to get with a welder/fabricator/machinist and enlist their expertise. You'll pick up some knowledge and have a professional product (for maybe $150-200 i'd say).

    Also, japan.webike.net is amazing, and dangerous for your wallet
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    Fuck all of you guys. Get into your little circle jerk and have fun. Thought this may be a pretty cool message board but damn, you guys are assholes.

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  5. #104
    Senior Member crazypj's Avatar
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    Quote Originally Posted by CaTacL1sm View Post
    With a proper suspension and frame bracing, why wouldn't it perform on the track?
    It would, the spec is basically what Honda used for Superbikes and 24 hr endurance racing in the 80's 750 was a better staring point with short stroke motor and wide bore spacing allowing 998cc The carbs are a total nightmare without stock air-box though, CR's would be a real nice option. 29's will supply erverything motor needs unless you are building a track only bike (it will still pull at lower rpm, below 6,000 or so)
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  6. #105
    Senior Member crazypj's Avatar
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    Quote Originally Posted by Teazer View Post
    Neither. Open velocity stacks IIRC.

    Way back in the day the late Leon Moss of LEDAR who was a bit of a motor and carb expert, tried to get a CB900 to run with an aftermarket exhaust and he ended up with external tubes to equalize pressure in the carbs. I don't remember all the details but I think it went from rich to lean and back again as the throttle was opened.

    I have no idea if that was all one big pressure differential issue or an exhaust resonance pressure wave timing thing, I have no idea.

    That does raise a question as to how owners of cars with SU carbs (more or less the same design) get around those same flow/pressure wave issues.
    I don't remember if it was you or Kopsicle sent me a lot of information on the Leon Moss modifications? It had internal bypass tubes and converted to 2 jet so they looked stock externally
    I dabble in rocket science, when I\'m not picking my nose
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  7. #106
    Senior Member crazypj's Avatar
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    Quote Originally Posted by tjurek51 View Post
    that's it. that's what i'd like to do, for the most part. i'm not much on the history of the sport, mind you. still learning, so you all sharing this is great! my pic is just a mash up of ideas from various posts. Mostly from a variation of the MotoGuzzi style bike of the same era. YES, a stretch from that to a 80's CB750 F, but wanted to start with some ideas. Here, btw, are some ideas on changes and reinforcements. your thoughts are appreciated.

    Attachment 96183Attachment 96185Attachment 96187

    for those who may recognize these ideas, I want to make sure I reference the project and give credit to the guys who did this. i'm not going to go to the extents they did, but I figure these mods are proven (by now)

    https://www.bikeme.tv/index.php/dons...-honda-cb900f/

    several questions still abound, like wider wheels, better forks or just mod what I have, etc.
    Those brace points look like stuff Tony Foal recommends and has tested. How many people here have his chassis book?
    I dabble in rocket science, when I\'m not picking my nose
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  8. #107
    Senior Member Cyorg's Avatar
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    Quote Originally Posted by Geeto67 View Post
    The 750 oil pump will not push enough oil to even support the oil cooler and you run the risk of top end oil starvation.
    I don't understand that.... basically all you are doing is adding length to an oil passageway. Once the line is full of oil, what difference does it make to volume or pressure?
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  9. #108
    Senior Member Geeto67's Avatar
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    Quote Originally Posted by Cyorg View Post
    I don't understand that.... basically all you are doing is adding length to an oil passageway. Once the line is full of oil, what difference does it make to volume or pressure?
    Length of passageway has an effect on flow rate - when you make passage ways longer you increase pressure needed.

    the DOHC bikes are wet sump, not dry sump, so they don't respond to an increase in volume like the dry sump on a SOHC would (which offsets the extra length). The sump doesn't know there is an extra quart in the system, it just knows it has to pump against increased resistance of the added length of pipe.

    IIRC too the oil cooler isn't just an extension on an existing passage like most of the oil filter based adapter kits for SOHC 750s, it is a separate loop that runs off the pump and into the sump:

    (page 12) http://www.kabalis.com/SuperMagna/CB900-Manual/Honda_1980_thru_82_CB900F_Service_Manual_Chapter_2 5_81_900F_Addendum.pdf

    Os it's not like adding an extension to an existing system so much as it is adding a new second oil circuit. The 750F pump can't keep up with the demands of pumping 2 circuits.
    Last edited by Geeto67; 05-16-2019 at 09:43 AM.
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  10. #109
    Senior Member DesmoDog's Avatar
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    Quote Originally Posted by crazypj View Post
    Those brace points look like stuff Tony Foal recommends and has tested. How many people here have his chassis book?
    I've got a couple versions of his book, I was keeping up with the updates for a while there.

    Or was that a rhetorical question? ;-)
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  11. #110
    Senior Member tjurek51's Avatar
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    Any recommendations for a performance high flow oil pump? Right now my plan is to use a 900F oil pump

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