81 CB750K carburetors

Commander_Chaos

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Just bought an 81 750K that's in super-rough shape. It runs, but only on starting fluid. Water infiltration is a certainty. Should I bother trying to rebuild these or find a better set? I wouldn't be opposed to changing to a completely different set of carburetors, if such a thing is possible.
 

Commander_Chaos

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Have you ever rebuilt them yourself? Most of my experience has been with the very primitive carbs on antique English stuff. I had a couple of cb750Fs about 20 years ago and my memory of the carburetors is that they were really complicated.
 
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brettp

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Have you ever rebuilt them yourself? Most of my experience has been with the very primitive carbs on antique English stuff. I had a couple of cb750Fs about 20 years ago and my memory of the carburetors is that they were really complicated.
I haven't broken them down to every bolt or screw. But as long as you clean the jets, fuel passageways, air passageways, throttle moves without issue, choke moves without issue, and piston valves go up and down without binding, they should work.
 

brettp

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I don't blame you. carbs aren't a lot of fun and now you have 4, and they share a fuel rail. Plus they can be a pain to mount if the rubber boots on either side are hardened.
 

Commander_Chaos

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I was figuring the rubber boots would be toast. I hope they're still available. Educating myself on how to do it properly will probably be worth it. I had an MG (car) with CV carbs on it. Back when they were new MG mechanics had the public convinced that you needed to be an astrophysicist to tune them, but I watched a video with a guy who really knew what he was doing and now I can do it in 15 minutes with a wrench and a screwdriver.
 

Commander_Chaos

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Cool. Is there a jet kit I can get so I can get rid of the air cleaner? I see that vintagecb750 sells jet assortments but I was hoping for a kit that just includes what I need for deleting the air cleaner.
 
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brettp

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Sorry, can't help you there. Jets are specific to your environment (specific intake and altitude). Search this forum and you might find somebody who figured it out, but it is like searching for a needle in a haystack.
 

Commander_Chaos

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Bummer. Ages ago when I had a Suzuki you could get a stage 1 kit for airbox change, stage 2 for airbox and pipe, etc.

It had jets, needles, and springs for your application.
 

Commander_Chaos

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Found it. The stages aren't like I remember them but it looks like the stage three kit is what I'm after:
 

brettp

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You gotta keep us informed after the install! Plenty of people asking questions about the very thing you're about to do.
 

SenseAmidMadness

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Many people have tried and *nobody* has ever posted dyno results or videos showing how "well" their pod setup runs at all RPM's under load. Conversely there are many many threads of users with a bike that has pods and doesn't run right.
Way back, a user *did* post dyno runs with both the stock airbox and "properly jetted" stock carbs with pods, showing a rather significant loss in horsepower.

You're welcome to try but it's a bottomless pit if you're researching and you'll spend a bunch on jets. The only way you ditch the stock airbox properly is to buy a different set of carbs -- which come in $650 or $1200 flavors off the shelf from Murray's and Cycle X. I have also read that certain years of Suzuki GSXR carbs fit with minor mods and take to pods a lot better but that will require some research and Ebay finding.

The stock carbs are CV models, highly sensitive to intake vacuum, and the stock airbox provides that evenly across all four when it's working right.


I will say that the Dynojet kit you posted tracks with what I've read. The instructions tell you to drill larger holes in the slides and they also call out a specific set of K&N filters by part number for in-airbox and pods. The slide drilling might make the carbs work better for pods, but it's a permanent mod unless you can sleeve the holes back down to stock.
 
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Commander_Chaos

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So there's posts on here where people have tried this kit? I tried doing just jets and shims on a gs650g and it was like chasing my tail, not worth the effort.
 

SenseAmidMadness

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In a brief search, the only thread I could find was one of our resident Old Farts saying it was junk and didn't work right.

Personally, if I had a spare set of carbs, I'd be tempted to try it myself and post detailed results with full riding videos.
 

Commander_Chaos

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In a brief search, the only thread I could find was one of our resident Old Farts saying it was junk and didn't work right.

Personally, if I had a spare set of carbs, I'd be tempted to try it myself and post detailed results with full riding videos.
That sounds about right. I'll post what I find out on here.
 
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