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'79 CB750F Super Sport -- Carburator Rebuild Kit

Luis Etchenique

'79 CB750F Super Sport
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Can anyone recommend a carb rebuild kit for a '79 CB750F Super Sport ?

I have been told the '79 is *unique* in that it had metal tabs on the floats and "will need a flat top needle and seat", so I wanted to make sure I get the correct product.

I would also like to replace the bolts with Allen stainless, and I think some kits maybe offer that option.

Any help will be greatly appreciated.
 

Wez_

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Follow this write up and you'll be a pro....

http://www.cb750c.com/publicdocs/SeanG/Honda_Carb_Manual_revG.pdf

Do your best on ebay to score an affordable rebuild kit with as many small parts and gaskets. Don't be cheap and go for the $5 rebuild kit. You'll be upset. Get yourself a decent $30 Chinese rebuild kit. Those small parts by todays standards can be made in China half way decently. We are talking o rings, gaskets and some small mechanical devices with holes. Also jets. If something is missing, the website 4into1 has many parts. That's what I did. The parts to watch out for are the cheap air cut offs. The Chinese parts are horrible and don't last. It's recommended to bypass them as the "new" replacements are made of inferior material compared to the 40 y/o materials originally used. Follow that write up and carb problems will be a thing of the past. I soda blasted my carbs and went through them on my own tooth and nail. When I read through the above pdf, I found that I missed all the most important nooks and crannies that matter the most. Good Luck
 

Luis Etchenique

'79 CB750F Super Sport
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Randakks carb rebuild kit / '79 cb750f ss

thank you Wez -- man, tons of info and certainly the right way of doing it; so ... from the link you included, I located this kit from Randakks, which they recommend:

https://www.randakks.com/honda-dohc-4-randakk-master-carb-overhaul-kit.html

so it looks like *VERSION-A* is what I need --I hope you agree-- and the tutorial is extremely detailed.

thank you for your help !
 

amc49

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'I have been told the '79 is *unique* in that it had metal tabs on the floats and "will need a flat top needle and seat".'

It's simply not true. Only crap needles do not have the tip with a spring in it. It makes up for vibration. Flat top needles have a rockover point when the float tab is not dead level with the tab, a silly cheap-ssed way of making them. I call bullsh-t there. Somebody has not a clue what he is talking about.

The only difference there is the floats are metal instead of the later plastic and requires absolutely nothing special in the way of the needles. Just get good ones. People like the metal floats and so would I but I've never had any trouble at all with the plastic ones and it makes setting the float levels a thing of the past. They cannot be set at all.

Biggest issue you'll find is that if they use ethanol in your local fuel it can be a problem with the needle tips which need to be made of quality ethanol resistant rubber and no way to know that other than the seller guaranteeing it.

Randakk's is indeed one of the best but where are the float needles in the pic there??????
 

amc49

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It is explained on another page...................

'Note: No jets or jet needles are supplied with our kits. Our experience is that these can normally be cleaned and reused. Aftermarket needles are not sized as accurately as the OEM needles and may introduce lean / rich problems where none existed. Unless your needles are worn or bent, we recommend reusing them.

Also, there are no float valve/seat assemblies in our kit. Many aftermarket rebuild kits include float valve/seat assemblies of dubious quality. In the past, there have been many problems with these aftermarket items. Most of the problems related to the aftermarket float needles being incorrectly sized (too short) resulting in unreliable (or nonexistent) fuel shutoff. Some are OK. We've not included them in this kit, because the rubber tips and seats on the OEM item will last nearly forever and can usually be cleaned and reused.So, we've left float valve/seat assemblies out of our kit to keep the cost down and give you a choice on what to buy if you think new ones are needed. Our strong recommendation: use OEM Honda float valve assemblies!'
 

Luis Etchenique

'79 CB750F Super Sport
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thank you very much, AMC49 -- so according to the info I have so far obtained, I'll follow the following steps: 1) fully disassemble carbs bank and the individual units; 2) full cleanup of all parts; 3) as I assemble, I'll replace all o-rings and washers, and ONLY THEN I'll decide which parts need replacement due to wear or condition; 4) I'll certainly use s/s allen heads

=========

simultaneously, the re-build continues -- including re-wiring electric system, custom ( from scratch ) stainless 4 into 2 exhaust fabrication, body work, ... and so much more !
 
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amc49

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The choke plate holding screws are staked to keep them from falling out. If you carefully grind the ends off they can often be reused if loctited to make them not fall out. If you simply remove them outright you often destroy the screws and the shafts. You don't have to remove all 4 simply one on each side, I generally remove the inner ones. Then all 4 carbs break apart.
 

Wez_

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You are likely paying for the quality of the rubber in that kit. I do like how they disclose the information regarding the material quality and recommend reusing jets. Thanks for looking into that AMC! The upfront cost of that kit is pricey. 4into1 has any small parts you'll need. My Chinese rebuild kit was missing some parts yes, but was considerably cheaper. It did include jets, but the air cutoffs were not supplied. I went with the bypass method explained in the write-up.
 

Luis Etchenique

'79 CB750F Super Sport
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... lots going on with the '79 CB750F SS resto-mod ( including exhaust build in progress )

at this point I am in need of the following O-rings for the carbs re-build:


 Qty 7 -010 Fuel rail O-rings (one spare)
 Qty 7 -007 Accel pump O-rings (one spare)
 Qty 5 -003 Pilot screw O-rings (one spare)
 Qty 5 -006 Float bowl drain screw O-rings (one spare)
 Qty 2 -901 Float bowl #2 accel pump O-ring (one spare)

any suggestions as to who sells these as a kit ?

most suppliers seem to sell complete rebuild kits, but all I need at his time are the O-rings

as far as the screws, I already have a complete set of stainless Allen socket-heads and button-heads

thank you as always !
 

Luis Etchenique

'79 CB750F Super Sport
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... replying to my question above -- I have found a source for the O-rings which are the Viton ( FKM ) spec for carburator/gasoline applications.

The company is www.rocketseals.com and they have an outstanding customer service. I communicated with Conner ( conner@rocketseals.com ), and my parts are being mailed as we speak.

The total for the complete set of replacement O-rings was $18.00 including shipping.
 
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Luis Etchenique

'79 CB750F Super Sport
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... in the process of rebuilding the carbs on my '79 CB750F S/S ( with stock airbox ) I now notice the jetting for the primaries is "68", and for the secondaries is "98"

my research tells me that stock jetting is 68 for the primaries, <<but>> that the secondaries should be 100 or 102 ... any opinions on this ?

I acquired the bike a few months ago -- had been sitting in a garage for the last several years; what could've motivated the prior owner to install the 98 secondaries ... ? ( bike had stock airbox/filter AND exhaust system )

thank you as always ! &#55356;&#57281;

-- Luis
 

amc49

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It's a miniscule difference and often done for the difference in exhaust systems using the same engine. May not be the OEM carbset. Thinking the number on left side is supposed to be VB42. My '80F had 100. There can be an A, B, or C after the number too, say VB42C
 

Luis Etchenique

'79 CB750F Super Sport
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https://photos.app.goo.gl/wvDDEcB2awcy54Zs7

https://photos.app.goo.gl/waAqhuwLthjfiE2H8

indeed, AMC49 -- looks like that's a positive ID if I ever saw one ...

so ... I intend to use a low-restriction exhaust ( still WIP ) and an airbox similar to the photo above

with that in mind -- should I stick w/ the 68 / 98 current setup ? in reality, I won't be racing the bike or trying to extract every possible horsepower out of it, I simply want it to run fine and that's all ...

https://photos.app.goo.gl/16WZkrjmUTuGesis8
 

amc49

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On a bike with tight motor to open slides fast and a good 4-1 header (early Kerker small primary tube and modded with no glass in it to let the outer can act like atmosphere) and separate pods (K&N) I used 75-115 to good results. Simply putting the OEM fiberglass back in would make that too much fuel and drop the low-mid torque by a definite amount that was feelable with no mistake. The Kerker OEM baffle with extremely small holes and about a million of them was critical to letting the exhaust 'feel' the outer megaphone like an open header. Enough that you got nothing at all from removing the baffle besides plenty of noise. And other replacement baffles would not run nearly so well even though they fit the meg perfectly. Most come with bigger holes and less of them and I feel that is most of the power loss.

It may help to know that the primary jet is used mainly from just off idle to slide beginning to rise up to maybe 1/8" and it fills in until the secondary main comes on line out of main fuel exit. The primary fuel amount adds to the secondary fuel after the latter comes online, both then continue to flow all the way up. The primary is what you run on mainly while at cruise rpm too.

The 1100 has more engine to pull fuel harder and why it doesn't have the primary setup at all, only secondary and why instead of around 100ish on the secondary jet it is around 130-135. That missing system though lends toward pinging at part throttle, the 1100 does it much easier.
 
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Luis Etchenique

'79 CB750F Super Sport
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... man, tons of reading homework ahead !

I will reassemble “as is” and when this thing <<some day>> starts back again, it should be easy to re-jet as needed — for I will rebuild without side covers or bulky airbox, will relocate battery & electrics ... so access to carbs will be simplified.

So far having a great time, and so thankful for the help. Hope some day I can reciprocate !
 

amc49

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The Honda idea of the separate primary circuit was to be able to get part/low throttle leaner to better lower emissions and increase gas mileage. When you are at cruise the fuel coming out of the main fuel exit (needle) can be less vaporized as the overall pull felt by the exit is less at lower rpm and load. That leads to less even fuel distribution. It aslo helps as being CV the butterfly works some slight amounts to varied low airflows before the slides move, there needing to be a fine tuned fuel amount while the needle is not even feeding.

The 1100 has more transition holes behind the butterfly to make up for slide not lifting momentarily, the rest is the bigger engine pulling on fuel harder to activate the slide thus needle faster. I for one think that ping issue would have been cured if those carbs came with the primary setup too.
 

Luis Etchenique

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work-in-progress ...

carburetor rebuild completed -- including bench-sync, and I must say thank you AMC49 and also state that the tutorial by McGregor Carb Services has been simply <<invaluable>>; thank you to both !

here is a pic during the carb rebuild; enjoyed every minute of it

https://photos.app.goo.gl/Do86YjQ8wpUE56xB8

as we speak ... resuming exhaust fab
 

pidjones

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Looking good. Remember to rig a test bottle and leak check them before re-installing. I use isopropyl alcohol because it has less smell, is safer, and if any doesn't drain out it will mix and burn,
 
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