CB750 Barn find project - First Timer

[hairygit]

Did you remove a retainer from the wheel itself, or from the separate sprocket carrier. Racking my brain here, and only recall 1 retainer on the wheel itself, plus a second larger one on the sprocket carrier.

[Underdog1]

Did you remove a retainer from the wheel itself, or from the separate sprocket carrier. Racking my brain here, and only recall 1 retainer on the wheel itself, plus a second larger one on the sprocket carrier.

Ive removed one from the sprocket carrier (no.3 in the pic) and the one remaining is in the wheel hub (no.4 in the pic). I think i even confused myself on that one haha.

For the card rebuild should i be ordering one of these for each carb:

https://www.davidsilverspares.co.uk/CB750K6-FOUR-1976/part_105211/

or will there only be specific things ill need to replace depending what i find on inspection?

[Trigger]

How much ? same set and you get all 4 >>http://www.ebay.co.uk/itm/Honda-CB750K-K1-K2-K3-K4-K5-K6-Carb-Repair-Kits-4-Repair-Kits-Include-48-1912-/261752454445?hash=item3cf1a97d2d   

[Underdog1]

How much ? same set and you get all 4 >>http://www.ebay.co.uk/itm/Honda-CB750K-K1-K2-K3-K4-K5-K6-Carb-Repair-Kits-4-Repair-Kits-Include-48-1912-/261752454445?hash=item3cf1a97d2d   

Thats much more reasonable, is there much difference in quality in these rebuild kits or should I be fine with the eBay unbranded one?

[Rob.b (Rob Birkett - RIP)]

How much ? same set and you get all 4 >>http://www.ebay.co.uk/itm/Honda-CB750K-K1-K2-K3-K4-K5-K6-Carb-Repair-Kits-4-Repair-Kits-Include-48-1912-/261752454445?hash=item3cf1a97d2d   

Thats much more reasonable, is there much difference in quality in these rebuild kits or should I be fine with the eBay unbranded one?

Morning.

I have been hanging round this site a lot of late, and I think that I have learned; if Trigger says buy something you should buy it !!

But I still recommend you watch: hackaweek "73 honda CB750 cafe racer rebuild " on Youtube.

R

[Chris400F]

How much ? same set and you get all 4 >>http://www.ebay.co.uk/itm/Honda-CB750K-K1-K2-K3-K4-K5-K6-Carb-Repair-Kits-4-Repair-Kits-Include-48-1912-/261752454445?hash=item3cf1a97d2d   

Thats much more reasonable, is there much difference in quality in these rebuild kits or should I be fine with the eBay unbranded one?

There are loads of people on here (myself included) who have used the Cruzinimage kits as in Trigger's link and they are fine.
As Rob says, if Trigger recommends something you will be OK!

[Underdog1]

Morning.

I have been hanging round this site a lot of late, and I think that I have learned; if Trigger says buy something you should buy it !!

But I still recommend you watch: hackaweek "73 honda CB750 cafe racer rebuild " on Youtube.

R

Yeah watched the first two episodes and couldn't stand the bloke hah

There are loads of people on here (myself included) who have used the Cruzinimage kits as in Trigger's link and they are fine.
As Rob says, if Trigger recommends something you will be OK!

Cheers boys 

[AshimotoK0]

Personally, the only aftermarket carb kits I will use are from Yamiya or kits like Gerben in Holland  sells.. Don't get me wrong there could be nothing wrong with other carb kits but they also sell inlet rubber kits and camchain rubber idlers that I know to be inferior to OEM and causing people on the US site horrendous problems. Gerben has the right idea ..he sells the 'O' ring kits sourced in Viton. He's got a really good reputation for rebuilding carbs. Rubber compounding is a science in itself. I worked for a company for 20 years that were experts in it, so I feel qualified to comment. DS will not tell me who he sources his aftermarket rubber parts from or give tech specs to check for myself, so again I have voted with my feet on that one.

http://www.ebay.co.uk/itm/CB500-CB550-4-Four-Keihin-carb-O-ring-set-VITON-rubber-for-4-carbs-/112047503140?hash=item1a168d3724:m:ms0_u4ZL-QLjaYiVzIQED2w

Dunno if he does kits  for 750

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[Underdog1]

Personally, the only aftermarket carb kits I will use are from Yamiya or kits like Gerben in Holland  sells.. Don't get me wrong there could be nothing wrong with other carb kits but they also sell inlet rubber kits and camchain rubber idlers that I know to be inferior to OEM and causing people on the US site horrendous problems. Gerben has the right idea ..he sells the 'O' ring kits sourced in Viton. He's got a really good reputation for rebuilding carbs. Rubber compounding is a science in itself. I worked for a company for 20 years that were experts in it, so I feel qualified to comment. DS will not tell me who he sources his aftermarket rubber parts from or give tech specs to check for myself, so again I have voted with my feet on that one.

http://www.ebay.co.uk/itm/CB500-CB550-4-Four-Keihin-carb-O-ring-set-VITON-rubber-for-4-carbs-/112047503140?hash=item1a168d3724:m:ms0_u4ZL-QLjaYiVzIQED2w

Dunno if he does kits  for 750

(Attachment Link)

Thanks for the link but already ordered the other kit mate.

Im still searching for a reasonably priced front caliper + all the mounting gear. Little confused as I've seen different types of mounts listed on the bay for my bike (76), some look like this (and so does the schematic in my haynes manual:



and others look like this:



The mounting point on my forks looks like this:



Which type do I need?

[Trigger]

The first picture is for CB750 K0 to K2, you need the arm in the second picture to fit the later forks

[Underdog1]

The first picture is for CB750 K0 to K2, you need the arm in the second picture to fit the later forks

Cheers bro 

Right so today I've had the carbs off, the carb bowls were full of some horrendous gunk but after a good few hours work I've got them pretty spankers



I took the floats, float valves, main jet and pilot jet out. Soaked everything in carb cleaner and gave it a good old scrub. Cleaned out the main body of the carbs lubed the sliders and reassembled.

The carbs were an absolute nightmare to get back on, overtime i got one side on it sort of pivoted and pulled the other side out. Ended up tapping one side on with a rubber mallet, tightening up the clamps then tapping the other side on.

Got my remote fuel tank hooked up and as soon as i opened the petcock petrol came pissing out of the same place as previous (i had no airbox on).



Mostly came out of carbs 1 & 2 but was still dribbling out of 3&4.

Any ideas?

[MarkCR750]

Did the float valves look ok?, did the little spring loaded pins in the float valves spring in and out?, did you check the float heights?, I found a good "how to" online for PD carbs which mine has, try googling for one for your earlier type carbs, next time you replace the carbs heat the rubbers up (carefully) with an electric hot air gun, they harden with age and are a pig to get on if not softened, the trouble is that because you don't know what previous owners have done it's going to be a bit trial and error, it's got to be a float related issue, here's another thought, do your floats float, they could be punctured and filling up with fuel, that stops them floating up as the bowl fills and stops them pressing on float valve via the arm to cut the fuel off.

[Underdog1]

Did the float valves look ok?, did the little spring loaded pins in the float valves spring in and out?, did you check the float heights?, I found a good "how to" online for PD carbs which mine has, try googling for one for your earlier type carbs, next time you replace the carbs heat the rubbers up (carefully) with an electric hot air gun, they harden with age and are a pig to get on if not softened, the trouble is that because you don't know what previous owners have done it's going to be a bit trial and error, it's got to be a float related issue, here's another thought, do your floats float, they could be punctured and filling up with fuel, that stops them floating up as the bowl fills and stops them pressing on float valve via the arm to cut the fuel off.

Yeah that little nipple on the float valves all spring in and out as they should. I'm going to take them off again tomorrow and check what you've mentioned. I had all the floats in a bowl of hot soapy water at one point..and I don't remember them actually floating hah.

Any reason why fuel would come out of that hole and not the drainage pipes out of interest?

[MarkCR750]

I'm not that familiar with the type of carbs you have, the holes that you refer to are balance pipes that should only have air in them (I think!), I agree that you would expect to see the fuel coming out of the overflows first, try squirting carb cleaner down the holes and see where it comes out inside the carb, that might give you a clue, hopefully someone with better knowledge of your carb type will join the thread!.
PS if you swap a float from one of the non leaking carbs into one that is leaking and it fixes it you'll know it's the floats.

[K2-K6]

Looks like the brass pipe inside the float bowls leading out to the overflow pipes could be blocked.

If the float valves don't seal then the fuel will get out another hole other than intended route,  it's probably coming out of the main jet also if you could see it. Those holes you've pointed out are primary circuit or air bypass as far as I know.

If it runs into the engine in any sizeable quantity,  it can cause a hydraulic lock above a piston and the bend a con rod when you turn it over so you need to make sure the correct overflow route is clear. At the minimum it will dilute the engine oil if it runs though the bores.