Carbs for 350cc upgrade

[masonmart]

"Wow." Would love to see a photo of that. All the best Jerry

A photo of what?

[GORDON BROWN]

Hello Masonmart

Sorry about that, what you said was they were fitted to good CB77 racers, usually good race bikes are the fastest ones so I admit I assumed ( bad thing, as well as being "nosey" ) that fastest was a reasonable term. I was not trying to alter the meaning of what you said.
Being curious / nosey, you mentioned experts, are these people on this site if so I am sure you can name them without any worry.
BTW. I have bought O.S. valves from Bernie ( and others ) just never as big, at least for a 350 CB77 or K.
Anyway as you explained your bike is a road bike which makes me even more curious about the need for the large valves but given that you have them all I was suggesting was to watch the quality of the springs and make sure there was plenty of clearance etc.
I did run a 350cc kit / 33mm valves in my CYB kit bike with modified std. carbs and it went fine so its possibly worth trying before spending ? ( been guilty of buying things in the past without really needing them if you know what I mean ).
Still hope you have fun with it.

Regards

Gordon

SAFOJ

[masonmart]

Hello Masonmart

Sorry about that, what you said was they were fitted to good CB77 racers, usually good race bikes are the fastest ones so I admit I assumed ( bad thing, as well as being "nosey" ) that fastest was a reasonable term. I was not trying to alter the meaning of what you said.
Being curious / nosey, you mentioned experts, are these people on this site if so I am sure you can name them without any worry.
BTW. I have bought O.S. valves from Bernie ( and others ) just never as big, at least for a 350 CB77 or K.
Anyway as you explained your bike is a road bike which makes me even more curious about the need for the large valves but given that you have them all I was suggesting was to watch the quality of the springs and make sure there was plenty of clearance etc.
I did run a 350cc kit / 33mm valves in my CYB kit bike with modified std. carbs and it went fine so its possibly worth trying before spending ? ( been guilty of buying things in the past without really needing them if you know what I mean ).
Still hope you have fun with it.

Regards

Gordon

SAFOJ

Gordon, reading what's written is the best path :-). I didn't measure the valves myself btw as the bike is in another garage and is now on the road. I hope that you don't mind if I don't strip it down again to measure the valves and to get a photo for Jerry. The valves could well be 33 mm and the 38 could be just a measurement mistake, I asked BS who sells them as a business and he didn't know what the diameter is; I'd guess as big as they can safely get without shaking hands. The lad who has done my 2 77's has done several big bore, big valve, 5 speed versions. He doesn't post here or anywhere and his name is his business but I rate him as in many areas peerless and not only on these bikes: my Thruxton Velo that he sorted for me is a magnificent road bike with 5 speed box, valves as big as the head can handle and a very large carburetor; is there a reason why a CB77 shouldn't be? Please note that I haven't bought bigger carbs and may not do so, the thread is a question on whether that may be necessary or beneficial.

I have bought the best valve springs I could find with titanium collets, they should be fine.

You ask why? I ask why not? I have a standard user 77 but in general I want my bikes to be as special as possible too.

[GORDON BROWN]

Hello Masonmart

I bet that Velo sounds great. Anyway better not get into that on the 305 Honda site.
Regarding the mods to the Honda's I think perhaps you misunderstood me, I certainly have nothing against modifications, I have posted a couple of my ones on this site which are far from standard so no worries there. I have also seen lots of mods that made things worse so was a bit concerned re. the valve sizes etc.
Hope you have fun with all of bikes

Regards

Gordon

SAFOJ

[G-Man]

Hi Masonmart

I think that we are just a little surprised at the 38mm valves. I know that G&S supply Bernard with his 'big' valves and the inlets are definitely 33mm or 1mm over stock.

If you want to optimise carb sizes with your formula of 75-80%, it is crucial to know the actual size of the valves. 26mm carbs would appear spot-on with a 33mm inlet for road use. People do go bigger with full-on race bikes and the Keihin CR carbs on my race bike are 29 or 30 - haven't measured them for a while. Useless for a road bike as they have no idle circuits.

It's a small world and I believe that one of your reupholstered seats will have a seat pan that I supplied and you will have one of my neutral switches in one of your CB77s....

Take care and have fun...

G

Hello Masonmart

Sorry about that, what you said was they were fitted to good CB77 racers, usually good race bikes are the fastest ones so I admit I assumed ( bad thing, as well as being "nosey" ) that fastest was a reasonable term. I was not trying to alter the meaning of what you said.
Being curious / nosey, you mentioned experts, are these people on this site if so I am sure you can name them without any worry.
BTW. I have bought O.S. valves from Bernie ( and others ) just never as big, at least for a 350 CB77 or K.
Anyway as you explained your bike is a road bike which makes me even more curious about the need for the large valves but given that you have them all I was suggesting was to watch the quality of the springs and make sure there was plenty of clearance etc.
I did run a 350cc kit / 33mm valves in my CYB kit bike with modified std. carbs and it went fine so its possibly worth trying before spending ? ( been guilty of buying things in the past without really needing them if you know what I mean ).
Still hope you have fun with it.

Regards

Gordon

SAFOJ

Gordon, reading what's written is the best path :-). I didn't measure the valves myself btw as the bike is in another garage and is now on the road. I hope that you don't mind if I don't strip it down again to measure the valves and to get a photo for Jerry. The valves could well be 33 mm and the 38 could be just a measurement mistake, I asked BS who sells them as a business and he didn't know what the diameter is; I'd guess as big as they can safely get without shaking hands. The lad who has done my 2 77's has done several big bore, big valve, 5 speed versions. He doesn't post here or anywhere and his name is his business but I rate him as in many areas peerless and not only on these bikes: my Thruxton Velo that he sorted for me is a magnificent road bike with 5 speed box, valves as big as the head can handle and a very large carburetor; is there a reason why a CB77 shouldn't be? Please note that I haven't bought bigger carbs and may not do so, the thread is a question on whether that may be necessary or beneficial.

I have bought the best valve springs I could find with titanium collets, they should be fine.

You ask why? I ask why not? I have a standard user 77 but in general I want my bikes to be as special as possible too.

[masonmart]

Hi Masonmart

I think that we are just a little surprised at the 38mm valves. I know that G&S supply Bernard with his 'big' valves and the inlets are definitely 33mm or 1mm over stock.

If you want to optimise carb sizes with your formula of 75-80%, it is crucial to know the actual size of the valves. 26mm carbs would appear spot-on with a 33mm inlet for road use. People do go bigger with full-on race bikes and the Keihin CR carbs on my race bike are 29 or 30 - haven't measured them for a while. Useless for a road bike as they have no idle circuits.

It's a small world and I believe that one of your reupholstered seats will have a seat pan that I supplied and you will have one of my neutral switches in one of your CB77s....

Take care and have fun...

G

G-Man, sorry, I repeated a value that somebody else had measured for me. Too late now as I've been overtaken by events and the standard carbs seem to be perfect for road use. The conundrum now is 2 virtually identical bikes with said mods done, one goes like a dream and the other one not so well. Main difference is that the one that goes well has newish carbs and the one that doesn't has old worn ones so maybe the carbs are critical.

I'll think of you when I sit on my newly upholstered seat and when I snick the bike into neutral. :-)