Subasteve750
CB750 Member
Hey everyone,
Im new to this forum as a poster, but im a long time lurker. Im sorry for the essay, just trying to be as descriptive as possible.
I went down a bit of a rabbithole recently, as I removed the stock carbs of my 1980 CB750f (VB428) to rebuild/clean them. They were leaking fuel and I also replaced all of the seals/gaskets and hardware. I made a couple of fuckups, both of which my fault and one of which probably unfixable. Upon reassembling the 428 carbs, I snapped the choke shaft, as I was careless, angry and stupid. I soon learned how rare that specific piece is on its own, as I simply couldent find the correct one. I thought I did, untill i found out the seller incorrectly listed the part and recieved the right part for the wrong CC size. wasnt long enough. Back to the drawing board. Then I decided to just look for a replacement carb or a parts carb. At the time I looked, there were no other VB428s on ebay that were reasonably priced, so i started looking at alternatives and read the shop manual to compare and contrast the carbs from all three variants (CKF) to see what i could do. I settled on VB42As that were in running shape (but still kinda crusty) and debated either taking the choke stem from that and using it in the VB428s, or just using the new carbs as is.
From all that I can tell after looking at the shop manual pdf, old posts on this forum, as well as reddit posts, these carbs are extremely similar in almost all aspects, however Ive noted that 81 and up Cbs started using vaccum petcocks on thier carbs, so ive plugged the little airhose with a screw as one post suggested and havent worried about it yet, as my 80' is gravity fed. The only other distinction I can find is noted very vaugely in the manual. It simply states that the VB428 has all the same qualities as the VB42A with the exception of "Venturi Bore" being listed next to the VB428 without any further elaboration whatsoever. So, are the Venturi diameter's bigger or fancier in the VB428s? When I cracked the VB42As open, from what I could tell, everything looks identical (except the extra air hose). my question is, am I making a mistake using these VB42As? Do the "Venturi bore" noted on the 428's make a difference that I would be losing? Am I gaining any advantages by doing so? should i just swap the choke stem?
Im new to this forum as a poster, but im a long time lurker. Im sorry for the essay, just trying to be as descriptive as possible.
I went down a bit of a rabbithole recently, as I removed the stock carbs of my 1980 CB750f (VB428) to rebuild/clean them. They were leaking fuel and I also replaced all of the seals/gaskets and hardware. I made a couple of fuckups, both of which my fault and one of which probably unfixable. Upon reassembling the 428 carbs, I snapped the choke shaft, as I was careless, angry and stupid. I soon learned how rare that specific piece is on its own, as I simply couldent find the correct one. I thought I did, untill i found out the seller incorrectly listed the part and recieved the right part for the wrong CC size. wasnt long enough. Back to the drawing board. Then I decided to just look for a replacement carb or a parts carb. At the time I looked, there were no other VB428s on ebay that were reasonably priced, so i started looking at alternatives and read the shop manual to compare and contrast the carbs from all three variants (CKF) to see what i could do. I settled on VB42As that were in running shape (but still kinda crusty) and debated either taking the choke stem from that and using it in the VB428s, or just using the new carbs as is.
From all that I can tell after looking at the shop manual pdf, old posts on this forum, as well as reddit posts, these carbs are extremely similar in almost all aspects, however Ive noted that 81 and up Cbs started using vaccum petcocks on thier carbs, so ive plugged the little airhose with a screw as one post suggested and havent worried about it yet, as my 80' is gravity fed. The only other distinction I can find is noted very vaugely in the manual. It simply states that the VB428 has all the same qualities as the VB42A with the exception of "Venturi Bore" being listed next to the VB428 without any further elaboration whatsoever. So, are the Venturi diameter's bigger or fancier in the VB428s? When I cracked the VB42As open, from what I could tell, everything looks identical (except the extra air hose). my question is, am I making a mistake using these VB42As? Do the "Venturi bore" noted on the 428's make a difference that I would be losing? Am I gaining any advantages by doing so? should i just swap the choke stem?
