• Enter the March CB750 Supply gift certificate giveaway! It's easy... Click here, post something, and you're entered into the drawing!

VB52A carbs

kirky

CB750 Addict
Messages
112
Reaction score
32
Points
28
Location
derbyshire uk
my bike is a 1979 cb750fz JDM model it is fitted with VB52A carbs and a 4 into 1 exhaust and standard air box. all the manuals I have looked at don't mention this model of carb. does any body know if these are the correct carbs although I am not looking for originality . the bike was running fine until one of them started to overflow when the engine was running but not when the petrol was just turned on as normal. the tap is a direct feed not a vacuum one. also when I lift the slides with a finger 3 drop straight away but one drops slower, any answers welcome , cheers
 
Correct carbs for Euro model 750 with no accel pump. The slides all should take like a couple seconds to go all the way down and pretty even.

Big flooding can happen instantly, lesser may take a minute to show up.
 
Correct carbs for Euro model 750 with no accel pump.
hello the two books I have managed to get say the carbs are vb42a or c and vb42b and 900ccf vb51a but they don't mention the fz model. this is a Japanese market bike that info on is a bit hard to come by even though I know they are all similar. do you think the japs fitted these or someone else? and what is the difference between the 42a's and the 51a and 52 a, cheers
 
42A, C are US spec 750 with accel pump needed for lean EPA emissions. 42 and 52 are 30 mm. the 900 carbs are 32's. Can't say what Japanese spec are. The only difference in 42 and 52 is the pump. Any letter after the dual number is minor jetting change for different models.
 
I have looked at the jets , the one with the rubber bung looks to be fixed the others are 68 and the one that's fits under the needle is 75? it has a 4 into 1 fitted do you think it has been jetted for this because the book says 102 and the only 75 I see was fitted to 350's. it is a JDM model with warning light in the rev counter so I don't think it was a restricted bike, why should it have the 75 . do you think I should send the whole lot to a carb man?
 
Last question is up to you.

68 front jet and 100-102 back. Somebody has been messing with it. The jet under the rubber plug is pressed in if no screwdriver slot in it. '79 is pressed in anyway.
 
back with an interesting result and to say these japs knew and know their stuff....my bike came with a 75 jet in the carbs and the books i have say 102, so when the carb people built my carbs i asked them to put 102 jets in. the bike wouldn't rev past 5000rpm and after getting other people to ride it we all thought it was electrical blaming a crack across one of the coils , then blaming melting spark units., then blaming leads and caps, then blaming stop switch, then timing!! it was none of these and a lot of money wasted i changed everything spark units etc etc. it was no better. long story short after much trial and re trial i removed the side cover and left the air filter out. it took off like a rocket. i did some extensive research and found the bike i have is the 750FZ JDM model. i studied air boxes and found the intake at the back on my air box was smaller than the 750f's of European market. i have put the air filter back in but left the rectangular cover off that fastens at the end where the air filter is. when the side panel is in place it pulls the extra air needed for the 102 jets in around the edges. i may consider putting the 75's back in now i know why they were there in the first place. morale of my story is leave as standard unless you know your onions:rolleyes:
 
Back
Top