Author Topic: Where to measure to determine carb size(28mm,30mm, etc..) (Read 18462 times)

scondon · « **on:** October 08, 2006, 12:44:33 PM »

I have been going on the assumption that the CB750 carbs are 28mm carbs. When I measure the ID of the outer edge of the carb throats(engine side) I get 31mm on the '73-'76 carbs. When I measure the '77-'78 carbs I get 32mm. I'm assuming that the throats are tapered and that the measurement must be taken from the center where the slides are. Is this correct?

What I'm trying to figure out is if the 77-78 carbs are actually 1mm bigger than the earlier ones, or if they just have a greater taper.

scondon · « **Reply #1 on:** October 09, 2006, 06:01:20 PM »

Sam Green Racing · « **Reply #2 on:** October 09, 2006, 06:17:13 PM »

Inside diameter of the end that goes into the rubber

Sam.

Sam Green Racing · « **Reply #3 on:** October 09, 2006, 06:17:55 PM »

and bump yaself

scondon · « **Reply #4 on:** October 09, 2006, 06:24:16 PM »

Quote from: samcr750 on October 09, 2006, 06:17:13 PM

Inside diameter of the end that goes into the rubber

Sam.

Thanks Sam

That's what I thought, but when I take that measurement I get 31mm for stock 750 carbs(32mm for 77-78). Have I been wrong all along in thinking that 750 carbs were 28mm

Sam Green Racing · « **Reply #5 on:** October 09, 2006, 06:57:45 PM »

I don't know Sean, I have only ever measured the carbs on my small Benlys.

On these carbs, the size is marked on them and have always been spot on when measured.

Sam.

Sam Green Racing · « **Reply #6 on:** October 09, 2006, 08:00:12 PM »

Sean, if your carbs have a venturi in them, it may be measured there.

Sam.

scondon · « **Reply #7 on:** October 09, 2006, 08:06:39 PM »

Quote from: samcr750 on October 09, 2006, 08:00:12 PM

Sean, if your carbs have a venturi in them, it may be measured there.

Sam.

Thanks Sam

They do have a venturi which I described as " where the slides are". Thanks for reminding me of correct terminology.

Now, if I can just find something to reach in there and measure with I can answer this silly question and move on to the next.

Sam Green Racing · « **Reply #8 on:** October 09, 2006, 08:15:39 PM »

A pair of inside calipers or if you'r carefull, you can do it with a pair of sissors.

Sam.

eurban · « **Reply #9 on:** October 10, 2006, 06:59:28 PM »

The late carbs and the early ones are both specced at 28mm. I don't know for sure where this is measured at but they should be the same.

scondon · « **Reply #10 on:** October 10, 2006, 07:05:03 PM »

Thanks, eurban, for saving me from poking my carbs with scissors

Sam Green Racing · « **Reply #11 on:** October 10, 2006, 08:27:22 PM »

OK smart arse,

get two lolly ice sticks, place them on top of each other, stick a thumb tac through them at one end.
Hey presto, you have a internal caliper

Sam.

Sam Green Racing · « **Reply #12 on:** October 10, 2006, 10:12:54 PM »

bump

scondon · « **Reply #13 on:** October 10, 2006, 10:48:58 PM »

Quote from: samcr750 on October 10, 2006, 08:27:22 PM

OK smart arse, get two lolly ice sticks, place them on top of each other, stick a thumb tac through them at one end.
Hey presto, you have a internal caliper

Sam.

Damn, this is just the type of simple, sound reasoning that escapes me when I'm scratching my head and staring at parts in the garage. Lolly sticks, OF COURSE!!!! Now the local sugar shop doesn't carry popsicles, would ice cream sticks work or are they too sticky. Also, I checked through all my drawers and couldn't find one damn thumbtack. I did, however, find two pushpins. Which one would work better, the yellow one or the blue one

Sam Green Racing · « **Reply #14 on:** October 11, 2006, 04:32:54 PM »

Pushpins

upperlake04 · « **Reply #15 on:** October 11, 2006, 05:54:05 PM »

Sam - they're large headed pins generally used in California that come in various sizes - the small ones are for holding grocery lists to the wall and the larger ones are for temporary seating.
Hope this helps

Sam Green Racing · « **Reply #16 on:** October 11, 2006, 06:06:33 PM »

Thanks Dave.

Sean, use the blue one mate.

Sam.

Sam Green Racing · « **Reply #17 on:** October 11, 2006, 09:30:11 PM »

Bump

scondon · « **Reply #18 on:** October 11, 2006, 09:35:56 PM »

Quote from: upperlake04 on October 11, 2006, 05:54:05 PM

Sam - they're large headed pins generally used in California that come in various sizes - the small ones are for holding grocery lists to the wall and the larger ones are for temporary seating.
Hope this helps

Don't know why that cracked me up so much upperlake. It is sooooo California of me to assume the rest of the world knows what a pushpin is. And soooo Canadien that you would have a picture catalogue of them

The blue one it is, Sam, as soon as I eat the ice cream off that second stick.

Sam Green Racing · « **Reply #19 on:** October 11, 2006, 10:10:48 PM »

.... I think in the UK they are called

push pins

Sam.

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Author Topic: Where to measure to determine carb size(28mm,30mm, etc..) (Read 18462 times)

upperlake04