carb drains or vents?

[hamburgler]

Can someone confirm if the nipple at the bottom of the float bowls are drains or vents? I am pretty sure they are drains, just wondering.

[Suzuki_Don]

Can someone confirm if the nipple at the bottom of the float bowls are drains or vents? I am pretty sure they are drains, just wondering.

Hamburglar, We don't know what carbs or what bike you are talking about. Are they VM or BS carbs. If they are VMs then the nipple will be an overflow outlet if the float level gets too high. If they are BS carbs then they don't have this system, they just have a drain plug/screw to drain fuel from the float bowl if required.

[hamburgler]

Hamburglar, We don't know what carbs or what bike you are talking about. Are they VM or BS carbs. If they are VMs then the nipple will be an overflow outlet if the float level gets too high. If they are BS carbs then they don't have this system, they just have a drain plug/screw to drain fuel from the float bowl if required.

Sorry, lol. I was meaning to post a pic right after my post but forgot. Anyway, its a 1979 GS750 with Mikuni carbs.

[hamburgler]

And does anyone know how these carbs would perform under 5 lb's boost? Thinking of doing a turbo system. Here is another pic of how they are set up right now.

[Gonzo]

1 and 2 in your pic are atmospheric vents, they usually drape back over the air box. The bottom four are your overflow drains.

I don't know about turbo stuff, but I imagine the jetting would be a friggen nightmare to get right.

[Suzuki_Don]

And does anyone know how these carbs would perform under 5 lb's boost? Thinking of doing a turbo system. Here is another pic of how they are set up right now.

Gonzo is almost correct. Just one small adjustment.

1. Is the vacuum outlet that has a hose going to the petcock/fuel tap usually. This is plugged on your carbs which is quite normal if a different petcock is used that does not require vacuum to operate.

2. These two outlets are to vent the float bowls to the atmosphere and as Gonzo has said they are usually run up over the lid of the airbox.

3. No number 3.

4. Float bowl drain outlets. The rubber hoses of these are bunched together and run down between the crankcase and the swing arm towards the ground.

[Steve]

And does anyone know how these carbs would perform under 5 lb's boost? Thinking of doing a turbo system.

You planning a blow-through or a draw-through setup?

If you are planning a blow-through, the carbs will stay pretty much where they are, but need to be totally enclosed to work properly. The pressure inside the float bowl is the reference for the air that is moving through the venturi to determine how much gas will be added. If you don't pressurize the bowl by enclosing the carb, you will simply stop the flow of gas. Running lean on boost is a very temporary situation.

If you are planning a draw-through setup, why bother with four carbs feeding the turbo? MUCH simpler to get a larger, single-throat carb and jet it correctly.

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[hamburgler]

Well I took off the flat bowls to confirm if they are drains or vents and I believe they are vents. From what I understand the vents in the enclosed bowl help with keeping the pressure at equilibrium.

[Steve]

The nipples coming out the bottoms of the carbs are overflow drains.

Your vents are attached to nipples higher up on the intake side of carbs #2 and 4.

Because of the way carbs work (difference in pressure caused by moving air - The venturi principle), the carbs would have to be TOTALLY enclosed to work with a blow-through turbo setup. It is much more common to have the turbo mounted where the airbox is now, and use a single side-draft carb on the intake side of the turbo.

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[Big T]

Well I took off the flat bowls to confirm if they are drains or vents and I believe they are vents. From what I understand the vents in the enclosed bowl help with keeping the pressure at equilibrium.

They are overflows

Adjust your understanding accordingly

Also, check with Blowerbike, he knows the turbo set ups