Proper float level

[Quickstep192]

Which of these is the proper float level for weber carbs (factoring in the meniscus)

[1QuickS]

Both are fine, the first image is not indicating the maximum fuel height allowable. The meniscus is the level of the fuel in the bowl so the bottom of the curve should be tangent with either of the two upper lines or anywhere between them. Be sure you run the engine to get a dynamic level reading under fuel pump pressure. Shut engine off and read the level.

A 0.010" shim under the needle will adjust float height approximately equal to the distance between the two lines.

Weber specified fuel pressure at the carbs is 3.5 psi; plus/minus .5 psi is what I recommend as the tolerance.

[Quickstep192]

Thanks for the info about the relationship between shim thickness and the ones on the gauge. That will save a lot of trial and error. Right now my float levels are where it's shown in the "B" drawing. I'm having problems that appear to be in the transition circuit; popping between 2,800-3,000 rpm. Do you think raising the level might help?

[1QuickS]

How about some engine and carb particulars first, as best you know:

• displacement
• cams
• compression
• header size and muffler type
• Weber IDA, IDAP, IDT, IDTP, IDS
• 40mm or 46mm throttle bores in Weber
• venturi size
• main jet size
• air correction jet size
• emulsion tube
• idle jet

I popping constant with constant throttle position at the 2800 to 3000 RPM range or is it during acceleration? If acceleration is is moderate (1/2 throttle) or WOT acceleration?

[Quickstep192]

This is a '73 car that was rebuilt to 2.7 by the PO, retaining the T Cams and adding the Weber 40IDAs. It had a sport muffler that I replaced with a stock muffler. After I did that, I spent some time working out the juuuust right jetting combination - 60 idles; 130 mains; F-26 Emulsion tubes; 185 air correction; 30 ventures; Bosch W8DCO plugs. The car ran extremely well with that configuration for years; like 10 years. Last year it developed this problem where it's popping between 2800-3000. It does it sitting still, or accelerating through the range, or cruising in that range. I've removed the carbs, disassembled and cleaned everything, paying special attention to the emulsion tubes and cleaning every passage.

It's driving me nuts.

[1QuickS]

Idle jets are if anything a size too large. Otherwise jetting sounds fine.

I'd try setting floats above top line and see if the issue gets better. If so then you could leave it there or try a smaller main air correction jet which would help bring in the main circuit a bit quicker. Another thing to try is to open mixture screws one full turn to see if the issue is improved.

This all assumes there are no issues with tuning and synchronizing the carbs. It would be good to double check side-to-side air flow balance at 3000 RPM.

Perhaps the fuel has changed enough in the past ten years to cause a running issue.

[Steve@Rennsport]

Originally Posted by 1QuickS

Perhaps the fuel has changed enough in the past ten years to cause a running issue.

OMG, yesss.

Today's sperm whale urine that's sold as gasoline has little or no resemblance to the fuels these carburetors were calibrated to.

The closest thing to the gas of old is racing gasoline, however its a tad expensive.