Car runs badly after Weber Re-build

[Quickstep192]

My winter project was to re-build my Webers after the last drive of the fall seemed to indicate that I had clogged accelerator jets. I cleaned and re-built both carbs and put the carbs back in the car today. To my delight, the car started easily after installing the carbs and chasing a couple of gas leaks. I checked the float bowl levels and adjusted the linkage to balance side to side. I checked the accelerator jets which are putting out about .7cc . I then adjusted the air correction jets until all six cyliders read the same on the sychrometer. I then adjusted the idle jets for max rpm and adjusted the air correction jets again. The car seemed to be running great..... until I drove it. While out for a drive, it felt like the car couldn't make any power; wouldn't go above 3500 RPM. Even when I tried to accelerate slowly, it just seemed to bog down.

What did I miss?

[Grady Clay]

What year/model car?

I suspect it is a plugged filter screen fitting at the gas tank outlet.

Couple of diagnostics:

First check the fuel filter at the engine.

Did you clean the filter screens in the Banjo fittings at the carburators?

Take a long length of 7 mm fuel hose from the 'tee' at the carbs and return the fuel to the gas tank filler.
Flow should be about 800 cc in 30 seconds.
Let it flow for a while, measure again.

Install a fuel pressure gauge 'teed' into the fuel line in the enine compartment.
If the fuel pressure drops when the running situation is present, screen filter.
Spec fuel pressure is about 3.5 psi.

Best,
Grady

[Joe Bob]

Blow out and/or ream the jets. Like Grady says...check presure and filters and screen. Something came loose when you cleaned the carb bodies.

[Quickstep192]

"Did you clean the filter screens in the Banjo fittings at the carburators?"

Yes, I cleaned the filter screens. Also cleaned all the jets and passages. I will definitely test to make sure adequate fuel is getting to the carbs.

As I think about it, I'm wondering if I could have a blockage at the float valves. Hard to imagine that all four of them are fubar, but I guess stranger things have happened. I didn't replace them because I couldn't get the retainer bolts off; I decided to go with the old ones rather than rick breaking something.

[carrera turbo]

Well im thinking maybe you may have something else and not completely carb related. check your basics plug condition, coil wire for corrosion, your timing etc. make sure your getting correct fuel pressure etc. i worked on a car last year with Weber's the poor carbs has been into several times for popping and poor runability, it ended up needing a valve adjust and a good tune and it runs great. not that you do not have a carb problem but dont get stuck on one area of the motor just because you where just messing about with that item or items. you could very well have another issue not carb related at all.

take a step back go through your basics and see what you find, sometimes you are chasing the wrong ghost.

cheers ed

[Peter Guldan]

Howdy chaps,

At some point in the near future, running issues with carbs will be out of our hands.

To stem the tide of the 300 million odd gallons of gas evaporating at U.S. gas station pumps, the EPA has decreed that fuel have less propensity to evaporate (atomize is operative word here) when exposed to atmosphere at atmospheric pressure.

Not a problem whatsoever for modern vehicles running injection pressures from 40 to 2,000 plus PSI but a huge one for carb equipped cars as that is the environment within your venturi give or take a few millibars. Instead of atomizing, that gas just runs down your intake into your cylinders at cooler operating temps and one is lucky not to foul a plug if they can even get the car to start. Especially an issue on cars with cam overlap or large intake ports relative to displacement that do not create enough port velocity to break up fuel droplets.

Likely traceable to our blends in the South/Southeast, it had become a critical issue for a KY based Pelicanite here thus the primary motivation for converting to ITB EFI below.

[brads911sc]

That was one of the factors that I used in selecting the PMO ITB's over Carbs. Also with Tuner Studio (for Megasquirt) you can connect, drive and in about 30 Minutes all the Maps are adjusted based on Target AFR. Runs smooth throughout the power band except when cold (which is a carb issue as well). With all the changes coming, not sure Id go with Carbs.

Originally Posted by Peter Guldan

Howdy chaps,

At some point in the near future, running issues with carbs will be out of our hands.

To stem the tide of the 300 million odd gallons of gas evaporating at U.S. gas station pumps, the EPA has decreed that fuel have less propensity to evaporate (atomize is operative word here) when exposed to atmosphere at atmospheric pressure.

Not a problem whatsoever for modern vehicles running injection pressures from 40 to 2,000 plus PSI but a huge one for carb equipped cars as that is the environment within your venturi give or take a few millibars. Instead of atomizing, that gas just runs down your intake into your cylinders at cooler operating temps and one is lucky not to fowl a plug if they can even get the car to start. Especially an issue on cars with cam overlap or large intake ports relative to displacement that do not create enough port velocity to break up fuel droplets.

Likely traceable to our blends in the South/Southeast, it had become a critical issue for a KY based Pelicanite here thus the primary motiviation for converting to ITB EFI below.

[Peter Guldan]

Howdy Chaps,

That's the beauty of this one, key it cold and go, no driveability problemsat all. In answer to some pm's - not really any more peak power to speak of than carbs, just far more accurate AFR's, better driveability in general and being EFI, now mainstream and in lock step with EPA dictated fuel formulation changes.

One small example of driveability that you'll note here. When you floor the throttle on carbs, between the accelerator pump draw and increased fuel demands through the jets, the float level drops slightly which means on throttle cut, the rpm dips below idle setting. Here it returns immediately to idle.

Carbs, have them on 10 of my machines and appreciate them for their simplicity but time marches on....accelerated (pun intended) by the EPA.

[Quickstep192]

Sure looks tempting. What's the ballpark cost to do that conversion?

[Peter Guldan]

Howdy Sir,

Haven't a clue, I stay out of the business side of Pat Williams Racing, but you can click here to send him a note.

[1QuickS]

check that you haven't reversed your secondary venturis during reassembly.

[Quickstep192]

Originally Posted by 1QuickS

check that you haven't reversed your secondary venturis during reassembly.

Thanks. That's exactly what I had done!

One on the drivers side and two on the passenger side were backward.