Jay,
I was careful to read your post to understand your problem. What I didn't notice was Jamie's post regarding the secondary vents. So I asked the same question he had posted 2 hours prior.
We haven't talked about venturi size and main jet size.
In fact we don't even know if the carbs are 40's or 46's.
Another question. Have you checked the ignition timing for proper advance at higher rpm's?
Should be at least 30 degrees at 6,000 rpm's.

You confirmed good fuel pressure. Did you confirm good fuel volume too? I suggest that frequently when folks experience high speed power loss.

About a liter per min. should be fine.


Sherwood

Sherwood, Is that a LPM per side or collectively?

I suppose the best way to measure is to disconnect the supply line(s) to the carbs and pump the fuel into a beaker to measure?

--Weber 40s, 36mm venturis. I don't have the jet sizes in front of me but I think either 150 or 160. The carbs have been set up this way for 5 or so years and have worked.

I checked to see if the nut on the distributor was loose b/c I wondered if the timing changed. It was tight but I haven't put a timing light on it yet to be certain that it is set right. Timing was checked about 1 month ago while at the shop to do the trans rebuild...

Jay,
From the fuel pump supply line. Yes. Include fuel filters as part of the source.

Be aware of fire potential.

Sherwood

Hi Jay,
It is good to hear your carb setup has run well for several years.
At this point I would focus on the "white stuff" found inside the carb bowl.
If it is in the carb, it is also in the fuel filters.
I have no experience with "white stuff" in my carbs.
I've been in my carbs several times, nothing but Chevron Supreme.
Have you used fuel additives? Stored the car for extended periods?
Perhaps someone else has seen this and can offer a suggestion.
I would check my fuel tank. Drain it and closely inspect it.
At the very least change the fuel filters.

+1

---Bingo! I just found out that my car used to belong to a Drug Smuggler. Apparantly he thought the float bows was a good place to hide his stash. It looks like the plastic bag disintegrated and polluted my carbs! man if I had only known.

I am reading this as humor, but if it were true, MAN, what a story. :p

Yep kidding of course.

The white stuff I think must be a common occurance if you set your car up for a while without draining the fuel out of the carbs.

:D

Yeah, typically aluminum corrosion if I recall correctly.

+1
More toward pot metal corrosion - same thing.

Sherwood

I took apart a carb on a lawnmower a couple weeks ago that was just packed full of a white, I assume, oxide. I was thinking this may be a result of water intrusion because there was quite a bit of water in the tank and I've seen many carbs sit long enough for the contents of the float bowl to evaporate with no problems. If you still had a small amount of water in your tank to be picked up when it's jostled just right you'd see quite a bit of power loss as small amounts of it are picked up and sent to random carbs and the effected cylinder drops out temporarily.

still scratching my head.

The engine wails like it is supposed to while the car is parked in the driveway. It runs and drives nicely while putting around in the idle circuit area (low rpm).

I'm getting full advance at 6000 RPMS. ~35 degrees

Under load it just goes flat and bogs down. I can't get the engine to let loose and scream...

It must be either starving for fuel or air is all I can guess...

How about checking for full throttle,since the engine and tranny were out.sen this on more than one occassion.

Had this same prob and fuel filters was the answer. Whats the white crud? contamination!

when the junk fuel we have today flashes off you end up with some white junk in the float bowls. I guess it's aluminum oxide or something else that grows in the carbs.

Park your car for several months and don't drain the fuel and you too can have some.

My car is parked for months at a time...mostly I run the fuel out of the carbs, but sometimes I forget. Every winter for 6-8 years. *No white crud* ever.....this is not normal or even common.....never heard of it till now, in fact.

Introduce a goodly amount of water into the fuel system and it becomes possible...not that I plan to try that. Corrosion in the internal passages of Webers will fuch them up big time.

-not a chemical engineer but I suspect that it's not due to water in the fuel system but the junk fuel we get today. Keep in mind that the climate here is quite humid too.

So..... put some of your gas ( not out of your tank) in a clean clear glass bowl and let it evaporate. Check for white crud & report back.:D

Anything left after evaporation should dissolve with a fresh addition of gas.....the usual "varnish" left over after multiple evaporation cycles (dark brown) often won't.