Weber float bowl baffle... How to?

[cstreit]

Has anyone here done their own modification to the weber float bowls to prevent the momentary starvation on hard left turns.

As my car has picked up grip, it has become an increasing problem for me. The pictures in the "911 Performance Handbook" seem pretty straightforward, but there is no clear indication as to how far above the bottom of the bowl to put the alum. sheet.

[jpnovak]

chris,

I did mine. Just mill the Main jet pickup from the pickup hole on top down through the side until about 1mm from teh bottom of the floatbowl. Then the sheet metal dam sits on top of the pickup "supports".

I took a piece of crayon and paper and traced the upper opening of the floatbowl. This became my template to cut the fuel dam.

[Walt Fricke]

Chris - when you open the carb up you will see where to put it. There are ledges in there it can sit on. Bruce's pictures are really all you need to do this. Make paper patterns to get the fit pretty close, then snip out of aluminum scraps and epoxy into place after grinding that lip by the entrance to the main.

While everyone calls this a baffle, I think what it mainly does is move the fuel pick-up point for the mains to the center of the bowl. So it is not that it stops sloshing around. Rather it puts the pickup in a place that is less likely to be uncovered (at least if you can't corner at 3G).

Do you only turn left?

Walt

[cstreit]

Thanks guys,

So essentially you grind down the set-off around the pickup and the remaining legs up it are what the "baffle" sit on. What does it sit on at the center of the bowl bottom?

Do you use JBWeld or is there some sort of special fuel resistant epoxy?

How did you get a nice bead at the edge of the alum. sheet?

My car is making excursions to 1.6G filtered with sustained cornering at 1.5G, and the left hand turns I am losing nearly all fuel. No power.

[Walt Fricke]

Chris - think easy. Grind one or two places, depending on which bowl it is. Suck out the grindings (I think I had the main jets out for all of this). Plop the piece in there. Run a bead of any old kind of epoxy around the three sides to seal it and hold it in place. Done, on to the next bowl.

The two I did I had on the bench. Bit more awkward in the car, I suppose.

That is really odd that you are cutting out going one way but not the other. Most tracks have plenty of right hand turns, so I don't suppose the lefts are longer. Two fuel pickups in your fuel cell, and two pumps sucking it out and then Td together to send it on its way to the engine? No correlation to fuel tank level?

You pull a hair more Gs turning left because it's left hand drive?

I run a vacuum modulated fuel pressure regulator. Of course I don't really know if it makes a difference, but the theory here is that you set your fuel level to the tippy top of the top line. Normally that would cause problems at idle when flow is low. But the vacuum causes the fuel pressure to drop, so you don't get pressure induced overflow. Then at WOT or thereabouts you get higher pressure, which is sucked out about as fast as it comes in, so no problem with overflow and so on.

The starvation I know only too well is in my SC if I let the tank get down much below a quarter. I suppose you know that as well, so you aren't confusing starvation with the problems of bogging you can get coming off a corner. Come on, come on, catch fire and go. That's what I had to fiddle around with for jettting and such. Never had starvation (except, of course, when I have run out of fuel in the tank). But I don't know what I am pulling for Gs.

Anyway, I bet you'll like the result of installing the plates.

Walt Fricke
PCA GT4R

[cstreit]

Walt,

Thanks for the info.

The lean-condition happens even with my fuel-cell full. I set the float bowls to minimum thinking I might have a spill-over issue, but that made it worse, then set them to max and that's where I am today.

I've pretty much eliminated any other idea.

[jstein]

I have stuttering issues on hard corning with my mostly stock SC (with webers of course); and no way I'm pulling 1.6Gs.

Long sweepers are the worst - turn 3 at blackhawk, turn 8/9 on north track at autobahn are horrible.

Note that those are both right hand turns.

I'll be trying the baffle modification as well..

[Walt Fricke]

Is this is a sociological phenomenon? What took you guys so long?

Of course, I am a monkey see, monkey do hot rodder. When first I got a carbed engine and race car, Bruce's book was the only game in town (and is still going strong, just like our old 911s). It showed this mod. Naturally that was something I did when going through the carbs before even running the car on a track. How could I not? Cost is zilch, effort miniscule, skill required none, downside zero. You guys know which way to turn a wrench.

Maybe it is the explosion of information and options nurtured by the Internet. If you spend time wishing you had the money for Nickies or had tried hollow titanium valves with 5mm stems (indecisions like this have slowed my SS2.8 project considerably), the other end of the scale can be overlooked. Or PMOs, which don't have the problem due to Richard's knowledge of the Weber weaknesses.

Of course the EFI guys must be chuckling, just as we do when they are puzzling over their laptops.

Walt

[Eagledriver]

This mod was not as straight forward for me as this thread implies. I looked at the picture in the book and thought I was building a little dam around the main jet intake. That is not correct. What you are really doing is making a "snorkle" for the main jet so that it sucks from the center of the bowl.

This is the same mistake the it sounds like Chris was going to make when he asks what the dam rests on in the center of the bowl. The answer is of course that it doesn't sit on anything, that is the "snorkle" entrance.

Needless to say in my case I went from a nice running car to one that died on every corner until I pulled the tops off the carbs at the track and ripped the dams out.

In addition I use JB weld and found it had softened from the gas exposure. Rich Walton told me they use the white Dow RTV that is used on the engine cases. (I think it's called 730, the expensive stuff).

-Andy

[jstein]

Did any of you guys who did the mod take photos?

[Walt Fricke]

Digital photography didn't exist when I did mine.

And I don't know just what photos would show that would differ from Bruce's in his book. Maybe the line of epoxy around the three long sides of the aluminum piece after installation? Once you know what the purpose is, and how it achieves it, duck soup.

But I've been grinning for an hour thinking of Andy's WTF moment at the track. I've had my share of those in other contexts.

Walt

[cstreit]

Walt,

I've known about this for years, and have had the problem for the same amount of time... However two things changed:

1. Better aero and wider tires have given me more grip and made the problem worse.
2. I'm now in a series where the competition is FIERCE. When a few hundreths seperate 1st thru 4th and the other guys are driving GT3's to my 1970, I need everything to be right.

So while EFI is in the not-so-distant future (as much for the knowledge and sheer "Technoliciousness" of it) I need something to tide me over because I won't run on EFI untill I am sure it is 99% of the way there for me.

Dow 730 eh?

Andy, my confusion was really more around the fact that this is essentially a baffle AND pickup location change vs. just a "flow baffle". (which also clears up some of my doubts about it working for me.