Help! weber fuel starvation during hard cornering

[jpnovak]

Background.

stock 78 SC 3.0 motor. SSIs, weber 40s. properly jetted and float bowl height.

I just did some suspension upgrades on the ST. The car performed flawlessly except for two turns.

Yesterday at the track I was getting serious fuel starvation under hard cornering. The two main corners it happens are left hand, tight turns - one sharp uphill (think near-switchback) and one off camber slightly uphill.

The car comes into the turn under hard braking in a straight line. This is followed by maintenence throttle to balance/rotate the car on turn in. Then hard acceleration to transfer weight before apex. Turn-in rpm is about 3000.

At this point the carbs responds well to initial load then surges (lean surge?), then sputters, looses power (drastically) and 3-5 sec later recovers back to normal power levels after the car straightens out.

I assume that this is a fuel starvation caused by sloshing fuel. I think the delay at apex is masked from the accel. pumps giving a shot of fuel. Any suggestions?

I have searched the archives about the float bowl mods including shaving the jet mount and installing a fuel dam. I assume my problems are on the right side bank. The left hand cornering would cause the fuel to slosh to the right leaving the pickup on the left side of the carb dry.

I will make and install a set of dams but need a few questions answered. How high from the bottom do you install the dam? Does it sit on top of the rib from the main jet opening or higher? How far across the float bowl does it go? 1/2 way or more?

Just looking for some previous experience.

Thanks

[moneymanager]

Can't answer your question but Bruce Anderson's 911 book has pics of Weber mods to deal with these issues. Take a look. His buddy jerry woods regularly does these mods.

[john walker's workshop]

you need more fuel pressure when racing than on the street.

[jpnovak]

John, The pressure gauge reads at 4-4.5 psi. I am not sure I should go much higher. How high can I go before the pressure overwhelms the float valves?

Of course, that measurement is at idle or when you blip the throttle. I have no way to measure/monitor it on the track.

[gumba]

You need the fuel bowl mods done by Jerry Woods or Bieker Engineering. Mine use to do that at turn 2 at Sears (Infenion) before the fix.
Harold
'75 Carrera RS replica 3.4 twin plug, 46mm Webers.

[jwetering]

Dude - Deja Vu

I had to reread the name on this post a few times because it's almost word for word the same as a post I made few years back. I solved my problem. Chck it out.

I did the Jerry woods foat bowl mod - no help (Your Results may Vary). The problem with mine ended up being a PMO modification where holes are drilled in the tops of the carbs which are meant to direct boiling fuel into the carb throats instead of out the vents and onto your (hot) motor. This is described in BA's performance handbook as well. The problem of course was that during big side loads, raw fuel would slosh up and get sucked through the holes drenching the spark plugs.

I suspected this from the beginning, but my suspicions were confirmed when course workers on the AX track reported a raw fuel smell when I slalomed by.

The fix was a dab of JB weld over each of the holes.

So, take the tops of the carbs off. The holes wil be located in the walls, or webs, of the top part of the float bowl.

I'm interested to hear of that fixes your problem. It's funny it hasn't come up before.

[jpnovak]

Jasper,

I read your old threads before starting this thread. Funny I don't have the same problem with my targa. I suspect it is a car setup issue with cornering speed. I am almost a gear higher in turns with this car.

I will check for the vent hole mod. Can you describe how big your fuel dam is and how far from the bottom of the float bowl its mounted.

Thanks

[jwetering]

Originally posted by jpnovak
Jasper,
I will check for the vent hole mod. Can you describe how big your fuel dam is and how far from the bottom of the float bowl its mounted.
Thanks

The dams sit naturally on the shoulder formed by the fuel channels cast into the bottom of the float bowl. If you didn't grind away the fuel pick up, then the dam would sit right in top of that. I estimate 1 cm, but it's been a few years since I did the job.

I cut the dam out of 10 thou brass shim stock, trimmed it as tight as possible to follow the contours of the float bowl, and then JB welded them in. I wsh I had pictyures, but I didn't have a digital camera back then. I promist I''ll photograph them next time the carbs are apart.

[jpnovak]

Thanks,

I'll post pictures as soon as I get the mod done.

[trekkor]

How about some pictures?

I can't find any.

BTW, my fuel starvation issues started after I lowered the fuel pressure.
I may just grind the main jet pick-up shoulders down and bump the psi back up to 5#'s.


KT

[jpnovak]

Sorry no pictures. I did this mod for a friend. Its simply a section of thin sheet aluminum that is shaped similar to the floor of the float bow. Then just put some epoxy on the outer edges and set down on the top of the jet section.

I converted my car to EFI. Now there are no problems and it runs SO much better. Plus even with the hot 3.2SS I can get 23 mpg on the highway running 80. Love it and would not go back.

[burch]

here are the mods i did to mine, and i haven't had an issue since. i would also check the fuel tank.