Webers 'die' on hard acceleration

In short - car is pro tuned and all was good for the last 2000miles. Overnight, I then find when asking 'all' from the motor from around 3000rpm and up, the engine chokes completely. However, if I ask for the power evenly/slowly it gets there. Likewise, when the car is at rest it revs with a few 'pops' but nothing like the problems when on the road. The guy who did the work can't look at it for six weeks!!. So does anyone know someone in Herts who knows Webers or is this more likely an ignition/timing issue??
Cheers, Keith

Russ Noble

GT40s Supporter
Lifetime Supporter
Keith, Most unlikely to be a tuning issue. For my money either fuel supply restriction or faulty fuel pump or ignition breaking down. From your earlier 'fuel fountain' posts it seems you have a fuel pressure gauge so presumably this still shows adequate pressure at high revs under WOT. That being the case I would first look at the coil and plugs and from there go through the rest of the ignition system. HTH Cheers,
Russ, thanks. I sorted the earlier 'fuel fountain' by an in-line fuel regulator. Thus no more fires! On pain of death the guy who did the previous tune said don't start fiddling with the carbs if performance goes off as it it is unlikely to be the carbs. Your mail gives me the confidence then that the issue can be about ignition. I'll start the process but boy these cars are hard work!
what pump jets and bypasses are you using? I would change the plugs first and see what happens . Webers run rich quite often and plug fouling is common. An easy and cheap first step.
Try changeing your jets it sounds like your getting too much fuel at once.Your mains sounds like there too big webbers are hard to get right even the idler jets may need to be changed. The other thing is getting a place that sells all the jets that you may need its a matters of changing up or down in your case to find the right ones.

You may find youll have to put up with feeding the power on as the revs pick up! But to me it sounds like an over fuelling prob than anything

Dimi Terleckyj

Lifetime Supporter
Hi Keith
If as you state all was well for the last 2000 miles It is highly unlikely that the carbs have a problem.
I would leave the carbs alone and check the ignition system.
I had a 350 Chev with the same problem and it was moisture in the distributor cap.
Started and idled ok but when putting on the power would break down
Carby jets dont change themselves, if they were running ok then the problem is elsewhere.
Check for a plugged air bleed. This happens all the time in the desert. A small piece of sand gets in and the tell tale "popping" is heard. Especially at idle. Beyond that the plug check is a good suggestion. I have had that happen often when tuning a set of carbs. Also check your wires as wires go bad twice as often or more than plugs wear out, although I realize the previous suggestion was for fouling. The other thing I have noticed is that when a vehicle with Webers sits for a while and is then run, it can take a few WOT runs to clean out the secondaries. As you state, gradual run up is fine but jumping on the throttle causes a stumble.

My suggestion would be to try to make a few WOT runs and see if it cleans out. If not, then check the plugs. If that doesn't do it, try just cleaning out all the carb jets, emulsion tubes included. These things are much easier and less drastic than getting into jet changes and fuel system issues. I would start with the easy stuff first.
Crash/Randy-- check the post dates, your trying to help on a year old thread--owner has probably bolted on a holley or sold the car by now! Rick was only trying to find out what caused the problem.