carb overhaul

Hello Russ, new here, I was browsing carb threads as I have some issues with an early 308, any way from my experience make sure all your valve clearances and timing are correct as they will adversely affect the carbs efficiency, in fact if the clearances, especially the intake, are too far out it will be impossible to fine tune the carbs at all, that said webers are truly simple pieces of kit, take your time be organized and remember, idle is tuned from the idle air bleed screws not the throttle plates.
I currently have 8 42DCNF carbs 4 from a 67 Ghibli and 4 from a 77 308 (fibreglass) to rebuild, Ghibli carbs are stripped down and out for ultrasonic cleaning, I needed two throttle shafts and bearings for that set because of water damage, otherwise just simple overhaul kits are all that was needed,
DCOE carbs are similar and usually only need a simple overhaul to achieve a return to efficient operation

 

Yes a lovely weekend, I was at Goodwood all day Saturday for the FOS.

I LOVE the 400, always thought it was an under-rated car, the lines are elegant and understated, it is a true grand tourer, they were never meant to be sports cars, but rather fast comfortable effortless "tourers", hence the GT moniker.
I lived in California for 22 years and at one point worked on Doc Severensons 400(johnny carsons band leader on the tonight show) and came to appreciate just what the car is all about
Last year I got to work on a "68 365 GT 2+2 (queen mary) another unloved car but boy what a driver, just loved it, and both cars have essentially a Daytona lump under the bonnet.

I also love the S3 E-type for the same reasons, which is why I own one, V12, comfortable, fast, A/C, room for luggage ,everything you want in a touring car. I have always bucked the established thinking when it comes to cars like these but it seems that people are now beginning to appreciate just how great these unloved cars really are.

Any way to the carb issues, it sounds like the progression is not quite right, did the issue start after something was worked on and or or adjusted or has it gradually come on. Webers consist of essentially three main circuits, idle, progression and main.
Idle is controlled by the idle screw, progression is controlled by the idle jet via a series of small holes that become exposed to the air flow through the carb throats as the throttle plate opens, (visable just upstream of the throttle plates when closed), and the main circuit is bought into play when enough air velocity brings the aux venturi into play, for some reason yours sounds like it is "going lean at part throttle, likely a good clean, rebuild, and adjustments will fix the issues, given that it is a stock engine the the original jetting as per ferrari should be right. Also be certain to make sure your float height is set correctly, it can make a difference.
Failing that you may have to alter the idle jetting. the idle jet controls the mixture of the progression circuit, which is in effect up to roughly 2800 rpm, so any issues in the rpm range up to that point are in the idle jet circuit, if you cannot tune it out then you may have to move to the next larger idle jet size.

 

Hello Russ, was thinking on this today, the symptom you describe is often caused by incorrect throttle plate settings,that is to say if they are too open at the closed throttle position,therefore uncovering a progression hole while the engine is in idle mode.
If you have the time it might pay to check these settings, basically, disconnect the carbs from the throttle linkage and each other, turn the throttle plate stop screws out until they are clear of the operating arm, then screw in until they are just touching the arm and then turn 1/2 turn past this point, no more! then leave them alone, the rest of the idle tuning is done from the idle screws.
If you carefully count how many turns out the screws currently have then you could return them to this setting later if there is no improvement made.
Andrew

 

couple more notes, depending on access you might check the idle jets for spec, you might even bumper them up a size as a test. A run on a dyno or using an O2 sensor might reveal some info on the fuel mix/flat spot.

With ultrasonic cleaning-be sure to VERY carefully check the state of the lead plugs used on these carbs, I have read about and personally experienced having one fall out while driving after this process. Fuel was being pumped out of the float bowl and down the side of the motor in copious quantities and I was luck not to have an explosive fire.

Apparently the cause of this, apart from just age, is the ultrasonic treatment vibrating these loose.