275GTB/6C carb issues

Yes. This is a serious problem. Modern fuels left in Vintage Carbs will cause this type of problem. There are two things that will help.

Replace the gaskets with ethanol resistant gaskets and put an in line fuel shut off valve or electric fuel pump cut off and after driving shut off fuel supply and idle/run until the car just begins to stall.

Some have also had luck with fuel additives that claim to help with this problem.

Best

 

I believe the spring loaded plate is your accelerator pump diaphram. These are made out of a rubber impregnated cloth material. Modern fuels often cause the rubber to swell when exposed to fuel. When they sit dry for a period time they tend to shrink and loose their seal (take a compression set). Before you replace them I would check to see if the screws are torqued correctly. Often they will be loose and will seal up when snugged down. I have also found that they will typically seal again, once they have been exposed to fuel for 24 hours. Twenty four hours seems to be the time required to make them swell back up. Rubber based gaskets in the fuel system often to need retorquing once or twice before they are reliable. Of course none of the above will help is the diaphram is ruptured. In my experience I would estimate that you have a 70% chance retorquing the screws will correct the issue.

Cheers Jim

 

One separate thing. Take off the air cleaner and make sure the mechanical choke is working properly. Choked cuts off air supply and you don't want to run car too long like that. It's probably open but check.

Best

 

Dave Helms and I have had many discussions...As Napolis states the modern fuels (will have ethanol and LOTS more) are blended by region and season, and lots of the additives are indeed very harmful to outdated products.

The problem is known but not the answer.

Mercury Racing was onto it several years ago with recalls...It least in our cars, we can walk home, swimming is a lot more challenging!

 

The accelerator pump diaphrams have always had that problem since long before the fuel changed. The Webbers with the exterior accelerator pump design which that, 4 cam and later cars had, shrinks when dried out after use. It is not unlike the hull of a wood hulled boat, the difference being it will not swell and reseal after getting immeresed. It has been pretty standard to need to replace them in such an instance since before they were considered old cars. It has been a pretty common spring service on many cars for as long as I have been doing this. The idea that allowing a carb to "Dry Out" has been considered something to be avoided since my father learned to drive in the thirties even on Model A's.

Sometimes just gently tightening the 4 screws at the corners of the pump diaphram cover is enough to control the situation.

 

I've used fuel cut off valves for years and it seems to have stopped this. Maybe it's keeping fuel from draining out of the carbs, back into the lines and tank and keeping the gasket soaked. I think it's also a factor in systems where a fuel source/line is higher than the carbs as on bikes. In the winter have shut them on my boat motors and never had a carb leak in the spring when opened and restarted.

Wasn't this an issue on some Lambo's with side draft carbs?

 

DCOE series has a fuel well cover plate on the bottom with a gasket made of the same material as the pump diaphrams but it is a single layer so the shrinkage is less of an issue.

 

Thanks.

 

Carb fuel leaks have caused many Ferraris demise from fires. Don't know if you have an elec fuel pump but with key on motor off its a good idea to run your fingers around the lines and carbs for leaks befire a run if its been awhile sitting. If you suspect the accel pumps are deteriorated you can look down the carbs with aircleaner off for the volume of fuel squirting down the barrels. You can check the amt with a vial if you want to get exact that should tell if they are healthy

 

The accelerator pumps hold far more fuel than they squirt and are constantly refed by the fuel bowls in any event. You could have a very large fuel leak with no change in the way the accelerator pumps work or the volume they discharge.


Same goes for your BB.

Your BB has adjustable pump discharge so there is a spec for that quantity. Not so DCN or DCNF.

Not all Webbers work the same.

 

Actually on the carb and fuel pump diaphrams the answer has been around for a good many years now. The problem is there are still a good many of the old parts floating around in the parts system and to this day I still get some of the old and some of the new when working on the Vintage cars. Used to be one could visually identify the good from the bad by color of the rubber material covering the canvas...not the case anymore. There is both good and bad black and red material.

Many only focus on the carb leaks as they are easy to see. Dont forget about the diaphrams in the fuel pumps, they suffer the same fate as the accel pump diaphrams. Years back the liner of the Yellow hose was changed to a working material but if those lines look old....keep a close watch on them!

With the way I have seen the fuel compounds separate in my tests, consider it essential to drive the car a few miles once a month just to stir things up and keep all of the fuel components suspended. This I now consider an absolute must with the current fuels out of the pump.

Dave