Leaking DCOE45 carb
Discussion
Hi... leaking fluids can take rather tortuous paths, so hard to be definite. :-) The airhorn tab holding stud doesn't go into anything that would leak, and the most direct way for gasoline, sorry, petrol, to hit that area would be by leaking from the interface to the main nozzles in the venturi, then running down the wall of the carb throat. From the carb throat it can run along and out between it and venturi/airhorn interface, and being caught by the airhorn tab, appear to leak from there.
Not the most usual place to leak, if it hasn't leaked before, but possible - especially, perhaps, in the cold.
Another more common area of leakage, is from the accelerator pump jets. If their cover screw gets loose, petrol will leak out around the pump jet shaft. This also occurs on occasion if they have been withdrawn and cleaned, but not supplied with a new washer. usually when these leak, you can see it drip from the pump jet shaft, or see it is wet, or test for wetness with a dry cedar wood pencil. In my experience they tend to leak more into the carb than along the throat and out from under the venturi.
I suppose leaks form other areas may trickle out the front after a time, but the two areas mentioned above are the major culprits.
The oddest thing I can think of is having too high a float level or jammed needle valve, and petrol running out of the breather hole, somehow... if that is even possible.
In tightening the auxilary venturi holding screw (under the carb), one has to be very careful not to distort the shape of the venturi, and make leaks worse. The two screws under the carb should also be safety wired or safety tabbed.
I hope this gives some ideas for investigation, and helps you out.
Not the most usual place to leak, if it hasn't leaked before, but possible - especially, perhaps, in the cold.
Another more common area of leakage, is from the accelerator pump jets. If their cover screw gets loose, petrol will leak out around the pump jet shaft. This also occurs on occasion if they have been withdrawn and cleaned, but not supplied with a new washer. usually when these leak, you can see it drip from the pump jet shaft, or see it is wet, or test for wetness with a dry cedar wood pencil. In my experience they tend to leak more into the carb than along the throat and out from under the venturi.
I suppose leaks form other areas may trickle out the front after a time, but the two areas mentioned above are the major culprits.
The oddest thing I can think of is having too high a float level or jammed needle valve, and petrol running out of the breather hole, somehow... if that is even possible.
In tightening the auxilary venturi holding screw (under the carb), one has to be very careful not to distort the shape of the venturi, and make leaks worse. The two screws under the carb should also be safety wired or safety tabbed.
I hope this gives some ideas for investigation, and helps you out.
Hi Canuck7. Thanks for the suggestions. I checked them out but found the problem was I had set the fuel pressure regulator at too high a psi. The electric fuel pump was squirting too much fuel into the carbs and No1 carb was flooding. I reduced the pressure down to 1.5 psi and the leak stopped.
Cool... so there is a way for a flooded carb to leak out the front. I guess it just runs down the main jets and out the venturi.
I'm glad you stopped the leak, but there may still be a problem...
Most people say that sidedraught 45s are happiest from 3 to 4 psi when running. The most common number mentioned is 3 PSI. One American specialty supplier swears by roughly 4 psi, if constant and smooth. Some people say that it is ok around 2.5 if your max consumption isn't too high. I have run my 48 DCOSPs at both 4 and a little under 3 PSI, and will probably adjust my regulator a touch higher, to about 3. In my case, I found that the fuel pressure drops by about 0.4 PSI (if I remember correctly), when running as compared to static. So I need to readjust for that. The benefit of having a permanent inline fuel pressure gauge that I can peer at from over the top of the scuttle. :-) Of course, YMMV. :-D (But I do think anything less than 2-something may be a bit lean/minimal under load.)
I'm using a carter rotary fuel pump that was made to flow to 300+ cubic inch V8s running hungry 4 barrels. It's a low pressure (internally regulated at 4 PSI), high flowing, smooth supply unit. I added in the classic Italian fuel pressure regulator near the carbs to get more control and drop things to about 3 PSI.
If you get leaks at even 2 to 3 PSI, I would think that one of your needle valves isn't functioning well. It might be worn just enough to let extra fuel flow through at moderate pressures, or have some varnish on it from sitting over the winter, fuel tank flotsam stuck on it, or have a weakened spring. Needle valves are inexpensive and only slightly hard to fiddle with,(easier than most things, harder than changing jets). They also are one of the things that wears the most. (Float fulcrum pins are the other thing). It might be a good idea to pop in new ones for your carbs... and those mini fuel filter baskets, too. Also check the torques on everything. When I got this caterham, all the internal jets were rattling around and leaking. Well, the whole car was rattling around and leaking - 3 years into the rebuild and it's almost safe, lol.
Good luck!
I'm glad you stopped the leak, but there may still be a problem...
Most people say that sidedraught 45s are happiest from 3 to 4 psi when running. The most common number mentioned is 3 PSI. One American specialty supplier swears by roughly 4 psi, if constant and smooth. Some people say that it is ok around 2.5 if your max consumption isn't too high. I have run my 48 DCOSPs at both 4 and a little under 3 PSI, and will probably adjust my regulator a touch higher, to about 3. In my case, I found that the fuel pressure drops by about 0.4 PSI (if I remember correctly), when running as compared to static. So I need to readjust for that. The benefit of having a permanent inline fuel pressure gauge that I can peer at from over the top of the scuttle. :-) Of course, YMMV. :-D (But I do think anything less than 2-something may be a bit lean/minimal under load.)
I'm using a carter rotary fuel pump that was made to flow to 300+ cubic inch V8s running hungry 4 barrels. It's a low pressure (internally regulated at 4 PSI), high flowing, smooth supply unit. I added in the classic Italian fuel pressure regulator near the carbs to get more control and drop things to about 3 PSI.
If you get leaks at even 2 to 3 PSI, I would think that one of your needle valves isn't functioning well. It might be worn just enough to let extra fuel flow through at moderate pressures, or have some varnish on it from sitting over the winter, fuel tank flotsam stuck on it, or have a weakened spring. Needle valves are inexpensive and only slightly hard to fiddle with,(easier than most things, harder than changing jets). They also are one of the things that wears the most. (Float fulcrum pins are the other thing). It might be a good idea to pop in new ones for your carbs... and those mini fuel filter baskets, too. Also check the torques on everything. When I got this caterham, all the internal jets were rattling around and leaking. Well, the whole car was rattling around and leaking - 3 years into the rebuild and it's almost safe, lol.
Good luck!
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