Ferret Carb

[Steve Mortimer]

Could anyone give me some info on tuning the carb on a Ferret. The carb is new, put on by previous owner but never run. I have set the slow idle metering screws? The two on the bottom back 1 1/4 turn out each, any other settings to be done? I also set up the choke controle and lubed the cable. Also looking for a couple parts, anyone have spares?

[Malcolm Towrie]

Is carb actually new, or a rebuild?

They will usually idle well with the two idle adjust screws out about 1 1/2 turns, if everything else is in good nick (ignition timing, plugs, wires, coil, points, condenser, compression).

You should see the idle speed noticeably drop and get rougher as you turn the screws in to 1-turn out and out to 2-turns out if everything else is OK.

The only other external adjustment is the screw on the throttle lever which raises and lowers the idle rpm.

What problem are you having? Just idle or all through the rev range?

You can find the manual for the carb by googling "solex_40nnipcarb.pdf"

Malcolm

[Steve Mortimer]

The carb has Marcus instead of solex on it so I'm assuming its new. It has never been run since the carb was put on so it was not set up. As far as I know this Ferret hasn't run since the military released it in 2007. What about the altitude adjustment? Does that make much difference in how it runs? Right now I will be happy if I can get it to run for more then 15 seconds.

[Jon Bradshaw]

I have one on my trailer now that seems to idle fine with just the fuel in the carb, but will flood if I add a fuel line. It won't rev up and seems to need some tinkering. Is there a manual that shows step by step what needs to be done to adjust the carb to "factory" or end user settings? I am thinking if there was something that said- set screw #1 back off 1 and a half turns, set screw #2 back off 2 turns..... etc. Robin you may have some thoughts? Lots of experience tuning these....

[Malcolm Towrie]

Originally Posted by Jon Bradshaw

I have one on my trailer now that seems to idle fine with just the fuel in the carb, but will flood if I add a fuel line. It won't rev up and seems to need some tinkering. Is there a manual that shows step by step what needs to be done to adjust the carb to "factory" or end user settings? I am thinking if there was something that said- set screw #1 back off 1 and a half turns, set screw #2 back off 2 turns..... etc. Robin you may have some thoughts? Lots of experience tuning these....

I have linked to the manual above which shows the basic settings.

I found there are a few things that make these carbs run rich or flood.
The fuel needle valve that is closed by the float to maintain a constant level in the carb could be stuck partly open, so when you connect it to a pressurized supply, it passes too much fuel. This can also be because the floats are sticking on the pivot pin. Sometimes tapping the carb gently will free things up.

Someone has adjusted the float level too high. I have found the 3/4" level specified in the manual is a bit too high and the floats can hit the cover gasket before they close the needle valve fully.

If you are using an electric fuel pump in place of the stock mechanical pump, they often supply fuel at far too high a pressure, which overwhelms the needle valve and floods the carb.

Every one of the four or five carbs I have rebuilt has had the accelerator pump diaphragms leaking. I suspect this is an ethanol problem. The leak is directly into the intake manifold and makes the engine run really rich. It also allows the float chamber to drain down overnight. So a good check for this is, after the engine has been shut down for a few hours, look down through the carb with the throttle plates open for a large puddle of fuel sitting below the carb in the manifold.

Malcolm

[Steve Mortimer]

The numbers on the carb are as follows
40NNIP
RE16434
849

The other side has
Marcus
British
Pat'd

[Richard Farrant]

Originally Posted by Steve Mortimer

The carb has Marcus instead of solex on it so I'm assuming its new. It has never been run since the carb was put on so it was not set up. As far as I know this Ferret hasn't run since the military released it in 2007. What about the altitude adjustment? Does that make much difference in how it runs? Right now I will be happy if I can get it to run for more then 15 seconds.

Steve,
As you say a private owner fitted the carb, check it is a 40NNIP and not a 48NNIP. The 48 was for some B81 engines, also the 40NNIP was fitted to 8 cyl engines of certain Marks and jetting would vary between 6 and 8 cylinder engines. If the wrong carb was fitted, this could be the problem.

If you can, make a note of any numbers on the carb and around the base flange (if any) and post them on here.