Carburetor Blues

[ejay]

So I removed my carb and took it apart to figure out if there was a problem with the float system that was allowing too much fuel. The floats, needle and seat looked great, which is not surprising because mine is a 2020 built carburetor.

I put the carb back in place and the motor ran great! I tuned the idle to a smooth 800 rpm and I was really in a happy place. The engine started and restarted like a champ.

A few hours later, I went to start it again and the same problem raised its ugly head. No ignition due to pooling of fuel in the carb, which I can see when I take off the flame arrestor. So I must have either a fuel pump problem or a carburetor float problem, because fuel is overloading the floats and spilling into the throat somehow. Any sage advice?

EJ
1978 Cat 30

[ndutton]

What fuel pump do you have?

[Dave Neptune]

Is the scavenge tube clear and in place?

How many "turns" is the idle air screw out off the seat?

Did you set the float level and if so to what clearance?

An "easy quick starting A-4" is usually indicative of an over rich condition. An "updraft intake system" requires choking and more than a few seconds to start. Sounds counterintuitive but true.

Dave Neptune

[ejay]

I have a facet electric fuel pump which clicks nicely when the ignition is on. I spent some time with the idle so that the engine runs well at 800 RPM, but perhaps I need to tighten the idle screw?

[ejay]

Is the scavenge tube clear and in place?

How many "turns" is the idle air screw out off the seat?

Did you set the float level and if so to what clearance?

An "easy quick starting A-4" is usually indicative of an over rich condition. An "updraft intake system" requires choking and more than a few seconds to start. Sounds counterintuitive but true.

Dave Neptune

I did not check the scavenge tube patency when I had the carb off, unfortunately.

I dont know about the idle screw, but I guess I could tighten it

The floats and needle looked great with the float parrallel to the body. I did not remove the seat however because it requires a large slotted screwdriver which I did not have on hand.

[ndutton]

What model # Facet do you have? Looking to cross reference the # to psi output.

[Dave Neptune]

My reference to the idle screw is for info only. The screw "averages about 1 1/2 turns off of the seat. Some engines like a bit more fuel and run about a quarter turn further in and some at a quarter turn further out or leaner. The screw adjusts air into the idle stream not fuel.

Is the scavenge tube "clear and installed"?

Did you check or set the float level to be sure it is in the stock position?

Dave Neptune

[ejay]

I spoke with MMI today and the PO bought and likely installed a Catalina specific facet pump which has a higher PSI. Why would my Cat 30 need a higher PSI, and could that be the problem? Could the higher PSI be forcing fuel past the float needle?

I did make sure the float was set correctly and the needle and seat were both clean.

[Dave Neptune]

The higher pressure required for the Cat 30 is due to the longer run from the tank. The higher PSI is no where near enough to force the needle off the seat.

Check the turns off the seat for the idle adjust screw so we know where it is.

You may have a compromised float IE a pin hole allowing the float to fill and causing it to sink and the fuel level to be to high. This is a rare scenario. You can shake the float to see if there is any fuel in it.

Is the fuel leaking while running or only when shut down?

If the carb is running to rich it will allow fuel to stick to the manifold while running and the excess can run back down when the engine is shut off. I suggest you take a good look at the plugs to see that they are a "beige to brown in color" not blackened and/or wet.

Did you use a "new" gasket and NOT the old one?

Dave Neptune

[ejay]

The engine runs fine, so I thought this was just a starting issue. ALthough the prior owner always complained of a gas smell after shut off.

I put new plugs in last November and they are already darkly colored.

The floats looked fine when I examined them the other day, with no apparent fluid shaking inside. The needle and seat looked great too, although I did not remove the seat.

If the pump is not the issue, then perhaps I should just replace the floats, needle and seat?

I will get a new gasket too, because I did reuse the old one.

[ejay]

From previous posts, you might remember that I thought I had a water incursion problem because the most aft plug (#4?) was always wet. Perhaps that was excess fuel?

[Dave Neptune]

Ejay, the dark plugs mean your way to rich and perhaps a timing issue as well.

Rather than going back and forth shoot me a PM and I will give you my number or send me yours. A little conversation goes a long way.

Dave Neptune

[Indy]

Did this get resolved? Just interested in knowing what the solution was 😊.

[ejay]

Here is an update.

I took the carb off and cleaned thoroughly..... again. This time I used new gaskets, copious amounts of carb cleaner and compressed air and a new float needle and seat. After reinstalling, the engine still would not start, but I was able to observe the main jet with the fuel pump running, and I could not see any fuel excess, therefore I am going to conclude that the floats are good and that the fuel pump is not overpowering the needle and seat.

Any excess fuel that I noticed in the throat of the carb I believe is dripping back down into the carb after prolonged, unsuccessful cranking in an updraft carburetor. Does that make sense?

I now think the root of my problem was a water incursion into the cylinders which prevented the engine from starting suddenly after previous normal operation.

[Dave Neptune]

Any moisture in the cylinders will be a no start or at least a really tough one. Did you try a shot of starting fluid?

Take a look at the plugs to see if they are wet, a sniff or taste will let you know if it is water. Did you close the water valve while cranking?

And yes after prolonged cranking some fuel can run back down from the manifold.

Dave Neptune