Identifying Carb issue?

[CRUX]

Hi All,

My situation is as follows...

Engine starts first time-every time with full choke and 1/4 throttle when it's the first start of the day and the engine is cold. Runs perfectly.

If I run the engine, then restart within 1 hour of running, it will start first time- every time with NO CHOKE and 1/4 throttle.

Now here is the issue. If I run the motor, then try to restart 2-8 hours later, it will only start with NO CHOKE and throttle WIDE OPEN, and it takes anywhere from 2-8 cranks. It will take 10-15 seconds to catch and stabilize the Rpms. Then once again runs perfectly.

To me these symptoms seem like it is flooded, since it will only start with the throttle wide open, then take a few seconds to clear the gas and run smoothly.

There is gasoline pooling in throat of carb, so I replaced the replaced the float valve assembly, including the dowel trick. I have also made sure that the float is level as described in other posts. Additionally, I have made sure that the choke is functioning properly as well.

Any advice?

Thanks in advance!

[W2ET]

Running rich?

How do the plugs look?

Bill

[Al Schober]

Gas in the throat of the carb is not a good sign.
Did you happen to check the float when you had things apart. Perhaps one chamber is flooded? It's easy to check the float for pin holes by putting it in warm water and looking for bubbles.

[CRUX]

Plugs are slightly fouled, nothing out of the ordinary for the length of time that I run the engine. I have also leaned out the idle significantly, so not sure if it is running rich.

I did not check the float for leaks, I have a float from an old carb that I can check for leaks and replace the current one with that if you think that could be the issue.

[Dave Neptune]

Crux, as well as checking the floats for a hole be sure of the float setting. I would also check to see that the scavenge tube is clear to insure proper function. What height are you setting the floats at?

A properly calibrated carb should require the choke for most starting situations except for "immediate" restarts after stalling. In most starting situations the choke should be required or you are just plain ole to rich!

As far as the plugs inspect them for moisture too. A good looking plug should be a creamy beige color and dry.

Dave Neptune

[ndutton]

Apologies for even asking the question but which way are you turning the idle mixture adjustment screw to lean it out?

[CRUX]

The float is set to be parallel with the carb body when it's upside down. I would consider it perfectly level.

I am backing the idle mixture screw out as I am making it leaner.

I will check that the scavenge tube is clear, along with checking the float for any leaks.

The carb is question is approx 3 years old, I have very clean fuel, and there was no signs of any debris, crud, or any other signs of dirty fuel or a clogged carb when I took apart last week.

[Dave Neptune]

Crux, when re-assembling the carb "top" be sure that the tube rising out of the bowl ABSOLUTELY seals with the gasket!!

When you take her apart look at the center area of the gasket and you should see a dimple that should be a full circle. If it is not a full circle it will really make things bad as there will not be any ariation of the fuel being delivered to the venturi which can cause "puddling" in the manifold. this raw fuel will then drain down to the carb once the engine stops. The center piece is the "emulsion well", thew heart and soul of the carb's metering!

Dave Neptune

[CRUX]

Thanks Dave, having a hard time picturing it without the carb in front of me but I will look into that!

If this dimple hole is not a perfect circle as you are saying, should I use a hole-punch, etc. to create this hole?

[Dave Neptune]

The dimple in the gasket means that it was being sealed by the gasket. In some cases a warped top half will make this "sealing" problematic.

Dave Neptune

[ndutton]

I am backing the idle mixture screw out as I am making it leaner.

Thanks, I had to ask. You'd be amazed how many get it backwards.

BTW, your carb setup sounds way rich to me. Something's not right.

[indigo]

Valve Seat

Have you per chance removed the needle valve seat? If so, did you replace the gasket between the valve seat and the carb body? My experience with that gasket is that it is good for one use only. After that, it will most likely leak and lead to a too high fuel level in the carb.

Don’t ask how I know this.

Tom Stevens

[CRUX]

Indigo, yes I have replaced the needle valve, the seat and the gasket.

[CRUX]

Update:

I leaned out the idle mixture as lean as she would run reliably. Smooth at 600 rpms. Immediate throttle response all the way up to 2400 rpms in gear. Still a ton of gasoline pooling in the carb throat overnight.


I removed the carb for the third time to continue troubleshooting based on everyone's responses. Double checked the following...

- Scavenge tube is clear of any restrictions
- Gasket looks to make a very good seal
- Changed out the float to one that I tested for pin-holes (all sealed)
- Float is set parallel to carb body when holding upside down
- New float valve assembly that I replaced last week looks perfect as well
- Choke is operating perfectly, closing and opening fully
- Spark plugs are dry, beige color as mentioned they should be, slightly fouled.

Not sure what to do from here, as I have tried all the obvious things. This pooling of gas seems like it MUST be the float valve as the gas must be passing through there? But that has been replaced, burnished with the dowel, etc.

Any more ideas?

Goes without saying, thank you for your help.

[edwardc]

At this point, it seems pretty clear that something must be keeping the float valve from closing properly. I see the list as:

1. Leaky float body
2. Worn needle valve seat
3. Worn needle valve tip
4. Incorrect float height adjustment
5. Dirt in fuel keeping valve from sealing
6. Fuel pressure too high
7. Float binding on something
8. Incorrect float and/or needle for carb model

You've already eliminated 1-4.

To test 5, you should try to run clean new fuel from a portable tank, with a new A1 rated fuel hose straight to the carb. Placing the tank a few inches above the carb will provide enough pressure for a gravity feed.

For 6, if you have an electric fuel pump, it may be the wrong model, providing too much pressure. This would overwhelm the needle valve and cause a limited amount of gas to overflow after stopping until the pressure bled down, instead of dripping continuously. This seems to match your observations. A pressure gauge right at the carb will tell if this is it.

7 is getting to the "grasping at straws" category. Check for excess gasket material protruding into the float bowl. Another possible cause of binding might be the little spring clip on the float end of the needle. You don't really need it and can leave it out upon reassembly.

8: Is it possible you have a slightly different Zenith carb model than the rest of us, and the float doesn't fit it properly? (beyond grasping at straws!)