Carb Flooding engine

One of my carbs floods so badly that fuel comes out the exhaust and runs out the pipe to muffler joint. The bike starts easily but that plug gets fouled with fuel almost immediately. I have read every post I can find and need clarification on the float gasket and pin interface. I have a 1974 Commando.

I rebuilt my low mileage original carbs, replacing all the seals, the float needle with aluminum viton ones, new gaskets, and adjustable floats. One carb works great but the other floods. I have removed the bowl numerous times and to no avail. I checked for debris and have even put the bowl assembly in a jig on my bench hooked to a gas line and the needle seals fine. I hold the ends of the float pin down with my fingers over the gasket. Also checked the float height and main needle.

Many have commented that the float can get hung in the gasket. The pieces of the gasket above the ends of the float pin do cover the pin more than on the old gaskets that covered the pin only about 25%. I replaced the new gasket with the old one and still the flooding. Before I start cutting on the new gasket and maybe ruining it I have this question. It seems to me that the float rotates on the pin instead of the pin itself rotating. Is the gasket supposed to hold the ends down so they do not rise up from the bowl and negate the pivot point.

I appreciate help.

I believe the gasket should hold the pin down.

Does this problem happen when the engine is stopped?

It’ll be yourself who finds or works out what is stopping your float valve closing, but the gasket is a likely candidate.

How does your oil smell....

Don't run your bike until you fix this.

Daft suggestion (my forte ) Is the float 100% sealed? Usual test is to immerse them in warm water to check for air leaks...

A simple test would be to check weight of both floats. Then changing the floats. If problem moves to the other side, you have an answer.

I don't know anything, but have battled a recalcitrant holed float in the past which would drain itself dry by the time I could get it out. Took me a good while to catch it in the act of filling/sinking on the bench. It wasn't an Amal but rather a carb off a Briggs..... still got the float as a reminder.

If you swap the float bowls, does the fault move to the other carb?

I have a float bowl that passes fuel past the outside of the brass seat that the float needle sits in.

You said you have adjustable floats - in other words StayUp floats? If so, they are not the problem - the seat/float needle/float height or gasket are the problem.

Thanks for the comments.

I have brand new Stay Up Floats and it had no gas in it when I took the bowl off. I will check to make sure that there is no gap around the seat but think it would have shown up in the bench test. I used alcohol and injected it in the line until the needle closed at its seat. Even with a head of liquid no more came in.

It seems to stop when the bike is shut down. I stick my finger in the horn and cannot feel gas leaking up the main jet. Note that the tickler works normally. Gas will spurt but then stop immediately when I let go of it. Therefore it seems like the float is up as it should be.

I have looked the gasket thoroughly and I cannot see where it could interfere even by wiggling the float to each side. Since the gasket issue keeps coming up it there a specific area that is common for the interference?

If it only happens when the engine is running, that’s different.

Sometimes engine vibration makes a float valve let fuel through.

the floats may not be the problem, but it's a good idea to rule them out. I check by immersing in water and checking for air bubbles. If no air escapes, you can move to step 2, checking the float height. For Amals, https://www.classicbritishspares.com/blogs/news/amal-concentric-float-height

If it only leaks when riding, it's probably a float height problem

Other than what's been suggested, have you looked at the tickler pin? If it is set too long, it may be holding the float valve open and giving the flooding. It is a roll pin with the lower end flared...should be easy to re-position as needed. Try testing with whole carb on bench and fluid/fuel filled.

Did you do anything to clean up the bushing that the float valve needle seats on? A good tip I found was to grab a q-tip cotton swap (even an unused COVID-19 Testing kit swab can work ;-) and dip it in a bit of Autosol metal polish, fit it in a drill chuck and polish the seating surface with the drill. Cleans up very well, ensures not crust down there.

Checked the tickler with the bowl off and it does not protrude.

I cleaned the seat exactly as you recommend with drill and Autosol. Maybe it was an old post of yours where I saw the idea. Worked well.

I think I am going to swap the bowls along with the respective floats to narrow down the search.

I checked the float height using the link that TomU provided and by using the upside down technique it seems that the float is set too high as supplied. I had previously set the height as soon as the float raised enough to let the needle touch the seat. Although that sealed with the small amount of fluid head in my jig, I realize now that the float was not high enough to actually hold the float down due to the slop in the needle groove where the float prong goes. I will adjust and advise. Thank you for all your input.

If a carb floods while the engine is running, it might be touching the frame or a bolt. Vibration can bounce the float and cause the needle to come off it's seat when the motor is running.

I have had the inside rim of the gasket foul the float after tickling, holding it down so the bowl overflows. Trimming the insides on the rounded edge about 2:30 in the clock (flat side at 12:00) fixed the issue.

Put the bowl on the bench with the float in and the gasket on the bowl, drop the bowl screws down into their holes to center the gasket. While holding the needle closed, see if you can move the gasket laterally to foul the float.

Well the new stay up floats were too high as supplied so I adjusted both and the right carb still flooded. I then swapped the bowls with their respective floats and gaskets and the right still floods. Therefore it seems that the problem is in the carb and not the bowl. The gas is overflowing the tickler even when the bike is not running seeming to indicate a float needle valve not sealing. However this bowl was fine on the other carb. I checked the tickler to make sure it was retracting when I had the bowl off and cannot think of anything ese on the carb that could affect the bowl.

Try switching the ticklers. Don't interchange components.

Lineslinger said:

Try switching the ticklers. Don't interchange components.

Click to expand...

I carefully peen the float pins bowl slots to hold the pins home in their slots.
Yes I too feel that as supplied the floats ride a bit too high. I bend the metal tabs a tiny bit to lower the stay ups a very small amount.

Well I think I found the problem. I removed the carb and found that the main needle clip had broken and the needle was stuck high up. The movement of the slide has scratched it thoroughly so I will need a new one. Thanks to all of you for your help.