M74 Carb From Hell

[pkmcgee]

Hi all,

Just discovered this forum and really enjoy the wealth of information here. I'm one who will be learning more than sharing any wisdom, but I guess it takes both to make this work.

I've got problems with the M74 on my stock 65 Electraglide. When the petcock is open the carb leaks like crazy - a constant drip. I took it off and removed the bowl to test the float and needle valve. I attached the bowl to the gas line and it did exactly what it's supposed to do. It's the brass type, but it did it's thing. The gas level rose until the valve closed and it stopped. Dead. It is set at about 1/4" which according to my shop manual is about right. I put double gaskets on it just in case the plane of the bowl and and the carb were a bit off.

When I put it back on, it leaked like crazy again and I swear I could hear it laughing at me.

If anyone can shed some light on what's going on, I'll dance at your wedding. Is it possible that when the bowl is attached something is binding and affecting the needle valve? The darn carb has been working perfectly for years and then suddenly this.

Patrick

[thsmith]

Welcome to the group. There are many post of this issue, I have a 49 so it may be different but I believe the float is suppose to be cork and adjusted the way you described but for brass I believe the setting is different.

As you search the post you will see that brass floats leak and will sometime not float well causing the fuel shutoff to not work well.

There is a Linkert expert here named Cotten. Search for all his post and you will get it. He makes a float that solves all your float problems.

There is even pictures in the gallary.

Good luck,

Tracy

[thsmith]

Welcome to the group. There are many post of this issue, I have a 49 so it may be different but I believe the float is suppose to be cork and adjusted the way you described but for brass I believe the setting is different.

As you search the post you will see that brass floats leak and will sometime not float well causing the fuel shutoff to not work well.

There is a Linkert expert here named Cotten. Search for all his post and you will get it. He makes a float that solves all your float problems.

There is even pictures in the gallary.

Good luck,

Tracy

[Cotten]

Please be aware that the brass float in this picture:



does NOT have a hole in it!

It was made by Kokesh, which are just boatanchors at 12 grams, that's all.
There are brasses on the market with much better workmanship (made in India), but they still weigh 9 grams, and their "English brass" material is brittle and prone to cracks, as well as even holes from corrosion.

Your Linkert was designed to operate with a very buoyant 3 gram float.
The more buoyant the float, the more pressure maintained upon the valve when shut.

In order to make the brass function at all, it is oversized. This, along with nearly all of its volume below the gas level, robs your bowl of reserve capacity. Reserve is why carbs have bowls.
With a diminished reserve, the main nozzle cannot re-fill quickly after acceleration, thus reducing its effectiveness as the "accelerator pump".
The necessary deep setting reduces how far the valve can open, thus slowing the replenishment of the reduced reserve.
The inertia of the heavy float not only wears quickly upon the lever and pivot, but it's sluggish cycle robs gas mileage.

The common problem of overflowing usually results from two causes. The enlarged diameter of the float is prone to hitting the wall of the bowl when properly offset (If not offset as in the attachment, it can hang up on the bowlstem), and the vibration of the motor 'bounces' the heavy mass enough to keep the valve from staying seated.

Brass floats were thought to be the only alternative when gasoline became so digestive that corks would gas-log, and 'Armstrong" floats would swell.
Please post me direct at liberty@npoint.net for the modern solution. Thanks !

[pkmcgee]

I appreciate the replies. I'll search the posts and probably need to get your float, Cotten. Makes a lot of sense.

[alazlo]

Any thoughts, good or bad, on the Gary Bang rebuild Kits. I just put one in and I am having the problem you describe. I'm okay, all day, at 55 mph but if I run 65 for a mile & a half the float bowel goes dry & it starts coughing... very frustrating al

[Cotten]

Al!

I haven't bothered to see what's in a Tedd kit, but most problems from poor hardware result in flooding, not starving.

How do you know the bowl is dry?
If it re-fills at 55 mph, doesn't it fill at a stop when you pull it off to look??
If it does, I would suspect EML.
(Evil Manifold Leak.)

Beware anyway of rubber-tipped valve needles that swell, and light-colored foam floats that quickly turn into dumplings in P4gas.

If your bowl is truly dry, it sounds much more like a restriction in your fuel lines, filter, or a gascap that is not venting properly.
(Beware that Tedd's repop caps are vented different than OEM, and the gasket will swell and cover the vents. I lost a $700 paint job to that one!)

Good luck!

....Cotten

[pkmcgee]

Cotten,

Got your floats and installed one of them in the M74. Turned the gas on and let the bike sit all afternoon. Not a drop. However, when I started it the flood gates opened wide. I'm going to recheck the float offset to make sure it's not hanging up because the on-again, off-again nature of this leak makes me suspect that might be the culprit now. The needle and seat looked good upon visual inspection, so I don't think that's it necessarily.

Thanks for the floats; I'll install the other on the 48 Indian this weekend.

Patrick

[VintageTwin]

Make sure there's no casting slag in the bowl that can snag an off-set float. Happened to me. Carb would flood. Removing the slag cured the problem.

[Cotten]

The entire bowl assembly can be inspected while removed by turning it upside down and sucking upon the gas inlet. A really good one will stick to your tongue!

Beware (again) of soft tipped floatvalve needles. Their fit within the standpipe of the valve body is tight enough to bind occasionally if the lever geometry is not perfect, making their operation inconsistant.