E28 Carb Jets

[Charles Reese]

In the process of chasing an exasperating slow leak via my carburetor, went through the basic steps (level the float, gaskets, etc.). Satisfied all was okay, moved on to the jets. Doing so, uncovered a dilemma (at least to me)

* Left: Holley (double venturi) lower bowl. Note large end with no solder in the cap jet. Assumed someone had cut off the top, making it shorter and likely the source of my overflow leak. Disassembled, found #19 stamped on the hex, found to be same height at Zenith (sorry, photo is a little misleading due to angle of pix).

* Right: Zenith (single venturi - no number on bowl). Note stepped end and small opening in soldered tip (with slight depression). #20 stamped on hex.

?? Is/should there be a difference in the style (#) of the cap jets (i.e. double vs single venturi)? Don’t have a wire gauge but the Holley jet (left) seems to be a slightly larger orifice than my Zenith (right).

PS: If my Holley cap jet does, in fact, need to be resoldered and sized, can someone suggest such a kindred soul?

[mot]

Charlie
the last photo showing the large opening sure looks wrong to me
ill have to look further to see what the problem is unless someone else pipes in
tom

[johnbuckley]

Charles, Like Mot I agree the orifice on the left looks way too large ... BUT...I have come across cap jets from very early carbs with the sized orifice at the base of the jet.- it may be one of those.
The only way of checking jets are OK is to flow test them - over the years people have enlarged the hole with welding wire so the numbers are often way out. Even the new ones can be incorrect.
A search on this forum will bring up all the causes of a leaking carb.- when trying to locate the site of the leak I find the only way is to use an airline to dry the carb followed by very close observation.

[H. L. Chauvin]

Hi Charles,

Both Mr. Steve Parteger & Mr. Rex Reheis in their carburetor manuals, (sold by Model a vendors), address the required concave tips of main & cap jets to prevent carburetor leaks.

In your lower left photo, one jet tip is properly provided with a concave tip ..... the other cut off tip is incorrect.

The concave tip is provided to counteract fuel capillary action that lessens carburetor fuel seepage & carburetor fuel overflow.

When re-sizing main & cap jets, the concave tip is provided after:

A. Soldering the opening orifice; &,
B. After drilling a new opening in both the main & cap jets with a #61 drill bit; .039" diameter; &,
C. Then a proper concave tip is provided with a #189 Dremel Tool.

Also, the top of the main jet should be 3/64" to 1/8" higher than the top of the cap jet to compensate for the angle or slope of the engine, or actually the slope of the entire drivetrain.

Just hope this helps.

[Charles Reese]

Originally Posted by johnbuckley

I agree the orifice on the left looks way too large ... BUT...I have come across cap jets from very early carbs with the sized orifice at the base of the jet.- it may be one of those.

as the youngsters would say OMG! indeed the orfice on mine is at the bottom end ... who'da thought?

so now, the chase continues

thanks everyone for your patience with my inane questions ... much appreciated

[Tom Wesenberg]

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Charles, my double venturi is just the same as your's, with the orifice at the bottom and an open tube on the top.

[Charles Reese]

is the paper gasket between the carb body halves sufficient, or add sealer?

[johnbuckley]

Originally Posted by Charles Reese

is the paper gasket between the carb body halves sufficient, or add sealer?

No need for sealant,- just clean up the mating surfaces and use the gasket. The fuel level should be well below the joint anyway.
Useful thread here for leaking carb..http://www.fordbarn.com/forum/showthread.php?t=153107

[H. L. Chauvin]

Could be a leaking float valve, hole in your float; however, on the other hand, maybe think of it like this:

1. Get a 50' water hose.
2. Hold both ends of the hose perfectly level.
3. Fill the water hose up to both hose end tops to where you can see water just about to overflow from "both" ends of the hose.
4. Imagine the end of the hose in your left hand is your carburetor jet ...... & the end of your hose in your right hand is connected to the fuel in your carburetor bowl.
5. Now, lower the end of the hose in your left hand, (to replicate a jet that is too short), & see water flowing from the top of the lowered hose.
6. Have another person continue to fill the end of the hose in your right hand which is similar to your "full" carburetor bowl with fuel at a higher level.
7. The hose end in your left hand, (just like the jet), will continue to leak & over flow as long as water is supplied to the end of your hose in your right hand mainly because liquids seek their own level when contained as such.

A. "If" your shut off valve is leaking; and/or,

B. "If" your float valve is leaking, even when parked overnight, your carburetor will continue to siphon & leak fuel all night "if" your jet "is" too short.

C. No carburetor gasket at carburetor halves will stop this leak under these particular circumstances.

[Ron in Quincy]

The Cap Jets in the early Holley and Zenith Double Venturi Carburetors had the orfice at the bottom of the Jet.

Ron