Hydraulic lock?

[setho]

Apparently my 2.7L engine is suffering from hydraulic lock when sitting for a couple of days. I guess the Webers are leaking bad enough to cause it.

I'm not too familiar with the Webers yet. Is this a design flaw, or is something specific worn that needs fixing?

Thanks for any help in advance.

Seth

[edmayo]

After you turn off the engine look down the carb throats and see if fuel is running out somewhere.

[1QuickS]

Fuel will drain from the float wells into the cylinders if the idle air bleed jet is blocked with crud or by a gasket that does not have the "chad" punched out. The idle air bleed allows air to be mixed with the fuel delivered to the idle jet and when the engine is shut down the air coming through the idle air bleed "breaks" the siphon action that otherwise will occur; since the progression holes and the idle mixture screw hole are below the level of the fuel bowl the siphon will drain the fuel bowl into the cylinder.

Crud can get past seals in your air cleaner housing or you can suck crud from rust inside your cleaner housing. There are other sources of rust as well, the vent pipes in the top covers of the throttle bodies will rust and drop flakes into your fuel well but these rust particles won't block your idle air bleed jet.

To check for blockage you must remove the top cover and check the bleed hole for blockage either with crud or by the gasket; typical hole diameter is 1.1mm for IDA carbs. You can use some 20 pound test mono-filament fishing line or other fine wire to check for a clear hole.

Picture shows one of three of these idle air bleed jets in the top of each throttle body just inboard of the idle jet holder (not shown).

[Haasman]

Paul,

Thanks for that thorough answer. Had no idea.

Haasman

[setho]

Many thanks Paul! Incredibly informative.

[1QuickS]

Thank you!

There are a couple of other possibilities:

1. If fuel "percolates" due to heat soaking after shut down and "anti-percolation" holes are drilled into the top cover then fuel could escape the fuel bowl and be directed down the barrels; evaporation would be slow since the throttle plates are closed so you could hydrolock in that fashion. A long period between driving would allow fuel to drain into the oil past the rings.
2. If the fuel pump is allowed to run before cranking then a sticking float or a faulty needle valve for the float would allow flooding of the fuel bowl (which was probably close to full from the last time the engine was run) which would then flood the cylinder via the main circuit.

[sithot]

Here is a bad case of hydro-lock. I've heard of "flood" engines doing this very thing. Water doesn't compress very well at all.

Tom

[M_deJong]

Is there really enough fuel in the float bowls to fill a cylinder? Wouldn't it leak out past the rings or exhaust valve after a few days?

I did hydro lock a cis engine once when I did't realize the metering plunger was stuck in the wide open position...

[1QuickS]

You don't need to fill the cylinder, just fill enough to prevent engine from going past TDC.

In post #6 I did mention that draining past rings would occur after some time.

[M_deJong]

Thanks Paul. I overlooked that the combustion chamber is pretty small at TDC.