Weber help!

[trekkor]

My one Weber triple does something strange and I can't figure it out.

Hot or cold it does the same thing.
After I shut off the motor the float bowl completely empties itself into the #3 cylinder. #3 and #2 share a common bowl, BTW, but #2 is not effected. It's never been any cylinder but #3.

If the motor stops with the intake valve open, the motor hydrolocks when I try to start it. I have to pull out the spark plug, clear the gas before it will crank.

Isn't it possible to bend a rod or something else serious due to hydrolock?

The only thing I can do to prevent the problem is to immediately drain the float bowl into a catch can when I shut off the motor. ( Which is a huge hassle )

What could be causing this?


KT

[BReyes]

First thing comes to mind to me, but I just ordered 4 new replacement floats from PMO.

Have you ever removed the top (lil 8 mm nuts) off your carb. Think you will find one of your floats has corroded and fuel has leaked into it, sinking it to leave needle valve open? Fuel pump still running?

Regards,

[trekkor]

Just rebuilt them.

This problem has plagued me for years, now.
It's hard to tell where the fuel is coming from. ( accel jet, aux vent or elsewhere? )

Floats looks fine. Float level is low if anything. ( I have them set to lower limit line on PMO sight vials ) Fuel pressure is 3.5-4 psi. Pump only runs when ignition is on.


KT

[BReyes]

Then, how about heat soak? Have you put on the phenol plates?

[trekkor]

Yeah, I have the heat spacers, but it does this hot or cold.
Yesterday, I rolled off the trailer early in the morning and drove to my spot.
Didn't even warm up the car.

When I went to start, CLUNK!

Scratchin' my head here.



KT

[kucharskimb]

Are you running a high pressure pump? If so, are you running a return line? I wouldn't think residual line pressure would be a problem, but maybe.

At one point, I had a problem with one of the squirter (accel nozzle) check valves sticking. Additionally, one of the needle and seats for the corresponding float got stuck after draining a float bowl. The result was a steady stream of fuel pouring out of the accel nozzle. But that happened immediately when the fuel pump was charged. I did learn my lesson that when refilling the float bowl, I had to do it in short bursts of the fuel pump so as not to wedge the needle/seats wide open.

If this problem happens warm or cold, couldn't you trouble shoot by taking off the left carb, hooking up a length of fuel hose, and then running your pump to bench test the carb. You should be able to see where it is leaking from. I'm guessing the problem exists even if you don't run the car, but energize the pump?...

I had a problem with the percolation and slightly high float levels sucking all of the fuel out when hot, but this doesn't seem to be your problem. Although any heat produced in the head flows straight up the manifold...

Keep us updated with any progress.

[rsscotty]

I've seen this only once in many years. It was a bad needle valve.

[Fishcop]

KT, if you've rebuilt them and this is an ongoing problem then I think you may want to have a close look at the floats to be super sure one doesn't have a leak. Can you also confirm the needle valves are working? (I've bought a brand new one that was faulty before).

Cheers

[trekkor]

Low pressure Holley Red pump with Holley one-in, two-out regulator.

Yes, a bench test is in order.

I thought about swapping the accel jets from #3 to #1 and see if the problem follows.


KT

[trekkor]

I just replaced the needle valves with the rebuild. It did it before, though.

Looks like it needs to come apart for a closer look.


KT

[Fishcop]

I note you have the PMO sight tool - how are the bowl levels when the car is running? I'm wondering if one of your floats has a tab bent too far that is holding the needle valve open at stop? I can't help but think something is holding a needle valve open... The PMO tool should tell you something when you cut the engine too.

[trekkor]

I did the check while running- low limit line.

After I shut if off, the level drops as the bowl empties into #3, but not shared#2.


KT

[Fishcop]

Can you quickly swap your needle valves around on that carb? Lets rule them out...

[trekkor]

I could, but this symptom happened on the last set as well a month ago.

And again, why only cyl #3 and not #2 ?!? It's crazy.


KT

[trekkor]

Oh and BTW, it gurgles, hisses and the one barrel fills with fine mist...


KT

[Fishcop]

Yeah, that's got me stumped also...

[trekkor]

:sips beer:


KT

[FPB111]

Float needles keep the fuel out of the float bowl. Once it is in there they would not keep it in unless you put it on it's roof, well probably not even then.
How do you keep #3 from running rich?
Bad seal at the main jet or emulsion tube for #3.
Maybe it has a porous carb-body casting by #3? It may be possible to seal the casting with "Kreem” or other suitable tank sealer? How could we test for that? Mount your leak down tester & pressurize #3 with the intake valve cracked open. Look/listen for air in the float chamber. Can anyone think of a way to seal the bypass circuit? Would closing the idle screw seal the bypass? Would we then get air leakage through the mains or emulsion tubes? Well it sounded simple at first.
Maybe pull the floats, to keep them from pressure damage, and then pressurize from the fuel inlet and see where the leak is?
Webbers were prone to casting problems. I think I remember when Richard Parr (PMO) was selling Webbers he had some kind of disclaimer that included tearing down your new carbs to inspect for junk and imperfections before you mounted them on your engine.

[trekkor]

You might be on to something here.

I'll have to look very closely.
Finding a way to use compressed air might work.

thanks!


KT

[FPB111]

You are welcome, I hope it helps.