Weird Weber behavior, any ideas?

[cstreit]

A friend of mine called me about a weird weber problem he's having.... I mulled it over and can't come up with a definitive theory. The carbs were recently rebuilt by a california outfit.

All jets, air correctors and emulsion tubes are the same and are installed correctly.

His 456 bank of cylinders only has #5 running. 4 and 6 are getting plenty of spark, but appear to be drowning in fuel. My only thought is if BOTH float bowls are overfilling and dumping raw fuel into the carbs this would do it. I can't find any indication in my weber book if the float bowls drain into all the floats, or just 4 and 6. Seems odd that they'd BOTH by off though..

THeories?

[jwetering]

IIRC, one bowl feed #4 and #5, and the other feeds the accelerator pump and #6. Either that or it's one bowl feeds #4 and the accelerator pump, and #5 and #6.

Either way you are right. If 4 and 6 are drowning due to a fault in the float bowl, then both bowls are failling.

[cstreit]

One bowl feeds 4, the other feeds 5 and 6 from what I remember

[jpnovak]

Yes, 4 feeds off the front bowl. 5&6 from the rear bowl. I suspect that the float levels are incorrectly set. Maybe the rebuilder forgot to put jets in the idle carriers. Highly unlikely unless its MM. Did they forget to put the float bowl valves in place on that bank?

the accel pumps are all fed from the front bowl. There is really no way that the fuel would spill over from this circuit. Is the linkage incorrectly set? This could cause the butterflies to stay open and inject a bit more fuel.

Are the air bleed screws set the same on each bank? I usually start all with 1.5 turns out.

[Eagledriver]

When you say drowning do you mean you can see the fuel going out of the Main circuit? I had a stuck float once and you could see the fuel running out of the center venturi thingy where the fuel comes out on the main circuit. If that's not it then maybe something is wrong on the idle circuit. Do the needle valves look ok?

It doesn't take long to pull the top off the carb and see how high the float level is.

-Andy

[cstreit]

So I had them check that all jets were in place when they called, that the needle valves weren't bent and that the accel-pump wasn't mis-adjusted. Still thinking floats myself but I'll check back with them.It wasn't MM but other than that I'm not sure

The plugs were soaked and they were mopping up gas underneath the car with papertowels apparently! That's why I'm thinking floats where else would so much come from you know?

Thanks for the ideas.

[RoninLB]

Originally posted by cstreit

The carbs were recently rebuilt by a california outfit.

fwiw... anytime I receive carbs in the mail I reset the floats. They are always imperfect. I figure it's the shipping not the mfg.

[lateapex911]

Originally posted by cstreit

The plugs were soaked and they were mopping up gas underneath the car with papertowels apparently! That's why I'm thinking floats where else would so much come from you know?

Thanks for the ideas.

Mopping up gas?? Wow..that has to be more than a bad jet choice, LOL.

Gotta be the float needle seat ...I have grose jets and they often do that after transporting.

Bad for the cylinders...

[cstreit]

Indeed.... Figured the consensus would be floats which I told 'em to check.... Thanks for the input...

[911pcars]

Chris,
There are a couple of ways to check float level. Not sure what method your shop uses, but just to be sure.

One method uses a strict mechanical measurement using the factory jigs with the top of the carb. removed. This is okay for an approximate setting, but doesn't include the effect fuel has on the actual bouyancy of the float.

The other method uses the external sight glass tool attached to the side of the float bowl. This allows you to observe the actual fuel level while the engine runs.

I assume the latter method is being used?

However, as Andy (Eagledriver) suggests, if the fuel level is too high, you should see fuel spilling into the venturi via the main discharge nozzle during idle and off-idle (not normal).

Mopping excess gas under the car seems like more than a high float level. No external fuel supply leaks? Once upon a time, one of my float pivot pins loosened and fell off after a rebuild (forgot to safety wire). The now unchecked fuel flow filled the carb throats. With the throttle plates open, liquid fuel dumps into the cylinder. With the TP closed, fuel backs up in the carb throat and overflows into air filter housing and onto the engine. Oil level too high as well? Does that sound similar?

Sherwood

[lateapex911]

Yeah, I'm trying to figure out how they have gas hitting the ground and they can't figure out the source! It's usually VERY obvious at that point, LOL.

Somthing is seriously amiss in any case.

[cstreit]

So they did check that the floats were properly installed (took the tops off) and they gas level in the bowls seemed approximately right when they looked... Curiouser and curiouser!

[RoninLB]

Originally posted by lateapex911


Yeah, I'm trying to figure out how they have gas hitting the ground and they can't figure out the source! It's usually VERY obvious at that point, LOL.

a bad carb regulator gasket could leak to the ground and start a fire. For the past 20yrs I haven't trusted those $20 Holley regs since the fuel has gotten so chemicalized. Somewhat recently at the Mallory talk info site someone mentioned that the old generation reg gaskets can be weakened by the new gas over time.


anyway while I'm on a roll some more carb bs
I'm 1/2 way home from outside L Erie. It's been 3-5k mi since I was playing with the carbs. In the middle of never never land at speed + 5-10 my engine starts missing. Didn't die but was ready to konk out. Played with the pedal and figured it was fuel flooding and not leaning. If I down shifted to 4th and kept the revs around 3.5 it would run very rich but good enough to keep the plugs clean. I wanted to drive it home like this. I was slowly loosing plugs after 20mi. I hit a rest stop and see thru the glass that on one side both glass was flooded. 15min later I figure it's safer to limp to the next town and find a safe place to operate. Operation complete. It was my fault at last carb opening.

the point is that with 3 venturis flooding bad I was still able to drive.

[cstreit]

The gas is coming out of the exhaust joints (multi-part racing headers)... It's flooding #4 and #6 cylinders completely so they will not fire. #5 is working fine.

I told them to get a long length of fuel hose and pressurize the carb with fuel on the bench so they could see what is happening. The leak is not external to the carb, that we know...

[lateapex911]

Hmmm.

Well, if it isn't something obvious like the float situation, and gas is leaking out the exhaust...

then you are right...get it off the car and on the bench. Perhaps there is a problem with a mating surface internally? A folded or missing gasket or o-ring could be allowing gas to basicallly leak inot the intake, regardless of float level and jets etc.

It's just back from service, right? I had the same issue with a race carb I got once...spent 4 hours dorking with it on a picnic bench at the track. (That wood won't rot anytime soon... )

[RoninLB]

maybe some parts are missing inside the carb ?

[cstreit]

Nothing obvious they say. I think it's going back to the rebuilder... Unfortunately it'll cost them an event...

[john70t]

Also check the fuel pressure while running. Should be 3.5lbs. (I think) and an adjustable pressure regulator is easy insurance.
I rebuilt with a bad kit and the needles didn't seat at all(nor did most parts fit).