Weber problem

gmiles · 12-20-2004, 05:43 PM

Why does the #4 barrel on my Webers fill with gas then the engine is off? I have pulled the carbs a few times to fix minor issues and this was one of them. Yesterday and today I was trying to dial them in. I noticed that on the #4 barrel when the engine was shut off, the throat would fill with gas. The throttle plate is closed and gas fills up on top of it. It's not dripping from the accelerator pump nozzle and it's not dripping from the venturi thingie in the middle of the carb. It's also not coming from the high rpm enriching circuit (S Carbs). The only thing I can think of is maybe the progression holes? But why? Fuel pressure is below 3.5 psi. The needle valves are new and move freely. Maybe a teaspoon of gas,total

gmiles · 12-20-2004, 06:15 PM

If it's heat related, then why only one barrell?

911scmedic · 12-21-2004, 02:33 PM

Had the same problem and I assume, when you say the #4 barrel that your talking about (as you face the front of the car) Right side front throat? Mine filled the throat at shut-down and cause condesation on the intake manifold. (I already have the insulators inplace) My solution was the adjustment of the float height (its was too high) for that front bowl. PMO and Redline sell indexing washers for the needle valve. If you do this indexing on the bench or in the car, both PMO and Pelican sell the float height gauge. It's pretty straight forward, other then removing all the nuts to remove the carb cover and doing this several times until it's right.

gmiles · 12-21-2004, 05:21 PM

According to my books, the needle valve should hang 18mm below the base of the carb top. Is it 18mm with the valve fully extended? Or is it 18mm to the base of the housing for the needle valve and the little ball actually hangs down farther, giving some slack for the float to take up. When I set them, I turned the tops upside down and measured from the bottom of the little ball that sticks out of the needle vavle, so with the vavle "closed" under it's own weight it was 18mm. I figured that the float level was 18mm below the edge of the carb and that it probably coincided with the closing point of the needle valve. At 18mm, the float is pretty high. 12mm above carb body, per my books.

So the way I set them up, if I let them hang, it's probably closer to 22mm, so the float will come into contact sooner and close sooner? Meaning low float setting?

Fishcop · Fishcop's Garage

911scmedic has called it right. The rear most bowl only supplies one throat where as the front bowl supplies two.

Don't try and adjust by measuring the needle as the other variable is the bend on the tab of the float itself. Do yourself a favour and get the float measuring tool - this will allow you to adjust the float without removing the carb or the top-plate. Simply shim the float with the supplied washers until the meniscus on the tool is between the top two lines.

Cheers

gmiles · 12-21-2004, 06:51 PM

I'll try the float gauge. The float is supposed to be measured two ways, and I thought I had them set right. Apparently not.Thanks for all the help, past and future.

gmiles

jmz · jmz's Garage

stuck needle & seat maybe

campbellcj · 12-21-2004, 06:58 PM

I had this problem recently when the needle valves clogged with junk. We had just finished redoing the entire fuel system and a tiny bit of AN-fitting sealant (or something else?) was already past BOTH fuel filters and found its way into a cozy little spot inside the needle, effectively jamming it open!

Scary to see a barrel full of gas like that, esp. when it's right over a hot exhaust :O

The needles are easy to check but IIRC you need a 16mm 5pt socket to have the best success on the shallow brass plugs they hide under.

Nitrometano · Nitrometano's Garage

Check needle valves. That is the only device that controls the fuel input.

gmiles · 12-23-2004, 08:06 PM

stuck needle and seat it was. the rubber line had deteriorated and some had gotten stuck. also, i spent 2 days trying to dial in the carbs. I got the right bank to dialed in, then still had problems so I rebuilt them. Then I got the left dialed in but not the right. WHAT I LEARNED: make sure the idle adjust screw is set low enough that the mixture screws actually do something to the idle. The first time, the left bank was idling too high and the mixture screws had no effect----idle was high enough to encompass progression holes----I had problems on each side until I figured that out. runs great now.