Calling all carburetor experts: Flooding problem

1880 Views 7 Replies 4 Participants Last post by RT, Jul 19, 1999

RT

Discussion Starter · Jul 18, 1999

The 2 bbl rochester on my '69 Malibu 350 is giving me fits. I removed the carb nd rebuilt it, followed the instructions to make all necessary adjustments. Reinstalled, it starts flooding after the engine is shut off. I mean fuel POURS out of the small holes above the throttle plates particularly on the driver's side, runs over the closed plates, out the throttle shaft and onto the intake manifold where it forms puddles. I've checked and re-checked the float level (3/4") and float drop (1-3/4"). The needle and seat is new, no dirt blocking it. One thing that I'm wondering about is the power valve. The small plunger in the center is contacted by a long spring loaded rod called the power piston. It seems like the force of the piston spring would push the rod down onto the power valve plunger which would allow fuel from the bowl to run into the venturi's. Does anyone know what could be causing this problem?
Thanks for your help,
Rich

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Tom Mobley

· #2 · Jul 18, 1999

RT,
Sounds like you've got the wrong gasket between the main body and the baseplate or under the cluster. Better have a look-see here. The power valve being open will not cause this, they've sat around open on millions of cars for decades. The fuel that goes through the main jets and/or power valve at the bottom of the fuel bowl has to go up a well that has an air bleed at the top that also acts as a siphon-breaker before going back down another well to the idle discharge. They're made this way so the bowl won't run dry every time you turn the car off. This is not unique to this carb, all conventional carbs are made this way.

Are the "holes" you mentioned actually the idle transfer slots? These are vertical slots that are partly above and partly below the throttle plates when the plates are closed. The idle feed holes are below the plates at idle, you shouldn't be able to see them without opening the throttle.

If your idle air bleeds are blocked for any reason or by any means, then you can get a siphoning condition that will drain the bowl.

If you have the wrong gasket between the main body and the baseplate you can have a plain old fuel leak.

I think you're going to have to tear this thing down and see what going on. Just go slow and be careful, hopefully you've still got the old gaskets for a comparo.

Tom

[This message has been edited by Tom Mobley (edited 07-17-99).]

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RT

Discussion Starter · #3 · Jul 18, 1999

Tom, Thanks for your reply. I do have the old gaskets, and I'll check them again. I can see the fuel leaking out from some opening just above the throttle plate as it is closed. The description of operation you gave is also helpful. I'll let you know what I find today.
Thanls,
Rich

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Coppertop

· #4 · Jul 18, 1999

When you find out let me know. I posted this same kind of question a few month back. I rebuilt the original Rochester 2GV on my '70's 307 with the same results. I TRIPLE CHECKED everything before reassembling. I made sure the gasket holes lined up between the base plate and the barrels. After shutting off the car, slowly I'd see the gasket around the throttle base get soaked and then gas would start weezing out.

I adjusted the float and needle seed twice with no change.

I think it is a conspiracy. They're not making rebuild kits like they use to

RT, are you using one of the original type seed/needle valves and a brass float.

DURO-Valves, TomCo's patented valve SUCKS!

That's my $.02
Joe

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Randy Mosier

· #5 · Jul 18, 1999

Guys, are you replacing the floats when you rebuild your carbs? If they are the black composite type they could be saturated. If so, no amount of adjustment is going to cure the flooding problem. The best way to check a composite float is to throw it on the floor, stomp it real hard with your foot, and then say to yourself, "Yep, it was bad." If you did replace the float, all you can do is double check your gasket selection when you put it back together. If all this checks out, check fuel pump pressure. I have seen fuel pumps that malfunctioned and produced a gazillion pounds of pressure, thus overcoming the needle and seat. The pump will still hold pressure for a while after shutdown.

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RT

Discussion Starter · #6 · Jul 18, 1999

OK, I may never know for sure, but the problem has stopped. Here's what I did:
I double checked all the gaskets, then looked over all the parts carefully. Tom, you're description of the siphon break made me Look very closely (which ain't as easy as it used to be) at the venturi cluster. That's when I found that the thin tube on the driver's side was clogged at the very top. I ran a thin wire through it as well as all other holes I could find. Just for good measure, I also picked up a new plastic float. So, It could have been the float, or maybe the plugged tube allowed a siphon to continue? Anyway, many thanks for saving the day for me Tom and the rest of you who gave your advice. BTW, the rebuild kit is labeled Borg-Warner and included an original type, rubber? tipped needle w/ brass seat, (but no float). Also, the carb, which has probably been messed with by someone, has #58 jets. Anyone know if these are correct? It still has a slightly rough idle, but smoothes out as soon as you hit the gas.
Thanks,
Rich

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Tom Mobley

· #7 · Jul 19, 1999

RT, the main jets won't have any effect on your idle. How far are the idle mixture screws turned out from seat? turn them back in til they seat, counting the turns. Then average them and turn them both out that amount. (ie, if one's out 4 turns and the other 3, set them both at 3.5 and try it.) Don't be afraid to back them out 4-5 turns, gas today doesn't have the specific gravity it used to.

Check carefully for vacuum leaks, these are often the culprit when there's rough idle problems. Pinch off the vac lines one at a time and see if the idle changes. This includes the PB booster.

Tom

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RT

Discussion Starter · #8 · Jul 19, 1999

Tom, Thanks once again for the good tips. I'll check for vacuum leaks further than I have already. I set the idle screws following a shop manual using the idle speed (tach) method. I'll also check the # of turns and try your average setting. One thing that has been an ongoing concern is the thermac valve. The valve is working when vacuum is applied, the switch in the air cleaner housing is new as are the hoses to the base of the carb, but there is always vacuum at the hose to the thermac, regardless of ambient temperature or state of engine warm-up. I would think that after warm-up it should be allowing cold outside air to enter. The heat riser butterfly has longe since rusted away, but once the engine is fully warmed up I would think that this component is out of the equation. Ideas?
Thanks,
Rich

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