Technical Rochester 2G matters:

So, what would cause a rochester 2g to be running "pretty good" for the last 2-3 days in test driving and then yesterday all of a sudden flood with gas coming out the top? (Note: carb is a late 70's chevy 2GC model which has sat on my shelf for a while and has recently been installed on engine. Rebuild history unknown)

1) The only thing i did different yesterday was to run a pcv line, from the valve cover to this port here, port "A" , whereas previously it was capped:



i'm not sure exactly what this port is for or if it is even manifold vacuum, but it seemed right......

2) i took the top off and the float does NOT seem to be leaking and there didn't seem to be any trash in the needle+seat area. i haven't confirmed if the float settings are correct, but based upon initial observation, they seem ok. Plus, if they weren't this doesn't explain it running good for the past few days----i test drove many miles.

3) Not exactly sure what the fuel pressure is, BUT this particular fuel pump is specified to deliver 4-6 lbs., and, according to the gm service manuals, these later 70's chevy 2G carbs are calibrated to take 7 to 9lbs! Also, if pressure was too high, wouldn't it have flooded right from the start? So, my hunch is high pressure is not the problem. i will install a gauge if necessary though.

4) i am running an inline 40 micron filter (the big blue thing). Is this enough? i cannot run the stock inside filter because the A/N inlet fitting won't allow this.

Any ideas?

 

a little dirt mixing with the needle....?

 

I had similar problems recently on my 3 carb setup and needed to reset float levels.No leaks since.

 

Had one the float had a small hole and it would flood on my rear carb from the 3/2's.It was a new float not soldered good enough.Filled carb up while top off and float went to bottom.Also looked down rear and up could see gas flooding while running

 

float level and/or needle seat issue. put a gross needle seat in it and it should be much better. todays gas is tough on the older parts. Could be adding to the issue.

 

What is a "gross" needle+seat?

 

Speedway $14.95 It does say "style" in the add so its probably chinese. Also states not recomended for ethonal fuels, assume they mean straight alcohol.

 

Instead of the usual rubber tipped needle the Gross uses a ball check valve. Supposedly they work better on carbs that get a lot of action like off road. They also don't swell up when attacked by Alcohol in fuel.

 

Yes I have them on my 3x2 348 and they have been great. Got mine from Larry Fulton out in Montna? at Automation Carb. I think Charlie Price at Vintage Speed may also have them.

 

Daytona Carburetor also makes nice floats and special needle/seats but not for all carbs

 

Check to make sure the float is good, no holes . Will fill up and cause this.

 

Check your fuel pressure, if the internal pressure relief in your pump fails the pressure can get high enough to sink the float..

 

Charlie Price has them he is the one I buy my carb parts from

 

float sink is the problem if its a old black float it might have a hole in it and is soaking up the fuel , replace the float and needle with a new one

 

Need to take it apart. Get a carb kit first, then check the float. Shake it close to your ear, if you hear slouching its full of gas and sunk to the bottom of carb. Needle valve is wide open. Look for a new float if possible. Can be repaired but is tricky. All gas has to be gone and be dry inside. Iceman

 

Usually a hung up float is the main cause of a flood or no-flood condition. Like a switch, on or off. I would take it apart anyway since they're a cinch to work on. Make sure the clip that hangs the float is on right.

 

Charlie has float but I did get a bad one from him but it was the bad solder job.Don't know who make them for him.But used the new type needle and seat in all 3 carbs

 

I had 20 year old Gross valves but modernized last winter. Now the back carb is leaky. I'll check the float and I think I'll reinstall my Gross valves. I have a rebuilt stock pump and it reads 5 lbs. I would like try 4 lbs but the regulators seem to be 1-4 or 4.5 -9. I havent't been able to find specs on Malpassi. I am looking for advice here.
Thanks Pat

 

5+ psi is too much,. regardless of what the GM service manual says. 2 - 3 is plenty of pressure. Higher pressure will cause leaking problems.

 

I went to the stock pump because my Holley elec (probably 7 lbs) was always rich. But I took out the Gross valves which had been holding. So... I believe you are suggesting the 1-4 pump. Thank you . The Malpassi does Webers at 3 lbs so I need to decide between it and the 1-4 low pressure Holley

 

It amazes me that all those cars we checked fuel pressure on in the 60-70s during a tune up or while diagnosing a problem that showed 7-9 psi ran at all , must have been a fluke of nature .....

 

Amazing how many of them had fuel stains all over the outside of the carb and manifold, must've been a fluke of nature....

 

I've no idea where in Nirvana you live , but every where else in the free world , carbs leak , or seep or weep , pick the description you prefer ...

 

Hahahahaha, I call BULLSHIT!!!!. Sheesh, what a joke.

It's a Rochester, not a Harley Davidson, no, it's not supposed to leak.......

 

This ones been on the car for 6 years now, NO leaks!!!!

 

Carbs that don't seep fuel from the gaskets?

True, they DON'T seep, until they are installed on the engine, and fuel lines attached.

As to the fuel valves, here is a link discussing the various styles:

http://www.thecarburetorshop.com/Fuel_valves.htm

Jon

 

Thanks Jon

 

What is the Best low pressure gauge as in 2 two 5 lb?

 

I've had a hard time accepting that the old shop manuals could be wrong. They are usually like the King James Bible and the J-2 engineers knew their stuff. That said, every GM car I've owned has run rich. Maybe a little extra gas with lead as a lubricant made up for limitations in oil and oiling. And maybe to get this concoction where it was needed took about 5 lbs of pressure. But maybe modern gas without lead is a) a poor lubricant and a good solvent(it eats paint) and b)maybe it pumps easier (lighter?) and maybe now 3 lbs. is best with today's gas.
Maybe..maybe...maybe...What do you think?

 

I run 2x450 Holley 4 bbls on a 388 stroker sbc, 7 psi at the carbs , normal cruising highway and city , I average 16.7 mpg , plugs are clean , needles and seats are 10 years old ,
I see no sign of internal or external leakage.