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Rochester 2-Jet Concerns

Discussion in 'The Hokey Ass Message Board' started by AAFD, Aug 1, 2010.

  1. AAFD
    Joined: Apr 13, 2010
    Posts: 585

    AAFD
    Member
    from US of A

    Forgive me for the long read...just trying to be as descriptive as possible...

    I rebuilt my Rochester 2-Jet recently due to it running rough. It wasn't in bad shape. I set everything to the exact specifications that were listed under the carb part number (motor/carb is from a '77 El Camino with 305V8)

    I bottomed out the two front metering screws, and backed them both out 2.5 turns (I read that somewhere on here)

    I started up the motor and it ran perfect. I adjusted the idle, and it has been great.

    The truck had some old gauges in it and I was leary on their calibration so I placed an order to Jegs and bought some new gauges. Along with those, I wanted some "tuning" gauges, so I bought a liquid filled direct mount vacuum gauge, a liquid filled direct mount water temp gauge, and an inline fuel pressure gauge, also liquid filled.

    About 2 weeks ago I mounted the fuel pressure gauge in the rubber line just before the carb inlet fitting. It's reading 7-8psi!!! It has a bone stock mechanical pump, 3/8" aluminum line from tank to pump, 3/8" hard line from pump to carb, then it has a few inches of rubber 3/8" ID line to a big clear plastic fuel filter.

    It was running fine, so I just assumed "whatever" about the fuel pressure and kept driving it. It has been fine since the carb rebuild almost a month ago...no other mods than the gauges. Everything seems tip top. I have a steady reading of 20 on the vacuum gauge, timing is set perfect, no vacuum leaks, plugs are reading fine.

    Then yesterday I drove it about 10 miles...parked for about 45 minutes, then went to start it up and it would crank and crank, finally try to fire off and then cough and sputter, smoke a little, then finally clear it's throat. It ran fine after that. I drove another 30 miles, parked it for an hour, and it did the same thing...then again after 45 miles, then again after 15 miles, then again after another 40 miles. This all came out of nowhere...it has always been an easy starting motor, even when hot.

    But once it fires off and clears out...it idles fine, and runs fine. I even calculated my fuel mileage after yesterday's driving, and I was getting 18mpg, which is average.

    WTF is going on? I'm assuming the fuel pressure has something to do with this. It must be pushing the needle up off the seat and flooding the carb after the engine is off. But why out of nowhere? Why all of the sudden?

    I'm sure I need a fuel pressure regulator, but why would it be fine all this time...then out of nowhere start acting up with no changes to the entire system?

    I cranked it off this morning to run into town and it started right up, but after a 5 minute stop...it cranked & cranked and cranked til it finally fired off. Cough, Spit, Sputter, then it roars again.

    :confused:
     
  2. merf
    Joined: Jul 24, 2008
    Posts: 105

    merf
    Member
    from new joisey

    Sometimes the gas boils in the carb and the escaping fumes flood the engine when the car's hot. It's called heat soak,I would try another gauge to verify the fuel pressure as it shouldn't be more than 6 or 7 pounds. The ethanol in our gas is making the gas boil easier and sometimes makes fuel pumps go crazy too.
     
  3. AAFD
    Joined: Apr 13, 2010
    Posts: 585

    AAFD
    Member
    from US of A

    But even 6-7 psi seems to be excessive fuel pressure for a single 2bbl. carburetor. 8psi is flat out crazy. The engine temps never see 190-degrees, and I have a phenolic spacer under the carburetor. It's just weird that it happened out of nowhere yesterday and today. I'm going to change the hard line coming out of the pump to a rubber hose with an inline regulator tomorrow, adjust it down to 4psi or so, and see what happens.
     
  4. Larry T
    Joined: Nov 24, 2004
    Posts: 7,740

    Larry T
    Member

    Do you have a vented gas cap on your gas tank? I've seen non vented caps to cause the gas tank to pressure up and push the needle off the seat.

    Have you looked at your fuel pressure gauge when the engine is shut off? How quick does it bleed down.

    I don't know if there is enough volume in the gas line between the pump and the carb to flood it when the engine is shut off. And the pump isn't pumping pressure or volume when the engine isn't running, so your problem might be somewhere else.

    Just some stuff to look at.
    Larry T
     

  5. AAFD
    Joined: Apr 13, 2010
    Posts: 585

    AAFD
    Member
    from US of A

    Yes, the gas cap is vented. I haven't looked at the pressure gauge after shut off, I guess I could.

    I know the pump isn't pumping after the engine is shut off, but the residual pressure that's still in the line could still be enough to push the needle off the seat, especially when the fuel pressure is up so high.

    I don't know. Even at 8psi, the engine should run funny, and it doesn't. I'll swap gauges when I install the regulator and new fuel hose and go from there. I'm just shaking my head trying to figure this out. I do appreciate the tips.
     
  6. Larry T
    Joined: Nov 24, 2004
    Posts: 7,740

    Larry T
    Member

    I think the best way to troubleshoot it would be to check the pressure when you kill the engine. Also pull the air cleaner off when you kill the engine and see if there is gas dripping from the boosters.
    If you have pressure built up with a dead engine, a regulator might help. If you don't have a high pressure reading and gas is dripping out of the boosters, you've probably picked up a little piece of trash that's holding the needle off the seat. It'll happen sometimes even with a good filter.
    Larry T
     
  7. gas pumper
    Joined: Aug 13, 2007
    Posts: 2,957

    gas pumper
    Member

    Sometimes the trash comes after the filter when the rubbber hose flakes off and chunks.

    The Rochester should have a paper or "stone" filter in the fuel inlet to protect the needle and seat.

    Oh and I had two pumps go crazy in the last year. One was delivering 11 psi and the other 15 psi. Took them both apart after the second failure and the issue on both was a broken spring in the pump.
     
    Last edited: Aug 1, 2010
  8. AAFD
    Joined: Apr 13, 2010
    Posts: 585

    AAFD
    Member
    from US of A

    I don't have a filter in the carb inlet, just two of the see-through plastic jobs inline. One is in the rubber line at the gas tank outlet before it turns to aluminum line, and the other, just before the carb. There is no debris in either filter, I checked that. I just changed them when I did the carb rebuild, and I'll change them again when I install the regulator in the next couple of days. I may just buy another fuel pump while I'm at the parts store, to save myself another trip into town.
     
  9. AAFD
    Joined: Apr 13, 2010
    Posts: 585

    AAFD
    Member
    from US of A

    I just ran out to the garage to check some things. I started it up, it fired right up. It has been sitting all day. I let it warm up, drove it around for about 2 minutes, then pulled back into the garage. I shut it off and watched the Fuel Pressure Gauge. It slowly dropped in pressure, and sat at 3psi for a few seconds, then immediately dropped to 0psi. I also looked down the carb after it shut off, and it is indeed dripping fuel from both of the boosters. It leaks for about 2-3 minutes, then pretty much stops. So, I'll dive back into the carb this week and see whats up with the float/needle/seat, along with installing the pressure regulator, etc.
     
  10. cartel
    Joined: Aug 22, 2010
    Posts: 3

    cartel
    Member
    from Hope BC

    Did you fix this?
     
  11. It is called vapour lock. You need a shield between the fuel pump and the block and you need to insulate the gasline anywhere it runs by a header or hot section of the block. Typical senerio is you drive it to the corner store, shut it off when it is warm, go in and when you come back out if you are in there any amount of time it doesnt want to start. You ask "is it out of fuel or is it flooded?" because it acts kinda astupid. After you fire it and let it run till it settles down (cool fuel back in the lines and pump) it is ok . It is because anti vapour lock additives are not used at all or much anymore because no car is now manufactured with an engine mounted fuel pump. Everything is pump fed from a tank mounted pump and the lines are pressurized . In the machanical pump it uses vacuum to pull fuel from the tank. When you reduce pressure you lower the boiling point and gasoline just loves to boil. The pump and the carb dont use foaming fuel very well so until solid fuel is back in the system it runs like crap if you can get it started. Never happened much back in the day because the gasoline had additives to stop it. Worst fuel for it today has ethonal mixed in although it is good fuel otherwise.
    If you want to prove or disprove this feel your fuel pump just when you shut it off. (It will be cool , sometimes cold even)Feel it ten minutes later. You may be surprised. (you probably wont be able to touch it) On the engines I specialize in (BB Mopar)we make a fuel pump shield and it cures the problem. Installing an electric pump will also cure it. yeah 8 psi is about the upper limit(install a regulator if you wish) but i think from your description it is vapour lock. If the carb cant handle the fuel presssure it would be a problem all the time. A Rochestor 2bbl is a very very good carb.
    Don
     

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