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235 running rough all of a sudden

Discussion in 'The Hokey Ass Message Board' started by chevypanel52, Aug 25, 2012.

  1. Went for a run today, about 10 minutes after I'm on the highway, my 235 Chevy starts running rough in a strange way. If I give it "the gas" it runs just fine, back off and it stumbles and feels rough. Turned around to come home and after another 10 minutes it was way worse, backfiring out the tail pipes, but still ran well if I kept my foot on the loud pedal.

    It's been running super sweet for over 12 years!, just got back from a 1200 mile road trip without a hitch and did a few shorter runs in the last couple weeks with no signs of any problems. Now this.

    235 with dual Rochesters on Offy intake with water cooling, Fenton headers, Langdon HEI (with fresh cap, rotor and plugs about 2500 miles ago).

    No smoke of any sort out the exhaust, no oil usage in last 1000 miles, no change in coolant level in last 2500 miles. Pulled the plugs ( they're OK), checked compression (OK), found a small vacuum leak (fixed), pulled the air cleaners off the carbs, found a lot of liquid gasoline in the rear airfilter, tightened up everything on the carbs, manifolds, etc. nothing in particular was loose. Idles "okay" but I can tell there's a miss in there somewhere cause she's shaking a bit and a bit of a pop out the exhaust.

    Any clues? Sending it to my mechanic on Monday.
     
  2. mike1951
    Joined: Jul 15, 2007
    Posts: 706

    mike1951
    Member
    from Colorado

    Fuel pressure within specs?


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  3. That's one of the things I cannot check ... so off to the mechanic she goes.
     
  4. pinkynoegg
    Joined: Dec 11, 2011
    Posts: 1,135

    pinkynoegg
    Member

    carbs probably need to be cleaned or rebuilt
     

  5. You're probably right pinky, they are 14 years old and have about 45,000 miles on 'em ... however just seems strange that it would happen so quickly, i.e. fine one day and crap the next ...
     
  6. George/Maine
    Joined: Jan 6, 2011
    Posts: 949

    George/Maine
    Member

    My guess its dist,put the stock one back. HEI maybe wornout.
     
  7. d2_willys
    Joined: Sep 8, 2007
    Posts: 4,101

    d2_willys
    Member
    from Kansas

  8. Mr48chev
    Joined: Dec 28, 2007
    Posts: 27,332

    Mr48chev
    ALLIANCE MEMBER

    My first thought.

    You didn't happen to stop at a different than your usual gas station? Like an old one that has had the tanks in the ground for many many years?

    crap in the gas or crappy gas is one thing that causes issues like that.
     
  9. mike1951
    Joined: Jul 15, 2007
    Posts: 706

    mike1951
    Member
    from Colorado

    I had a weird fuel issue in my car and it was caused by a rotting soft line between the frame and engine... it was sucking a bit of air. The car ran ok til it got hot and then it would behave like vapor lock. I was getting pressure but not enough. Check those lines.


    Posted from Jalopyjournal.com App for Android
     
  10. Pop-Rodder
    Joined: Oct 6, 2011
    Posts: 325

    Pop-Rodder
    Member

    Sounds to me like the jets are plugged. Rebuild your carbs, or at least blow out the jets, and then make sure your fuel filter is replaced or cleaned. Is your gas tank in good shape, no rust, etc? I have a rusty tank on my vw running dual carbs and get this alot, just like you described. Constantly cleaning out filters and jets.
    Just my .02
     
  11. mike1951
    Joined: Jul 15, 2007
    Posts: 706

    mike1951
    Member
    from Colorado

    He's got a valid point. Do you see any varnish or nastyness in the carbs?



     

  12. Current tank of gas is from my local Shell station where I buy it regularly, always fresh, though this tank was Regular and not the usual High Test.
     
  13. Yeah but it's the weekend and I don't happen to have a garage to work on the truck in ... my mechanic's fair and reasonably priced.
     

  14. Quite a bit of liquid gas in the air filter housing of the rear carb, suspecting a stuck float maybe? Not about to take a carb apart on a Sunday in my driveway.
     

  15. Tank has never been pulled that I know of, so no idea of condition, but the truck has run fine for me for 23 years. That said, the recent long road trip with some nasty bits of Interstate might have knocked something loose in the tank and it's taken it's time making it's way to the carb. Thanks.
     
  16. d2_willys
    Joined: Sep 8, 2007
    Posts: 4,101

    d2_willys
    Member
    from Kansas

    Have sticking float problem on my Willys. It'll leak and I just slap the carb with the handle of a screwdriver, float good after that.
     
  17. Thanks for all the suggestions guys ... it was simply dirt in the rear carb. Simple old school solution for an old school problem. Pinch the rubber fuel line til the motor almost stalls, then let 'er go. The surge of gas flushes out all but the most stubborn crap stuck in the carb. The dual carbs made the dirt-in-carb problem less than apparent ... one carb still functioning normally allowed the motor to run okay, second carb over-filling with gas was sending volumes of raw fuel into the rear cylinders. So we've plumbed in some new filters and replaced rubber fuel lines, just to be on the safe side.
     
  18. JBOLTON
    Joined: May 24, 2006
    Posts: 243

    JBOLTON
    Member

    nice easy fix! I always put emphasis on fuel filters as well. I have one on before my elec pump, and one after. They are cheap, easy to replace, and prevent that crap getting into your jets.
     
  19. Funny thing is the fuel filter is the only thing I didn't replace before my long road trip, stupid auto parts store didn't know what I was talking about, they needed a part number or a year/make/model and their listings didn't go back into the '50's ... it's just a plain ol' inline fuel filter for #&@& sakes !
     
  20. rampant150
    Joined: Dec 30, 2010
    Posts: 31

    rampant150
    Member

    SSSSSHHHHHH! Don't get these guys started on parts stores!
     
  21. mike1951
    Joined: Jul 15, 2007
    Posts: 706

    mike1951
    Member
    from Colorado

    Best part is you fixed it yourself!
     

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