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Another 308 carb problem

Discussion in '308/328' started by bl10, Apr 21, 2020.

  1. bl10

    bl10 Karting

    Jun 8, 2011
    106
    A little history: My 1978 308 gts had been sitting in my garage for the last 27 years (I drove it for 10 plus years then just parked it) . Never started and just moved it to clean the garage. Decided to resurrect it about 6 mos ago.
    Did following:
    Changed cam timing belts, didn't change idler pulleys as they felt OK.
    Changed O rings in AC system.
    Changed AC compressor oil due to new Freon. AC works great. 45 degrees on 110 SoCa day in traffic.
    Changed engine, oil and filter as well as trans axle oil .
    Made adapter to pre-oil engine. (It had to be pretty dry inside)
    Changed the plugs to iridium.
    Changed fuel pump, fuel filter and all fuel lines. Tanks were clean only screen filter inside tank deteriorated.
    Changed the vacuum lines. (Its a Calif car) Not, however the brake vacuum booster line.
    Cleaned all four carbs No new parts just cleaning. Amazingly even the accelerator pumps still work. Have never loosened or reset the throttle blades.
    New battery of course.
    Synced and adjusted the carbs.
    Flushed brakes.
    Reinstalled R2 points with micro switch and set timing per manual.
    Reinstalled smog pump.
    Put a set of used cats on as mine had the media broken out.
    Adjusted clutch per Birdman.
    New tires (kind of flat spotted after siting for 27 years).
    Changed oil pressure sending unit.
    Passed Ca smog with flying colors. (guy tested it twice as he didn't trust the 1st test)
    Fixed some minor electrical glitches and repaired fuse block.
    Changed water pump (should have done it when I did the belts but O well)
    Everything works except it was breaking up above 4500 rpm. Figured it was the points.
    So I installed a Pertronix 9MR-183 in the rear distributor and that cleared up the high speed breaking up. Am running the original coils without the resisters. Tach works fine.
    Now for the problem.

    I set the timing as 34 degrees BTC at 5K per the manual which put the idle timing at about 10 degrees. (Yeah I know its supposed to be 7 but that's where it comes out.
    It was idling a little fast so I went back and synced and readjusted the carbs. Three of them are perfect at about 3.5 + KG, however the drivers side rear is about 6.5 KG and won't close any more. The idle screw on the rear carbs is all the way out and 6.5 is as low as it will go. Idle speed is a heavy 1K. (faster than I like and faster then when the R2 points were in it).

    I can put pressure on the LR Carb linkage and it closes further but still not enough and can't be adjusted any more anyway.

    So I'm wondering if the brake vacuum booster or vacuum line could be leaking and causing the high reading. I guess I could try blocking it off as a quick check.

    I could retard the timing 3 or 4 degrees which would probably slow the idle enough that I could readjust the carbs to equal the air flow but feel I shouldn't have to.

    Just looking for ideas as to why the LR carb won't close or if it is closed why is it still flowing so much air.

    Thanks
    Barry
    FYI this site, Birdman's and other misc sites are a God send.
     
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  3. Dr Tommy Cosgrove

    Dr Tommy Cosgrove Three Time F1 World Champ
    Rossa Subscribed Owner

    May 4, 2001
    31,336
    Birmingham, AL
    Full Name:
    Tommy
    I'm just wondering how you could resist driving it for 27 years
     
  4. BigTex

    BigTex Seven Time F1 World Champ
    Rossa Subscribed Owner

    Dec 6, 2002
    74,136
    Houston, Texas
    Full Name:
    Bubba
    Drill in and examine the problematic carbs, stick slide, float jammed, a lot of problems and you have to sort them out one by one...

    Welcome back...!!!
     
  5. bl10

    bl10 Karting

    Jun 8, 2011
    106
    Just got interested in other things. My wife and myself started pylon racing model airplanes which is a much bigger thing than it sounds. My cars at the time were the 308, which we put over 70K miles on it and had a great time with, a Fiat X/19 as plan B. Wife's car was a Turbo T Bird, all totally impracticable for what we were into. So I just parked it. I was curious as to what it would take to get it running again so off I went. Still have a ways to go as it needs a valve adjustment and some paint and body work, not much rust but some scratches and such. So far there hasn't been anything major and it is a kick to drive.
     
  6. Dr Tommy Cosgrove

    Dr Tommy Cosgrove Three Time F1 World Champ
    Rossa Subscribed Owner

    May 4, 2001
    31,336
    Birmingham, AL
    Full Name:
    Tommy
    I have always wanted an X1/9. I'm 52 and they were running around when I was at a very impressionable age.

    No room in the driveway yet. Maybe one day.
     
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  8. Patrick Dixon

    Patrick Dixon Formula Junior

    Mar 27, 2012
    784
    UK
    X1/9s don't take up much room ...
     
  9. kiwiokie

    kiwiokie Formula 3

    Aug 19, 2013
    1,010
    Tulsa, OK
    I had one as a daily driver in the mid‘90’s -fun car. But needed a 2.0l twin cam :)


    Sent from my iPad using FerrariChat
     
  10. bl10

    bl10 Karting

    Jun 8, 2011
    106
    Yeah the X1/9 was a fun car. Mine was a 74. Put many many miles on it along with a couple of engines. (blown head gasket between cylinders. Lack of AC made it miserable for my wife and myself on those Az and Death Valley trips. Finally ended up dropping a intake valve so I gave it to our gardener. The 308 on the other hand served us well for over a decade. Great trips to Yellowstone, Utah, Colorado, Idaho, Nevada, Arizona and of course up and down the west coast from Mexico to Canada. The belly pan and front valance are pretty beat up along with paint chips from all the semi-offroad excursions to tour ghost towns and other out of the way attractions . Never once gave us trouble that I couldn't fix in a local parking lot. The lack of electronics and fuel injection make it simple to diagnose all though at times a pain to work on.
     
  11. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    19,912
    Texas
    Full Name:
    Steve Magnusson
    An air leak below the throttle plates will raise the RPM (if there is also enough fuel), but it won't raise the airflow reading on the Synchrometer. Either the air bleeds are (wrongly) open (and, at least, one of those should always be fully closed) or the mechanical position of the throttle plates is wacky and they are just not closing enough.
     
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  13. bl10

    bl10 Karting

    Jun 8, 2011
    106
    Steve
    Yeah that makes sense. I think all the vacuum connections are all below the throttle plates. Both air bleeds on the LR carb are fully closed so it pretty much has to be the throttle plates are not closing all the way. Not sure how that could happen but I will pull the carb and go through it completely. (that's a lot easier than replacing the vacuum booster vacuum hose). What would you say the average air flow in KG/hr should be on each carb barrel when properly tuned, warmed up and at 1K idle keeping in mind its a NA version?
     
  14. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    19,912
    Texas
    Full Name:
    Steve Magnusson
    Depends on the 1000 RPM warm idle timing:

    At 7 deg BTDC (R1 only) = about 3~3.5 Kg/hr

    At 3 deg ATDC (R1+R2) = closer to ~4.0 Kg/hr

    (I would guess that the two barrels that you are currently measuring at 6.5 Kg/hr aren't actually contributing anything at idle -- otherwise, the idle speed would be much higher.)
     
  15. bl10

    bl10 Karting

    Jun 8, 2011
    106
    Thanks Steve
    As I said its idling at a very heavy 1K. I'm just using the car's tach but it's fast enough that a lot of the lope from the cams is gone. If I were to guess I'd say its at least 1100. Just been two lazy to pull the coil cover so I can hook up and external tach. I just installed the Petronix 9MR-183 which increased the idle lead to 7+ degrees BTDC with the corresponding increase in idle speed. It wasn't until then that I noticed I couldn't close the LR carb enough. I always ran both r1 and r2 points which, of course, made the idle a bit easier to set. It is running on all 8 at idle at lease the plugs are clean.

    Thanks for the info
     
  16. Steve Magnusson

    Steve Magnusson F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    19,912
    Texas
    Full Name:
    Steve Magnusson
    #13 Steve Magnusson, Apr 22, 2020
    Last edited: Apr 22, 2020
    Not sure that the super-mild cams in a '78 US 308 shouldn't have any "lope" at all ;).

    Just to be clear, when you say:

    "however the drivers side rear is about 6.5 KG and won't close any more" -- this is the carb serving cylinders #3 and #4?

    "The idle screw on the rear carbs is all the way out and 6.5 is as low as it will go" -- this means you've also physically disconnected the 3/4 carb linkage from the linkage rod at the bottom?
     
  17. bl10

    bl10 Karting

    Jun 8, 2011
    106
    Yes cyl 3 & 4. Yes I have the linkage disconnected and also adjusted the connector that connects both rear carbs (LR and RR) as originally (yesterday) the LR carb was holding the RR open so it also was flowing at about 6 KG. After adjusting the connector the RR carb is flowing 3.5. All the air bleeds are closed except one on the RF (passenger side front carb) is opened a bit to equalize it. When I say lope I know the cams are mild, however, it has always had a pleasant rumble at idle which naturally smooths out as the RPMs increase.
    The idle speed screw on the LR carb is all the way out. I can put pressure on the carb levers where the linkage or accelerator pumps attach / slide and it will drop the flow as well as the RPM. The pressure required is way more than the throttle return spring could ever apply. I'm hopeful that either the throttle plates are misaligned or something is holding them open. I cleaned all four carbs while getting it running and didn't find much debris in side. However I wasn't looking for anything as they worked fine 27 years ago when I drove it last.
     

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