GS 350 Poor performance.

Discussion in 'Small Block Tech' started by Andrew350, Dec 26, 2018.

  1. Andrew350

    Andrew350 Member


    I have recently bought a 1970 GS 350.
    I'm wondering if anybody on here could tell me how a stock GS350 4 barrel should perform.

    I know it aint no 455, but It feels very sluggish on take off and believe that it should screech the tyres at the very least on take off which it doesn't.
    Mid to top end it seems okay.
    The car starts and runs perfect, idles smooth, no flats spots, no bogging down or surging, id say it runs like a fuel injected motor, but take off is very sluggish with WOT, should these 350s run like that?

    Its a stock 350 with factory spec camshaft and stock intake.
    4 Barrel Quadrajett (750cfm) rebuilt
    Brand new TA PERFORMANCE HEI Distrubtor, timing set to recommended specs.
    New spark plugs and leads
    3.42 gears

    I have noticed the intake manifold looks to be a later pollution manifold, could this alter performance?

    Could anybody point me in the right direction as id like to get this car running right and liven the motor up.

    Any help would be appreciated.
  2. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    If the intake is wrong there is a 95% chance the original 350 is long gone and its been replaced by a low compression later 350. The engine code will be between the first and second spark plugs stamped on the deck. It should be SP if it's the original but it doesn't seem likely at this point.
  3. Andrew350

    Andrew350 Member

    Hi thanks for your reply,

    Surprisingly the car is matching numbers.
    I’ll check if it has SP.
    alec296 likes this.
  4. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    It's a huge red flag to have a smog intake on a 70. There would be no reason to switch it from the much more desirable 70 intake. I don't think a late intake will go on an early motor either. I'd inspect your engine very carefully.
    Andrew350 and alec296 like this.
  5. techg8

    techg8 The BS GS

    Check the release rate of the carburetor pulloff. It controls the opening rate of the secondary air flaps.

    If it is too slow, it can feel like you're waiting for the power to come in.

    When well tuned, and everything working together, a 350 has plenty of get up and go. It should not feel sluggish.
    alec296 likes this.
  6. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Did you set the timing? Did you check the mechanical advance, and how soon it is all in?
    alec296 likes this.
  7. alec296

    alec296 i need another buick

    I agree to check engine code stamped in block, probably a different engine. But it just may need the proper tune. I believe spec for distributer is 4 advanced for timing. Hei ussually runs much higher. 12 atleast. Carb may need a rebuild. Or possibly an issue with choke. Pull out a few spark plugs and check if they are wet or black after running.
  8. MrSony

    MrSony Well-Known Member

    I've got a '70 SP GS350 engine in my Regal, and it hauls ass for what it is. Stock with a cam, TA HEI, and a good qjet from EverydayPerformance. Hopefully you didn't get swindled and you have an SO or SB engine (or worse, a sub 8:1 smogger). My engine did pick up quite a bit of oomph down low from bringing the timing in.
    alec296 likes this.
  9. Mart

    Mart '71 350 GS, almost stock

    alec296 likes this.
  10. No Lift

    No Lift Platinum Level Contributor

    What timing specs did you set them to? Since the distributer probably is set up nicely from TA you want around 34* total timing and the initial timing is what it is. Total timing is what really counts. If you set it to some factory spec then you are way off base. Also you did disconnect the vacuum advance when setting the timing, correct?

    Post a clear picture of the intake manifold. One picture tells a thousand words.
  11. Andrew350

    Andrew350 Member


    Attached Files:

  12. Andrew350

    Andrew350 Member

    14 initial
    36 total
    I did disconnect the v
    Vacuum advance was disconnected.
    I set it at 14 int
    36 total.

    Attached Files:

  13. Andrew350

    Andrew350 Member

    I tried searching for the SP stamping but really
    Couldn’t see anything.
    Could it possibly be the heads were changed hence the later style smog intake?

    Attached Files:

  14. buick64203

    buick64203 Just plum crazy Staff Member

    I had that issue with my Aquamist car. The choke pull off wasn't unloading fast enough. I wound up using a pin drill and enlarged the restrictor. Didn't take much.
    techg8 likes this.
  15. Mart

    Mart '71 350 GS, almost stock

    Keep at it, fine draw file maybe or scrape with razor blade. Doesn't look like block was decked, the letters should be there....they are faint.

    Attached Files:

    Last edited: Dec 27, 2018
    Andrew350 likes this.
  16. Waterboy

    Waterboy Well-Known Member

    Andrew, this is "oldman" John Carroll. I'm a bit buzzed because I dislocated my shoulder, and broke the top of it's corresponding humurus bone. Surgery Jan. 2nd. Drank some beer today, but wait......... You have some of the BEST diagnosing your problem!!! My glass is always full. I hope your problems are easy, like the back carb. flaps, or something. Listen to these guys, and if they seem hard, say, "Excuse me, what??? o_O
    It is all fun, and challenging.
  17. gsgnnut

    gsgnnut Well-Known Member

    Bad news andrew. Your motor is clearly a 72 it's in the casting in your photo.
  18. Andrew350

    Andrew350 Member

    I really do appreciate everyone’s reply’s and help.
    I didn’t mention that I’m from Melbourne Australia.
    How did you do that John? I wish you a speedy recovery!
  19. MrSony

    MrSony Well-Known Member

    It says it on the block itself not the heads. Pic of mine before the rebuild. Driver's side below a headbolt between cylinders 1 and 3. It should say SP then three numbers (mine says SP 252). If it's gone it may have been decked.
  20. Andrew350

    Andrew350 Member

    I’ll keep at it lol, it 39 degrees here today.

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