350 rebuild gremlins still lingering

Discussion in 'Small Block Tech' started by 70skylarkcusto, Oct 8, 2018.

  1. 70skylarkcusto

    70skylarkcusto Well-Known Member

    The stems themselves were different between each exhaus and Intake valves, so all the exhaust push rods are he same length respectively but are different from the 8 intake valve push rods.

    I’ve did a leak down test last night, leak down % was between 5-7% for all cylinders, previous compression tests were between 146 and 151 psi for all cylinders
     
  2. 70skylarkcusto

    70skylarkcusto Well-Known Member

    Here is a short video. It’s hard to tell in the video how much of a rough idle there really is just from the video, so I put a glass of water on top of the air cleaner. Believe me it really rocks the whole car and is not a fun ride.

     
  3. alec296

    alec296 i need another buick

    You should not have different lengths between pushrods. That’s more a quick fix for a bad valve work. Either way, that’s not a lot of shake, did you rebuild or replace balancer? Flexplate new? Was rotating assembly balanced? What torque converter? When you did leak down, did you check exhaust pipe, intake thru carb and PCv system to find where leaking was? Check radiator for air bubbles? .
    What do spark plugs look like? Any difference in them? One side cleaner or wet, or other color unevenness?
     
  4. 70skylarkcusto

    70skylarkcusto Well-Known Member

    I did not rebuild the balancer, the rotating assembly was balanced, torque converter is 2000 stall, but definitely going to go with a 2400. And yes I checked all the above with the leak down test. All sparks look great no difference between cylinders. I have a local speed shop that I’m going to on Friday to try a different carb and see if we can get some answers on that end. I think some of the other members may have a point about my q jet. I will report back
     
  5. Mark Demko

    Mark Demko Well-Known Member

    That doesn't look bad in the video, tho it is rocking back and forth like a bad cylinder, NOT like a lumpy cam
    You said it smooths out above 1500 rpm?
    Leak down was good
    Compression test was good
    You said the whole car shakes? Or theres a vibration?
    You sure something on the engine isn't hitting/resting on the frame causing a vibration?
     
  6. Matt Knutson

    Matt Knutson Well-Known Member

    Have you tried unbolting the torque converter and backing it away from the flexplate and starting the engine?
     
  7. MrSony

    MrSony Well-Known Member

    Mine's got a crower level 3, shimmies a bit less than that. Doesn't really bother me that much. Engine runs fine, great in fact, for what it is. It's not stock, so i don't expect mine to sit there and idle like new.
     
    alec296 likes this.
  8. 70skylarkcusto

    70skylarkcusto Well-Known Member

    It does smooth out in higher rpms, the tests were better than I was expecting but yes it seems to shake the car, sometimes to the point where I pop it into neutral at stop lights so it idles up a bit and isn’t as rough. I’m positive there’s nothing else hitting the frame.

    Yes I have tried ubolting the torque converter to fully isolate the engine, there was absolutely no difference
     
  9. Fox's Den

    Fox's Den 22 years of racing the same 355 Buick motor

    Do the video at the exhaust, you can usually tell by that if the engine has a miss or not. Reset the carb with the car in drive and wheels blocked. get highest vac reading and idle from the idle jets on carb.

    Check plugs out to see if one is not firing good, if that is ok then start to check for a vac leak at the intake. If you can close all jets on carb and there is not much change there is vac leak. or the blades are opened too far to let the jets work.
     
  10. Mark Demko

    Mark Demko Well-Known Member

    I weeding thru your post here for ideas:cool:
    "low and bouncing vacuum readings"
    Post a vid of the vacuum gauge.... in park, then in gear..... fully warmed up.
    Reason I ask, is the vacuum can and will vary slightly with a lopey cam at idle... the needle will hang at 15" then maybe dip to 13 or 14" for a few seconds, then back to 15"
    A "bouncing" needle, one the pulses from 15 to 13 in time with valve action indicates a leaky valve.
    What is your compression ratio?
    How far "in the hole" are your pistons?
     
  11. 70skylarkcusto

    70skylarkcusto Well-Known Member

    Alright... so here’s the biggest update I’ve had in a while. Brought the car back to a speed shop on Friday and had them swap my q jet for an Edelbrock performer... instantly the car idled better and pulled harder, not a 100% improvement but 50%.... so as the story goes I said screw trying to make this a jet work and they talked me into buying a QFT slayer sv 750 on. Boy that made ALL the difference. The sound of the engine changed, the idle is now calm and boy you can really hear that cam. It was idling a little rich, think I might need to jet down one or two sizes but as of now this thing is finally purring. I’ll take another video of the finished product when I finally get the carb fully tuned to where I’m completely satisfied but this must have been my issue all along. I guess the idle circuit of the q jet just couldn’t keep up with that big cam.
     
  12. alec296

    alec296 i need another buick

    Jets do not control or feed idle.
    The reason the qjet didn’t work for you was probably idle air bleeds dirty or to small .
    You should invest in an air fuel meter. The new carb will need jetting or other tuning for mid and top end power. The air fuel meter will let you see if your rich or lean top end.
     
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  13. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Like I said, the Q-jet can be modified to work and it will still get better MPG, if that matters to you at all. I use a 1000 DP Holley carburetor at the track, but on the street, I much prefer the Q-jet. Mine was built for the engine. I can swap carburetors in 15 minutes or less.
     
    Last edited: Oct 14, 2018 at 11:04 AM
    70skylarkcusto, Dwayne B and alec296 like this.

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