1972 350 Surging Under Load When Stopped and at Operating Temperature

Discussion in 'Small Block Tech' started by Carlisle72, Feb 22, 2019.

  1. Carlisle72

    Carlisle72 . . .But, these go to eleven.

    Hello, all!

    So, here's the first gremlin I've had to tackle with my new old 1972 Skylark I bought a few days ago, and consequently, here's my first real post. I've been scouring the forum and internet in the last two days, and I can't quite find any info on problems like this. Granted, I'm a novice, so if it's been covered over and over again, I'll take this thread down.

    I've finally had the chance to put some miles on it in the last couple days, and I've noticed a consistent problem in that it seems when it's fully up to operating temperature, it's running strange and surging while at stop lights, signs, etc. The car is running its original, stock Buick 350 4-barrel with the Rochester Quadrajet. It's still on points, but the previous owner said he replaced those. (maybe not properly adjusted?)

    I've adjusted the idle mix screws out to where the motor sounded happier thinking it might be a little lean. I checked the timing, and it was set at 0 degrees BTDC, I did advance it to 10 degrees BTDC and it seemed to help the motor run smoother while idling, but it's still surging (and, forgive me if surging isn't the correct term) at stops.

    My next ideas were to check the carb out, and verify the float level, but I'm not sure if that's contributing to my problem. I also wondered if the fuel pump is on the fritz - my gut says it's a lean condition, but the fact that it only seems to happen when it's fully warmed up has me a little puzzled.

    Thank you all for any insights, sage wisdom, and right-in-front-of-my-nose observations.

  2. rex362

    rex362 paint clear and drive

    start with the simple things ...I would check for vacuum leak

    btw ....I had a surge problem once upon a time and ended up being the fuel pump
  3. Carlisle72

    Carlisle72 . . .But, these go to eleven.

    I forgot to mention checking for a vac leak was one of my next ideas as well. And, I should've worded it as a question if the fuel pump could potentially cause that. Thanks so much, Frank! I'll get on it.
  4. BYoung

    BYoung Stage me

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  5. rex362

    rex362 paint clear and drive

    also once you figure out the surge problem ...dump the points and go for simple electronic ignition conversion
    BYoung and Carlisle72 like this.
  6. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Surging can be caused by too much timing. Simply checking the initial timing will tell you ABSOLUTELY nothing. The mechanical advance and vacuum advance add timing as soon as you go above idle. The 1972 Buick 350 got distributor part number 1112109. I highly doubt that distributor is still installed in the engine, but check and see. It has likely been changed to something else.

    The carburetor can also cause this. If the carburetor hasn't been gone through in a long time, it will need to be rebuilt with ethanol resistant gaskets/parts. Also check the part number on the Quadrajet, for 1972, it should be 7042244. Again, there is probably something else on there, and no, not all Q-jets are the same. A common problem when using a Q-jet is to have the throttle plates open too much. That can cause the carburetor to run on the main circuits and not the idle system. It will not idle or run right like that. You have some investigating to do. Wouldn't hurt to put a vacuum gauge on it and see what it is pulling at idle in Park/Neutral fully warm. Should be 18-20".
  7. Carlisle72

    Carlisle72 . . .But, these go to eleven.

    Will read that in just a moment - thank you!

    Totally agreed - I have the kit in my basket at Jegs, just waiting for payday. ha..

    Larry, thanks for all of the valuable information! From what I could tell at idle, my vacuum gauge was around 15" with the idle mix screws at their highest settings, so I wonder if it's a vacuum leak, as previously mentioned. Like you said, I've got some investigating to do, and I'll try every idea listed here.
  8. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Unless it has a cam in it, 15" is low. Stock motors usually make 20"if everything is correct. Could be a vacuum leak.
    alec296 and Carlisle72 like this.
  9. rex362

    rex362 paint clear and drive

    another check ...while checking vacuum.....keep an eye on your ignition coil for any possible arcing ,in the dark works best
    I have had this situation once happen to me and boggled me for a month ,accidentally found it by popping the hood open at night
    but only happened when revving the motor to higher rpm's not at low idle
    It was arcing from center post to one of the terminals ,cracked ...usually you would be able to also hear it snap
    Last edited: Feb 22, 2019
    Carlisle72 likes this.
  10. Carlisle72

    Carlisle72 . . .But, these go to eleven.

    I'll absolutely try this as well. I love the real-world, "this is what happened to me," input. Thanks again
  11. alec296

    alec296 i need another buick

    15 is low for vacuum. I would say that can lead you to the problem. I would also change gas filter in carb. And any other gas filter.
  12. Carlisle72

    Carlisle72 . . .But, these go to eleven.

    Thanks for the recommendation, Alec! I’ll try to find that filter.

    And here’s a little update, gang: I must not have gotten a good seal when I used vacuum gauge the first time, it’s now pulling a touch above 19”. I tried to find a leak with some Gumout, didn’t really notice any changes in idle anywhere. Cupped my hand over top of carb, and it killed it, so I think a vacuum leak is ruled out.

    I talked to my brother-in-law, who’s a mechanic, and he also suspected lean condition like I was thinking. Why? Who knows. I’m going to try to get at ‘er tomorrow. I’ll check that filter, and I’ll open the q-jet up to see if anything looks obvious. I’ll keep updating the thread so anyone who runs into this kind of issue in the future can see what worked for me.

    You guys rule.. thank you for your help! \m/,
  13. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Jake, like I said, not all Q-jets are the same. Get the part number off your carburetor. It may be jetted all wrong or an emissions carb. The part number is near the throttle shaft on the driver’s side. Also the distributor number and see where the timing is going when you rev it.
    Carlisle72 likes this.
  14. Quick Buick

    Quick Buick Arlington Wa

    Also your coil can be worn old near dead..
    Cold they run great
    OTemp they lose power
    the cap did that also on me drove me nuts it was a new cap put on by PO cold fine. got warm,
    Check the capacitor also..

    Btw there is nothing wrong with a points system.. Points will always get you home... thousands of races have been won on points.. And a Buick is so easy to set the dwell.
    Carlisle72 likes this.
  15. Carlisle72

    Carlisle72 . . .But, these go to eleven.

    Going out to grab the carb and distributor numbers - just to verify, the rotor spins clockwise on these 1972 350s, correct? I saw the firing order was going clockwise. I know a few spun counter, and just wanted to make sure this isn't one of those.

    Also, I ran the motor last night in the dark to spot any arching. I did not see any arching, but I could see the plug wires glowing in some spots - like lightning on a cloudy night, to try to paint a picture. I've never really looked at plug wires while the motor is running in the dark, but is that normal? Or are they really crappy wires? I'll grab a number for those, too.
  16. Carlisle72

    Carlisle72 . . .But, these go to eleven.

    I wouldn't be surprised if the coil is super old. It looks a little cruddy like it's seen some years. Great feedback on this one - thanks, Quick!
  17. Quick Buick

    Quick Buick Arlington Wa

  18. rex362

    rex362 paint clear and drive

    put some plug wires on your list also .....
  19. Carlisle72

    Carlisle72 . . .But, these go to eleven.

    lol.. Thank you - I'm flattered! :D

    And here we go, Larry:

    Carb - 7042944 [space] KH

    Distributor - 1112109 [space] 3019

    I should say that previous owner swore it ran great all last year, and I believe he said he put it away in September/October. You never know with people, but he seemed really trustworthy, and he's a big BOP fan. Assuming he's telling the truth, would that indicate something has fouled? It does have new wires, rotor, and cap, maybe one of these items is defective? Or coil like Quick said?
  20. Quick Buick

    Quick Buick Arlington Wa

    Carb - 7042944 [space] KH. California Car Cool. No Chi town Cancer
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