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Technical Chevy 235 struggling at high rpms

Discussion in 'The Hokey Ass Message Board' started by 4doorsformorewhores, Sep 18, 2021.

  1. 4doorsformorewhores
    Joined: Jul 7, 2021
    Posts: 61

    4doorsformorewhores
    Member

    So here’s where I’m at, hoping y’all can help me equip myself with a few troubleshooting procedures. Just put on a langdons mini HEI distributor with his suggested plugs, wires, and the heavy duty square coil a few days ago on a 54’ 235. Timed to approx. 16 degrees advanced with an advanced light. Firing order correct, oil pump engagement, correct cast iron gear for the distributor, all that good stuff. Now what’s happening is the car bogs down and sputters bad once I get to 2000rpms. If I shift early it seems to run fine, but pushing her to the higher rpms it instantly doesn’t like it. Also at first fire up she idles good at 500-600 rpms. After tapping the gas a few times, or driving a bit the rpms hover around 1000 or even higher. Read the plugs after a few miles yesterday and they’re pretty roached. So I was thinking of giving it a 1/4” in turn at a time and taking a quick drive to see if the hesitation get better. Carb is new-ish also, and manifold vacuum reads a pretty steady 17-18 at idle. Any other ideas here that I can obsess over?o_O
     
  2. Budget36
    Joined: Nov 29, 2014
    Posts: 8,438

    Budget36
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    How did it run with the old setup?
     
  3. 4doorsformorewhores
    Joined: Jul 7, 2021
    Posts: 61

    4doorsformorewhores
    Member

    Not like this. It had its own set of issues though. That distributor was pretty clapped out, as it was the original. I went with the HEI set up for reliability as this old girl is my only car to putt around town. But the sputtering and bogging down is new
     
  4. 6sally6
    Joined: Feb 16, 2014
    Posts: 1,898

    6sally6
    Member

    "new carb"...........check the basics first
    1. spray Brakleen around carb base/intake for vacuum leak.
    2.Don't be 'skeered' to give the timing a good twist! Advance it and see if it clears up.
    3.Hook up a vacuum gauge and adjust carb to get the highest vac. reading
    4. Gas cap vented?
    5.Gas tank old & rusty?
    6. Fuel filter new?
    6sally6
     
    gary macdonald and VANDENPLAS like this.

  5. theboss20
    Joined: Dec 30, 2018
    Posts: 274

    theboss20

    Make sure you don’t have a partially plugged muffler or exhaust…had a similar issue and at higher rpms a broken baffle in the muffler would move a block the exhaust enough to cause it to stumble…best test…remove the muffler.
     
    gary macdonald likes this.
  6. Budget36
    Joined: Nov 29, 2014
    Posts: 8,438

    Budget36
    ALLIANCE MEMBER

    What carburetor are you using?
     
  7. 4doorsformorewhores
    Joined: Jul 7, 2021
    Posts: 61

    4doorsformorewhores
    Member

    Cap not vented, but it wasn’t before the swap and the car drove fine. Tank is new as of 2 years ago, with all new hard lines to the pump, and from there to the carb. Filter was installed at the same time. I’m not sure timing is my problem here, unless it’s the advance curve because it fires right up on initial start, and runs well at those lower rpm ranges
     
  8. 4doorsformorewhores
    Joined: Jul 7, 2021
    Posts: 61

    4doorsformorewhores
    Member

    An adorable little Rochester B single barrel. Intake is stock
     
    VANDENPLAS likes this.
  9. 4doorsformorewhores
    Joined: Jul 7, 2021
    Posts: 61

    4doorsformorewhores
    Member

    Another strange thing is, at idle with the vac advance hose unhooked it instantly starts to run rough, plugged back, and it smooths out
     
  10. Budget36
    Joined: Nov 29, 2014
    Posts: 8,438

    Budget36
    ALLIANCE MEMBER

    Take the cap off and give it a try. I assume you used the proper gauge wire when you put in the HEI.? Does the ballast resistor need to be bypassed with his unit?
     
  11. Budget36
    Joined: Nov 29, 2014
    Posts: 8,438

    Budget36
    ALLIANCE MEMBER

    Unhooked and not plugged?
     
  12. 4doorsformorewhores
    Joined: Jul 7, 2021
    Posts: 61

    4doorsformorewhores
    Member

    Ah yes forgot that detail. Ran a new 10 gauge primary wire, and deleted ballast resistor. Vac hose unhooked and plugged with my finger over the flex hose
     
  13. Budget36
    Joined: Nov 29, 2014
    Posts: 8,438

    Budget36
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    Just for a sanity check, you are timing it with vacuum advance disconnected?
    Now, I always timed my 235’s as was laid out in MoToRs manuals.
    Disconnect and plug line.
    Idle speed approximately 500RPMs (I forget exactly).
    Light on #1 and adjust timing/idle until the mark is shown on the flywheel.
    Drive and put in 4th (only had manual transmissions) and accelerated moderately. If no ping, advance timing more. Reset idle.
    Go again and repeat until it pings, then back off a bit.
    I guess with a good dial back light you could figure out total advance, but that’s not something I ever looked at on mine.
    But, maybe also try leaving the vac advance off and plugged, and take a quick spin. Not for too long as it will start to heat up in the exhaust, just around the block.
     
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  14. 4doorsformorewhores
    Joined: Jul 7, 2021
    Posts: 61

    4doorsformorewhores
    Member

    I’ve checked with a light on a bit of both. Vac advanced unhooked and hooked. Per langdons instructions it says you’ll land anywhere between 8-16 degrees advanced. Which lands you roughly right around the UTC and BB mark leaving the flywheel window. Which is spot on with where I’m at. I can try a quick drive without vacuum, but again it idles roughly when you disconnect it
     
  15. theboss20
    Joined: Dec 30, 2018
    Posts: 274

    theboss20

    Be sure to plug the vac line…golf tee works great
     
  16. Budget36
    Joined: Nov 29, 2014
    Posts: 8,438

    Budget36
    ALLIANCE MEMBER

    Well, you have to set base timing with no vacuum advance. I don’t recall if my 235s had vacuum at idle or not, it’s been awhile;).
    What is your idle RPMs when setting base timing?
     
  17. jimmy six
    Joined: Mar 21, 2006
    Posts: 11,025

    jimmy six
    ALLIANCE MEMBER

    I bought one of Tom’s complete systems also with the recommended hei coil. His recommendation, actually mandatory, said manifold vacuum. We struggle to get it to idle at 800+ rpm. Yes it’s multiple carb, 10-1 compression, a mid range cam:etc. but it just didn’t make sense. I finally used Venturi vacuum and 8-10* at idle with it disconnected. Idles at 550 and runs right up to 5500 if we want. Something it wouldn’t do his way. I’ve been racing GMC/Chev 6’s for over 50 years and never had one not rev if everything was good.
    Yours sound like it’s running out of fuel but it was good before I would look to something on the ignition.
     
    Cosmo49, VANDENPLAS and Budget36 like this.
  18. Keep giving it more timing snd see what happens.

    try ported vacuum

    when you say the olds distributor had its own issues what where they ?

    those Rochester B carbs are good little carbs easy to build and plentiful.

    but do leak fuel and air around the throttle shafts and the castings can warp and leak fuel and vacuum as well.

    the fact it runs like crap at idle with the vacuum advance disconnected is strange.

    make sure your timed 100% correctly on number one, then advance your timing and set your carb accordingly.

    sounds like your chasing a couple problems and they are overlapping causing anger and frustration!o_O
     
    Budget36 likes this.
  19. 4doorsformorewhores
    Joined: Jul 7, 2021
    Posts: 61

    4doorsformorewhores
    Member

    Interesting, when I spoke to him he said he suggests ported vacuum, but that I could try manifold. To me manifold vacuum seems a little counter productive as vacuum drops under load, right? That would retard timing when it’s needed, but then again, I’m just a fucking kid, so I could be wrong. Yea I doubt it’s running out of fuel, because she smells rich as hell driving, and like I said I did read plugs after a few miles and they were blacked
     
  20. 4doorsformorewhores
    Joined: Jul 7, 2021
    Posts: 61

    4doorsformorewhores
    Member

    Sits happy at 500-600, until you give it gas, then it jumps to 1000 and stays there pretty consistent
     
  21. 4doorsformorewhores
    Joined: Jul 7, 2021
    Posts: 61

    4doorsformorewhores
    Member

    The old one was a floppy, and the vacuum advance canister had ruptured, so I figured if I’m going to go through the trouble of pulling the dizzy, I may as well give the old girl a spiffy new one
     
    VANDENPLAS likes this.
  22. Dave Downs
    Joined: Oct 25, 2005
    Posts: 912

    Dave Downs
    Member
    from S.E. Penna

    If the engine is stock except for the ignition 16 degrees static sounds like a lot -
     
    6inarow likes this.
  23. 4doorsformorewhores
    Joined: Jul 7, 2021
    Posts: 61

    4doorsformorewhores
    Member

    I thought so too. But Tom suggested it, and again, my knowledge is slim on these old cars, but it doesn’t feel like it too advanced. My symptoms (I would assume) don’t point to that anyway
     
  24. 4doorsformorewhores
    Joined: Jul 7, 2021
    Posts: 61

    4doorsformorewhores
    Member

    Shot in the dark here, but is it possible I’m just running way too rich? And it’s choking itself out? Or is that something that would be more consistent across all driving conditions?
     
  25. Cosmo49
    Joined: Jan 15, 2007
    Posts: 1,332

    Cosmo49
    Member

    IIRC the spark plug gap for HEI is considerably wider than a stock distributor.
     
    Lloyd's paint & glass likes this.
  26. 4doorsformorewhores
    Joined: Jul 7, 2021
    Posts: 61

    4doorsformorewhores
    Member

    Stock is .035” I’m running .050” currently for the HEI which was the suggested plug gap
     
    Cosmo49 likes this.
  27. jimmy six
    Joined: Mar 21, 2006
    Posts: 11,025

    jimmy six
    ALLIANCE MEMBER

    Stock is 6* BTC. I’d start there. It’s checked thru a hole in the bellhousing. The triangle is TDC; the ball bearing ball is 6*. To see the triangle you need to remove the flywheel shield and clean the surface to see it. I paint it; white same with the steel ball.
    Unless you added a 360* tape and a pointer off the timing cover and found true TDC you might be just guessing. Good luck.
     
    Cosmo49 likes this.
  28. jaracer
    Joined: Oct 4, 2008
    Posts: 1,482

    jaracer
    Member

    Vacuum advance only advances the timing at light load for fuel economy. Yes when you "get on it" you will lose the vacuum advance. That's the way it is supposed to work.
     
    ottoman and Cosmo49 like this.
  29. Truck64
    Joined: Oct 18, 2015
    Posts: 5,316

    Truck64
    Member
    from Ioway

    Post a a clear head on picture of a spark plug or two. If they look "roached" with modern gasoline the carb is setup pretty far off the beam.
     
    Cosmo49 likes this.
  30. 4doorsformorewhores
    Joined: Jul 7, 2021
    Posts: 61

    4doorsformorewhores
    Member

    78528656-5BF6-4E2F-BAAE-F12222D4CE85.jpeg
     

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