Mystery Problem

Discussion in 'Technical' started by im devestatingly handsom, Oct 9, 2008.

  1. Engine: Chevy 305
    Crank and Pistons: 20cc dished, Stock Recently rebuilt, very solid
    Heads: New 1984 305 HO heads 1.92 int, 1.5 exhaust
    Intake: New Edelbrock Performer RPM series, 1500-6500 rpm
    Carb: New Edelbrock 600 CFM
    Exhaust: Hooker 1 5/8" headers, 2.5" exhaust single muffler
    Distrubtor: New MSI HEI
    Cam: Comp Cams 280H - .48" lift, hydraulic flat tappet, came with springs. rated for 6500 rpm, 2500 stall
    Stall: stock 1300-1500 rpm.
    Rockers: New Roller Bearings

    Car requires much more throttle than before to idle. Will run decent out of gear, but will randomly stall and die after 10 seconds or an hour ( very random ). Seems to be slightly misfiring when no load is on the engine. When load is applied it stalls. I have to power brake and can barely stop in order to keep it alive, unless I constantly put it in neutral when going less than 10 mph. Power will randomly drop between 4000 and 6500 rpm, then sometimes after half a second picks back up for 1000 rpm. Seems sluggish. Sounds healthy in high rpm, and revs very well.

    Vacuum is perfect.
    Carb is brand new and works great.
    Heads are brand new and perfect.
    Distributor is new and adjusted spot on.
    Fuel pump isn't perfect, but get's the job done.
    Rockers are perfectly adjusted.
    Stall is stock but should not be causing this.

    I can only think of two possible reasons for this.
    A: The distributor is off a tooth or two. Now how this would effect anything is beyond me, but my latest shop guy suggested it. As far as I know, as long as it lines up with the oil pump and slides in you are fine, then set the ignition timing right. He says it would make a big difference. Could this be a possibility with my symptoms?

    B: The cam was either installed off a tooth, or else the chain has slipped or skipped a tooth. When I installed the cam, I was sure the dots lined up and I double checked a hundred time, but I still doubt myself sometimes. I reused the chain that had been put on 2 years earlier because I didn't want to pull the crank gear, and the chain seemed to be in perfect condition. Could this be a possibility with my symptoms?

    I have been plagued by this for 6 months, and I know my engine has far less power than it should and it runs like pooh. It's much harder to drive than a manual right now... and it's an automatic. With it dieing randomly in traffic, it is a safety concern as well... as I experienced today. I'm angry.
  2. "When load is applied it stalls. I have to power brake and can barely stop in order to keep it alive, unless I constantly put it in neutral when going less than 10 mph. Power will randomly drop between 4000 and 6500 rpm, then sometimes after half a second picks back up for 1000 rpm."

    I had something similar when my fuel pump was dying
  3. Get a timing light on it to see if your timing is off, check the plugs, etc.
    Going from a points distr. to HEI you may have to adjust your spark plug gap?

    And is your fuel pressure good?
  4. Make sure you have at least 7" vacuum at idle and go through Edelbrocks FULL idle set procedure. If that doesn't do it you've got a deeper problem.

    Timing chains stretch and the gears aren't always lined up with the dots perfectly from the factory. Cams aren't always lined up perfectly either. I've heard of comp cams being over 10 degrees off right out of the box, the degree wheel is really your friend. Hopefully your cam isn't wiped out already, the missing at idle is an early sign.
  5. Vacuum is not the problem. Timing is right on, air-fuel mixture is perfect. The car comes standard with an HEI type Dizzy, and I simply replaced it with a new one, that has adjustable vacuum advance.

    The car has been doing this ever since I put the cam in, but seems to have slowly gotten a little worse, but I can't really tell. I have suspected the fuel pump, and I replaced my higher volume one with a new stock one just to check awhile back, and it made no difference.

    Fuel pressure has not been checked because it kept stalling and they told me I needed to replace the carb because that was the cause of stalling. Another shop said distributor, another guy said it was the heads and the valves which he was right and they were very shot, but still held a decent seal ( all exhaust valves were light tan, intake more charcoal colored ). Unfortunetly that wasn't the cause either.

    I did put in different spark plugs and I think the gap maybe be a little smaller than it should be .035 instead of .045, but this made no difference to the problem because i had .045 gapped plugs in before when it was doing this.

    I'm taking it back in next week and they are going to look at distributor "teeth" as well as fuel pressure. I'm half tempted to have him look at the cam, but the cost of that goes way up.

    I did not degree the cam... I put it in at stock settings because it was recommended. The valves appeared to open perfectly ( eyeballing it ) with tdc.

    Is there anything else that could be causing this? What should I look at first?
  6. If the carb and distributer are properly adjusted and there is good fuel pressure/vacuum you've got what you've got, get a converter.
  7. I've talked with transmission shops a few times and they always explain that it is not the stall converter causing this. It does the same thing in neutral as it does under load, it just often takes longer, but it stalls in the same exact manner. Rpm's start to drop turns into a tractor, then dies. If I keep tapping the throttle it will keep it alive. It shouldn't be dropping fuel pressure if fuel is always in the carb when I tap the throttle, and it never dies at speed. Only when rpms are too low aka below 1000, or it randomly decides to stall. Everything about this problem is inconsistent except for low rpms and load.
  8. A little off-base, but why did you downgrade to an Edelbrock carb? A properly setup Quadrajet will out perform even Demon carbs.
  9. It had a stock 2 barrel. It was replaced 4 years ago with an edelbrock 600 cfm carb by a shop that rebuilt it. That carb went bad and replaced it with a 600 cfm edelbrock that is meant for slightly higher duration in the cam. Carb isn't too much of a concern since it is just a 305, and it would probably run better with a 500 cfm.

    Problem is that it is not running right at all, and so many systems are in perfect working order and mostly new. If a lobe or two really did go flat, than why did it have this problem right from the first drive with the new cam? Could it wear that fast within the first half an hour?
  10. I've read that they have changed the chemical composition of many oils including the one that I use and removed zinc and other agents that were necessary to keep a flat tappet cam from wearing down at a very rapid rate. Turns out many people have had this problem including a few that have wiped up to 5 lobes in the first 10 minutes of running even with the break in oils on the cam and running it at 2000 rpm. This would make sense since I use 10w-30 and without the zinc it will wear extremely rapidly.

    Do my symptoms seem like something wiped lobes would cause?

    Wiped exhaust for the idle problem as well as possibly wiped intake. I haven't noticed any metal in the oil, but I haven't really looked for it, but oil has been randomly disappearing lately, so maybe the metal has damaged the rings. Possibly bearings too? I have valve train noise even though all the rockers are tightened with 1/2 turn past no lash, and the valves and valve guides are perfect.

    Thanks for the help.... just really sick of my car embarrassing me and dieing. It died at 20 mph randomly today... all I can say is that it is getting worse.
  11. #11 sbctimh, Oct 12, 2008
    Last edited by a moderator: Apr 25, 2016
    Most modern oil sucks for breaking in old flat tappet cams. There are oil additives you can buy to doctor them up. Joe Gibbs break in oil is the way to go.

    I don't know if you have a wiped cam, really it sounds like something in the carb or electric side. Is the choke hooked up? Have you reset the idle per Edelbrocks instructions? Most of the time your on the idle curciut cruising around so it could be the cause of all the problems since your power curcuit seems to be fine. If the idle mixture screws don't have an effect on your idle your in the power curcuit when you shouldn't be and need a weaker spring. Where is your accelerator pump linkage set?

    I'd pop the valve covers and retorque the rockers to spec, then check to see if any of them barely move compared to the others as you turn it over.
  12. I actually just checked the rockers before I read this. I was hoping it was the cam just to get done with the problem, but cam is fine as far as lobes. Every rocker had equal and full lift.

    On the carb, I have everything stock out of the box on the new one, and it made no difference. I did take out one of the two throttle springs recently and that made no difference. I have tried adjusting the two idle mixture screws on the front of the carb, but they have made no difference to the idle speed, when before they did. The accelerator pump is at a stock setting. Before I put in the cam, I could literally have the throttle screw out all the way, and it would still run at 600 rpm in park. Now it needs way more throttle to stay running, as in 1600 rpm in park. Even then it will die sometimes. I have it turned down to 1000 rpm, just so putting it in gear isn't so hard on the tranny.

    It could still be carb or distributor related but I have taken it to several shops to get tuned, none of which solved the problem even though they said every setting was spot on for carb and ignition.

    It could still be something with the cam timing, but I don't really have the tools to diagnose it without tearing apart the engine.

    Also, if the distributor is "off a tooth or two" could it actually cause this problem? The last shop I took it to suggested it could be the problem but I don't see how that could effect anything since all it does is spin and as long as the spark occurs at the right time, timing should be right on, especially since it has been tuned several times.

    Edit: Which spring are you talking about? I had the weakest spring possible hold the metering rods up because whenever I let off the gas I would smell nothing but gas.
  13. If you have the blue(weakest) step up springs on the metering rods and the idle mixture screws still don't work then that is your problem. The carb is either dirty or defective, try removing the mixture screws, cleaning them, and blowing out the hole with an air gun. Reinstall the screws until they bottom out, turn them 1 1/2 turns out and set the idle per Edelbrock instructions. If that doesn't do it email Edelbrock and tell them about it.
  14. How/where are you taking your vacuum reading from?
  15. #15 84FordMan, Oct 12, 2008
    Last edited by a moderator: Apr 25, 2016
    Run diesel oil, so many weights of it nowadays (15W40, 5W40, 0W40, 30). Diesel oil still has the ZDDP additive that was found in motor oil decades ago, when flat tappet cams were the majority of factory camshafts.

    Lucas also sells a break-in additive, which is ZDDP as well.

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