hurst1

Hello.

We noticed a misfire while we are in gear. While in park we notice nothing. Shifting into drive we notice a sudden drop pretty consistenly. then it cycles through and we notice it again. Pretty much feels like its in the same intervals. We are a 73 omega with a olds 350. Where should we start our first? Cap? rotor? Arching? Plugs. We are at a loss due to it only happening while in gear.

Thanks for the help.

Bill

oldcutlass

When was the last time it was tuned up? What is the timing and dwell (if applicable settings)? Have you adjusted the carburetor air/fuel mixture screws? Pull the spark plugs and read them to see what they look like. Look down into the carb when the engine is idling to see if there is any big drops of fuel dribbling.

hurst1

I have a pertronix ignitor inside distributor, timing is set at 14-16, in the last 3 months we had the carb professionally rebuilt byKen at Everyday Performance. I have done no adjusting to the air/fuel screws. I will start with the spark plugs, and move on from there

Thanks Bill

Fun71

Sounds as if it happens when there is a load on the engine, which makes sense. As said, start with a full tuneup.

rocketraider

Set the plug gap at .045 and make sure you have a good hot coil. The Pertronix coil is made to work with the Ignitor and is a good start. Also- is the Ignitor wired to switched 12V? They'll work if they're wired to the factory coil resistance wire, but start and run better on 12V.

Check resistance on all the plug wires and make sure they have good connection at the cap and spark plug ends. 10-12,000 ohms maximum resistance per foot of length.

Check rotor tip and tower terminals inside the cap for any corrosion or signs of arcing. Also check cap closely for hairline cracks.

Torque the carb mounting bolts to 10-15 lb/ft and sniff around for vacuum leaks. No vacuum hose or accessory is beyond suspicion. If you have a dwell-tachometer, adjust idle mixture to get highest rpm in DRIVE at normal curb idle speed. If you have a vacuum gage, aim for highest manifold vacuum reading at normal curb idle speed.

If car still has all its emissions equipment, you need a 73 Olds factory chassis service manual. Some of that stuff can make an engine do weird things, especially a leaking or stuck EGR valve.

Good luck!

coppercutlass

Check the timing at idle and then have someone check it while you put it in gear. Your timing could be cutting back as you drop RPM. If you advanced your timing you may be setting up your timing on the centrifugal . I ran into this issue recently. My old engine ( stout 350) liked to idle between 800 to 850. The new engine which was a few hairs hotter with a solid lifter cam liked to idle about 950 to 900. It was enough to start ramping up the timing at idle and it would start to idle really bad in gear and I would drop RPM gradually until it died. I changed my advance spring and problem solved. The timing could be bouncing at your on load idle speed. Check for steadiness too.

hurst1

Thanks eveyone for the tips and tricks. Found a vacuum leak on the underside of the PCV hose connected to the carb. Amazing that this leak would create such havok. Changed out to PCV Gasket, Valve , new hose, new plugs, and found that the Distributor Cap was loose. Must of not been secured properly with those little twist clamps. Re-alligned cap with rotor, made sure its snug and completed. What a difference something so small makes. So much quieter, adjusted timing. Will wait til rain stops to adjust timing up to 14-16, and work on Fuel Mixture and check vacuum and make adjustments if necessary.

Any tips and tricks for Checking Vacuum and working with Mixture screws.

Thanks Bill

Vintage Chief

To adjust vacuum correctly, IMO - you first need to know what the expected vacuum should be per your CSM (or, as listed on your radiator shroud tag).

(1) Ensure your distributor contact (breaker) points have the correct gap;
(2) Ensure your dwell angle is adjusted correctly per your CSM (or, radiator shroud tag);
(3) Adjust your ignition timing.

Hook up a vacuum gauge correctly as per either your CSM or via the instructions supplied w/ the vacuum gauge - very easy to perform. Be certain you follow the directions for unplugging vacuum lines correctly when adjusting dwell angle, and when monitoring your vacuum.
Example: On my 350 CID I can get upwards of 21-23.5 in. hg of vacuum but the engine will be completely incorrect based upon vacuum alone. My engine operates optimally @ 17.5 in. hg. Therefore, IMO, it is important to start the process in correct sequence. Dwell angle>timing>carburetor.

Only after the above three are adequately adjusted should you then maneuver about your choke (fast idle), slow idle & mixture settings, IMO.

Vintage Chief

FWIW, here is probably one of the best explanations of how distributor advance timing operates and (IMO) why it is critical to first ensure your breaker contact point gap is set correctly, your dwell angle is set correctly and your timing is set correctly before you maneuver (throw air & fuel) in the cylinders. Dwell and timing are critical. You're wasting fuel or not using enough fuel if you don't get the dwell & timing correct - first. You might consider the football is the amount of air & fuel the receiver must catch.

Vintage Chief

Maybe I should have paid better attention (LOL). You have a pertronix ign so it makes the breaker contact point gap mute. None-the-less, the sequence is still critical, IMO.

hurst1

Thanks for the information. I will attempt once the weather warms up a little.

oldcutlass

I always adjust my carb last after timing. Hook your vacuum gauge to a manifold vacuum port. The 2 air/fuel screws should each have pretty close the same amount of turns from fully closed to the point at which registers your vacuum gauge registers the highest vacuum. This is trial and error with a bit of waiting in between small adjustments until the engine settles and you may have to reset your idle speed a few times. Once you get them adjusted I turn each one in an 1/8 turn.

hurst1

Thank You. Ill update once the weather clears here.