69oldsguy

Hey guys. I've got a '69 Cutlass with the low compression 350 motor. six months ago I decided to change the 2 barrel for a four barrel. In the process of swapping out the intakes I learned that the engine has not had regular oil changes throughout its life because it was pretty chunky and crusty inside. Some of those chunks were falling down as I was removing the intake. I did my best to see and extract all of the chunks, but I can't say for certain that I got them all.

I installed a factory cast iron four barrel intake. Intake had been tanked and shot peened. It was clean. I installed a brand new Holley 650 carb. When everything was buttoned up and I started it, I had a completely dead cylinder. #3. Engine was running fine prior to this so I was pretty sure that there was nothing wrong in the ignition department, but I replaced everything anyway. Still #3 dead.

I was now concerned that a chunk had got down in there somewhere and was causing me grief. So I started running through possibilities in my head. A chunk down an intake port hanging a valve open. Doesn't seem possible, but something affecting a lifter causing a valve to not open. Problem with both of these scenarios is that it seems like I would be hearing something if I had a valve hanging open or a lifter collapsed. There would have to be some valve train noise. There is nothing. The motor is dead quiet.

I have looked at all of the plugs just to see what they look like. They all look good. Timing light says spark is present at all cylinders. Wouldn't be it, but timing is good and rock steady. I ran a compression check expecting to see something. Nothing. All cylinders including #3 are within a few pounds of each other at 125lbs. If you believe the odometer, the motor has just shy of 60,000 miles on it. I believe the odometer because I am the third owner of the car. The second owner was a 17 year old kid that had the car less than six months before he side swiped a parked car. Mom and dad sold the car to me. The original owner was in his 80's when he sold the car to the kid. This car was extremely unmolested. It still had a very original looking voltage regulator on the firewall when I bought it.

Regardless of the mileage, I still have no smoking gun and getting baffled. I know it's what I should do, but I really don't want to tear the motor down right now. I've got too many other irons in the fire right now. Odd thing is that if I crank the rpms up to 2000-2500 with the idle screw, you can hear it trying to clear up. As soon as I bring the idle back down it's still there. Could I have a lobe on the cam that has gone flat on me? That would be the all time coincidence if it did.

What do you guys think? I'm running low on ideas.

olds 307 and 403

This is a weird one. I have never seen a stock low performance Olds cam go flat. When my flat tappet aftermarket cam started losing lobes, it had a very noticeable tick. Really check everything over for a vacuum leak, that is probably your issue especially since you changed every ignition component including spark plugs, coil, plug wires, cap, rotor, points and condenser correct? What brand of spark plugs? I know some have had spark plugs fail out of the blue.

69oldsguy

I thought of that as well. I have not put my vacuum gauge on it, but If I cup my hand over the carb throat she should pick up if there was a leak. Nope. She just chokes down. It is only #3. With the motor running and warm I have pulled every plug wire off one by one and each time the cylinder drops out and picks right back up as I reconnect the plug wire except for #3. It's confusing the hell out of me.

I have not changed the coil because it would affect all cylinders. I'm running Autolite 86 spark plugs. I like the idea of a bad plug, but this is the second set of plugs and still missing.

Fun71

Normally I would suspect the intake manifold gasket for an issue that appeared after an intake swap.

You say #3 has spark, and it has compression, so what else could cause a problem?

69oldsguy

I have not been driving the car since this started. Only troubleshooting. I have had the timing light on all wires and am seeing that. Maybe there is enough voltage to trigger the light but not enough to jump the plug gap. I have not ohmed out the wires. I will have to do that tomorrow. Either way, I ordered my third set of everything ignition related today. The plug wires that are currently on the engine are from OReilly's. Don't remember the brand or if they were just generics. Everything I ordered today is coming from Summit and the wires are 8mm MSDs, but I will ohm them as well before I install them. I'm with you about what's left. My heads getting raw from me scratching it.

olds 307 and 403

Try NGK XR5 for spark plugs, the Japanese plugs are better than the now Chinese or Mexican made Autolite and A/C Delco plugs. Your carb is rich at idle, my Qjet since the retune is the same. With the original 78 idle tune I could spray carb cleaner down the throat and the idle would pick up a bunch. Now it almost instantly stalls if I spray carb cleaner or cup my hand over it. A vacuum leak will provide a miss, the leak might be right over the number 3 cylinder. Pull the plug and ground it, does it have consistent and healthy spark? You have a square to spreadbore adapter correct? There may be a leak there as well. Does the Holley have even streams of fuel on both sides at idle and above? None of this makes sense, sucks when an upgrade turns into a poor running car.

coppercutlass

A weak coil will do weird things. Specially if it's starting to go and starts having issues when hot. We had a brand new coil work perfect as soon as the temp of the cool would hit 170 it would buck miss and then not start until it hit 160.

gs72

Put a vacuum gauge on it before you buy more parts. If the needle is bouncing all over the place you have some junk hanging a valve open and it might not make any noise. I have seen chunks of carbon or even a small bolt float around in the intake and hang open a valve intermittently but compression test show no problem. Also the intake can leak from the underside and not be detectible from up top. You have to plug both valve cover breather holes and see if vacuum builds in the crankcase to verify this.

69oldsguy

Well, Thought I'd do an update on this. So everything is getting proper spark. Moved plug wires and plugs around, no difference. Installed my new plugs, wires, cap, rotor and points, no difference. All wires ohmed out good. Vacuum gauge was not dancing as a stuck valve would do, but it did have a wiggle and was low so I definitely have a vacuum leak. Took starting fluid and sprayed all around the mating surface of the intake and heads, nothing. Sprayed around the base of the carb, nothing. It must be leaking into the valley. So since I have to pull the intake back off and the motor is as crusty as it is, I'm not going to just clean things and re-install the intake. I'm going to pull the motor and rebuild it. I'm not going to play with it because I plan on daily driving this car.

Oh well, didn't want to do it right now, but it is what it is. At least the motor will be clean, fresh and running right.

gs72

A small steady wiggle on the vac gauge could be a exhaust valve not seating. A hard run on a test drive might dislodge something stuck in the valve. Otherwise you are on the right track with a rebuild. If the engine has good oil pressure and isn't burning oil I am more into repairing it instead of a full blown rebuild. But it is personal preference and also depends on what you find when you start pulling apart.

69oldsguy

I was hoping that as well. Took it out and put about 40 miles on with several WOT high rpm runs. No change. If it were not for how chunky it was inside, I would probably just do a valve job and reassemble. But I see no point in getting that far in it and leaving it all mucked up on the inside.

So it must be telling me it is time. I wanted to rebuild it anyway, just not now. But hey, this will make a perfect never ending pandemic project.

gs72

I hear you brother. I just came off of a 5 week covid leave. I’m Finally going back to work on Tuesday. I got all kinds of things done on my Cutlass while I was off. My experience with Covid was nothing more than a mild flu. Not saying it’s not serious but I’m 59 and it’s not the death sentence we were led to believe.

69oldsguy

Glad you're past it. I don't know what to think about it. I may or may not have had it. In the last year I've been sick with mild flu like symptoms, but never got tested because I never had the prolonged high fever that they required for testing here. On the other hand, it took a good friend of mine. He was 52 and seemed the same as me health wise. It seems to do nothing to some people, but others it has extreme prejudice. All I can say is whatever your opinion about it is or experience, stay healthy. Do what you feel is right for you, but stay healthy. I've seen both ends of the spectrum. A coworker had it and all he had was a sore throat for a few days. he is older than me. Then there is my friend. So I don't judge anyone. I just miss my friend.

gs72

I did say. I am not saying its not serious. But statistically it’s not what they say it is. But the virus does seem curiously selective doesn’t it.

69oldsguy

I'm sorry if it sounded like I was saying that you were down playing it. I wasn't. I'm in agreement with you about the information the gov is spreading. My beef is with the virus itself. At our age I don't like giving up a year of my life for anything and I damn sure don't like losing friends to it. I was just meaning that since there is no way for a person to know how it is going to affect them. They have to be the one to make the call as to what they feel safe with. If you ask my wife, I am too lax about it. But it's like I said, I don't like having a year or more of my life taken from me.

So, stay healthy and enjoy / live life.

gs72

Thanks. I think our thoughts are in total alignment. This has been a very frustrating year for all of us. God bless you and your family.