Rough Run

[geunther]

Ive been fighting very rough running. In looking at previous posts on the subject it appears there are many culprits. Ive checked everything twice and still can't find out why.

I checked dwell and it is right at 30 degrees with little fluctuation. When I try to check timing I find that it is all over the place. One moment its at 6 degrees, then it bounces off the mark, guessing it to be 14 to 18 degrees (vacuum disconnected, port on carb plugged). Obviously this coincides with the rough running but I don't know if the rough running is causing the timing fluctuation or the other way around.

I pulled the distributor and the end play is about .080. I am finding conflicting information if this is out of spec or not. My instinct tells me it could cause a timing fluctuation but not sure it would cause the 10 to 15 degree fluctuation.

72 350, stock points distributor 1112047

Thoughts?

[Arnulfo]

A loose timing chain can cause what you've described.

[geunther]

Originally Posted by Arnulfo

A loose timing chain can cause what you've described.

Good call. I have a water pump on its way to me. When I replace that I will pull of the timing cover and check things out.

[geezer#99]

Easy to check timing chain.
Point rotor at #1 plug wire on the cap.
Manually rotate balancer first one way and then the other and see how many degrees of deflection you have.
A good chain might have only 2 to 4 degrees.

[asolde]

Have you checked for air leaks around you intake? Take a can of carb/choke cleaner and spray around your intake manifold while your engine is running and listen for rpm increase. Your intake gaskets may need to be replaced,

[special-K]

It sounds like a worn distributor. I've had a timing chain so loose it slapped the timing cover when I let off. I had the parts, but my boss borrowed the truck and came back walking. I guess he didn't baby it like I was. This led to a rebuilt engine because pushrods and valves got bent (yeah, I think he was in it when it happened). Why the story? Because I don't think a timing chain could be any more worn than that one and that truck ran great. Nice and smooth, certainly not rough. In fact, it ran so good my boss was out enjoying himself. If it was the timing chain causing the rough running, wouldn't it only be when the chain slacked-up?

[67 chevelle]

distributor is way out ,should have 10 thousandths play , not 80 , here is a great link , and yes that is causing timing fluctuation
http://www.rustynutscarclub.com/HEI.htm

[geunther]

Have you checked for air leaks around the intake?

I did check and found no issues.

here is a great link

I checked out rustynutscarb earlier and the .010 it describes as being the tolerance makes sense. Problem is some other sites say much higher and admittedly I don't know. .010 to .015 seems to be what I should strive for.

The confusing part, it ran like a top up until a couple of weeks ago. Then it sputtered once or twice, then it got worse. Over the course of about 15 minutes and ~10 miles.

I may throw a HEI in just to see if that corrects the issue. I want to stay with the stock, or at least stock looking distributor. As you all know, the worst part is not knowing what it is. I can handle having to fix anything. Ill definitely update the post once I check out the distributor/timing chain and figure it out.

Thanks!

[Sklptrljay]

Originally Posted by geunther

I did check and found no issues.



I checked out rustynutscarb earlier and the .010 it describes as being the tolerance makes sense. Problem is some other sites say much higher and admittedly I don't know. .010 to .015 seems to be what I should strive for.

The confusing part, it ran like a top up until a couple of weeks ago. Then it sputtered once or twice, then it got worse. Over the course of about 15 minutes and ~10 miles.

I may throw a HEI in just to see if that corrects the issue. I want to stay with the stock, or at least stock looking distributor. As you all know, the worst part is not knowing what it is. I can handle having to fix anything. Ill definitely update the post once I check out the distributor/timing chain and figure it out.

Thanks!

You might want to check out a distributor system made by pertronix. It's electronic and can installed inside a points distributor.

[Redline novdog]

Sure you don't have a stuck/sticking valve? It would run rough and create havok on your vacuum.Would a bad plug wire do such? I found I have a bad cyl. with an ir thermometer from harbor freight. Bought it for my powder coating. works good on cyl temp at the exhaust /header.

[geunther]

When I checked the vacuum it was fairly steady, a little low I thought at about 10, but steady.

Regarding the mechanical advance. With the cap off, how sloppy should all that be? It seems I can move things around and move it to advanced pretty easily. Seems loose to me, but then again its been 30 years since I worked on one of these.

[special-K]

Have you checked your points? With the distributor running out it may have caused excessive wear in the points and the moment it started running rough all at once was the moment the points failed. May run better on a worn dizzy with new points. If you are happy with original, no need to go electronic. HEIs wear out too, just as all other distributors do. I've had more trouble from electronics than I ever have with points

[geunther]

Originally Posted by special-K

Have you checked your points?

I installed new points and it ran fine long enough to drive down the road about 5 to 8 miles. Now its doing it all over again. Because of that I don't think its distributor end play or excessive timing chain stretch. This is very frustrating.

New plugs, new plug wires, new (rebuilt carb), new fuel filter, etc. I can barely keep it running long enough to move from the cab to the engine compartment.

The pic is of the first set of points.

[GunNuts]

Do you have a remote starter button?

Use a remote starter button so you can do all your work from under the hood.

When I was a kid I liked 100 dollar cars... You wear out helpers like that so I started using remotes.

I wonder what I ever did with those some times.

[geunther]

Originally Posted by GunNuts

Do you have a remote starter button?

I remember those things too, and man they made life easier. But you can't even find a dwell meter hardly any more so I bet the remote starters are in the same bin. I called a parts store looking and the clerk actually asked, "What is it used for?" My response was, "Never mind". One would be easy to make though.

On to the rough running. Sadly I think I know what it is. After I try to start it or after it runs for a short minute, I can hear some significant clicks. I think I was believing them to be "cooling clicks", you know the tink tink after something has been run hard. Well obviously it is not getting hot enough to have such significant cooling clicks. What I now think is happening is some valves are sticking and after a moment or two (when not running) the lifters are being pushed down by the valve springs. I actually started to count the clicks to make sure it was not over 16. I will do some more counting but that is where I am leaning. (As mentioned by redline novdog)

I guess there is a rebuild in my future.

[cypressbog]

Maybe try cleaning the valves before a tear-down. Some old school methods is to get your rpm's around 2k to 3k and slowly pour ATF down the carb until engine starts to choke, then stop to let engine recover. Continue doing this until you use the entire quart of ATF. It smokes like crazy, so do this outside with the wind going away from neighbors, etc. sea foam or marvels mystery oil are alternates. Don't try kerosene, trust me.

I've seen mechanics use straight water to steam clean the valves and piston tops, but I couldn't ever feel comfortable about that.

[geunther]

Originally Posted by cypressbog

Maybe try cleaning the valves before a tear-down.

Not sure I can get it to run that long, and that high of an rpm. I am back to square one. Compression test showed 120 ish for all cylinders.

It is clearly beyond my capabilities. I literally do not know what to try next. Sorry for the whining, just frustrated beyond belief.

[elkniks]

It has been a while since I have seen a set of Chevy points, is the condenser attached to the points or a separate unit?

[geunther]

Originally Posted by elkniks

It has been a while since I have seen a set of Chevy points, is the condenser attached to the points or a separate unit?

Its a separate unit, clamped in distributor across from points.

So after all the drama, here is where I am at. I do believe the first issue was the points as you can probably tell from the picture. But in chasing down the source of the problem I damaged my fuel inlet. I then moved to another carb.

I am fairly sure my current issue is a vacuum leak, but for the life of me I can't find it and it is sporadic. I started the truck a bit ago and it ran great. After it warmed a bit it started slugging around again and running rough. I can't replicate the leak but after its warmed it goes away for a few moments at a time and runs well again, then back to rough running.

I have sprayed so much carb cleaner Id venture a guess I have one of the cleanest out there by now. I have plugged all the vacuum sources at the carb for isolation. I don't think its the idle mixture screws as it runs rough at all RPMs and throttle positions.

Thanks for listening.

[Security guy]

Put a timing light on the plug wires one by one.. When it starts running rough, see if its an electrical problem. I don't think you need a rebuild because you said it runs fine sometimes. Isn't there a capacitor in the points distributor? Possibly failing when it gets warm not allowing full voltage to the points? Just thinking out loud..

[clemsonteg]

What about the condensor? Was it replaced with the points? I had some similar issues, I ended up replacing te points with a petronix unit, rebuilt the carb, and replaced the gas tank because I wanted it out of the cab and I found most of the filter sock in the carb. That seemed to have cured my issue.

Before replacing the points I had previously replaced the distributor with a reman unit because of a locked up centrifugal advance on my old one.


Do you have power brakes? Maybe a leaky booster causing a vac leak?

[leftybass209]

Since you do have some play in the distributor, you should consider rebuilding, or switching to HEI. Sometimes it's tough to track down crazy issues like this. Do you know if your vacuum advance is in good condition? Also, what port are you running the advance hose to?

[clemsonteg]

Originally Posted by leftybass209

Since you do have some play in the distributor, you should consider rebuilding, or switching to HEI. Sometimes it's tough to track down crazy issues like this. Do you know if your vacuum advance is in good condition? Also, what port are you running the advance hose to?

Good point. I would have to say that I had to replace the vacuum pot on the reman distributor after a few months because of a busted diaphragm. That was one of the reason I replaced the old distributor. Sometimes new parts fail right out of the box.

[leftybass209]

Originally Posted by clemsonteg

Good point. I would have to say that I had to replace the vacuum pot on the reman distributor after a few months because of a busted diaphragm. That was one of the reason I replaced the old distributor. Sometimes new parts fail right out of the box.

Also, some vacuum cans are designed to advance at differing times. If you don't have the right one, your engine may be advancing too early, or too late. There's a lot of variables to consider exactly what could be happening if that's the problem. A new VA and worn springs won't work well either.

[geunther]

Originally Posted by Security guy

Isn't there a capacitor in the points distributor? Possibly failing when it gets warm not allowing full voltage to the points? Just thinking out loud..

Admittedly I did not change out the capacitor, but I did test it. Tested fine and not sure how they are affected by heat. Might be worth a try to put a new one in.

Do you have power brakes? Maybe a leaky booster causing a vac leak?

I do have power brakes, but I plugged the vacuum port on the base plate to isolate. But...I reinstalled after it ran fine. I may disconnect again to see if the roughness comes back again after warm up. Would issues caused by a leaky brake diaphragm be sporadic?

Originally Posted by leftybass209

Do you know if your vacuum advance is in good condition? Also, what port are you running the advance hose to?

The VA is a little worse for wear, I may tinker with that a bit. Running VA to the pass side of carb (see pic). It was disconnected at times but the rough running was still present.

I seriously appreciate everyone's input. I know it gets old to keep reading the same post over and over because I keep positing to it and moving it up.

I agree that I am probably chasing around a couple of different issues. Ill tinker some more but if no luck I will wait until my carb gets repaired.

I do want to upgrade my distributor, just not sure of the path. I buddy may loan me an HEI just to see if that is the issue.