RPM varies wildly small block

[MoparLeo]

A little safety tip to throw out there. Number one. Always, always have a properly rated fire extinguisher handy when working on the fuel or electrical system on your car.
The only purpose of spraying around the intake manifold. carb base with a "fluid" is to find a vacuum leak by finding an RPM change, Correct ? Does it matter if the RPM's go up OR down to find the leak? It is very dangerous to be spaying ANY flammable liquid on a hot/running engine.. We always just used a spray bottle with water. The RPM's will drop when there is a vacuum leak detected with water and No chance of any fire/damage in the engine bay. Another way if you must use a flammable is with propane gas. Heavier than air, won't swell the gaskets from soaking them .
https://www.hunker.com/13414896/how-to-find-a-vacuum-leak-with-propane

 

[BSB67]

There has to be improvement from all work he did now right?
Strange thing that only some of the old rockers had so much elongation and some were still close the OEM specs, maybe a few were already replaced in the past by a previous owner or so?
You would say they wear out evenly all together.

With the information provided, I'm not necessarily convinced one way or the other. A stamped hole in a stamped rocker with elongation built into the design will have variation. Second, the "top" part of the the hole has no importance as does the relationship between the rockers shaft saddle relative to the top of the hole. A better measurement for wear is the actual thickness of the rocker saddle, or the saddle relationship to the rocker valve tip and push rod cup. Finally, hydraulic lifters have a lot of forgiveness.

The OP is touching/changing a bunch of things and hopefully he fixes is problem(s). But it's hard to believe that rocker arms cause or even contribute to idle rpm fluctuation.

 

[Wietse]

With the information provided, I'm not necessarily convinced one way or the other. A stamped hole in a stamped rocker with elongation built into the design will have variation. Second, the "top" part of the the hole has no importance as does the relationship between the rockers shaft saddle relative to the top of the hole. A better measurement for wear is the actual thickness of the rocker saddle, or the saddle relationship to the rocker valve tip and push rod cup. Finally, hydraulic lifters have a lot of forgiveness.

The OP is touching/changing a bunch of things and hopefully he fixes is problem(s). But it's hard to believe that rocker arms cause or even contribute to idle rpm fluctuation.

I know what you mean with regards to the holes in the rocker, but that elongation must have come from the bottom side wear the contact surface is.
And indeed, a hydraulic lifter will compensate the wear for some time, until it runs out of pre-load.
Then you end up with a variable camshaft
Lots of things found and corrected but all for the good.
The fuel feed being poor would not really cause an issue here i think, getting 2 psi or 6 psi fuel pressure at idle would not make a difference at idle.
The deviation seen in fuel pressure is more likely an effect of the fluctuating rpm than the cause.
A leaking float valve could be, and cause the fuel bowl to overflow?
If the engine is getting sufficient air the additional fuel will increase the rpm.

 

[BSB67]

Of course if you run out of pre-load and becomes a positive clearance (lash), it will start sounding (ticking) like a solid lifter and will be readily apparent. But it won't cause the idle rpm problem described.

 

[Wietse]

But it won't cause the idle rpm problem described.

Agreed, this is another issue but i will obviously run better after it has been rectified.

 

[Scott19_72]

Hi All,

It's been about 9-10 months from my original post. In case anyone is looking at this thread for conclusions. YES, I did get it sorted out and have a perfect idle. I'm not quite daily driving my car but I drive it quite a bit now.

I did not have burned valves or any type of cylinder pressure problem, which is what I was most afraid of (I would have needed to go with aluminum heads if I had pulled them. And I wasn't going to skip putting TTI headers on if I had to swap the heads. It would have become a $3K problem. Lol!).

In the end the following problems were present:

1) Bad Chrysler electronic ignition box. $50 house brand parts store chrome box improved idle significantly. I was always told electrical boxes either worked or you get nothing. Turns out ours will let an engine run rough. Start with this if you have wild RPM variation like I had.

2) Fuel. I bought a new 1405 Carb to replace the one I put on in '99 or so. Cleaning my old one over and over or adjusting the floats again and again didn't buy me very much. I also added a gauge and then a regulator. I was running between 6 & 7psi out of a 20+ year old mechanical pump. Regulating it to 5.5lbs with a $30 Mr Gasket regulator seemed to smooth it out when I was driving it and especially accelerating. Do these things next.

3) Valve train was sloppy. See the video I posted in the comments. I had a miss I just couldn't sort out with plugs & wires. As pictured in my reply above the variation in these tolerances was ridiculous. Some rattled to the touch. I must have got a 50/50 split between "They just do that" and "Whoa! Those are bad" comments everywhere I posted questions. They don't just do that. Call Mancini and get yourself a new set for $225. I had a weak lifter in there too (I could push the pushrod down with my fingers and I couldn't do this on any others). Can't tell for sure if it was the culprit but I replaced it for $8 at the local parts store. This is more involved but was worth the effort to me.

I hope this helps if anyone has an issue like this, good luck out there!

 

[Scott19_72]

It's not clear from your post. Is the problem fixed and the car runs well? Always cautious to not take the victory lap too soon.

Good luck

Yes! I posted a quick follow up to stay online for the ages. Everything I did yielded incremental improvement. The ignition box and carb were the biggest.

 

[Scott19_72]

There has to be improvement from all work he did now right?
Strange thing that only some of the old rockers had so much elongation and some were still close the OEM specs, maybe a few were already replaced in the past by a previous owner or so?
You would say they wear out evenly all together.

I rebuilt this engine in '99 and put the rockers that were on it then back on. I proceeded to drive it everywhere at 120mph after that and didn't do them any favors. I was looooong overdue for a new set, it turns out.

As far as did this improve the idle, it did to an extent but you're spot on, it wasn't the root cause of the issue. The ignition box and carb made much bigger improvements. It holds smooth idle and perfect, steady vacuum now between all of these things. I posted a quick conclusion just now to help anyone else out who may need it down the road.