I had a 2056cc built from my short block about ten years ago. The shop that did it specialized in track & street 911s and didn't have much experience with Type IV engines, but I provided a lot of guidance from 914world. It's got twin EMPI 40 IDF carbs.

A few years ago, I started taking the car to a different shop. The owner is the regional PCA expert for the 914.

The first time he did the valve adjustment, he insisted that I don't need Chromoly pushrods, and replaced them with stock pushrods from his inventory. This confused me since a 2056 has different valve geometry from stock and needs cut-to-length rods, but he insisted. This was a few years ago.

About a year ago, he noted that a single cylinder (#3 if I remember correctly) isn't getting fuel at idle, but seems okay under acceleration. It led to a pretty lumpy idle, but was inconsistent. Sometimes it would idle smoothly, other times I'd have to feather the gas pedal to keep it idling smoothly -- or at all.

I went to a local cruise event in May and the car ran beautifully. Idled well, had plenty of power. The next time I drove the car (about a week later), it was clear to me that it was running on 3 cylinders. Sounds bad, low on power. I've avoided driving it since, except once or twice to see if it was a transient issue.

I suspect one of two things:
1. I need a carb rebuild (jets gummed up?)
OR
2. The valves have gotten way out of adjustment, perhaps because of the stock pushrods, causing one cylinder to have no compression

What's my next move here?

Is there anyone local to DC/NOVA who wants to tinker with me? I'm not capable of doing much myself but I'll buy beer for those would can offer help, tools, etc.

Verify the intakes and carbs are totally sealed up. Even a small vacuum leak in the intake gasket will cause a low enough signal to not draw fuel at low rpm. Does the cylinder come back at higher RPM?

You said it was intermittent before. Is it still intermittent? Do you know which cylinder it is? Can you pull that plug wire and verify (ie. no change)?

It could be a distributor thing as well. I don't know much about the pushrod wisdom.

Even though you think it's fuel, I always look at spark first. Could be a plug wire has come loose or gone bad. Always start with the easy first.

Happened in my bug a few times.
Definitely the first place id look.

When were the valves last reset ? worth doing anyway,ignition system all good ?,have you checked the spark plugs for instance?,if you can check #3 throat on the carb with a sychro-meter you will find the imbalance @ idle from the other throats,if you don't have one its a handy tool worth buying if you have carbs,you can't tune carbs without one besides.
Your carbs may not need a rebuild but worth checking the idle jets are clear,a blocked one will cause the issue you have,appears the IDF design is prone to this and the Empi copies shouldn't be any differant ,I have a six 911 engine but still run 2 fuel filters ...cheap insurance for this issue.
You could have a vacuum leak but IMO you would have that on both throats on that side of the engine,I'am not a big fan of the thick gaskets that come with Empi inlet mainfold kits and don't use them,they are soft and under tension they compress and leak.
Good luck sorting this,cheers.

If you don't mind making the trek up to mount airy, MD we can check it and you can use any and all of my carb tools. I'm no expert, but know enough to be dangerous.

if the empi carbs are like redline weber 40 idf's, i have had the same issue (on 356), usually with the #3 cylinder - my #3 idle jet gets clogged - i carefully remove/clean/replace - if the car sits, it happens more - it took me a while of checking everything else before realizing this was the problem - hope this helps

Increasing the cylinder size by 2mm does not change the valve geometry. If there was no cam change, there would be no reason to change the geometry. If the Chromolly pushrods were cut to the proper length, they are an upgrade. Changing back to sodium filled rods will not cause one cylinder to just drop out. Your problem is in the carbs, or the valve adjustment itself.

I would start finding another mechanic.

The first shop built your engine with specific valve geometry that would give it more efficiency and a longer lifespan - as well as making the valves much easier to adjust. Your current mechanic threw that all out the window because he did not understand something that was not stock.

Do you know what cylinder isn't firing? That's a really helpful bit if information, and is easy to find.

With the car running lumpy, remove spark plug leads one at a time from the dizzy. When you pull a lead that cylinder will stop firing and the car will idle very poorly. Put the lead back on. Try the next lead till the car's idle does not change. That is your bad cylinder.

That said - I would give your car a full basic tuneup.
* clean the heck out of your carbs. At the very least pull the idle jets out of the side and blow them clean an clear.
* adjust your valves
* replace the cap and rotor on your dizzy
* replace your spark leads
* check ignition timing
* Check (and maybe replace) your fuel filter.

And I would give serious thought to going back to steel cut to length pushrods. I bet he pulled them and then did not mark which one went in which bore and did not want to take the time to figure it out. I can't believe your mechanic trashed them. But this would require going through all the testing to make sure the pushrods were the right length, which is a pain and maybe impossible with the engine in the car.

Zach

I think a lot of shops want to put in chromoly pushrods because they're more idiot proof – less likely to burn a valve because they don't expand as much as the engine with heat. The down side is you won't get as much lift at running temperature if you start with the same gap. Unless you have heavier valve springs, there's no reason to run them.

You say they built up the motor from the short block meaning the cam and lifters wouldn't have been changed, so no reason to change the pushrod length from stock. I think your new mechanic is fine.

Wait what?!

The chromoly push rods are used for 1 reason -

They are there to get the correct valve geometry and lift based on cam. You can't necessarily get that with the stock pushrods. I was able to on my 2056 build, but only because tabari was able to remove the end of the stock aluminum PR end and trim it back, then re-attach.

One of the benefits they have is that you are able to run 0 lash. You can do this because unlike aluminum they do not expand when hot. The aluminum does this which is why the valve lash is set cold. When both engines are hot the amount of lift should be the same. If anything you would get less lift on a cold engine with the stock PR.

It's correct to say that a cut to length pushrod is used to get the correct geometry. You could use aluminum or chromoly cut to length pushrods. It's another discussion about which will give the most lift at running temperature and cold. As you say, they don't expand as aluminum does, so if you run them at 0 cold, when the engine expands at operating temps, you get less lift.

Still not following Nathan.

The valve lash is not put in because the engineer likes a little gap. They put them in because they decided that when the engine is up to temp the aluminum would have expanded .006/.008.

Let's assume the valve lash was set a 0 for both aluminum and chromoly PR on the same engine. When cold and the engine is rotated lets say the full lift is .400. When at temp the chromoly PR show a full lift of .400. The chromoly is not expanding the rod therefore you can run 0 lash. With the aluminum PR they now have a lift of .450 and are not allowing the valve to close completely. I don't have the correct math on the full lift of the expanded aluminum PR, but you get the idea. That lash for the aluminum PR is there as a barrier to allow for expansion. If they are set at the spec of .006/.008 accordingly, then once up to temp the aluminum PR have what should be 0 lash between the lifter and the rocker. The lift should not be any more than .400 as the additional gap has now been removed. Therefore, aluminum PR should not provide any additional valve lift.

I understand that the engineers at VW spec .006–.008" gap for aluminum pushrods because with expansion of the motor and the pushrods this was determined to give, at operating temp, close to 0 lash.

I'm not an expert, but as I understand it....

Both chromoly and aluminum pushrods will expand, it's said aluminum twice as much as chromoly. The jugs, case and heads also expand though. This means that the aluminum pushrods aren't just expanding .006–.008" to reach 0 lash hot.

I believe it was Jake Raby that came up with setting chromoly pushrods to 0 lash loose. That provided the best lift at temperature. You can't set them any tighter than that or the valve wouldn't close cold, and you wouldn't be able to start the motor (no compression).

Iirc, testing results said that chromoly pushrods would be running at .004" lash hot. That's why people say chromoly pushrods are noisy. Now granted a hot motor requires less fuel, but I think that should be built into your jetting if you have carbs. If you want to maximize your cam, that aluminum PR's are how you are going to get maximum lift.

Like I said, I'm not an expert, but that's how I understand the discussion.

I set my chromolly's at 0 lash.

After reading thru this, I have a question. I have a -6 (not bragging, it pertains to the topic), so no pushrods. Rocker is right on the cam on one side, and valve on the other. All of them are steel. So if the valve lash is solely because of push rod expansion, why shouldn't/couldn't I run with near zero lash?
Factory manual says 0.10 and 0.15mm lash on the valves and that's what I do. So there must be something on both engines that affects rocker/value clearance besides pushrods.

Can't help with the original 3 cylinders except to agree on checking plug/ignition first.

Different things are expanding in the rocker on cam setup in the 911 engine, rocker, the cam, the valve, the head. As Nathan stated expansion is happening in the engine when getting to temp.