My fiat runs on 3 cylinders only

[MNspiderman]

After my rebuild a month ago, my fiat still runs on 3 cylinders. the number 1 is the dead cylinder. Today i am going to check if my valve clearance magically changed, if not, I am thinking I have a broken rings. It runs great but only on 3 cylinders. When i pull off the plug wire, there is no change. I changed the wire, I changed the plug, I checked the 44idf's, they are all squirting, I changed the ignition to MSD, I put on a header which don't really matter except that the black paint on the number 1 cylinder is still on the header and the other three have burn'd off. And I can touch #1 exhaust tube while running. Still #1 is dead. If the rings are good, it can only be the valve gap. I believe all mine are set to .012 cold. could be .016 Intake and exhaust. I think i got that from guy croft, maybe. So any suggestions

[So Cal Mark]

perform a compression test before you do anything else. Broken rings won't result in 0 compression so the cylinder should fire, but weaker than the other 3.

[pope]

lack of spark or gas.
agree with Mark its not likely compression.

runs on three cylinders? Sounds like you might get a green rebate from the government motors

[wengr]

have you confirmed no spark at number 1? if so, could you have a bad #1 terminal in the cap?

[mbouse]

i agree with gary and greg. you may have changed wires, but you mention nothing about confirming there is spark at both ends of the wire. cap and rotor are suspect until proven otherwise.

[MNspiderman]

Ya, I did forget to mention that part. OOPS... #1 Sparks like a lightening bolt when i put the plug to the body and/or the plug wire. That MSD literally will throw the spark right out of the wire without a plug in it. So definately there is spark. Ya, I was pondering running over to Northern tool and getting a cheap compression gauge. I'd like to see myself what is going on in there. And as a recap, The exhaust pipe is cool, I pull the wire off the plug and there is no change in engine speed or idling charactoristics, etc.

[kilrwail]

Did you actually test the "new" plug? (Not just the wire.) Is it gapped at least 50 thou? MSD needs that.

[MNspiderman]

I tested the plug, two of them, gapped correctly. The cylinder wasn't working when I had the dual points set up in it right after the rebuild. It was sparking but weak. So I was hoping by putting in the MSD that it woulda fixed the dead cylinder. I probably have had it running a total of 1hr all together after the rebuild. just idling in the driveway. I haven't even had it running good enough for the 1500 rpm / 45min breakin period. I'm starting to question the valve shim gap. as soon as i have time, that is next.

[So Cal Mark]

is #1 firing at the right time?

[majicwrench]

Don't need a compression gauge to check compression. Disable ignition and crank engine. Should go "r-r-r-r-r-r-r", if it has a dead hole (one with no compression) it will go "r-r-r-uh-r-r-r-uh". Seriously, as the starter cranks against the cylinder without compression it will speed up momentarily.
On the other hand a compression tester is pretty cheap.
Large vacuum leak in the #1 runner will also keep that cylinder from firing.
Good luck, let us know!
Keith

[MNspiderman]

I'll give that a try Keith. I bought the distributor cap all ready on the dizzy. I hope its the right one. I heard they make two caps that look identical but aren't. something about rotor height or something. As for your question Mark.... with my aftermarket intake, it only has one vacuum port right on an intake runner neck. nothing on the carbs. The dizzy i got has a vacuum port as well. I don't have anything hooked up to that at the moment, I am figuring I didn't need any advancement at idle. Unless I have this all backwards in my head. Cuz old fords run off zero vacuum at idle and vacuum is gradual via a variable "vacuum" venturi port at the base of the carbonator. I am assuming fiat vacuum is the same where no vacuum is present at idle making it irrelivant if i have a vacuum line on my dizzy until i rev'er up. Right?

[MNspiderman]

FINALLY FIXED. Dont forget I installed 44IDF's with a PBS aftermarket intake which has single runners. Ended up being I had a piece of rubber stuck in the end of my jet on cylinder #1. So therefore no fuel. I appreciate all the advise from everyone. Especially the guy who said see if its getting fuel.

[sptcoupe]

This is the most common issue wth otherwise properly jetted, tuned and balanced carbs. The idle jets are tiny, and the smallest piece of dirt can block or partially cut off the fuel, and it will run on three cylinders, or perhaps run very rough at idle, because one cylinder is not getting all the fuel it needs. When you have either of these symptoms, do the following.

First, see if the engine smoothes out as you raise the rpms. If it does, it means the idle jets are likely clogged. If it doesn't, it is likley the main jets are the culprit. At around 3500 rpms, the carb transitions from the idle jet circuit to the main jet circuit, so this is a quick way to figure out if you need to look at the idle jets or the main jets.

If it looks like an idle jet problem (most likely between the two), one at a time, turn the idle mixture screws in until the engine idles worse (another cylinder falls off). Carefully keep track of how many turns you go in before the engine falls off, and return the screw to its original position. When you screw in a mixture screw and nothing changes, that is the clogged idle jet.

If it seems to be a main jet problem, then one at a time unscrew the emulsion tube and check to see if there is anything clogging the main jet or the draft holes right above the main jet. If you don't see anything, then you probably have something laying in the main intake ports at the bottom of main jet seating tube. Get a can of carb cleaner and spray it down the main jet seating tube. Put the emulsion tube back in and see if it improved. If so, you will need to take off the carb top and see what is lurking around in the float bowl.

BTW, you would be stunned at the things I have found in carbs - even new ones. Worst was a 1" X 1" piece of napkin in a float bowl on a set of carbs a frustrated owner sent me to look at.! Even new carbs have all kinds of small metal flakes and manufacturing debris (small rubber bits, small metal flakes, rubber pieces and some white stuff I ahve never been able to identify) left over in them. And as a final note, be very careful using compressed air to clean them, as there are "one way" channels that you can push things into that will never come out, you can make your accelerator pump look like a ballon, and you can damage the floats or change their adjustments pretty dramatically.

One more tip. I always use the in-line fuel filter frm a 1973 or 74 Datsun 240Z, as this is an in-line filter that is designed for a FI system, and is much more effective at stopping the small stuff coming from that 30 year old fuel tank.

[narfire]

Another post I'm gonna copy!!

[So Cal Mark]

this situation would be unique to either a dual carb motor or FI