Dropping cylinder issue

compression test the cylinders?valve adjustment check?

One bad on each side ….. you've already checked some items , this is what I would do next: 

1) Check for good spark by pulling one wire at a time at cap

2) Check for good spark all four plugs

3) Pull valve covers , confirm all is in tact and valves are set to .006 ( if chrome molly .001aka finger twist)  then with coil AND electronic ignition disconnected, crank engine to confirm all rockers are operation normally

3) Do a compression check  the bare minimum is 90 lbs in each cylinder for it to run.

3) Do a leak down test on all cylinders

This should show the issue

Alan

I have few things to do this am before I can get back to the car.  I will go down your check list and report back.

"I thought it might be an issue with the distributor cap. I had a spare cap and switched it out.  The  non-responding  cylinder jump to the other side of the engine."

OK, sounds like a couple of bad distributor caps (it happens) that might have corroded contacts inside.  Switching plug wires won't change anything if the cap is bad.

After that I would swap out the plugs (they're cheap) and see if it is plugs fouling.

What plugs are you running (make/model) BTW?

Hi Bobby, is the non firing cylinder (s) at idle only or does it remain the same as you open the throttle? If it is only occurring while the carbs are in running on the idle circuit and goes away once you transition to the main jets you may need different size idle jets or your compression is weak and doesn't pull enough vacuum to draw fuel through the carbs as it should. The dual carbs will bring to light all engine issues that you don't usually see with a single center mounted carb. The engine must be balanced on the compression and leak down within reason. Good luck. I have been exactly where you are with engines I have owned. Be patient, you will figure this out and when you do, oh the joy of the happy running engine. Nothing like in my book!

Re-read his post.  It had been running fine for two weeks, then started running rough.  Nothing major has changed on the engine and I seriously doubt the compression has changed - possible, sure, but unlikely.

Bob, there is a slight chance that you have a vacuum leak between cylinders where the intake manifolds meet the heads.  There isn’t much metal between ports and I have seen that center section get sucked out, especially if you used those super-mushy CB manifold gaskets.  You can detect it with a spray of carb cleaner from the outside because it’s on the inside.

Apart from that, I’m still thinking disti cap, rotor or plugs, but I assume you used a third disti cap that came with the new Pertronics disti so that eliminates another variable.  All that I see left is plugs or internal manifold leak.

hey guys 

I have not had a chance to get back to the car yet.  But have check for vacuum leaks at the manifold cylinder head by spraying carb cleaner near the matting area and the idle does not change.  I did a compression test a month or so ago  when I discover the original vacuum leak.  All cylinders were good on compression.    I have cleaned both carbs numerous times over the last week so I am sure they aren't the issue.  I feel like it is an electrical problem by the way the dead cylinder keeps changing.  What could cause an inconsistent weak spark  between cylinders?

I am getting ready to watch my Spartans get all beat up by the Buckeyes.  So I probably won't get back to the car today.

Gordon

I did replaced the coil, cap and distributor with all new pertronix brand.  I really thought that was going to be problem.

Sounds like a short somewhere! GO BUCKS!!!!!!

FYI the best method to check for vac leaks is using an unlit propane bottle, shoot a bit of propane around .   FYI some of the carb cleaners are no longer flammable.

How old are the plug wires?

Also, any significant change in the weather there in the past two weeks? Like first rainy weather in a while? Or first cold mornings in a while, with frost and/or dew?

If there's a leak between the intake ports you won't find it from the outside. Gordon typo'd that; he meant to write "you can't" detect it from the outside. 

Ed's right on my Typo.

If the leak is between cylinders you can't detect it from the outside.

Ok Guys

I am starting at square one with manifold gaskets.  I have removed the intakes and cleaned them up.  I will probably do the sand paper on a sheet of glass to make sure they are perfectly flat.

I am looking for recommendations on gaskets and/or sealers.   I know there are rubber type gaskets and fiber types.  I have also heard mentioned Loctite 510 with no gasket.  Any guidance would be welcomed.

Thanks 

If you can't access gaskets easily you can by a roll of gasket material at NAPA and cut them using the old one as a template

As far as I know, I’m the only guy running Locktite 510 flange sealer with no gasket on a T-1 engine.  It was recommended by Jake Raby and works well, for me.  I really opened up the ports on my heads with very little “meat” left between ports (about 1/8”) so it kept sucking the gasket material out between intake ports.

I took a chance that the flange surface on my heads was already flat and even because the engine was in the car and inaccessible to try to polish it, but the light milling marks were there on the head so I figured it was pretty flat and it was.  I sanded/polished just the lower end intake manifold flange.  Sandpaper on a sheet of glass with 300, 400, 600, 800, 1200 paper.  Once you put it together with Locktite 510 it will be MUCH harder to remove the manifolds in the future.  That can be a problem for CMC owners because often the intake manifolds must be removed to install/remove the engine for clearance with the rear frame horse shoe.

When I ran gaskets, I had much better luck with stock thickness gaskets than with those thick, mushy gaskets from CB.  My engine would suck the mushier ones in regularly, while the stock thickness seemed to last longer (years).  

Just food for thought.   Gordon

Gordon:

I order the empi intake gaskets below.  I was thing of using permatex permasheild to dress the gaskets on each side.  What are your thoughts?

https://www.amazon.com/Permate...essing/dp/B007VIGCJW

https://www.amazon.com/gp/prod...00?ie=UTF8&psc=1

From the perspective of eventually separating the manifolds from the heads, that stuff sounds a lot better than the 510 that I used, especially since it remains flexible rather than curing in place so they should come apart with a little torque applied to the top of the manifold.

With mine, I practically need to use Dynamite to get them apart.

If the symptoms are the same, the source of the trouble is likely the same as well.

I used to use  "Velumoid" and make my own gaskets. Since I had to modify the crap out of the gasket to match the ports, it wasn't much more trouble. "Velumoid"  (not sure of the spelling here) is a green colored gasket material used by Steam Fitters on high pressure steam piping. It's tough as hell and not hard to work with.  Mr. Stan from Galatville may have better info on this product............Bruce

@Bobby D- I would buy a couple 3 sets of those brass exhaust nuts as well- use 1 set for the exhaust (if you've ever had to heat an exhaust nut to get it off and it's so rusty it comes apart in pieces you'll agree with me) , 1 set for the intake manifolds  and maybe an extra set for spares.

update

I pulled the manifolds and replaced the gaskets.  Still only hitting on two cylinders.

#1 and #3 are not hitting.  When I put my RPM lead from my timing light on #1 and #3 nothing registers.  I switched the #4 wire with the #3, but still no signal on #3.

I am completely stumped.  What could cause this?  I replaced distributor including the cap and replaced the coil.  The plug wires are less than two years old and have switched them  around with no change.  Could there be a short somewhere?  I don't know what to do next.

Same old spark plugs or did you swap them for new ones, too?  

If they are fouled somehow they won’t spark and your inductive pickup on the timing light/rpm meter won’t register anything.

Plugs are less than 3 months old

Ok then, swap 3 & 4 and see if the dead cylinder moves.

Gordon

I will give that a try tomorrow.

What carbs are you running ? I had this exact problem a few months ago on another speedster ..Pulling 1 and 3 wires did nothing ..It had dual Empi 34's and would only run on 2 an4 cylinders at idle because of poor EMPI vacuum design..... Larger idle jets and a cross over manifold balance tube helped some.

Alan

I have Empi HPMX 44's.  They have worked great for the last 2 years.  I don't think it's the carbs.  The fact that my timing light can't pickup the spark on #1 or #3 tells there is an electrical issue somewhere.

Anyone else have others ideas for me to check?

Are you getting a full 12 volts to your distributor? many of the electronic distributors wont work well with less than a certain level of voltage. I have had this issue with bad or loose grounds and too small gage power wire acting as a resistor dropping the voltage. As always good luck, you have a tiger by the tail. Many of us have been in similar situations with type 1 engines.

Jimmy,

I just went out and check it.  I turned the ignition on, pulled the primary spark wire going from the coil to the cap and measured 15+ volts.

Just a thought is your distributor  out 180 degrees ?

Arden

I am sure it is not out 180 degrees.  

get a suby motor and be done with it...

It was just a thought you asked for ideas 

"...my timing light can't pick up the spark on #1 or #3..."

"...I switched the #4 wire with the #3, but still no signal on #3..."

"...I checked the spark and all are firing, but spark doesn't look the same on each.  Seems weaker on one of the non-responding cylinders..."

"...plugs are less than 3 months old..."

So, if you "checked the spark and all are firing", but your timing light doesn't trigger from #1 or #3 wire, I assume you checked the spark by pulling the wire from the plug and holding it near a ground to verify spark? But then, with the wires reconnected to the plugs, not enough pulse through the wire to trigger the timing light?

And the plugs are fairly new, right?

So... did you gap the new plugs when you put them in? The gap on new, out-of-the-box plugs is often way off. Are the plug tips in the cylinders that aren't firing fouled?

I think the next test is to do what Gordon suggested - switch the plugs in #3 and #4 (or #1 and #2) to see if the problem moves with the plug.

You said your spark plugs are 3 weeks old that doesn’t mean anything I had plugs foul all time with the motor I had before  try a new set they are cheap if you haven’t already

Are the spark plugs the proper heat range? It doesn't take very long for plugs to either start misfiring or foul/die if they are the wrong heat range for the combo and driving conditions, especially if the ignition system is marginal.

Try NGK 2120 spark plug