Diagnostic help: #3 cyl. acting funny

[scott s]

 Long post, but bear with me....

 I barely drive my '63. Last year, I probably didn't put 300 miles on it. A few months ago I smelled gas in the garage. Turned out it was a crappy fuel pressure regulator. Since I have a CB Perf. pump and filter up front, I just eliminated the regulator and put in a straight piece of hose out back.

 Fast forward to a couple months ago. Started up the car (after cranking for 20-30 seconds) to take it for a spin. I let it idle in the garage for a short while then took it up the road. I probably made it 2-3 miles before she started stumbling and running rough. It would idle fine, but when the revs got up to ~3-3500, it stumbles and runs bad.
 Turned around, took it home and found that it wasn't running on #3. No vacuum when I put my hand on the velocity stack.
 
 Long story longer, it WILL run on #3, but only when it gets past ~3-3500.
 To cut to the chase, here's a list of things we've done and what we've found out so far:

*New plug. Made no difference.
*Check spark and plug wire.All good, getting spark.
*Adjusted valves. They were good.
*Did a compression test. 155psi. For comparison, #2 was 160-ish.
*Did a leak down test. Less than 5%. Looked fine.
*Cleaned jet stacks on IDA's. Found no trash. Blew compressed air into holes.
*Visual inspection of ports and intake gasket. Look great.
*Checked for vacuum leaks. Found none.

 I pulled the right hand carb today. Our best guess is that when I replced the fuel line a while back some trash got inside the carb. Maybe inside an internal passage? Would that explain why it won't run on that cylinder at idle but WILL run on that cylinder once it gets into the other progression circuits?
 Any other ideas?

 Before I send the carb to A.C.E., is there something I can clean/check at home?

[scott s]

Oh yeah, some specs:

 2276cc, full MSD ignition, 48 IDA's with 3rd prog. hole and 40 vents.

[John Palmer]

You have a vacuum leak, most likely at the base of the intake manifold.

[scott s]

 That was my thought, too....but why can't we find it? No change when we spray carb cleaner down there and, most importantly, no change when we spray cleaner into the throat of the carb.
 The nuts for the manifold were tight, the gasket is in great shape, no damage or cracks on the manifold.

[John Palmer]

 Before I send the carb to A.C.E., is there something I can clean/check at home?

You asked...........and the OLD GUY says..............you have a vacuum leak!  You just need to find it.

Pull the manifolds (both of them) and check the gasket impressions closely.  If OK, then turn the carbs upside down and make sure that the throttle shaft(s) are not twisted after you back off the idle stop screws.  A twisted (as in bent) shaft will act like a vacuum leak (because if bent they allow more idle air to one cyl. 

Remember, It's usually something really simple that causes these types of problems.

[scott s]

 OK, that's the kind of info I needed. The gasket impression looks great. I can try to get some pics, but it's tight in there. The narrow strip in the center, between the two ports, is even in good shape. I've had trouble with it before because the ports are so big.
 The carb is on the bench and I'll probably start checking it out tomorrow....just wanted to get some ideas first.

[fiatdude]

Scott -- I'd get close to that #3 cylinder and just ask it what it thinks is so funny

[scott s]

 Tried that too.....he ain't talking.

[Brandon Sinclair]

Hey Scott,

I had a vac leak that I could not detect from the spray test.  I ended up using a length of vacuum hose as a stethoscope and was able to hear the air leak with that.  You may want to check that the manifold base is flat and no cracks at the ears, I am sure you will be taking the carb apart when it is out on the bench and cleaning out all the passage ways, and maybe replace that spark plug wire with another if you have one handy.  Good luck.

[scott s]

 OK, I'm doing my best to listen to you guys and figure this out. Here's what I did today:
 Checked the mounting ears on the manifolds; all OK.
 Put a straight edge across the manifolds. Look fine. Not warped.

[scott s]

 Re-checked the intake gasket. It looks fine to my untrained eyes. See anything here I don't?

[scott s]

 I re-cleaned the jets and passages the best I know how. I did not remove the carb top, but I did spray carb cleaner down through the jets and passages. I took the mixture screw out and sprayed that passage. I get cleaner out the progression holes.
 When I spray down the main jet stack, I get cleaner out of the nozzle in the venturi.
 When I spray into the hole the idle jet goes in, I don't get any cleaner out through the carb anywhere...but I'm not sure if I'm supposed to.
 I also used compressed air in all the passages I could get to.
 The only thing I noticed was that the #3 side has some carbon or whatever built up on the butterfly around the shaft. The #4 side is much cleaner.

[scott s]

 Oh, and I backed out the idle adjusting screw and checked the throttle plates. They look exact to me. Both close completely with no gap
 Now what? Check something else or put it back together and see what happens?

[John Palmer]

OK, here's some more things to think about.

Remove the idle speed screws and hold the carb up to a light (sun light is good).  See if both throttle plates seat equally.  If not, loosen the plate screws a half a turn and re-seat the plates.  The last photo does not "look seated" to me, but maybe its the angle of your photo.  Curious why you have not taken the carbs apart?  Cleaning a carb is much more than just spraying it on the outside with throttle body cleaner.  IDA's are one of the "most simple" carbs ever made, they are basic circuits that you can easily clean and check.  When you state that you sprayed the idle jets and nothing came out, was the "idle jet stack" out of the carb, and in your hand?  Are you not running "intake gaskets"?  If you using only RTV you still need to take the same care in sealing the manifolds to the heads.  If you just stick them on and tighten them up you end up squeezing the sealer out of the gap, which is what it did by going into your intake ports in the photo.  You show that the manifold flange is flat and straight, but how about the matching head flange surface?  Have you tried to snyc the carbs "without any throttle linkage connected"?  I have had problems like this with something as simple as having the throttle cable "too tight" and not allowing the carbs to return to idle without binding.

Hope this helps   

[fiatdude]

How long did it set between trips? could the carbs evaporated all the fuel and gummed up the carb -- -- It looks like it is just dumping gas down the carb with out enough air to burn/fire the cylinder

I still say slap the bitch and tell it to stop acting that way

[scott s]

 John, when you say "idle speed screws", are you talking about what the Weber handbook calls the "Idling adj. screw"? Number 39 and 39A in the diagram?
 There's only one on each of my carbs. I took it out to close the throttles. I'll do it again and check against sunlight, but I didn't see anything the first time. Both plates look "synched" to me.

 I haven't taken the tops off yet in hopes that I could find something simple. That, and I don't have another gasket should I damage mine. I've been through plenty of Mikuni carbs from my Yamahas. I'm willing to give these a shot.

 The idle jet stack was out of the carb when I sprayed the passage. I also sprayed back through the jet stack and made sure it was clean.

 I'm running intake gaskets. NOT RTV. What you see in the pics are gaskets that have been compressed. I have "fiber" (or whatever you call gasket material) gaskets all around.

 Please be patient with me....I'm trying to learn and do it myself here. My knowledge is weak in this area. My local shop closed last year. I have limited help available here and may not be as familiar with terms or procedures as some of you guys, but I'm willing to try.....
 

[scott s]

How long did it set between trips? could the carbs evaporated all the fuel and gummed up the carb -- -- It looks like it is just dumping gas down the carb with out enough air to burn/fire the cylinder

 It sat for way too long. Months. I do keep Sta-Bil in the tank. If you look back at the initial post, you'll see that I replaced a leaking fuel pressure regulator with a straight hose. It sat for another couple of months after that before I drove it.
 The problem didn't even start right away, but about 2-3 miles up the road.
 I'm still wondering if there's debris from that repair in a circuit in the carb somnewhere...

[scott s]

 OK, so I got brave and took the carbs apart. Still don't see anything crazy.
 I sprayed the idle jet circuit with cleaner and air again. The only thing I can NOT confirm is if the passage from the idle jet holder to the idling feed holes is plugged or not.
 I can get air from the holder passage into the float bowl. I removed the mixture screw and I kow it's clean at that end. IF the passage is plugged, would that be a problem?

 I'm about to slap 'em back together and throw them on the car unless ya'll can think of something else I should check.....

 Oh yeah, John....with the idle adjust screw backed out, both plates seat the same. I can see a tiny sliver of light around each throttle plate when I shine a strong light down the throat, but they're both the same. They would appear closed to the naked eye if it weren't for the strong light.

[Clinton DdK]

When you spray air through the passage way where the idle jet goes in the air should make its way down to the three little holes next to the butterflies (there will only be two if you haven't had your carbs drilled for the third progression hole).

[scott s]

When you spray air through the passage way where the idle jet goes in the air should make its way down to the three little holes next to the butterflies (there will only be two if you haven't had your carbs drilled for the third progression hole).

 I can feel air when I spray it in there. I can't get carb cleaner through that way like I can everywhere else. When I take out the mixture screw I can see daylight through the holes and get carb cleaner through there.

[Clinton DdK]

It has been awhile since I have been into my IDAs but I think that ou should be able to get cleaner down through that passage. Take out that brass plug below the mixture screw and try again. You may have to take the carb top off to.

[toysandprojects]

idle jet #3 is plugged.

[scott s]

idle jet #3 is plugged.

Wish it were that simple. I've cleaned it 4 or 5 times. It's open. I can se through the hole and get carb cleaner through it both ways.

[fiatdude]

In the old days when I would start having problems with a carb like this and after treating it to nice long bath in carb cleaner and putting it back and it still was acting stupid, I would invite the carb to a little party I was having on the work bench -- whereupon I would beat the living chit out of with a Big Frigging Hammer -- -- The carb still wouldn't work right but I would be feeling a little less flustrated -- Then I would go out a buy a replacement and the problem would go away amazingly. ( wasn't into selling my problem to someone else ) -- Have I said I really HATE webers.

Just to really piss you off I saw AJ had a adapter where you could run a single 2 barrell 500 Holley on your car -- Doesn't look or sound as cool but doesn't cost as much when it comes to Hammer time LOL

http://www.youtube.com/watch?v=vIRQf0S3oD0

[scott s]

 She lives!!

 Not sure what did it....I cleaned the carb really well and re-installed. I went and bought a deep 10mm socket so I could get another bit of thread on the #3 intake stud (I have to use those small, shouldered 10mm nuts on that side b/c of the welded intake. The #4 side will fit a tall 12 mm nut).
 Fired it up and she runs on all four cylinders now. I adjusted the mixture screw on #3 just a tad and tweaked the idle screw. I need to read over my manual and check the proper procedure. I am getting full throttle on both sides.
 Just a little fine tuning is all that's left. That and she needs a bath! It's good to have the old girl down off the jackstands, though.

[fiatdude]

There was something in there somewhere -- trying to find it can be a bitch

[scott s]

 OK, this problem is still here.
 The car has been parked most of the Winter, but on the last trip before I put her away, I noticed a little bit of the stumble had come back.
 Took her out today and the more I drove it, the worse it got. There's still no vacuum on #3 cyl. at idle. It runs OK at lower RPM's...I think it could be better, but OK.
 Once I get up around ~3800-4100, there's a bad stumble. I had it out on the highway today and it actually stalled. Started losing power in 5th, so I downshifted to 4th, trying to keep it out of that "window" where it runs poorly. Kept giving it gas and the revs kept dropping. Dropped to 3rd, same thing until it just shut off.
 Pulled over, turned it off and it fired immediately. Got off the four lane and drove it home gently.

 Sprayed carb cleaner all around the carb, intake, throttle shaft, etc. Nothing. If I spray it in #4, it will stumble. Same if I put my hand over the #4 stack. But #3 is non responsive while sitting there at idle. If I rev it up, I can get a vacuum on #3.
 Rocked the carb/manifold by hand back and forth, sideways, etc. Tight as a bell. No movement whatsoever.
 I sure seems like a vacuum problem but I cannot, for the life of me, find it. Scroll back up this thread....see the pics of the throttle plates? Think I could have a leak around the shaft?

[scott s]

 Oh yeah....one thing I have not done is switched plug wires from 3 and 4 cylinders. But I have a strong spark and a new plug in #3.
 If it was a spark problem, would that cause the "no-vacuum at idle" deal?

[fiatdude]

IF you want to find out if it is the carb or something else swap carbs from side to side -- that will tell u if it is the carb or something else

[scott s]

 Showing my ignorance here: I guess that would mean having to swap the, what are they called...the parts that the linkage arms attach to, from side to side as well in order to swap carbs from side to side, right?

[Clinton DdK]

What is your fuel pressure? You stated that you took the regulator out of the picture. Your carbs aren't overflowing are they?

[Brandon Sinclair]

Good point-double check that fuel pressure.

If it is running spray some carb cleaner down the throat of the carbs-if rpms increase then that barrel is lean meaning you either have a plugged jet or slight blockage in the carb or you have an intake leak.  If ti stumbles or does nothing then that barrel is ok.

[fiatdude]

Showing my ignorance here: I guess that would mean having to swap the, what are they called...the parts that the linkage arms attach to, from side to side as well in order to swap carbs from side to side, right?

WHich ever way is the eastiest for u -- Manifolds up or Carbs up  what ever -- it will eliminate guessing what it is

[scott s]

What is your fuel pressure? You stated that you took the regulator out of the picture. Your carbs aren't overflowing are they?

 I took the regulator out b/c it was leaking. I didn't replace it b/c I'm running the CB Perf rotary fuel pump, so it SHOULD be 3.5 lbs. http://www.cbperformance.com/catalog.asp?ProductID=577
  I don't have a way to test fuel pressure. I can't see any fuel overflowing. I obviously can't see what's going on back there when I'm driving down the road, but #3 is the only cyl. that's not acting right at idle.

[scott s]

Good point-double check that fuel pressure.

If it is running spray some carb cleaner down the throat of the carbs-if rpms increase then that barrel is lean meaning you either have a plugged jet or slight blockage in the carb or you have an intake leak.  If ti stumbles or does nothing then that barrel is ok.

 If I spray cleaner in the #4 throat, it stumbles/RPM's drop, then recovers. If I spray carb cleaner down #3, nothing at all happens. Idle doesn't change up or down, it doesn't stumble, nothing.

 Also, on the fuel pressure: I installed the regulator years ago chasing what turned out to be a needle valve problem. The CB Perf pump was installed later and I just left the regulator there. It started leaking, I knew the CB pump is supposed to be set at 3.5, so I just took out the regulator.
 What's optimal fuel pressure for IDA's?