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When I was at Keyport in the 80s and we were in the yards at Lake Union Shipyard and I had some work done on our Cats by his shop when he was there. Summit has P45s that should make a difference. I'd try those first. Once you clean up the fuel system, they should run fine for you.
 

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Discussion Starter #22
Thanks again for all of the help Dacofa.

Things still are not right on my engine. Here are my latest observations:
  1. Newly rebuilt 1968 Thunderbird 429 with mostly stock parts except: Pertronix III ignition with Flame Thrower III coil (12V bypassed the pink resistance wire), new Holley 4160, Autolite 45 gapped at 0.045”
  2. Still needs to idle fast around 900
  3. It usually dies as soon as I put it in gear
  4. It needs lots of advance, like 20 to 25 degrees BTDC on idle
  5. I’m getting fluctuating vacuum reading from the intake manifold between 12 and 17 at idle
  6. The plugs finally look OK after leaning the carb idle
Do you have any recommendations?

Does it sound like I still have a vacuum leak? I have all vacuum ports on the carb and intake manifold plugged except the one that goes to the vacuum advance on the distributor. I can hear a very slight whistle that sounds like it is coming from the carb. I tightened the four bolts that hold it to the intake manifold, and that seemed to help a little.

Thanks, Tony
 

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Time to pull the valve covers and check for broken spring or wiped lobe. I'm assuming you have torque down rocker arm nuts or are they adjustable?
 

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Don't worry about hotter plugs.You have to fix the rich condition first.Will it still run with the mixture screws all the way in? If so,you are pulling fuel from the main fuel circuit,not the idle circuit.Turn the screws out 1 1/2 turns,adjust your timing by ear till it runs the best,no matter the rpm,within reason,and set the idle with the throttle advance screw to see if it cleans it up.
 

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Discussion Starter #25 (Edited)
Time to pull the valve covers and check for broken spring or wiped lobe. I'm assuming you have torque down rocker arm nuts or are they adjustable?
I do have the non-adjustable rockers, and they are torqued to spec. I used new pushrods, and they are all just slightly tight (I can turn them using medium force when the valve is closed). The springs all looked good and had solid force when I rebuilt the heads two months ago. I sure hope the cam is OK too, it is new. The cylinder compression is good at: 154, 150, 148, 148, 152, 152, 146, and 150.

Don't worry about hotter plugs.You have to fix the rich condition first.Will it still run with the mixture screws all the way in? If so,you are pulling fuel from the main fuel circuit,not the idle circuit.Turn the screws out 1 1/2 turns,adjust your timing by ear till it runs the best,no matter the rpm,within reason,and set the idle with the throttle advance screw to see if it cleans it up.
@dacofa helped me with the idle air/fuel mixture. It is running much leaner now, but the plugs still get a little black around the edges by the threads. I’m pretty sure the engine will die if I turn the screws in all the way, because anything less than 1 1/2 turns out causes the engine to really stutter.

I’m wondering if I still have a vacuum leak, because I’m getting low vacuum that is not steady at idle, and it does not want to idle less than 900 rpm.

I just ordered a new gasket that goes between the carb and intake manifold. It is Holley 108-12 and is really thick. I’m hoping that might help. I have all the other vacuum ports plugged except to the advance vacuum on the distributor. I’m also going to try new plugs gapped at 0.050 this evening, because maybe the fouled plugs are the issue (even though I cleaned them really good with a wire brush and fine sandpaper).
 

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Go back and check for vacuum leaks. That and is the dist vac to the correct port? It will advance and that will speed up the engine, not letting it slow down. Or could the dist breaker plate be advancing and sticking?
By the way, do you know the specs on this "mild" cam? Sometimes what's mild to me isn't to you.
 

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Discussion Starter #27
Thanks again for the great advice. I will check more carefully for leaks again this weekend. I plan to pull off the carb and install a better gasket this weekend too.

I’ve got the distributor vacuum advance hooked up to the port on the carb. I spent an entire weekend cleaning the distributor, everything moves very smoothly now. I compared it to the feel of a newly rebuilt one for reference. I think it is operating correctly. I can see it advance the timing as I give it some gas.

You got me thinking about the cam too. My machine shop guy suggested this cam to give the engine a little rumble. Here are the specs:

92072


How does this cam look? Also any tips for finding vacuum leaks?

Thanks, Tony
 

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Open but don't light a propane torch and slowly run it around the carb base and intake to head area. Check the pcv valve and hose for leaks and proper function and seal the valve cover on that side,remove the breather,oil fill on the other side and shoot some propane down the hole.This checks for internal intake leakage. If rpm picks up during the testing,you've found a leak.
 

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View attachment 92072
How does this cam look? Also any tips for finding vacuum leaks?
Thanks, Tony
[/QUOTE]
Cam just a little bigger then stock. But it shouldn't hurt vac or idle rpms. Sometimes with a big cam, idle at 1000 rpms is as low as they'll go. Specs does call for a little looser then stock convertor. 1600-1800 rpms. What vehicle is this in, and rear gears? If your valves are adjustable, have you readjusted them? Have you checked the main jet size? If they're big that will also let to much fuel be sucked up the idle circuit. That and check the power valve while in there. If it's a high (8.5 etc.) number, it will open/close with idle numbers and make a rich blend, even at idle.
 

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Discussion Starter #30
Thanks for the tips on finding vacuum leaks @thermod. I was not sure if that technique actually works. I will try it out today.

@dacofa - The engine is in a 1968 Thunderbird. Rear axle is WDT-AG 9 3/8” ring gear, 2.80:1 ratio with 42/15 teeth. The valve rockers are not adjustable. The main jet size is 64 with a primary power valve of 65. How do those specs sound?
 

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Discussion Starter #31
Well... I still could not find any vacuum leaks. The propane technique worked good when I tested it with a manifold simulated leak with a leaky vacuum line. No rpm changes around the carb, intake manifold, pcv, and manifold ports.

I put in new 45 plugs gapped at 0.040”. I replaced the thin carb gasket with a Holley thick carb/manifold gasket, and torqued to carb bolts down. I double checked the carb and it is running much more lean at idle, but not too lean.

It still cannot idle at anything less than 900 rpm and has unsteady and low manifold vacuum at idle, and dies when put into gear. The advance also must be set really high, like 25 to 30 degrees to idle at 900 rpm.

I will try a larger plug gap tomorrow to see if that helps.

Any more suggestions?
 

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While you have the plugs out, do a comp test. You might have a wiped lobe making it need to run faster to stay running.
 

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Discussion Starter #33 (Edited)
@dacofa and @thermod - Thanks for all of your help. Your guidance and recommendations and tips have really been helpful.

Each cylinder has 150 +/- 2 when I did the comp test again. I’ve got the engine running really good, but it still will not idle at anything below 900 rpm. I also have a high initial timing at 18, but it sounds perfect. I’ve triple checked the timing marker at TDC, so I’m confident I’m reading the timing correct. I’ve ended up leaning the carb and swapping the Pertronix III with the original Pertronix and a new coil. It idles and revs perfectly in Park or Neutral. It also drops almost 200 rpm when I shift it in Drive or Reverse. The transmission wants to go forward a bit at this rpm, but it feels OK...meaning it is not going to take off on me.

I’m thinking I should drive it around and see how it feels. If It drives OK, then I just won’t worry about the idle at 900. What do you think?
 

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You have your timing light connected to number 5 cylinder as seen in your picture post #6, it needs to be on number 1 cylinder which is passenger side front cylinder. I don't know how many degrees retarded that makes the timing but it would cause most if not all the symptoms you are describing. I suspect once you correct that and set timing to #1 you will find it runs better....
 

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Discussion Starter #35
@amthatiam - Wow, thanks for looking so closely at the details of my problems. I just ran outside to double-check, because I completely rebuilt this engine and was 100% sure I had cylinder #1 in the right place. I’ve got the timing light hooked up to #1. #5 has the clamp for my tachometer/dwell meter. Again, thanks a million for your careful review of my posts.

What do you think about having my idle around 1,000 and initial timing around 18 degrees BTDC? The engine sounds great at idle and does slightly jerk in to gear when I shift in to Drive from Park. It idles fine in gear now. I have a mild cam upgrade with a new 750 Holley carb and Pertronix ignition, everything else is stock. Stock idle is 650.
 

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1000 is a bet high, lower it with it in gear and someone behind the wheel holding the brakes on.
 

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Discussion Starter #37
Yep, it does not feel quite right idling at 1000 rpm, but anything lower and it dies when I put it in gear.

I tried your suggestion to lower the idle while gear, and I could lower it... but only 50 rpm before it died. It goes from 1000 to 650 when I put it in gear, which does not seem quite right either.

I just took the t-bird out for a quick spin around the block, and it has plenty of power from a stop and what felt like great power in third gear too. It does jerk more than I’m comfortable with from Park in to gear. I need to figure out the idle issue.

My son pointed out a “funny” hissing sound from inside the car a couple of months ago when we fired up the engine for the first time. I completely forgot about that and have not been inside the car at all since I started trying to get it to run good.

This era of t-birds have lots of vacuum lines running inside the car: each door has vacuum locks, the heater valves, truck release, rear defroster, etc.

I know I don’t have any vacuum leaks under the hood, but could a vacuum leak on a small line under the dash cause my idle/timing issues?
 

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Sounds like a vacuum leak to me, and, to answer your question a leak under the dash or in a door or a headlight door will absolutely cause the issue. Disconnect all the vacuum lines with the exception of the brake booster, trans, distributor, and PCV then see how it runs.
 

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All the dwell meters I've ever owned never had an inductive connection on it, just the two leads to connect to the coil +/- That inductive clamp on the number 5 plug wire sure looks like an inductive timing light pick up, are you sure that is part of your dwell meter? Please don't take the question the wrong way, I have no idea who you are or your abilities and experience. Just want to be thorough.
 

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Discussion Starter #40
Thanks @amthatiam for your very positive way of making sure I’m not doing something dumb. I had to buy a new dwell meter, because I could not find my old one from 30 years ago (the last time I worked on cars). This fancy new digital dwell meter also has the pickup clamp that I put on the number five cylinder to get RPMs. I have my timing light hooked up to number one. Thanks again.
 
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