Good morning Y-Blockers!

I have two minor nags that I could use some advice on.

My 312 has idled flawlessly for about the last 500 miles. Now (at idle) it has a slight miss about every 5-8 seconds. Just a little "bump" that you can sense only for a slit second.

The second nag is at a steady cruise speed (+-60mph) the car surges a little. It stops pulling for just a second, then starts pulling again. If I hit the gas, it pulls as it should. The car has a new gas tank, fuel lines, mechanical pump, fuel filter, carburator, distributor, plugs and plug wires. None of these items has more than 1,000 miles since new.

Would any of you have some ideas as to what might be causing these two glitches?

Thanks, in advance, gentlemen.

pops (AKA) Clay

'56 Thunderbird

I’ll suggest looking at the carb first.  Idle fuel mixture could be just slightly off for the intermittent miss at idle.  The ignition spark being on the weak side or the spark plug gap being excessive can also be contributing factors.  You might try a vacuum gauge on the engine and look for any blips in the gauge reading that correspond to the intermittent miss as that can point you towards a valve or valve adjustment issue.  For the surge while cruising, then double check the fuel float level in the carb.  If that checks out, then double check both the mechanical and vacuum advance curves in the distributor.  Knowing more about what carburetor and ignition system you have might also help pin point some other items.

Lorena, Texas (South of Waco)

Your surging while cruising sounds like a lean surge. In other words the size of the main jets are right on the edge of being adequate. Trying increasing the main jet size up one or two sizes.

Jeff Petersen

According to Holley each size increase in jet size increases flow by 4%.You need to go 2 sizes to really see a difference in performance(according to the Holley book).

  

UPDATE:



I have not looked deeper into the carburetor, and have put several hundred more miles on the car since this initial post. Most of those miles had the consistent surging a cruise speeds and I just sort of learned to live with it. But this past Sunday the car suddenly got far worse. This time on the lower end of the speed. It started bogging down severely while trying to accelerate. It has had a little hesitation or stumble, but giving it a little more throttle had made it respond. But on Sunday, I had all I could do to get the thing home. I really had to feather and jab the throttle to keep it running.



I had good confidence in all the shorter runs I was making for a big one that I need to make in the next week or two as I am moving from Chambersburg, PA to Cleveland, OH and its a 275 mile trip for the Thunderbird. I have lost the confidence needed to drive the car in its present condition, but need to make this trip.



So, yesterday, I went out and purchased a vacuum gauge and timing light. I need a lesson in the correct order of tests, but this is what I did:



1. Disconnected the vacuum line to the distributor and plugged the hole in the carb where it was attached.

2. Started the car and let it fully warm up to operating temp

3. Checked the RPMS (via the timing light) and they were about 850-900 in neutral.

4. Checked the timing and if I did this correctly it was 55 degrees advanced at idle without vacuum advance!



I've never used a digital timing light before so I'll explain what I did:



Hooked up the light and could not see the timing mark on the damper at all. There are two buttons on the light marked advance. I pressed one of them until the timing mark lined up with the pointer on the block. The timing light was showing 55 degrees!



I thought I have read here that initial timing should be about 18 degrees. So, I loosened the distributor and turned it counter clockwise until I could get the timing light to register 18 degrees with the timing marks aligned.



The idle dropped substantially so I upped the idle speed back to around 900. I then shut the car off to see how it would restart. It started fine. I then took it for a very short trial to see if this improved things. It was drizzling, the top was down so it was a very short run. It still has the slight hesitation when starting out, couldn't drive at cruising speeds to see if it was still surging, but the severe bogging and cutting out at low speeds was no longer evident on this short run.



I'm assuming (a stretch) that I did the timing correctly. If so how could this have had 55 degrees of initial advance?



Have I done something wrong to get this reading? I have not yet attached the vacuum gauge, nor have I opened the distributor or looked at the plugs. And as mentioned above, I have not touched the carburetor yet.



I suspect I might be starting in the middle when I should start at the beginning looking for my problem. Could you guys suggest a sequence I should use to troubleshoot this issue? I'm under a bit of a gun to move this car either this upcoming weekend or very latest next weekend.



Specs:



'57 312

'57 Ford Distributor with/tach drive

Holley 84057-5 / 1786 carb. Looks to be a 600 CFM aftermarket carb built 178th day of a year ending in 6

Ford O Matic 2-speed automatic





Sorry to be so long winded and thanks, in advance for some needed help.

pops (AKA) Clay

'56 Thunderbird

The idle speed seems a bit high. I would check that. My manual says 450-500RPM in drive for the Fordomatic and 6-8 Degrees initial timing. Also, make sure you are using #1 plug wire for the timing light, #1 is the front(nearest the radiator)spark plug on the passenger side. After that, I would check the plug wires for arcing. Easiest way to do this is to fill a sprayer bottle with water then at night or in a darkened garage, mist the plug wires with the engine idling looking for sparks along each plug wire. A surge can also be caused by a leaking vacuum advance diaphram. Pull a vacuum on the nipple of the distributor advance mechanism and make sure it holds. If it leaks down, it will need replacing.

57 Black Tbird 312/auto

If its a 600 Holley and you dont really know whats been done too it I would says its on the lean side as the Carb is a little too big.

Look here and this may help http://www.y-blocksforever.com/forums/Topic51072-3-1.aspx?Highlight=600+holley

Dissy doesn't sound right either, Go with whats been suggested, knock the idle back to closer to what it should be, A little high is ok with the Holley.  Your intial timing is best around 10 - 16 degrees but you will have to see what your total mechanical advance is. Plenty on this if you search..

Also I found that marking the crank pulley in stages to be just as good as using a dial back light.



"Came too close to dying to stop living now!"

While you didn't say, based on the TBird forums have seen you on I guess its a Tbird you are talking about. The timing marks on a Tbird are not on the damper - they are on the pulley nearest the pointer. Check the pulley carefully. Time usually has made these marks hard to see, but they should be there. Mark them with white paint.



Once you locate the marks, then you can check timing. Start with around 10 degrees, vacuum plugged.



TBird and sedan engines are basically the same, but there are important differences. The balancer assembly is one of them.

54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

Thank all of you for the tips so far.



I mis-spoke about the timing marks on the damper. They are, in fact, on the pulley bolted to the damper, and there is a white paint mark on what I assume to be TDC. I did get the idle down to about 550 RPMS, but I have yet to bring the initial timing down to ~10 as it is presently at ~16. At 16 acceleration (under load) seems more sluggish than when it was before. I hope to be able to spend more time with it tonight or tomorrow.



Dwell is showing to be ~17. The Ford spec says it should be ~26-28. Should I be concerned about this at this stage?

pops (AKA) Clay

'56 Thunderbird

Couple of things I wanted to mention.Initial timing at 16 is too much.8-10 maximum.You should also regap the points however I am not sure if resetting used points to the specs is correct procedure because they are used.You should try it and then check the dwell and see if its correct.Changing the point gap after setting timing will change the timing.Total timing advance adding initial+vacuum+centrifugal should total preferably 42-44 max.How long have the points been in service?Not a bad idea to replace with a new set depending on how old yours are.Also backing the timing down to 8-10 will bring the idle speed down so you may have to bring it back up.Before you do too much more I would get the points situation fixed up as the points have a lot to do with how well your ignition system works.Without proper dwell the the coil does not build up sufficient spark.You should replace both points and condensor as a set.