This is just a wild guess, but I guess you have tried everything common. Years ago the hose going to the heater control got hard as a rock. Every time I would shift gears, the engine would move and cause a vacuum leak. I didn't figure it out until the first cold spell and I couldn't get any heat. It cost several $5 bills and the embarrassment of seeing tail lights.

Kenneth

Fredricksburg, Texas

No need to apologize.On any vehicle that does have a vacuum mod valve it is a common item to fail and cause a vacuum leak.The Fordo uses a link from the accelerator linkage to control the  fluid pressure (shift points) in the transmission.

  

Wooops, now I know why it was never brought up, sorry.

Bud in Northern Arizona on route 66 in Winslow (standin' on the corner)

If you're American, buy American

631/2 Galaxie 500XL 406   55 T-Bird

Good suggestion BUT the Fordomatic in 51-56 and later I think maybe to 59 are all mechanical.They dont have a modulator valve and no vacuum connection to the motor.I have used a propane torch(unlit) to check around the intake and carb and found nothing leaking.

  

Well, I've been following this thread from the beginning and have seen all of the troubleshooting ideas possible from the best troubleshooters on the site and nothing has seemed to help.  If I could humbly throw in my two cents worth and ask Ted and the rest of the guys that work on automatic transmissions if there is a vacuum circuit in the trans that would be pulling to much vacuum when it is dropped in drive, like a leaking valve or whatever . I'm not a automatic transmission guy but that is about the only place that hasn't been mentioned yet. If there is vaccum to the modulator valve and servos, just maybeeeeee-.   Good luck on your witch hunt.

Bud in Northern Arizona on route 66 in Winslow (standin' on the corner)

If you're American, buy American

631/2 Galaxie 500XL 406   55 T-Bird

Mark:

I used a Rollmaster chain which is index-able. I ended up advancing the camshaft 4 degrees. That smartened up the low end torque problem, increased the compression by 30# and increased vacuum about 1" Hg. I have not had a change to hook on the trailer for a good test due to bad weather, it hailed week ago Thursday night with lots of lightning, then on Friday had snow to nearly a whiteout, then very heavy rains and high winds all week. Those fellows from Montana can stop sending us their unfavorable weather. Oh well could have been worse as Calgary got. There were still snow drifts south of Lethbridge yesterday and the Sweetgrass hills in Montana were all snow covered.



As to down side of advancing the cam I guess one could go overboard and end up with lots of bottom end torque with the running out of power at too low RPM's and no top end power or speed.

Thanks Marvh.I will look into a couple of your suggestions.Regapping the valve clearance to .020 is easy to do.The machine work on this motor was done by a local man who has been doing this for years and years.He also assembles complete motors as part of his services.He has done many Y-blocks over the years  and actually had a finished 312 on an engine stand when I took mine in for work.I trust him that the work that needed to be done was done if required such as the valve guides(which were not done).I supplied a complete set of new quality US made valves and he did exhaust valve seat inserts and machined the guides for better stem seals than the stock ones.I got  8 of the bigger 1.92 intake valves as replacements. Just curious-is there a downside to advancing the camshaft as you have done?Did you just go one full tooth or did you use an offset key?By the way the new replacement cam I used is a stock grind from Clevite.Hopefuuly it is correctly made as I would have no idea how to check it.Thanks for taking the time to give me your suggestions.

  

Sorry for a long winded spiel however here is some ideas.



I don't think the converter is the problem unless it got damaged during engine installation by not having the splines engaged or by using bolts to draw the transmission to the block. Mark, given that you did the rebuild I think likely this is not the case but for other readers it is good info and a checklist



One should have felt the converter drop three times onto the transmission, first into the stater, then the pump drive and then the impeller spline. When fully installed the converter should have been below the bell housing surface slightly if all splines are fully engaged and about 1/4" plus clearance to flexplate when bell housing is bolted to the block. Did you add a couple of litres of trans fluid in the converter before installing on transmission after draining. This helps to get the converter primed.



To check the idle/converter issue I would leave the car in park and turn the idle adjustment screw on the carb out to lower the engine RPM to about 450-475 RPM which is about were idle is if in drive with your foot on the brake. If engine still has rough idle or dies likely not a converter problem, to further check if converter problem disconnect drive shaft and slip a spare trans yoke in place so oil does not leak out, place in neutral and start engine again at slow idle. If still rough and stalls further proof not converter problem as converter now has no drag.



I think likely something has happened to the carb over winter in that a gasket has shrunk or a piece of dirt or metal has gotten somewhere not supposed to be. I would get a rebuild kit and rebuild the carb or borrow a known running carb from a friend for a test.



I have found on the y-blocks if the compression is low rough idle is very susceptible to valve lash adjustment, check setting and open valves to 20 thou.



You said the engine was rebuilt. Did you have the heads done and valve guide clearances checked as worn guides will give rough idle as the valves will not seat themselves properly always and hold the valve partially open. This problem is more pronounced at an idle. It does not show at higher rpms as the valves seem to centre themselves easier.



As others have said low compression could be an idle effect due to timing chain out one cog or camshaft needs to be advanced.



I just had to advance the camshaft on my fresh 312 as it had poor idle and poor low end power. Advancing the cam brought the compression up to 160# across from originally 130# and smoothed the idle out. Crappy weather has not given me a chance for a test yet



I just had an experience on a 57 yblock (Autolite carb) that had a stalling idle issue due to the carburetor arm was ever so slightly loose on the butterfly shaft, you had to grab and twist to find the looseness. When one adjusted the idle speed screw RPM would hold steady until you put it in drive then the jolt would turn the shaft inside the arm causing the butterflies to close dropping the RPM's as the linkage held steady the idle would be rough and stalling . I had to peen the end of the throttle shaft to tighten the lever.

You can check that also.



Ted, you probably have checked this already, just my thoughts on the problem



On the teapots I have seen rough idle issues on account of a damaged o-rings on the brass fuel inlet tube that goes between the carb base and the float bowl. When the machining happened for the inlet tube on the carb base a sharp edge was left which will shave or cut the o-ring and a leak will develop. I take a knife and made a slight chamfer to prevent cutting the o-ring, then lubed the o-rings for easy slip. If this o-ring is leaking fuel will drip into the secondaries.

Fuel will also leak in the secondaries and cause similar problems if the gasket is leaking at the needle valve cover. The original gaskets were copper and if not annealed leaks often happened. Today they are using composite gaskets. I use a socket to tighten as an ordinary screwdriver does not tighten it sufficient. One of the T bird suppliers is reproducing this cover with a redesigned gasket to stop this needle valve leak problem



marv

Low compression would cause these symtoms, you say its a fresh rebuild, what did you use for oil to break the engine in? the incorrect oil and your rings may not have seated yet. Was it a known engine builder? are the cylinders true?

Do you have another carb to try just to rule that out, it doesn't sound like the carb at this point but its worth a shot if you have one or can borrow one.

Just a thought, hope you get it sorted soon, that would bug the crap out of me.

55 Vicky & customline

58 Rack Dump, 55 F350 yard truck, 57 F100

59 & 61 P 400's, 58 F100 custom cab, 69 F100, 79 F150, 82 F600 ramp truck, 90 mustang conv 7 up, 94 Mustang, Should I continue?

Thank you Ted! Sounds like the same symptoms I am having.I am going to do a compression test just to see if anything is obviously wrong like the cam gear being out one tooth.Hope not because I was real careful about making sure it was right before going further.Appreciate your input.I do not think it is a carb problem now after checking it over.Adjusting the mix,speed or timing has had absolutely no effect.Looking for something else.