In April 2012 I purchased an unrestored original (no modifications) 1925 coupe. Over the course of several months I did much work and got the car running great (on battery or mag) but this summer it has developed an annoying miss or stumble at all speeds. It's not constant or rhythmic but occurring at random. Same symptoms on battery or mag. Pur pur pur pur doh pur pur pur pur doh doh pur pur doh pur pur doh doh pur pur and etc... if you know what I mean. Very annoying after running so great since last year.
Here is what I have done to try and find the issue:
Compression check- 56 PSI on all 4 (hot)
Patterson coils in 2012
Tried 4 other Patterson coils this summer
New plugs and wires
New harness with soldered ends
New battery cables and a good ground
New Anderson style
New Wiltshire style
Timer not hitting bolts
Carb removed and cleaned and checked
Removed and cleaned ignition switch
Installed alternate switch with new internals
Checked for leaks with starting fluid
Drained gas and filled with more
Checked fuel flow
Looked for arcing in the dark
Coil box has wood with no tracking
Soldered coil box terminals
And I could go on...
Car starts right up on battery and I have even started it on mag. Pulls hills with no problem. It does not backfire out the muffler or the carb. Adjusting the mixture does not help.
Any suggestions would be greatly appreciated.
Have you checked to see if you have an air leak around the intake manifold?
Also that your gas cap is vented properly?
Sticking valve? Try some Marvel Mystery Oil into the spark plug holes.
What type of timer?
Change it and see what that does.
Does anything effect it?
Moisture? Weather etc.
You still may have internal arcing in the coil box wood.
Tom, you've got me thinking about a sticking valve. Even though a compression check gives me 56 PSI per cylinder isn't it possible that this is not conclusive? After all, hand cranking a motor is very different than a running motor and it seems that this problem doesn't develop until the engine warms up.
Sticky valve, mine had the same problem. random hiccup, but noticeable. seemed to get worse the warmer it got. Also, How about valve clearance?
Given that the problem is spractic I would install one of John Reagan's plastic coil box kits. Just because you don't see carbon tracks doesn't mean its problem free. Check your wires going to the coil box and the timer with an ohm meter. Move them around a little, It could be a busted wire breaking concat every now and then. Im guessing its electral. I don't see a valve sticking just a little. They either stick all the time or not at all.
I had that mess,coil box wood,change it to something.The plastic kit would be trouble free forever. I opted to make 1 of my coil box linings from white oak.The other 2 purty red cedar since 1 will be visiable in the speedster engine bay.
If the lid is on the coil box and it is not in the engine compartment ('26-'27), how would one know if you were running wood or a polymer coil box liner?
John, I had the coil box out when I soldered the coil box terminals.
I have one of John Regan polymer coil box liners in all three of my T's. They are problem free, Even in pouring rain I'v never had a problem with spark control. Just my 2cents
I had the same issue, rebuilt the coil box with a Fun Projects kit, and now it runs smooth as butter. I think the wood can still be shorting out or arcing, without leaving obvious clues. Also, valves can stick open while driving, and be working fine on a compression check. Is the engine itself grounded to the frame?
Ed, the motor is not grounded to the frame. A sticking valve despite the compression check has my attention. Kind of like a false positive medical test. A compression test only lets you know what's happening right then and there- not what's happening when it's running.
I have the same problem with my 24, it has the plastic coil box , Anderson style timer, coilman coils, R V Anderson mag ring, timing is set correctly,valves have been checked many times and i still have a loud hammering valve and an intermittent, most times it runs good on three cylinders, i drove it today to a little car show and pushed it pretty hard, if it breaks i will know what to fix, if it quiets down it fixed itself, but it did not change, i will pull the timing cover to be sure i didn't get it one tooth off when i put the new cam and scat crank in, if that doesn't fix it ,i will pull the engine again and have it completely rebuilt and i have another engine i will have rebuilt at the same time, this has been going on for four years, that's why i don't drive it much.
Have you closely checked the terminal block on the firewall? I built my 1919 Runabout several years ago and after I got it running it developed and intermittent miss. It gradually got worse and it was driving me crazy.
The last thing I checked after many other checks over and over was the terminal block.
It turned out the repo block was made of ground up tires and it had small pieces of wire in it from the tires! The block had continuity across all of the terminals!
I checked it with a volt-ohm meter to confirm it.
I gave Snyders a call and they replaced it and started using another supplier for their terminal blocks.
Are the tabs on the coil box lid keeping the coils down in the box? Had a very similar problem and the tabs were not doing their job. One or more coils would lift a bit and the engine would miss. I had to stuff shims down the box to keep the coils from lifting up.
Easy way to see if that's the problem. Drive the car until it misses and then look at the top of the coils to see if one has lifted.
check your sediment bulb under the gas tank. make sure your not running out of gas at the sediment valve. I open and drain while sticking a piece of wire in it every month. open the drain and see if its blocked. cheap and takes 2 secs. good luck!
My question about detecting the presence of plastic had nothing to do with YOUR situation. I addressed that comment to Mack since I thought he was saying that the plastic was too visible so he went with wood. I just didn't think it was at all easy to tell what someone was actually using without pulling the coil box lid and looking inside with a coil pulled out.
I am not trying to talk you into anything but in my mind you have not eliminated the coil box. There is no way you can test the wood to see if it is causing the miss fire other than trying a different coil box or different coil box liner. The carbon trail arcing that often causes intermittent miss does not have to appear on the surface of the wood, it can be anywhere in between its fibers as well. It most often begins at a time when the wood is wet but then after that even when dry the carbon trail is laid down and can cause problems. I would see if someone would loan you their known good coil box for a ride in your car.
Not just any plastic will work as a coil box liner so be careful what you buy since I know you guys like to save money.
Jumper across the switch and see if this makes a difference. The switch in our 13 became intermittent causing similar problems like what you have described.
The only way you rule out sticking valves is to
admit about 40 lbs on shop air piston up valves
closed, if not corrtect air is either to come out
of the tail pipe or the carb. I just went through this today with the two front cylinder. I checked
lash with (no head on) with no springs, then with
springs, the spun with a electric motor and rechecked. Todays first start it ran like a shithouse, only 3 & 4 working. take side over off
sure enough 1& 2 intakes too tight, how I got no clue (not adjustables) I will not take the head off.
Remedy, with a spring compressor I put more tension on the spring now the lash is even tighter. Take off the generator collapse spring,take out retainer pin, to insert very small screwdriver to move valve around and up and down while shop air is enacted. Next rags, more rags and a shop vac, with the right stone on my air die grinder, I surgically removed a couple thou at a time. Have to release spring compression with pin
inserted and recheck lash. same with no. 2. Again I'm using stem cups best thing invented befor adj. lifters. (you grind to much, you add a shim). One key thing to I think about is, its spororatic cant spell, but your case, lash 'thats out, that stays
the same rain or snow, sticky (not seating, could be, dont thing so,points, go by your ears not the book, while eng off and ign on should be a good gizzzzzzz, turn point nut till you get it you wont
get the electric chair, and last, trust me, this is a registered business so I aint blowin smoke, 90% we buy from Napa and plugs are junk out of the box. How? We happen to have from the 1940s a Champion tester, no more than a "T" coil but with
induced shop air. you can see the fire throught thick glass, Crank up air regulator and amazing
how many plugs crap out even at below "T" compression and are new. Today I bought new Motorcraft plugs from Napa. the gaps were -0- .004 none even close. Lastly over looked are coil caps. Cap.s act just like a cat or a woman, one moment sweet, and next they shut you off. Google capacitors some live long some live short and seem
to be cold blooded.
moment, they shut you out.
I had problems with both original and repop terminal blocks that drove me nuts. (not too hard to do anymore)
I got one from a boat shop that doesn't look quite like original but none of the experts have called me on it.
Works like a charm.