I did a compression test on my merc the other day. The numbers are good, I did dry and wet test. I'm getting a popping that I can't get out. When I drove it down the road it felt like it ran out of steam around 1500 rpm. Plugs are all good-.030, wires are new, points have been gapped-.015 and fuel pressure is regulated to 3-3.5 psi. Now I'm onto timing. I had it running for 10 minutes or so and then got out my timing light... what the hell am I looking at!? I see what I'm calling a******* on the crank pulley about 1/4" away from the pointer. I'm****uming the******* is the TDC mark but I'm getting mixed things from the Google. Some say it's 0 degrees, 2 degrees and even 4 degrees and some say point the pointer at the*******! What's correct for this motor? It's an 8CM flathead motor bone stock and as far as I know original with just shy of 100k miles on it. Here's my compression test results
The bump on the pulley is 2 degrees BTDC. Better to use a dwell meter and set points to 27 degrees, then adjust timing.
What carburetor is on that engine? Your loadamatic distributor advance runs on Venturi vacuum. You should see a vacuum line running to the bottom of the carb. It will not run correctly hooked up to a manifold. Check your advance and make sure its working properly. The rubber diaphragm under that distributor fails after time. Pull your vac line and give it a good*****. You should see your spring loaded points plate move in kind. Your compression looks sufficient for an engine with that many miles.
Your fuel pressure is too high for a Holley carburetor. Those aftermarket mechanical fuel pumps put out too much pressure. Definitely change that. Holley carbs require 1-1/2 to 2-1/2 lbs. absolutely no more. Run a 1-5 pound fuel regulator after the pump or just adjust manually by placing thick gaskets under at the manifold seat of the fuel pump stand. The higher the stand the less the pressure. [“I'm****uming the******* is the TDC mark but I'm getting mixed things from the Google.] QUOTE No no no. Get your info from here or even better Fordbarn.
The carb is a stock mercury model 885 back draft with the factory metal vacuum line running to it. I'll check the diaphragm today. I have an electric fuel pump with a regulator and gauge. The original catalog I have shows 3.5-4.5 psi is what the original mechanical fuel pump put out. I've played with fuel pressure a lot and it seems happiest at 3-3.5 psi. My pointer is about 1/4" to the left of my timing bump with everything hooked up now and it's popping out of the exhaust. Thank you for the link!
Does the popping noise happen mainly at higher engine operating temps, or at cooler engine temps as well? Do you hear it in neutral, with no load on the engine, regardless of RPM? Or does it only occur under a load when driving or accelerating? How much manifold vacuum does it pull at idle, and how much at a steady cruising speed under light throttle? Is it a steady reading or does it fluctuate?
I've got my flathead set up to run 14 BTDC at idle, all-in at 28 with an MSD ready-to-run. Pulls strong with virtually the same compression readings as yours. The bigger difference is that I'm running 3 throttle bodies that look like brass-era carbs. What distributor are you running? Front or side, stock or aftermarket?
According to the 1949-51 Mercury Overhaul Manual (Page 42 of Vol. 1) the correct fuel pressure for the stock Mercury fuel pump with stock carburetor and distributor is 3.5 to 4.5 psi. The correct timing is 2 degrees before TDC which occurs when the timing mark on the timing cover lines up with the raised dot on the crank pulley.
I've driven this car less than 10 miles in the year that I've had it now. 8 of those miles were last week. It was in no way ready for the road when i bought it but it's getting there now, very close. Most of the popping is at sitting in my driveway since I don't really have much of a road test to go off of. It does it more cold and starts to smooth out with higher temps but does not go away, all sitting in the driveway with no load. I had my wife follow me on my 8 mile drive last week, she said it was popping while I was driving also, I couldn't hear it. It falls on its face at what I'm guessing is 1500 rpm or so. Vacuum i have no idea, i havent put a gauge on it. Stock distributor on the left front of the motor.
I dont disagree with the ford books on the stock fuel pump pressure. The carburetor requires 1-1/2 to 2-1/2. Many have questioned why ford applied that much pressure to the Holley carbs. You realize that’s why many leak. I’m sure too you’ll find specs on how to drop the fuel pressure in the book also.
I have tried lower fuel psi and it wasn't happy. There's always a chance at me being an idiot****uming something was correct before I started a project. I will double check the firing order today. I'm going to plate it today!!
Back yard initial “idle” timing try. not to be confused with “advance” timing issues. Before starting place a chalk mark to be able to return to your original distributor position if needed. Install a vac gauge onto a “manifold” vacuum port. Advance your distributor to advance your timing until you get the max vacuum. Then retard your timing slightly to drop a few pounds of vacuum on the gauge. Tighten up your distributor. Old timers taught me this.
It’s been sitting for some time,,,,,,do you think it might be a valve sticking open some ? Popping will usually be ignition system , or a valve issue ,,,,,,the majority of the time . Tommy
I'm home now. Going to check firing order, mark the current time, check the diaphragm in the distributor, disconnect the vacuum line from the distributor-plug, check vacuum, adjust to highest valve - lower 1-2psi - lock it in, change oil, put the new temporary tag in the back window and hope for the best. Yes the car sat for years before I got it 5+ it was a literal barn find.
I would double check that diagram (the picture is of an earlier flathead). On the 8BA's I have, #1, at the bottom of the distributor by the clip. The firing order in it is correct.
I figured out what is going on here with the firing order. I drew a picture. The firing order is correct but according to the diagram I posted in my last post it's off one space. I'm going to pull the plugs bring it up to TDC on #1 and verify where the rotor is facing and see if it falls within my #1 place on the cap/plug before I do anything else
I found out the other day testing a vac gauge that I could only***** @ 2 lbs vacuum with my mouth. When testing your advance diaphragm be sure you find someone who is a good reliable*****er to go much higher vac than that.
Firing order is correct. My diaphragm is in good shape, everything moves freely even without petejoes special abilities that I was not able to replicate (yes I tried). Found the windshield wiper vacuum line is in terrible shape-capped it off for now. Pulled the vacuum line off of the distributor-capped it. I checked the timing marks before I moved anything and the pointer and dot on the crank were lined up almost perfectly. I was able to get -18 on the vacuum gauge rotating the distributor. It felt like it could go more but the diaphragm hits the head - I locked it in right next to the head. I rehooked the vacuum line to the diaphragm and she's as happy as could be I turned the idle screw out almost 3/4 of a turn to settle it down to a nice idle. I snapped the throttle real quick and it responded instantly- never had that before! Let it idle for a minute while the wife came home went to snap it again to show my handy work (thanks to you guys which she knows about)and the motor died on me... go figure. She pointed out I have the right T-shirt on.... Roadkill... I have no idea what my timing is really at but before it died on me my timing dot was about an inch and a half to the left of my pointer and there was very minimal popping - pretty much none actually. I'm going to let it cool for a little bit and see how it starts. Hopefully it's not advanced too much now because it was idling better than I've heard it idle in a year I've had it!
I'm still working on it. It runs ok, I drove it around the yard a handful of times until it died on me. I actually got it into what I guess would be the powerband. She has some power! I took it a little too far with the advance. Once the choke opens all the way she falls on her face. I had to up fuel pressure to 4 psi
Great news. You’re getting there. I too am struggling with the same symptoms on another 8ba. Yes your advance may move freely. But you will definitely need to check the diaphragm with some type of vacuum. You could check to see if it’s advancing with a timing light on your timing mark when increasing rpm. If you can’t advance it enough to get your max vacuum on your gauge because it’s hitting the head, someone before you may have stabbed that distributor too far advanced and run the spark plug wires accordingly. That wouldnt allow you to advanced the timing enough. A fix to this would be to pull the distributor and rotate it counter clockwise 45 degrees. But you will have To Reposition your wires so number one is at TDC. Warning…. Your wires may not be long enough to reach the proper holes and you may have to make wire length adjustments.
What year is the motor? There seems to be a little difference in the timing between some of these engines. My 8CM of '52 (?) origin states that 4 degrees advance is right. I have given it a little more advance just to see what it liked and 4 degrees is where it's happiest. Fresh bone stock engine with about 4K miles on it, the thing pulls really hard and comes into it's peak at about 3500 RPM, where it really takes off. Peak HP and torque are at about 3800 RPM. Check the distributor cap and rotor for tiny carbon tracks. Coil tower, too. Check the plug wires for insulation breakdown at night in the dark with engine running. If you see little lightning bolts between wires or to ground, replace them. Other causes for popping are lean fuel mixture: The carburetor power (economizer) valve may be faulty and not supplying extra fuel needed when under wide open or heavy load conditions. Weak valve springs. Plugged muffler. If it still has an exhaust crossover pipe, take it off and check for heavy carbon build up restricting the exhaust. I had one years ago that was completely plugged with carbon. Boy, was that thing a dog. Compression is the key to getting what you want out of these. A good valve job with new guides, seals and springs with stainless valves, seats ground and lapped in will show a remarkable improvement. Worn guides can allow the valves to flop around off center and delay seating. Not good.
When I checked timing earlier I started with the diaphragm hooked up, my dot was about 1/4" past my pointer. When I unhooked the vacuum line my pointer and dot were pretty much spot on. I advanced the timing with the vacuum line unhooked until I hit the head, that's where it stopped popping. I shut it back off, hooked everything back up, put the light back on it and seen that my dot was roughly 1-1/2" away from each other. I know that my advance is working based off of that... how accurate I have no idea. It idled great and reved great until the choke opened all the way. Once that happens it will not stay running without me staying on the gas and throws a fit, popping, inconsistent reving. I'm thinking it must be advanced too much. I don't know. As best as I know it's an original motor to the car so a 1950 8CM. Before the choke opens all the way up this thing has power and is peppy! Driving around my yard I was able to get to the start of the power band before I had to let off. Tire spinning on grass feeling like a cool kid . Once the choke is open I couldn't drive over the 1" rise between my driveway and yard... only one tire was in the yard and I was stuck. I feel like the car has everything it needs to do what it needs to and I'm just the idiot who isn't knowledgeable enough with a flathead to figure it out yet. On an upside I did put insurance on it today and registered it so once I have some confidence in it I can hit the road! I bet it'll take me all the way to where it stops again
You’re getting there. Properly Verify idle and max advance readings before making any changes to the carb. Just for*****s and giggles.. Tighten up both idle screws and rotate them both out at 1-1/2 turns. The carb investigation will be next you know…..
"Before the choke opens all the way up this thing has power and is peppy!" If that's the case, the problem is very likely the carburetor, not timing or spark. The engine is telling you what's wrong....just have to listen to what it's saying. Terry
The Jalopy Journal
