440 Timing Issue

I think its a 1973 440. If I set the initial timing at 10 degrees with the distributor advance vacuum hose disconnected and plugged it often back fires through the carb when I road test it. Seems worse when cold. It runs better at about 20 degrees BTDC but still isn't right. Any ideas what to do to to set it at 10 degrees and tune from there. Its always been like this with different carbs. I have check firing order countless times. Any ideas how to approach this? I dont have any history on the car but the motor still seems to be in decent condition.

Road test it with the vac can hose unhooked/plugged. Confirm the reluctor gap is at .008" with a brass feeler gauge (or eyeball it & want it fairly close but not touching) & confirm the springs are retracted which they should be (not stuck) & when you twist the rotor CCW that it springs back smoothly. With a 1&1/4" socket/breaker bar hand bump the dampener CW till the magnet is dead even with the tooth that places the rotor under or near under the #1 cap terminal (don't go backwards & if you go past then back up & creep up on "dead even" again, & at that point see where the timing marks are on the dampener and how far away the rotor is from being straight under the #1 dist cap terminal outside "bulge". this'll get us started. On the fuel side it may have a vac leak (valley pan). EDIT ported or manifold? MORE EDIT way way lesser potentials are timing chain sprocket dot error/slipped dampener but we'll start with the easy potentials first. the more I think about it the more I potentially think vac leak/lean. clamp the PB hose for a quick test just to get that out of the way.

Thanks RR, Ill have a look at it. It has the stock cast iron manifold on it. I did replace the manifold gaskets on it a few years ago, When I bought it someone had disassembled it to the timing chain cover, so I also know the timing chain is not worn out. I'm thinking not a vacuum leak because when I run it advanced it idles pretty good and you can hit the throttle and it will come right back down to the same smooth idle and the RPM's don't wander around.

at that point if it is all good can you leave it there? but it still backfires?

maybe it's not a timing issue but a fuel problem,....?

It doesnt backfrire but will ping when you load it with some throttle on the street. I have to back it off on timing advance to stop it from pinging but Im still way advanced.

Possibly I think it has a 650 Edelbrock carb that I put on there new a few years ago. Just bolted on a new one not knowing much about the details on the carb. It ran the same with the old holley I took off.

I'm going to try to go out there tonight and fool around with it some.

Ok I reverse engineered RR's procedure and lined up the timing mark at 10 BTDC, opened up distributor, loosened the distributor and rotated the distributor until the pick up coil center lined up with the rotor star to line up with the pickup coil. Gap was close to .008 as it was. The big rotor on the end of the distributor shaft also lined up center of contact in distributor for number 1 plug wire.
Cranked it up and checked timing with the light and it was dead on 10 BTDC. Adjusted carb a bit to raise idle and set both idle jets. Pinched booster hose and no change there. Put vacuum guage on carb port to distributor and vacuum increases with throttle but not sure if it is the correct amount of vacuum.

Still not right but will test drive tomorrow.
Thanks, Ill let you know how it goes tomorrow.

Alright we're getting closer. what does not seem right? I would bump it to 15 (which likely will require shortening the slots to get it back to 36-38) & the FBO $22 plate is by far the easiest/cheapest way to do this. My bone stock 85 318 does great on 19 initial. are you on ported or manifold?

Ported off the carb. I have zero vacuum at idle and it progresses vacuum as RPM increases. Just running it in the garage its just not responsive as it should be and runs rough with no load. I think Ill bump it up to 15 as you suggest and run it down the road tomorrow. Maybe you are into something suggesting initial 15 and limiting the max advance to stop the pinging.

I'm not really looking for a lot of performance, I just want a good running engine. It is crusty looking though. I have had the car (1972 Roadrunner) for over 10 years. Its always been able to move on its own power and is close to being able to drive on the street so that's all I'm really trying to do.

Understood, we are getting closer. EDIT I forgot about the pinging, we cannot allow it to ping. what is the total (with the can capped) and what springs are in there. we might need stiffer springs to stop the pinging (& limit the total to 36).

Ported vacuum source? .... as air speed increases through the Primary venturi it creates high pressure in the center to fracture the fuel into small particles, the opposite and equal reaction is Negative wall pressure. If you look at the primary venturi you'll see a small hole in the venturi wall...That is the vacuum source for Ported Vacuum. So as you accelerate the vacuum increases with air velocity and draws more timing into the distributor via the vacuum can. It will pull the amount of timing into the motor based on the numbers stamped on the vacuum arm x 2 ie: 6.5 Arm X2 will give you 13* at the crankshaft.

So if you have the initial timing set at say 6* and the distributor has 28* of mechanical timing in it then as you build rpm you will hit the 34* based on the spring tension (6* initial + Mechanical of 28* = 34*)and THEN it will advance another 13* of ported vacuum timing for a total under load of 47* PING PING BOOM!

Ported Vacuum is for emissions controlled engines with a OBD1 computer that will retard the timing based on the data it receives from multiple sensors such as TPS, O2, knock sensor, engine temp sender, MAP and others as they became more sophisticated.

Think about the fuel formulation your trying to burn in these cars, it's designed for extremely lean burn, sophisticated combustion chamber, high combustion chamber temperature engines, this new fuel is formulated to run in a Injected aluminum V-Tech designed for MILEAGE not your old cold iron push rod motor.

Yes some of the old factory stuff was hooked to ported but look at the timing numbers some as low as 5* BTDC with total at maybe 25* and then the ported vacuum would pull it up another 10-12* to make it run.... very inefficient and always a 5-10MPG gas hog but gas was 28 cents a gallon who cared?

GM perfected the Vacuum advance distributor hooked to Constant Manifold Vacuum and all GM cars were always connected to constant, they also made over 300 different combinations of distributors by using different vacuum cans, vac arms, pin positions on the advance plate and limits on mechanical advance cans to accommodate everything from their 6 cylinder trucks to a 427 corvette.

In today's real world we need to have all the initial timing the motor will take without kicking back or dragging the starter down, that number depends on the compression ratio and the cam duration or valve overlap, the bigger the cam the more initial timing you can run. The Vacuum canister needs to be adjusted to read the manifold vacuum level at idle and then it needs to be set to the correct amount of timing (usually in the 28-32* range)at idle and at part throttle cruise (42-46* range). Where the mechanical curve is set is whole set of different perimeters but it needs to work together with the vacuum timing to maximize engine performance at all loads and RPM levels.


If you have a performance engine the distributor needs to be curved to be compatible with modern fuel and still achieve reasonable fuel economy and still squeeze all the power you can get out of it. Although our 6 position disc really helps in tuning your distributor it's not a $25.00 tune up in a plastic bag. Even after you get the distributor all dialed in you still need a good ECU that won't drop output when hot, retard the timing under load or skip cylinders because of an inadequate coil. Just because someone says this is a "The Best Coil" you have no way to test it to see if it's marketing or engineering data? We do, we tested over 30 coils and then programmed our Microprocessor to optimize it's efficiency even further without compromising longevity or reliability.

ANY ECU utilizing slow old 1960's transistors will NOT do the job in today's world I don't care what color it is or what ridiculous claims they're making there is NO Substitution for Modern Level 5 Electronics using Intel Technology microprocessors and Good Ole American Manufacturing Skills and Quality Controls.

Our .0053% failure rate over nearly 6 years and well over 5000 units says that loud and clear.

This should be permanently posted to the top of the board! Who is "our" in your post? cuda66318 are you a vendor here?

A plug for the FBO plate. I have used it on two cars now, it is a really great, easy, way to alter total mechanical advance. I bought extras just to have them.

Edited for content

We are FBO Ignition, Oregon

Thank you all for your constructive comments.

Thank you Dave Hall for the Kudos, glad you appreciate our factual information. Between Jim and I we've been tuning distributors for over a 100 years.

"A plug for the FBO plate. I have used it on two cars now, it is a really great, easy, way to alter total mechanical advance. I bought extras just to have them."

We appreciate you as a customer and we're very happy that you appreciate our products. Recently we went to a more polished stainless steel to make them look even better!

Cuda I enjoyed your article.

I have also edited my response, thank you for taking the time.

Email me direct from the Email on my web site and I'll send you a free email version of my book... Tuning to Win

Don't like flim flam

The wrong way to tune an engine is find out where it pings, back down timing and let the initial timing fall wherever it may... classic MP manual nonsense.

At least get two pieces of the puzzle correct at a minimum, initial and total. Initial is MORE important than total to overall driving performance. Adding in vacuum is a bonus on street cars for sure.

As a side note, vacuum advance shouldn't do anything on a full throttle dyno run. If it does, something is wrong.

Stock 340 and 440 like in the 14-18 range for initial timing. Start adding in larger camshafts and that number increases.

set the initial with the "vacuum gauge method" then with that # in hand shorten the slots with the FBO $22 plate to get 36 (initial+mechanical) then toss the heavy spring with the elongated loop & sub in a mr gasket/MP/Transdapt light spring in its place for a start (keep the OE light spring) & mix/match from there staying just under the pinging point at WOT up thru the gears on your hottest/driest (most likely to ping) day then plug in the can to ported & adj it with a 3/32 allen wrench staying (same deal) just under the pinging point in everyday driving under varying RPM/load conditions. CCW slows its curve (amt at a given in hg) but not the total. Bottom line NO pining allowed & there is silent ping & peoples' hearing varies so give yourself a cushion. You want to get close to the line but never over it.

RR I guess this needs be my next attempt. I cant get it to run half decent any where near the 10 degree mark in the garage. The mark on the damper is at about 10 o'clock with the timing light, just to get the engine to smooth out to readjust the carb needles and idle. The motor does sound responsive just setting by ear.

So I will hook up the vacuum guage to manifold vacuum, plug ported carb vacuum source and unhook can on distributor (not sure about this but will try connecting can on distributor also, using a tee for my guage). Maximize vacuum on guage at idle by turning distributor and then back off about an inchof vacuum and see where that gets me as a starting point. Then I will street test it if it seems close and then work on the ping.

I appreciate all of the suggestions and time you all take to respond.

on finalizing the ign with the "vac gauge method" do not T into the can, go strickly off manifold. As you twist the dist the idle speed will rise so keep reducing the idle speed back to your lowest/normal in gear RPM which is what it will be at stoplight to stoplight. then when the vac in hg is highest then go back till the in hg drops 1" of vacuum & reset the idle speed if needed then see if it will crank OK when hot & if it balks then drop the INITIAL not the vac (1) degree & repeat. You would only T into the can if you are going to tune on manifold as opposed to ported & I know that is what Don at FBO is into & some people swear by it. I have no exp with it so I cannot say if it is the way to go. I'm thinking there still might be another issue tho besides this.

Just asking but when you are using your timing light, do the marks stay steady through all RPM ranges? I've seen old polymer bonded harmonic balancers cause issues like you are describing.