Jump to content

Stumbling Engine


Phil 32DL6

Recommended Posts

Time to turn to the "Brothershood" for some advice on a problem that's had me vexed for the past four months. The engine in my newest 1932 DL6 begins hesitating and stumbling with soft popping after driving fine for 2 or 3 miles and then exceeding around 35 MPH or putting a heavier load on the engine.

When I got her last May everything worked great. The former owner, Sandy Jones, said that in the past year he had had the gas tank steamed and sealed, fuel lines blown out, fuel pump and carb professionally rebuilt, then tuned and timed the engine. Sure enough, she started up quickly, purred at idle, drove smoothly for miles.

Then, on a 90 degree day in June, I took three passengers on a ten mile Sunday drive. On the way home, the engine began to falter with soft popping noises under the hood. I quickly pushed in the clutch, pulled over, and feathered the gas and kept her running...sort of. But when I tried to get underway, the same thing began all over. Figuring classic vapor lock, I let her sit for 1/2 hour with the hood open to cool off. I off-loaded the passengers to a friend's car and managed to get home alone in fits and starts.

Sandy had installed a modern in-line gas filter just before the pump and it was half full of air most of the time...so I removed it. I also tried shielding the pump, settling bowl and fuel lines from the engine heat with aluminum foil, but it still stumbled...like the engine was starving for gas!

Sandy had removed an aftermarket Bendix electric fuel pump that a past owner had installed right on the engine pump flange, and replaced it with a professionally rebuilt original AC mechanical pump. Figuring, maybe the mechanical pump was failing to provide sufficient flow as demand increased, I reinstalled the electric pump (back near the tank) to provide positive pressure to the fuel line, wired it on a separate toggle-switched line, and left the mechanical pump in. I verified that there appeared to be no fuel line leaks and the electric pump was doing its job and supplying ample flow.

In road tests, I could still drive for 2 or 3 miles on the mechanical pump alone before she'd stumble, and if I then switched on the electric pump, it would seem to help briefly, but then she'd begin stumbling again. Even using both together from a cold start made no difference. So, (not being sure if it was an open, pass-through design like the Bendix) I decided to bypass the mechanical pump entirely by hitching the main fuel supply line directly to the carb inlet. No change. Warm or cool weather, dry or damp conditions make no difference: same stumbling and muffled popping.

It seems to me I've eliminated fuel delivery and vapor lock as the cause, so I'm suspecting the carb. But, before I start tearing it apart, I thought I'd send out an S.O.S. to see what others have done with similar symptoms. :confused:

Link to post
Share on other sites

Could it be that your valves are set slightly too tight? This problem would show up on hotter days, or heavier loads, or longer runs, etc.

If your engine is fairly fresh your valve adjustment would be straight forward. If however, you have some wear on the valve train, like my '25, valve adjustment is tricky because not all parts wear evenly, especially the tappets and cam.

Get your engine really hot so that you have the same symptoms, then spin the valves and see if they are tight.

Link to post
Share on other sites
Could it be that your valves are set slightly too tight?

I haven't checked the valve clearance yet. Actually, I've got very mild (what I would assume is normal) tappet noise all the time even when fully warmed up. It's very even and not too loud so I've figured there's at least sufficient gap, if not the correct setting. It's been on my "to do" list.

Link to post
Share on other sites

I use the lifter 'sound' also to make sure things are adjusted right.

My engine has never been rebuilt. I have at least three lifter/cam lobes that are so worn that they phase in and out for softer and louder taps. If I set the valves tighter, the engine runs like your symptoms, if I open them up, they sound like a train coming though!

Link to post
Share on other sites

I always keep the gas very fresh, but I've wondered if the modern blend can cause this sort of hesitation. I've been using regular 87...anybody have experience with upping the octane?

I'll have to try out tinkering with the choke again when it stumbles, but my experience is that, once warmed up, she runs best wide open.

Sandy said he spent a lot of time tweaking the timing and advance, but I really need to spend the time to double check those, since so far I've been assuming this has been some sort of fuel/air mix problem.

BTW, the plugs show perfect characteristics as described in a thread here a few months ago.

Link to post
Share on other sites

Regular gas is fine. The octane rating measures the burn rate of the fuel only, nothing else. In the 20's and 30's octane was probably 40-50 (a guess).

Modern fuel is very different than old fuel...a lot of that has to do with smog controls. Your car ran on junk fuel when it was new.

BTW, fuel is more volatile today and it does vapor lock easier.

Link to post
Share on other sites

My '41 Buick will do the same thing and I'm wondering also if something is not quite in adjustment with my carburetor. It doesn't lose a lot of power, but on an easy acceleration it will want to pop and snort some through the carb. I have put a paper filament in place of the oil bath one, and I'm thinking that may have a little to do with it. It would seem to me that the oil bath cleaner would put a little bit more resistance in the air flow and they would have had to design that into the system when it was new. But you have a manual choke on your car, so if it's too lean you would be able to bring it back to life by using your hand choke. Maybe I'll have to re-check my valve clearance as well, but I've gone through it once already and it does sound like it should. I have a 1922 book on cars and it claims that when the car backfires out the tailpipe it's usually too rich and when it's out the carburetor it's usually too lean. Ruling everything else out....

Link to post
Share on other sites
Have you considered swapping the coil ?
No, I haven't tried that. The coil is mounted under the dash on the firewall. Would it get hot enough there to effect the spark?
I believe that the problems are due to accelerator pump issues. That is what it sounds like to me

My current thinking has been to check out the carb first, but I haven't figured out yet what (if anything) would be time or temperature sensitive. I would expect a sticking needle valve or float issue to give different indicators?

Link to post
Share on other sites

1. The coil will get hot of its own accord as it operates with current flow.

2. The accelerator pump would not normally be operating at steady throttle openings, can you shut off the engine as soon as the problem appears and lift off the carb top to view what fuel level is in the float bowl ??

Link to post
Share on other sites
1. The coil will get hot of its own accord as it operates with current flow.

Chris...once a coil gets hot enough to cause weak or intermittent spark, wouldn't it do that under ALL engine conditions, or would it only be a factor at higher speeds or under load as I'm experiencing? Wouldn't poor ignition cause plug fouling and possibly backfiring from unburned gas? Curious minds want to know.

Link to post
Share on other sites

Check your condenser and points. If your condenser is suspect it will show up when it heats up, -as will the coil break down under heat and pick up again when it cools right off. Inspect the points, if there is a smokey discharge coating around them, change the condenser.

John

Link to post
Share on other sites
Chris...once a coil gets hot enough to cause weak or intermittent spark, wouldn't it do that under ALL engine conditions, or would it only be a factor at higher speeds or under load as I'm experiencing? Wouldn't poor ignition cause plug fouling and possibly backfiring from unburned gas? Curious minds want to know.

Well consider the environment in which the plug is operating and relate that to the work the coil has to do in achieving a desirable output.

At idle, cylinder temps and pressures are at relatively low levels, so a weak spark from a poorly performing coil will probably do the job; now put the car on the road and open up the throttle, cylinder pressures and temps rise in quantum leaps and the coil just cant hack it.

As also mentioned a bad condensor will give similar problems, but I would start with the easy swapouts ( coil ) first.

If you are up to a challenge, whilst the engine is misbehaving, take any lead off a plug with engine running and hold it close to the plug top so as to see the spark jump from lead end to plug, it should be a nice healthy white/blue spark ( perhaps best done in shade or dark ) and should jump at least 1/2 inch. If it is weak/ intermittent and orange coloured then your problem lies within the ignition system. I mentioned challenge because you will need good insulation between yourself and the lead whilst disconnected.

In all of this I dont discount the fuel side of things, however sticking floats / blocked jets etc. would tend to be present at all times; I find it does help if you can eliminate other causes.

Link to post
Share on other sites
The condensor can be disconnected to prove if it is the troublemaker. Engine will run with or without it.

Agreed, and as john18 pointed out ( no pun intended ) the points will show evidence of arcing with pitting on the contact surface. However most points will accumulate a buildup of residue over time so analysing their condition really depends a lot on how long they have been installed.

And harking back to an earlier item re the spark plug analysis, as good as the article is at describing symptoms you really do need a practiced eye to accurately interpret their condition.

So to get back to the beginning if you are convinced the fuel is good; I suggest do the the easy bits first, check the points, check the spark,blow out the fuel feed line,swap the coil, all in a logical progressive manner and then if you are no further advanced,perhaps we need to look more deeply into the carb and distributor.

Looking back through this thread it seems to me you may have inherited a problem considering the work done by the previous owner; was he chasing the same problems ??

Link to post
Share on other sites
Looking back through this thread it seems to me you may have inherited a problem considering the work done by the previous owner; was he chasing the same problems ??

I don't think so. Sandy had found the car stored in a CA barn and did all of those good and obvious things I mentioned (and more) to get her up and running. He also is a stickler for authenticity. He said she was running great and I can confirm it was...at first. It's logical that after another 300+ miles something new might show up.

Anyway, I can see by all of the wide-ranging suggestions so far that I've got my work...er, FUN, cut out for me! Fortunately, I've got some replacement parts (I could use a new condenser) on the shelf...and the other DL6 to test swap components.

Sounds like others have had the same symptoms, so I'll update my progress.

Link to post
Share on other sites

I definitely plan to do things scientifically: only one thing at a time and keep copious notes.

I didn't have too much time today but I got some simple things out of the way:

Cleaned points, rotor and distributor cap contacts, started and let the engine warm up for 5 minutes, then did a road test: began stumbling within 1/4 mile. Playing with the choke while underway didn't help. Pulled to the side and let the engine run for a minute several times while the engine idled smoothly. Each time starting up again car ran OK for several hundred feet before stumbling and popping back through the carb. Back in the garage, pulled spark plug wires one at a time and observed 1/4" fat, yellow spark for each plug. Tapped on carb with hammer to loosen up any potentially stuck float or needle valve without any effect during subsequent drive. Removed condenser wire from distributor, but car wouldn't start so reattached. Back in driveway, engine stalled out, then gave two loud backfires through exhaust while restarting. Removed air cleaner and drove a final time without any effect on stumbling.

Next up: swap the coil and condenser, blow the fuel line, maybe check the distributor's advance mechanism to see if the weights are sticking?

<!--EndFragment-->

Link to post
Share on other sites

I have not read the whole post, but does your manifold have a connection on the "inside" or engine side? I found one on my DH6 and it was leaking. You need a mirror and a flashlight to see it.

Link to post
Share on other sites

I cannot see it in the manual. Seems to me it's near the center of the manifold. I will try to see if I can photograph it with a mirror and some light on my car. Maybe I can do that this evening.

Link to post
Share on other sites

The Kettering electrical ignition system will not operate without the condensor/capacitior in circuit. In fact you risk welding the points together just turning the engine over.

Our cars ran on 'white gasolene' when new ,basically camp fire naptha,and with no lead and an almost zero octane rating since octane rating didn't even come into vogue until Kettering invented tetraethylead as an octane booster. Our cars must be smiling running down the road with 80/87 octane and all it's additives.

Backfiring can be caused by an extremly lean mixture or the ignition too far ahead (out through the carb) or too far behind(out through the exhaust pipe).

Since pulling out on the choke,which would enrichen the mixture, did not help I'm going to guess the problem lies in the ignition system timing.

I no longer use the terrible leaky/shorting/crappy original wax paper condensors but have moved on to modern polycarbonate capacitors from Seimens Halske. From what I can see all the Kettering systems were tuned, because that's what it was, to a frequency using a .22 mfd. to .25 mfd. capacitor. The originals had maybe a 50 volt breakdown voltage rating the 600 volt average of todays caps far exceeds the peak voltage found in the point area. Once you replace the condensor with a new modern poly you can forget any fault in that area and the points no longer burn/corrode because the cap finally does the job Kettering wanted it to do but had to put up with the junk condensors of his time.

I often wonder how many antiques out there are having starting and running problems because the old condensors are still in circuit? How many faults are causing head scratching by owners who take out one defective condensor only to put back in a 70 year old piece of junk and still have the same fault?

Link to post
Share on other sites
Since pulling out on the choke,which would enrichen the mixture, did not help I'm going to guess the problem lies in the ignition system timing.

Great stuff for all to hear!

I've since heard from Sandy that he did replace the old condenser with a new one, but did not replace the coil. However, what looks like the original dash-mounted Delco-Remy coil (with a key still stuck in its integral ignition switch) was in a box of parts that came with the car. Sandy said the coil that's now mounted under the dash on the firewall probably is a "universal" model that was there when he got the car and, so far, I don't have reason to doubt that, or can date its age.

Sandy confirmed that he spent considerable time doing the timing, but I need to get in there to verify it's still in proper adjustment.

What I'm wondering about most right now (and nobody here has really addressed it yet) is whether the distributor advance mechanism might cause that sort of symptoms if it's not functioning properly?

Link to post
Share on other sites

Phil...I tried to get a photo of the plugged hole on the inboard side of the manifold of my driver '31 that I know has an opening, but it's too tight and I cannot even see it with a mirror. You may just have to feel around behind there. Watch out for black widows. I do remember that the car ran considerably better after the hole was plugged.

Link to post
Share on other sites
  • 2 weeks later...

I have an old timing light that's basically a fancy neon bulb in a black casing. Since the coil is under the dash you could connect one of these up so you can see it in the cockpit on the floor facing up towards you. The flashing should be rythmic until you experience the 'fault'. If it is the coil/condenser/points acting up, then the flashing should become erratic.

If you have a modern 12 volt timing gun you would have to supply 12 volts to it,either 6 volts in series with the 6 volts of the car or a 12 volt battery on the floor, and tape the trigger 'on' so you can watch the xenon flashing while you drive.

Link to post
Share on other sites

Still in the "process of elimination" stage. I ordered (Hagen's Hiway Auto Parts, Inc.) and installed a brand new coil and condenser without any change in the stumbling performance...then touched up the already-clean battery connections with no change. I checked the ground cable connection to the engine, and, while grease coated, it looked good. (I tried to get a wrench or socket on it but it's a tight squeeze and it was getting late. Greased up the shifter guide while I was in there, and boy, that made a difference.)

I'm going to check the distributor and timing one more time, but my money is still riding on the fuel system. The stumbling is so predictable, I know alongside which house down the street it's going to start!

BTW, John, feeling around behind the intake manifold, there was no open hole, but the vacuum line for the windshield wiper connects there. Is that maybe what you plugged?

Link to post
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...