High Load Miss

[meadowbrook]

Hello Gentlemen.

 

On my '50 Meadowbrook, I have an original 230 with 84000 miles. It misses a couple of times on low RPM high load situations like if I stop it in traffic with the clutch out (relying on the fluid drive) and then take off. I hear the miss through a slight hole in my muffler as well as feel a bit of torque fluctuations at the same time. As I am underway, it clears up.

 

The plugs, cap and rotor are about 5 years old and the wires are maybe 2 years old. The points' age is ??. I checked the dwell and it is between 32 and 38 degrees (32 at idle and 38 when I rev it).

 

I think the spec is 32. I am wondering why it varies.

 

Also, timing has been set at 5 deg BTDC for extra pep. No knocking whatsoever.

 

So any tips?

[Don Coatney]

Have you done a compression check and taken a vacuum reading?

[Phil Martin]

Mine does the same thing when taking off under those conditions. Misses for just a few seconds then runs great. Only time it misses. Haven't found a reason for it. If I use the clutch when stopped it takes off fine.

[Bingster]

While we're on the subject of compression tests.  How much are the testers?  Any better brand? 

[Dodgeb4ya]

Point gap.     .020"  Point angle (dwell) 34-1/2 to 38 degrees... Points could have high resistance...I'd pull the dizzy to check it out and the vacuum/mechanical advance too.

 

Carefully check the wires inside of the distributor for insulation chafing.

 

Check plug gap @.035"

 

Might also check the accelerator pump jet for a full strong squirt (idle to full throttle) engine off of course. 

With the carb top off also can check the step up piston for sticking-inside the carb... just remove the carb top to check it for easy up down movement.

 

[James_Douglas]

It sounds a little like the vacuum advance is not working correctly. When they start to tear, you get behavior like that.

[meadowbrook]

Thanks all. The compression is 100 psi on 2-6 and 85 psi on #1, I know not great.

 

Vacuum is about 19 " at warm idle.

[VFFFrank]

I"d suspect a fault in some secondary ignition component.....plug, plug wires, etc.  When it's dark.....really dark (like in the garage with the lights off) open the hood and watch for a light show. Don't inhale any CO.

F

[VFFFrank]

Oh....a wandering dwell angle may suggest some looseness in the upper dizzy bearings. The closer the points are to the cam, the smaller the angle and vise versa.

F

Edited April 28, 2016 by VFFFrank

[TodFitch]

Oh....a wandering dwell angle may suggest some looseness in the upper dizzy bearings. The closer to the points are to the cam, the smaller the angle and vise versa.

F

 

 

That sound right to me.

 

I"d suspect a fault in some secondary ignition component.....plug, plug wires, etc.  When it's dark.....really dark (like in the garage with the lights off) open the hood and watch for a light show. Don't inhale any CO.

F

 

Agree, the higher the pressure in the in the cylinder, which happens with the throttle is wider open, the hotter the spark needs to be. So too wide a gap on the plugs, bad wires, bad condenser, weak coil, etc. can all cause this issue at wide open throttle.

[soth122003]

Hey Bingster,

 

Harbor Freight, $30.00.

 

Joe

[ptwothree]

Wandering dwell with everything else right, is usually worn shaft bushing in the dizzy.

[Merle Coggins]

While we're on the subject of compression tests.  How much are the testers?  Any better brand? 

 

Just be sure to get one with a short tip. Some have a long thread end that will hit your valves and cause great damage.

[soth122003]

The H.F. test kit has the short tips and comes with 3 different adapter for spark plug size.

 

Joe

[Bingster]

Thanks. I'll be doing that this summer.

[Sharps40]

From Motors Repair Manual, Trouble Shooting Section:

 

ENGINE MISFIRES: When Car is Accelerated...

 

If the engine misfires when car is accelerated but does not when idling, the reason is that the spark plugs stop firing because of increased compression pressure caused by:

 

1 Weak Spark

 

2 Plug gaps too wide

 

3 Plug fouled or damp

 

4 Plug porcelain below par

 

When at low or idle speeds

 

faulty plugs

 

spark gaps too narrow

 

dirty/corroded secondary circuit connection or faulty ignition cables

 

cracked/faulty dizzy cap, radial contacts burned/dirty/worn

 

dirty air cleaner

 

leaky valves

 

ignition point gap too narrow

 

Faulty carburetion due to float level, float valve leaks, incorrect/loose jets, restricted idle air passage/jet, air leak into manifold/other, air leak at throttle shaft

 

Vacuum leaks at other locations

 

leaks occurring at fuel pump check valves

 

air leak at intake valve stem due to excessive stem to guide clearance

 

 

But....five years since the dizzy was serviced....I'd start their and focus on electrical as your most likely issue.

 

 

[VFFFrank]

Just an interesting note: I had my '47 Hudson (I know it's the "wrong" make) hooked up to an oscilloscope as part of a troubleshooting exercise and noticed that the dwell went up and down about 6 degrees with each revolution of the distributor. Hmmm. I took the dist out and checked it to find that the bearings were excellent (I had just put new ones in it) but the small diameter portion of the shaft above the bearing, the part that the centrifugal advance rotates on, had been slightly bent to the tune of about .003". This wasn't a wandering dwell angle, but a regularly variable one. Needless to say, one can't accurately time an engine if the dwell angle, and thus the timing, is a moving target.

I mention it because it's something to look for regardless of the make.

Just my two bits worth.

Frank

[DonaldSmith]

Didn't the Briggs Co. make the bodies for Hudsons and Packards?  So they are sort of sister cars, or at least cousin cars.  And the mechanics were much the same.  So, no apologies needed. 

[VFFFrank]

If you dig deeply enough, you can find business relationships between almost every automobile manufacturer there ever was.....and is. Consider that the first Cadillac was powered by a Henry Ford designed/built engine. That was about '03.

Although I reside mostly in the Hudson world, there are many things that aren't specific to any one make, so , if I think I have something to offer, I'll throw it out there.

Frank

[meadowbrook]

What a hot topic I started !

Maybe I can start another on...what's the best engine oil???

Just kidding.

 

I will start by checking my dizzy to make sure there is no wobble on the shaft and the points are ok. Maybe new ones are in order.

I will also check the plugs and maybe clean them or replace them.

One thing that I am curious about is the coil. Mine is a replacement NAPA one. The original still works, I just figured it was old so I replaced it. Is there a way to check the actual voltage a coil is capable of producing?

 

Items I cannot, or rather, will not fix at this point are compression or valve guide looseness, etc. I know all my cylinders are below spec, with 2-6 at 100 psi and 1 at 85.

 

The vacuum is around 17 inches at warm idle and it does flutter between 16 and 17, so a possible leaky valve is there.

 

One day I will rebuild the engine but I like that as it is it has never been rebuilt and is very reliable.

 

If I rebuild I will likely build to the 1957 spec, I think by then the power had risen to 130 HP? Mine is rated 103. So I guess that would imply a 2 barrel carb, intake, cam and maybe exhaust?

 

If I had the facility, I would like to use British style side draft carbs. That would stick out in a show no?

[VFFFrank]

Funny you should mention the NAPA coil. I tore out most of my remaining hair trying to find what manifested itself as a fuel problem only to find (after much work on carbs, etc.) that the new, made in you-know-where coil would progressively fail as the engine warmed up. Each time I thought I had found the culprit, I'd go for a test drive and it would start/run great for about 2 miles, then run worse and worse to the point that I couldn't go over about 25. If it quit, I couldn't get it started again 'til it cooled. I was suspecting carb heat-related issues. Just on a hunch, I put the old (probably original) coil back on and have never had it miss a beat since. I had recently driven from Seattle area to San Francisco and back during which the problem had started and gotten progressively worse. I was lucky to have made it home. The new coil was installed to assure reliability on the trip. So much for being prepared.

F

[soth122003]

VFFFrank

 

Well I hear this alot on this site and in your case it proved true. 90% of electrical problems are the carb, and 90% of the carb problems are electrical. But I do know what you mean. My P-15 is giving me static now. I drove it to the end of the street and it just died. Since I was on my way to work, got my step-son to help tow it home and went to work. Got home that night, it started right up and now I can't find the problem. It will start and idle fine in the driveway for hours, but when I hit the road it stutters some times and makes me nervous. Like you, I believe the culprit is the coil but I'm not sure.

 

Joe

[Jerry Roberts]

Mention the new coil problem to NAPA even if it is not under warranty . They should be informed if they are selling poor products . 

[VFFFrank]

Good luck finding some one who gives a rip. They may take it back and refund the $ but any suggestions will fall on deaf ears. All you will hear is, "Next!"

I do think that they have two levels of coil quality and I had the lower one, however, no one advised me of an alternative at the time. I'm using the Pertronix Epoxy-filled unit now on my other cars but the one in the previous example is still running on the old (presumably AuotoLite) unit.

Frank

[Jerry Roberts]

I have seen several 6 volt American made coils on ebay , many for good prices . Some NOS . I like to keep a couple of extras on hand .