Backfiring on 1954 Waukesha FC

[Ianscape]

I have a 1954 Fairmont A5-C railcar with a Waukesha FC engine that started to give me trouble last week. Engine and car were running fine, but after a 70 mile trip I had a flex pipe on the exhaust break, and the engine started backfiring.

I repaired the exhaust with a new flex pipe and it is still backfiring, but not as much. Engine does not start hard, and does not need to be choked to run. Gaskets on the engine intake had been replaced 4 months ago. The engine backfires most of the time when I am on the top end of 1st gear, or the low end of 2nd. The engine will appear to lose power, backfire, and then continue normally, or sometimes stall the engine.

Hints, suggestions?

Thanks,
Ian

[Bud Tierney]

Are we clear on our terminology here re'"backfiring"?
Backfiring is a residual fuel explosion in the exhaust system, often from unburned fuel going into the exhaust and exploding when it hits hot spots in the exhaust. It never ? stalls engines, just blows mufflers and exhaust pipes off..,
"Coughing back" thru the carb (aka "spitting", "popping back" etc) often a sign of leanness or fuel starvation, can and sometimes does stall engines...
That being said, I'm dam--d if I can guess why a broken exhaust starts an engine backfiring; while it might have an effect on computerized engines with their rats-nests of interconnected sensors, I just can't see any connection on a simple engine like the FC. Hopefully someone else will.
Is your FC mag or dist? Crank or elec start? (Can't see how it would make any diference, but someone else might).
For my own curiousity, does your FC rotate CW or CCW??

[Craig A]

This, to me, sounds like an ignition problem.
Unfortunately faulty carburetion and ignition symptoms are identical......but I'd start with the ignition.

[Bud Tierney]

Sometime in the middle of the night last night it occurred to me I probably had the cart before the horse here---that it wasn't the backfire that started the trouble, but the first outward symptom of trouble developing, blowing the exhaust...
Several sites come up under Googling "engine backfiriring" with lists of things to check; you'll just have to start with the things you can check yourself, then the cheapest, etc.. As Craig says, it could be either ign or carb. Good luck.

[Bud Tierney]

I meant to add that I stand corrected on the terminology...after browsing thru various sites I find backfiring (through the carb) is generally used and accepted language...so much for nitpicking!

[Ianscape]

Turned out to be an ign problem. You can definitely tell that this was backfiring through the tailpipe and not the carb while watching and listening.

The system is electric start, and the problem was located in the system that was installed years later to change it from a 6v to 12v system. There is a voltage-dropping resistor just before the coil and I found a cold solder joint that had broken. As the engine would vibrate it would momentarily lose contact on that solder point and a cylinder would not fire.

Bud, mine is a CCW rotation.

Quick question for those familiar with this engine.... I have recently been able to get a hold of the manual for it that was included with the Fairmont manual, and it shows the option of adding a belt driven air compressor from Waukesha. I had planned on using a York compressor, but heck, if one is already made for this I'll go for that. I tried plundering over Google for hours but can not seem to find any additional information.

[Bud Tierney]

Looked in the FC parts book I have (M-2584 5/57 on all the pages) but it has no compressor listed, which isn't surprising considering I've seen FC variation numbers up into the high 200's...
In the couple years or so I've been interested in Wauk etc I don't recall any posts or mentions of FC's with compressors, so it's possible it was a railcar assessory only.
I assume you belong to one or more of the railcar groups, and follow their sites (the only one on my list is narcoa.org--which I hardly ever get into--but I assume there are more) and I'd guess that'd be the best place to look for info. I believe there's also an AU railcar site, and while they're a long way away you never know where helpful advice will come from.
Many thxx for the heads-up on rotation; I didn't know different model FC's rotated in both directions until I accidentally saw an ign catalog listing diferent dist's for CW and for CCW!
Good luck with the compressor search.

[Ned L]

Good to hear you found the problem, simple fix too.
People get the terms confused a lot (Backfiring- flames back out the carb. Afterburning - flames out the exhaust.) As an FYI, another thing to check as a cause for backfiring can be excessive carbon build up in the cylinder. Run the engine hard & the carbon heats up to the point where there are some residual red hot embers which ignite the fuel as it enters the cylinder.