Engine's got me stumped?- No Power

T

Tim

Senior Member
This was a great running A motor with a 6:5 head, Fairbanks Morse Mag, Single downdraft and a cast iron header. It began to run really rough and acted like the carb was going bad.

So I rebuilt a 97 I had and put it on there, no change from the 94?
Put another one I know ran well from a friends car, still no change.

Ok- 95% of all Carb problems are Ignition and not the carb, Checked Mag. Good solid spark and starts right up. Change carb back, still idles great but no power, and I mean not even enough to get out of the driveway?

So this weekend I pull the MAG out, and replace with brand new Mallory, new plug wires, plugs etc. I changed the whole system out to 12 Volts this weekend and made it negative ground in the process just to be sure.

It starts right up, idles great but if you rev it up it dies and stumbles like crazy. The idle mixture screws have an affect on the RPM so I know they are not clogged. The plugs are black but mildly rich notto the point of no spark and they are new. Timing is TDC 0' advance to start and the mechanical advance takes over from there. I put a timing light on it and it stays in one spot and doesn't jump around. A compression test revealed 85-90 PSI in all the cylinders with no leaks.

The intake is a Burns, I let the car idle and sprayed starting fluid around the ports and carb base with no change in idle.

I have tried all my tricks, What am I missing here?

Is is something as crazy as a plugged muffler, it's a stock A if it makes a difference?



Tim
 
Sounds like either plugged muffler or insufficient fuel supply...

Connecting a vacuum gauge will determine the former...

Did the poor performance happen gradually, or "overnight" ?
 
Valves out of adjustment will cause loss of power but not all at once. A clogged muffler (banana in the tailpipe) will certainly cause this as well. I think you can rule out carbs. Any issue with the intake gaskets well I guess not since you sprayed around them.
 
Crank the engine up and let it idle.

Put on a pair of gaunlet type leather gloves, extend your arms and stand back some with your face and head out of the way and squirt bottle a little gas spray down the carb throat while using your other hand to open the throttle. The engine should rev up briefly if it has not been getting enough gas.

If this procedure chokes the engine down worse then look for an exhaust restriction. If it can't blow it won't suck.
 
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I couldn't find if you said whether you're running points or electronic ignition. I'm not sure if I should automatically know the answer based on the fact you're running a mag. Anyway, if you're running points, it sounds like the points have closed up.
 
Thank you for the quick responses! I will try all the remedies suggested and report back. I am running points not electronic.


Thank you again,

Tim
 
You can sometimes get a larger piece of debris in the fuel delevery system that will let only so much fuel by. Make sure you have a good flow of fuel to the carb. Both ignition systems having same problem is a little more of a stretch but is possible. Condenser maybe?
 
This may seem stupid, but have you tried fresh gas? I just went thru an issue with my softail, haven't ridden much this year, but the thing sat with about two gallons in 5 gallon fat bobs for about a month and a half the crap a** 10% ethanol gas I got last went bad. Left me sittin a couple of miles from the house, got it back home and could get it to run, but ran rough. Drained the tank and put in fresh gas, runs like a scalded dog....
 
While driving down the road and it starts to loose power, pull the choke a bit to see if it helps some. If it does then you are short on gas. Check for good flow to the carb and check the carb for any plugged jets or passages.
 
Tom Wesenberg said:
While driving down the road and it starts to loose power, pull the choke a bit to see if it helps some. If it does then you are short on gas. Check for good flow to the carb and check the carb for any plugged jets or passages.
Click to expand...

Not sure that he has a working choke but if he does that's a good idea that many of us have done many times. He said he couldn't even get out of the driveway but pulling the choke a bit would still work. Moreover, he could also just cover the air horn with something briefly to choke the carb while standing there in the driveway.
 
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I do have a working Choke. Pretty proud of the linkage I made for the stock hole, it looks factory on the inside. But that's another story for another time. When I pull the choke in it dies. It's getting plenty of fuel, I looked down the throat of the carb and I can see it pulling out of the tubes like it's designed to. This really has me stumped, I'm going to adjust the valves. It doesn't make noise has good solid compression and the exhaust is pushing out lots of air. The coil is not hot, the points aren't burned and the gas is within a 60 day period. I'm going to change the gas anyways and see if that's it. I know it's something really simple but it eludes me still. I'll keep after it, I have to I love driving this car.

Thanks again for your help,

Tim
 
I never saw Frank's questions get answered. The answers would help us.

Also, I don't see if you have a fuel pump, but you have a downdraft carb. If no fuel pump, is the gas tank full?

You say it was a good runner. Was that with all the modifications? And, how many miles did it run good?

Do you have at least 1/4" good blue spark?
 
Tom Wesenberg said:
I never saw Frank's questions get answered. The answers would help us.

Also, I don't see if you have a fuel pump, but you have a downdraft carb. If no fuel pump, is the gas tank full?

You say it was a good runner. Was that with all the modifications? And, how many miles did it run good?

Do you have at least 1/4" good blue spark?
Click to expand...


Yep, not enough information.

Also, one's description may be completely different than what someone else would actually observe if they were there to see it.
 
I assume you know about the ferrule length on the gas lines going into the
carb and sediment bowl/bulb? Should be about 1/8" beyond the ferrule. Too
much length will cause fuel starvation when placed under a load of any kind.
JMHO

Jack
 
Just thinkin' out loud! Flathead V-8s (on rare ocassions) would corrode a hole between the intake plenum and the heat riser passage. This drops intake vacuum big time, and dilutes the air/fuel mixture with exhaust gas. A small hole lets the engine run......poorly. A larger hole will not allow the engine to run at all. I don't know your setup, but this is something to consider. Porous castings?
 
Special Coupe Frank said:
Sounds like either plugged muffler or insufficient fuel supply...

Connecting a vacuum gauge will determine the former...

Did the poor performance happen gradually, or "overnight" ?
Click to expand...


I will need to tap the manifold for a vacuum gauge. No biggie, just need to tap for a 1/8" pipe. Tomorrow.

The performance went like this-
Ran really good for 3 months, took it to the reliability run and made it through that no problems at all. I have driven this car all over in various conditions. Most people are amazed to see an old Tri-Colored Phaeton cruising with them on the highway. It has a V8 gearbox, 3:54 '36 rear, and juice brakes. So it goes pretty good with minimal strain and I don't abuse the RPM's because I don't want to break it. It started to falter just off of idle, I though it was the 94 carb and the power valve maybe blown. I drove it like this for 3 months. Then on a drive it really started to pop and buck. I made it home and thought it was the carb or Magneto. That's where I am today.

I lossened the fuel lines all the way along to check for flow into a bottle. they all drenched me. So I'm pretty sure the gas supply is ok. The carb is below the tank and with over 1/3 I should be good. The float is also set low to prevent flooding from a gravity feed scenario. But not so low the carb starves. I am looking froward to reading the vacuum tomorrow. Even though I sprayed starter fluid all over the manifold and carb areas today with no pitch change I am going to try it again. The symptoms are like a bad Condensor, big Vacuum leak, or water in the gas. I appreciate the help and I know it'll be a learning experience for me. I just hope it's not the long course.

Tim
 
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I know zero about 94's and 97's but back in my younger days, my charger had a similar problem. It ended up being a perferated accelertor pump on the carb, it wouldn't transition from idle to main. If the 94's and 97's have a accelerator pump, check that out.
 
Many years ago our 1929 coupe developed this situation after running for a while. After changing out all the electrical parts and the carb with no improvement, my mentor suggested getting some Bardahl to run thru the engine. Couldn't find any, but tried some STP 'motor honey' thru the carb and the last bit into the crankcase. After three starts with a longer run each time, it solved the problem which must have been badly sticking valves.
 
You may be getting "plenty of fuel" at idle, but not enough for running under load / at speed.

"Popping / Bucking" are classic signs of fuel starvation ( again, if it only shows up under high volume demand such as hills, or moderate to high-speed running), OR incorrect valve timing, although if that were the case, idle should also be affected.

By chance was the gas tank cleaned and coated at some point? It is not unheard of for gas tank sealers to break down and start coming loose and restricting / plugging the fuel system... either due to poor prep and / or modern fuel belnds that dissolve the tank coating. Had this very problem with a '48 International pick-up about 20 years ago, WAY before ethanated fuels came on the scene... every so often, it would die, like it was out of gas, and I would open the fuel lines are various points, and find long pink wisps of gas tank sealer in the fuel line / pump. May not apply to you, but it gave me fits ! ( Thank you, previous owner ! )

If your issue is not enough fuel supply, pulling the choke probably won't help or will only help momentarily, as there's already not enough fuel in the carb.

Since you describe the car as having "run fine" with this set-up, and the problem not having gone away with different carb , fresh ignition, that seems to suggest either restricted fuel supply or timing issue...

Or, as Steve Wastler mentioned, it might rotten gas...
 
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