A4 running badly

[wlevin]

Our A4 was running fine then we couldn’t get more than 1600 rpm under power. Rotated the distributor and things went back to normal (2300 rpm available). Then the original problem came back. In addition, the engine started running rough and then we could not get more than 2k rpm even with no load.
With a friend we:
Replaced points, condenser, rotor, cap, plugs, wires and rotated the distributor to highest rpms. Still rough running with limited rpms. All cylinders tested between 105 and 110 pressure, all plugs dry and firing. We removed plug wires one at a time and each degraded the performance of the engine to the same slight degree.
Plenty of pressure at the exhaust outlet of the hull.
On to the fuel. Some small amount of crud in the racor fuel filter/water separator and in the line between the electric fuel pump and the polishing filter. Fuel pump pumping plenty of clean fuel into a jar. New polishing filter installed and carb back flushed after backing out the high speed jet. Engine still running like junk after all that.
Currently have the carb home to clean. Also, could the fuel line between the polishing filter and the carb have deteriorated? (How did any junk get past the Racor and the polishing filter?}

Any ideas what to try next? I’ll try to attach a video with sound of the engine running badly. Can you hear a sucking/ moaning sound from the carb?

Bill and Jeanne
T34C #453
Otter

[hanleyclifford]

If you were initially able to get an improvement by rotating the distributor, you may have a problem with the centrifugal advance. Suggest you go back into the distributor and clean and oil the advance mechanism. Then timing should be set to TDC at low idle.

[Mo]

I agree with Hanley...sure sounds like the centrifugal advance. You should be able to remove the two screws on the plate ...the screws on the perimeter of it. Your points and condenser sit on said plate and you should not have to move them...just disconnect one wire if my memory serves me correctly.

I oil those springs during each winterization procedure and that seems to be enough to keep them working well.

[wlevin]

Glad to clean and oil the advance weights tomorrow when I get back on board with the cleaned out carb. But why should sticky advance weights lead to a rough running engine? Just asking.
Bill and Jeanne
T34C #453
Otter

[hanleyclifford]

This is speculative

The theory might go something like this. The centrifugal advance mechanism got stuck in the fully retracted (retarded) position. Engine would not go beyond 1600. You moved the distibutor to advance and the engine liked it at cruise rpm, but was not happy at idle where in addition the mechanism might have freed itself and now you have too much advance. Whatever. The solution is to make sure the mechanism is free to advance with increasing rpms but first you need to reset the initial timing at TDC at as low an rpm as you can attain. This is best done with a strobe timing light using the crankshaft roll pin in it's vertical position as a guide.

[Dave Neptune]

Info

Bill, the c-adv is the power curve from idle to higher RPM's as the load and RPM's increase so does the advance curve. It is controlled by the strength of the springs and should reach it's max at around 1750-1900 RPM's.

When you set the timing for your max RPM's were you in gear and under full load? If not you may have the timing way to advanced which can cause a very rough running engine and a loss of power.

Dave Neptune

[wlevin]

Thanks guys. I'll try it.
Bill

[wlevin]

out of ideas

What started with an inability to get over 1700 rpm under power has gotten much worse. Now I can't get over 1000 rpm under no load at the mooring and this is not a nice 1k rpm idle. It sounds like crap. Wheezing and gasping and uneven. Lots of air pull at the spark arrestor.

I've tried everything I can think of. Compression is good. Spark seems fine. Timing reset twice with all new ignition parts, including coil. Carb cleaned and reinstalled. New Racor and polishing filters. Fuel pump output seems ok (not sure to know how to judge this, though). Slight dirt in fuel but tried to run motor off a can of gas with a priming bulb. No difference.

Today I'm resorting to pulling the exhaust hose to check for internal collapse (not optimistic since output at exhaust outlet seemed good).
Local boatyard mechanic is well over $100 an hour now, if we can get on the schedule.
HALP!

Bill and Jeanne
T34C #453
Otter

[roadnsky]

From The FAQ'S...

FAQ: General Information

15. What would cause my engine to run with almost no power in forward, while it runs OK in neutral? It also seems to have more power in reverse than in forward?

This condition is usually the result of low power caused by something that was done incorrectly during recent engine maintenance.
The reason the engine seems to run better in reverse is because the reverse mode has a 1.27 to 1 gear reduction. Here are some examples of maintenance problems that we've heard about:

Three to five times each year, spark plug leads were found to be installed in an improper sequence following a tune up! Cylinders 2 and 3 can apparently be reversed, and the engine will run fairly well in neutral, but will have practically no power in forward. According to one caller, his plug wires were reversed for an entire season before he found the cause of his power loss.

Another recent maintenance "oops" involved a minor repair of the exhaust system which required that the manifold be removed. On reinstallation, the old gasket was improperly installed, resulting in intake leaks and very poor power under load.

Assuming that there was absolutely nothing done to the engine since it was last running OK, check the following areas for potential problems:

1) Check for something hanging on to the prop.

2) Check basic integrity of the engine by a quick compression check. For the purpose of diagnosing a major power loss, a simple check using your thumb over each spark plug hole is more than adequate. If your compression is sufficient so as to make it impossible for you to hold your thumb over each spark plug hole while cranking the engine with the starter, the cause of your power loss is not a major mechanical failure. If compression is weak in two adjacent cylinders, or water is observed in any of the combustion chambers, the head gasket has probably failed. If compression is "zero" in any of the cylinders, a valve has probably stuck open. If you are using a compression gauge, compression values over 80 psi are considered adequate.

3) Check for proper carburetor function. Normally, an Atomic 4 will accelerate almost "explosively" as you flick the throttle forward. If there is any hesitation or mild backfiring, a lean condition caused by dirt in the main jet is the most frequent cause. In most cases, a problem related to a fuel issue will manifest itself in neutral as well as in forward, but in mild cases, a lean condition might be missed in neutral, but will surely show up under load.

4) Check for proper ignition. As in the case of subtle lean fuel mixtures, there are subtle ignition problems that can show up under load but not necessarily in neutral. In this category, plug condition is the best indicator. If one plug is noticeably blacker (or oilier) than the rest, look for the relatively few things that can affect only one plug, such as the plug itself, the plug lead, or a cracked distributor cap. If all the plugs are badly fouled, check things that can affect all plugs, such as a loose condenser, badly worn points, shorting coil (or oil leaking from the coil), cracked distributor cap, or a bad coil lead.


Are you SURE your plug wires are in correct order?

[roadnsky]

Bill-
Another thought...

A real quick test would be to pull one plug wire at a time and see if that affects the engine's running at all.

[wlevin]

today's effort

I think the wires are in the right place. I know the compression is between 105 and 110 on all 4 cylinders. No obvious obstructions in the exhaust system. (Hot section is home for inspection tomorrow.)
I'll try to post a picture of the wire placement, a video of the exhaust with white smoke, and a sound recording of the engine running (barely) at 1000 rpm (all I can get, even with no load) and sounding terrible.
Bill and Jeanne
T34C #453
Otter

[ndutton]

Have you taken a look at spark quality? Is it a hot, snapping spark or a wimpy Nancy-boy spark?

As a test for something entirely different, see if removing the flame arrestor makes a difference.

[wlevin]

Removing flame arrestor makes no difference.
Also, I am not impressed with the spark quality. The lead taken off the distributor and held over the block makes an orange spark that can travel about a half inch. New coil and condenser, though. Also, running a wire from the battery positive to the positive on the coil does not improve this.
Bill and Jeanne
T34C #453
Otter

[ndutton]

When were the plug wires last replaced?

[tenders]

My difficulties fitting this description turned out to be a crack in the rotor leading to increasing misalignment between the rotor and the cap. By the time the engine quit altogether there were pieces of the rotor scattered around the distributor and what had happened was obvious.