Runs great, but stalls out under power

[roadnsky]

Thanks Neil.

Catfish-
Can you try a test with the Stuffing Box loosened up?
Loosen it so it's really dripping please.

[Catfish]

I understand. This isn't my first A4. I like to think I'm a methodical troubleshooter, but this engine has me throwing parts at it, doing ritual dances, creating new swear words, and losing my religion. I'm tapping out for this evening. Going to hit it again in the morning.

[roadnsky]

Cat-
Please don't take us wrong...

Very easy to do with putting our thoughts down in writing on the interweb.
We don't want to insult and most certainly we're not inferring you aren't anything but very capable to solve this.
We ARE on your side.

Also, please don't get discouraged.
It'll probably be something very simple that we're missing.
You've got this!

[JOHN COOKSON]

John - I have the choke cable disconnected so it is completely open. I've visually verified as well.

Did you look at the choke butterfly while the engine was running? With the cable disconnected the choke butterfly is free to be in any position while the engine is running the position determined by the vibration of the engine alignment of the planets so on.
If the choke is open and the cable is disconnected how did you start the engine?
What am I missing here?

ex TRUE GRIT

[ndutton]

How many turns is the idle air mixture screw off its seat? Does the engine stumble before dying or does it quit like flipping off a switch? To pile on John's question, are you starting it without the choke cable attached? I think I read that.

[Peter]

One thing that has yet to be considered here is the exhaust - it it was partially blocked it might permit the engine to run ok when not under load. This has been mentioned on other threads on this forum.

It seems that the engine is getting fuel - reading the thread it seems that the entire fuel system has been bypassed - and spark as the engine seems to run fine when not under load. Shaft apparently turns freely and stuffing box is cool.

There is not much else other than exhaust is there?

On other threads it has been suggested to disconnect exhaust and run the engine that way to test. Perhaps others have better ideas on how to test as I am not sure I would like to run my engine that way

Peter

[Dave Neptune]

I have been reading this post and have delt with similar issues a few times. I have seen this mostly with the mechanical pump when very old. The pump was still good and gave 2.5 PSI at idle but under load when "good flow is required" the pump could not maintain enough pressure to move the gage and thus died. This is a classic fuel flow issue.
You seem to of covered this with the gravity feed and such but still no fuel pressure reading under load ~~ no flow no go. This is still a minor possibility. The gravity feed will idle but not make any real power due to the LACK OF FLOW AT PRESSURE. This also points to a flow at load issue.

Now to the exhaust. If the exhaust is plugging up it could be after a load is applied the internal lining of the hose collapses causing no power or very little. But this will not usually cause a stall. There are a few ways to check that are a bit messy but not bad to do if well prepared.

One concern is the sooty plugs, if they are sooty she is way rich which indicates to much fuel not a lack there of. AND exhaust back pressure can cause plug fouling too.

I like many others would like to see a pressure reading under load and at idle.

Did this issue just happen all of a sudden or did it just start getting worse over time? What did you set the float at and did you use a new gasket? The new gasket will insure that the emulsion well is sealed at the top a real problem in this carb. If the well is leaking air the carb will go very lean and not work under load.

Dave Neptune

[Catfish]

Jerry - Thanks for the encouragement and I'm not insulted at all. I was just reassuring myself lol. I appreciate EVERYONE'S input thus far. Sorry if I'm skipping around a bit. I'm getting suggestions from everyone.

The choke cable is disconnected, but held open with a spring. The engine starts right up without applying choke.

I have a new fuel pump (verified it's pumping). With a gravity feed into the fuel pump OR directly into the carb the engine runs in gear tied to the dock and then after one to two minutes I can hear the rpms start to drop and it stumbles to a stall. Applying choke when I hear the rpms drop doesn't help it recover. If I quickly pop it into neutral it will sometimes stay running. But always immediately starts right back up. This issue is consistent with 2 separate carbs. I've got to go grab another big wrench to tackle the stuffing box. I repacked it last year and the shaft turns freely by hand with a about 2 drips per minute while running.

This problem started all of the sudden a few months ago. I limped the boat home and figured it was old fuel or gunk in the carb. Life happened and I've just recently got back to trying to fix it. Looking into the carb after running it appears dry, no pooling of fuel inside. To answer how much fuel is in the carb when it stalls, I shut off the fuel and opened the main jet plug after a stall and plenty of fuel came out. I've attached 2 pics.

[Catfish]

Neil - The idle air mixture screw is out 1 and 1/4 turn. Seems to idle best there.

[Catfish]

Firing order appears correct. Plugs seem pretty sooty to me (but dry). They were new last week and only used for troubleshooting, probably less than an hour of run time. I'm going to search the forum for collapsed exhaust hose test proceedures.

[JOHN COOKSON]

The choke cable is disconnected, but held open with a spring. The engine starts right up without applying choke.

You are running way to rich. It should be impossible to start an A4 cold without the choke closed.
The plugs are excessively sooty for being almost new.


ex TRUE GRIT

[Catfish]

Aside from an adjustable main jet is there any way to rectify the too rich situation?

[edwardc]

You are running way to rich. It should be impossible to start an A4 cold without the choke closed.
The plugs are excessively sooty for being almost new.


ex TRUE GRIT

John beat me to it. Indications are that you are running way too rich.

Since you've swapped out the carb, fuel tank and eliminated the pump, It's got to be something else that's in common to all test scenarios.

Just spitballing here, but in each test, did you use the same flame arrestor? I know mine can get rather gunky, and a clogged flame arrestor would be just like running with the choke on, resulting in a rich mixture and high fuel consumption.

[Catfish]

I have been running the same flame arrestor, so I'll check that now! But I did run for quite awhile without it on the carb and experienced the same thing.

[Dave Neptune]

Catfish, since you have stated that it started all of a sudden and switching carbs made no difference as well as new fuel. A sudden change is usually ignition related or something breaking. In this case I think it just may be an exhaust hose shot kraps.

If the inner wall came loose it would do so somewhat suddenly whereas the "exhaust plugging with deposits" is a gradual scenario and both can cause extreme loss of power but not usually stalling. It could be a combination of a carb issue, not a bad one as it runs and indicates rich being exacerbated by a collapsed hose creating the stall. How old is the exhaust hose?

Dave Neptune