Dirty Stuff In Carb (not particulate)

[campbdon]

After I thought I solved my engine starting and running issues I ventured out on a cruise. Three hours each way with overnight in between. On the way out had to motor then motor sail the the whole way due to wind, waves and time constraint. Normally I cruise at 1500RPM but having read that 2000 is a better rate I tried that but saw increased black smoke out the exhaust and the water temp was at max on the gauge (didn't note the temp for max). So decided to throttle back. Next morning on return engine started up right away but with noticeable oil or soot on the water outside the exhaust. Despite that we motored about 20min to clear harbour and with perfect sailing conditions cut the engine. Close to home tried to restart but no joy. Needed a tow.

Background: Before this problem engine starts up right, fuel pressure ~4PSI but always have dry sooty plugs (rich mix) so was advised on some things to check on your forum. Haven't yet acted on those except trying the higher cruising RPM.

Next day at dock here's my observations:
a) Engine tries but won't turn over. Am sure batteries are good and I start on shore power. I will recheck spark at each cyl but that was good 1 month ago.
Compression: "cold" engine All plugs and dist centre plug removed, fuel pump disabled.: Cyl1 (90psi),Cyl2 (70psi), Cyl3 (80psi), Cyl4(80psi)
A few weeks back all about 90psi (warm engine)
b) Added few oz MMO to cyl 2-4
c) Changed oil (very dirty but at normal level). New oil change 1 month ago.
d) Remeasured compression, much better now:
Compression: Cyl1-4 (>100psi)
e) Removed flame arrestor, noticed that choke not fully closed at full choke, so readjusted that.
f) Drained different sections of fuel hosing and noticed some debris and in polishing filter (MM 10 micron) some water trapped in barrel.
g) Removed carb. GAS INSIDE WAS DIRTY (OIL or EXHAUST SOOT?). Recleaned with carb cleaner and rechecked float level (7/32" including gasket and seated parallel to carb bowl as per Dave N). No leaks detected

Am about to reinstall carb and retry but am concerned I have some underlying issue that will simply foul everything up again. I will be installing a water separator ASAP. Any advice please? Am starting to wonder if I have exhaust or backpressure issue but am more scared about how to diagnose that part of the system or attempt to open up engine.
Thank You
DonC

[campbdon]

Photo of stuf from carb. Looks like thin gravy or black coffee. BTW forgot to add that oil was dirty but not like milkshake (water)

[JOHN COOKSON]

Most likely dirty fuel in the tank is going through the fuel system and landing in the carb. There is one way to confirm this: try running off an auxiliary tank with clean fuel.

ex TRUE GRIT

[campbdon]

Thanks John, but the fuel in the tank is nowhere like what I found in the carb. At the dock I did capture a few cups of fuel from the tank and worst I could see was a few fleck of sand-like particles and a little water (in polish filter). When troubleshooting a month ago I did it from a jerry can but not for 3 hours and at the RPMs of latest cruise. It seems like when I pushed the engine the problem happened (??)

[sastanley]

The syrup is not good..something is wrong. +1 on John's suggestion. Run on an aux tank if you can and see if things change...but clean the carb before to try to level the field.

[campbdon]

Ok I'll give that a try, but I'm very nervous about getting stranded again. The safest place is while tied up (double lines) at my slip. Would a static test as follows seem reasonable:

a) Run in idle 15 min 800-1000RPM. Observe exhaust emissions (Colour/sound/water volume). Stop engine. Check oil (dipstick). Check gas (carb bowl).
b) Repeat in forward at 1500 RPM.This is was my usual cruising speed before trying 2000 before failure.
c)Repeat in forward at 2000 RPM.

Am concerned that the water temp gauge (showing max) was not misreading, that in fact was overheating and contributing to the problem. If too high maybe a block in exhaust or intake as I never exceeded 2000 RPM. I will troublshoot cooling from thruhull hose forward as per https://www.moyermarineforum.com/for...ead.php?t=8830
Seems the colouration in the gas can only be from raw oil or soot from combustion. Would a dirty oil and gas mixture show any obvious signs that oil is present?
If due to raw oil doesn't that point to leakage from engine (how?)?
If the carb is running way too rich (sooty plugs also)that means choke not closing fully, float level wrong (too high?) or gas leaking into it, or idle adjustment off (am 1.5 turns out)? Have already verified these as ok. Have fixed main plug (so nothing to adjust do there except get adjustable ?)


Sorry for the musings and ramblings. I look forward to retesting and your valued inputs.

Thanks
DonC

[capnward]

I certainly am not an engine expert, but I don't know how soot can get from the combustion chamber into the carb fuel, other than pushing the engine too much, so that not enough clean air is getting in to flush the soot out of the exhaust. My engine struggles to get to 2000 rpm, and the vacuum gauge is around 5, indicating the engine is not inhaling air as well. So I usually operate around 1750 rpm at 10 vacuum. This gets me 5.5 knots. I have never seen dark fuel in the carb. Since fuel from the tank is not that color, it must be getting that way from combustion particulates being forced past the intake valves into the carb. In my uninformed opinion. Luckily for us these engines don't need to run at high rpms, and can hammer away all day purring like a cat.

[ndutton]

Do you have a PCV valve?

[campbdon]

Yes Neil I have PCV valve. When shaken something rattles and I can easily blow air through it.

[ndutton]

Originally Posted by campbdon

Yes Neil I have PCV valve. When shaken something rattles and I can easily blow air through it.

May I assume you installed the PCV system to manage excessive blowby smoke inside the cabin?

[campbdon]

I don't know. It was installed by one of POs.

[ndutton]

Here is what I think might be happening and something I'd like to see, perhaps, eliminated:

At first I was thinking sour fuel supply but you report you've drawn off a sample and it does not appear to be the case. Taking that at face value, if the goo isn't coming in with the fuel, the only other way into the carb is from the manifold. I'm guessing the PCV system is drawing very oily blowby into the manifold right above the carburetor and coating the intake with an oil slick. When the engine is off the residue is running down into the carburetor throat. Remember, it's only a guess.

Nobody installs a PCV system for fun, there had to be a reason and the only reason is blowby management. If you're up for it, remove the carburetor and have a serious look inside the manifold where the carburetor attaches to see if it's coated with oil. You may need an inspection mirror, cell phone camera, borescope or manifold removal to have a really good look in there.

edit:
when was the last time the carburetor was rebuilt?

[campbdon]

Hi Neil, I cleaned and rebuilt (using MM kit) earlier this summer. Recleaned it yesterday and verified float level, idle screw backed off 1.5 turns. Plan to reinstall today after checking for the oil at the manifold and reporting back.

The PO's explanation re PVC hose...
"The PVC valve I installed is an aftermarket item from Indigo or Moyer. The original crankcase vent was a hose that went straight into the carb mouth, not a good setup. The PVC valve goes into the intake manifold, so its blowby gases would never go to the carb. I don’t know why your carb would have black gas."

Also, may have forgotten to mention, I usually cruise no higher than 1500RPM. On this trip I had it up to 2000 for awhile (based on some advice read on this forum about A4 optimal cruising speed and to see if that would clean up the sooty plugs), then noticed some black smoke from exhaust and the water temp gauge at max!!. Oil temp was normal range throughout. Lowered back to 1500. The PO advised that on this engine I should never exceed 1700 RPM.

+++++++++++++
Back from the boat. My PVC etc as per photo. Checked for oil residue in manifold. Very little to be seen. (see photo) Paper towel with vinegar pulled little dirt out. Assembled and installed carb, tried restart, no turnover. Compr 90 PSI all cyl, fuel press 4 PSI at carb, Spark at all cyl. Eventually discovered a carb jet/washer buried in the container of soupy gas from carb . Screwed part into main drain fully seated then main drain plug. Motor starts, some initial oil and white smoke from exhaust but this clears up soon. Ran engine 10 min 900 RPM (H2O 180 F, Oil press 45PSI) , checked carb gas (clear), and oil dipstick (clean). I will continue to monitor by testing under load (<=1500 RPM) at dock.

Thank you for your advice and motivation


DonC

[indigo]

DonC,
You indicated in you initial post that you did a good deal of motor sailing due to wind and waves and time constraint on the day prior to your starting issue. I had a similar incident many years ago when my son and I went out and had a grand time smashing through some rather large and unusual wave. Trusty A4 had performed very well up to and through that event. We motored back to the marina uneventfully. Several days later, I was preparing to go out for an evening sail and the A4 would not even think about starting. After much troubleshooting, I removed the carb to find the main jet totally plugged with very fine something or another. The carb bowl was also filled with very nasty looking gasoline and considerable fine debris in the bottom of the bowl. It was not as black as what you experienced though. I did have a filter in the fuel supply line but I do not recall what kind. After cleaning everything up, she fired right up and we had a nice evening sail.

The only thing I could conclude was that the thrashing around in the waves stirred up debris in the bottom of a 25 year old copper fuel tank. I never had that problem again and did replace the copper tank with a plastic one some time later.

Food for thought.

Tom Stevens

[capnward]

I once left Point Roberts to go to Vancouver, motored into some big waves in the Strait of Georgia, had raised the sails and was preparing to turn off the engine, when the engine started running rough. I turned around and went back into Point Roberts. The carb and the Racor water separator had a lot of jellified brown gunk in them. I cleaned out the carb and, after waiting for a new filter and inline filter, I was able to proceed to Vancouver. Since then I carry filters, and am wary about motoring in chop. The brown gunk stopped appearing after I changed to non-ethanol fuel. Once a gas dock mistakenly filled my tank with diesel, and pumped out the tank. I think that got rid of some crud in the bottom of the tank. I have not had that kind of carb-clogging experience since, but if I get into bigger waves I try to get into a calmer place before motoring. Luckily for me that is easier to do here than in some places.