Sooty Plugs Create Problems

[daveinrenton]

Don:

I wrote a month or so ago about sooty plugs, the probable result of an overly rich running fuel/air mix. After running off and on all day on a recent trip from Elliott Bay, through the Ballard Locks and up to Lake Washington, the final 200 yard leg, after a brisk beat upwind, failed as the engine turned over but did not fire. I pulled up to the dock under jib power and looked into things the next day.

I suspected that the fuel pump had pooped out and investigated on the site the night before I returned to the boat. The majority of issues decribing my symptoms related to pin-hole, air ingesting fuel leaks, not fried pumps. When I pulled the cover off and tried another start, I had the same result as the night before. I ran the pump for a while before trying and it clicked away like normal. The next thing on the list was to check the plugs fearing that the hard cranking from the night before may have sucked some water into the chambers. The cylinders were thankfully dry. The plugs, however, were heavily fouled by dry, black soot like before. I cleaned them not expecting much. Upon re-trying the engine, it sprang to life and I was able to move the boat from its unofficial resting spot on a guest dock to it's proper slip. The fouling this time, created a debilitating and dangerous situation.

I am pretty certain that the fouling was caused by a very liberal main jet. I had noticed before that when trying to push to max RPMs while in gear, I was getting poor firing as though the choke was on. An excess of fuel could cause similar symptoms. I had already ordered an adjustable main jet from you that should arrive in the next day or two. I will replace the suspect part, replace the plugs, adjust it and the idle mix for max smooth-running leanness and see what difference it makes. I'll report back to see if we have a good fix and cleaner plugs.

Dave

[Don Moyer]

Dave,

Thanks for your report. Adjustable main jets can definitely improve the air to fuel mixture somewhat from the "one size fits all" orifice of the fixed jet. However, we're usually talking about a much more subtle difference than you're reporting. So even if you can adjust away from your acute problem, I have some concern that there may be something else going on that's affecting your engine.

Do you have any sense of how much fuel you're burning per hour? We don't usually see the degree of fouling you're reporting until fuel consumption gets up in the range of 1.5 gallons per hour. Since the engine apparently runs so well immediately after cleaning up the plugs, I'm more suspicious that you may have a restriction building up in the exhaust system, perhaps in the area where the cooling water enters the hot section. Elevated exhaust back pressure in the range 2 to 3 psi can cause symptoms very similar to a rich fuel condition.

Don

[daveinrenton]

Don:

That is food for thought. I did have a clogged elbow fitting that restricted flow from the raw water pump last year. Once that was replaced and hosed out, proper water flow out the exhaust was restored. It's hard to guage the engine emmissions, however, being mixed with the robust water flow. Fuel consumption seemed normal on the trip from the Sound to the Lake. I got horrific per hour gas consumption on a 16 mile trip south in December but I was slamming into 25 mph sustained winds and 4 foot seas for a few hours so that did not seem off to me.

How does one inspect the various pipes in the exhaust line to ensure no obstructions? I have a good old stand pipe muffler with the coolling water ejection at the top of the standing system as is common. Should I just start yanking things apart? What should I be looking for?

Dave

[Don Moyer]

Dave,

Unfortunately, it's usually very difficult to check the hot section without removing it and actually looking inside. On most installations, the hot section transitions to a short piece of rubber exhaust hose immediately after the water is introduced. If your hot section is configured in this manner, you may be able to remove it in one piece and simply look up into the end of the pipe.

Don

[daveinrenton]

Don:

What would an exhaust occlusion look like? Sort of like a clogged artery? What have you seen or heard to be seen when such a condition was caused by the exhaust being pinched off?

Dave

[Don Moyer]

Dave,

The restrictions we've seen have been calcified mineral build up along the inside of the hot section where the incoming engine cooling water hits the hot pipe. The minerals apparently precipitate out as the water splashes against the hot metal.

There's another type of restriction that seems to be popping up more and more frequently. This restriction is caused by the inner layer of rubber breaking away from the inside of the exhaust hose within the first couple feet just downstream of the water lift muffler. After the inner layer breaks free from the rest of the hose, it collapses inward and crumbles up on itself, creating big-time resistance within the hose.

Don

[Administrator]

Attached is a slide from one of Don's workshops.

[daveinrenton]

OK then, time to pull out the wrench and take a look! The easiest fix will be if the rubber deterioration theory is in evidence. I'll just replace the final exhaust hose run. I would think that a loose flap of rubber in the final run would seriously diminish the water flow out of the tail end of the exhaust whereas the calcified deposit would act on the gasses alone. That leads me to think that if this is indeed the problem, the deposit issue is probably it. My honest hope is that my recently cleaned carburator is simply allowing too liberal a flow and that the new jet will give better control and resolve the issue. I am thinking that the removal of the exhaust pipes has fun and knee-ache factors of -1 and 10 respectively.

Good to have a handle on all of the possibilities, however, and I'll inspect as best I can. Thanks for the insights. As, before, as soon as the new jet appears, I'll head down to the craft and dive in and let you know what worked and what did not.

Dave

[Don Moyer]

Dave,

The only part of your plan that I would tweak is the part about the deteriorated exhaust hose. The piece of hose that deteriorates is not near the back of the boat but rather just downstream from the water lift muffler. People who discover this problem can usually get away with replacing only the first 3 or 4 feet of hose behind the muffler (or where the engine cooling water enters, if there is no muffler).

If you do get into replacing a section of 2" exhaust hose, a 6" X 1 1/2" pipe nipple and a couple hose clamps will work nicely to couple the new hose to the old.

Don

[daveinrenton]

Don:

My muffler is not a water lift type, it's a stand pipe. The exhaust from the engine routes directly into a tall (approx. 3 foot) vertical tube within a tube. When the hot air hits the cap of the vertical inner tube and exits through openings immediately under the cap, the water from the engine pump showers the exhaust, now flowing down the outer tube, then the combined flow routes out to the flexible exaust hose (approx. six feet worth) attached between the muffler and the exit pipe in the transom. The only parts that I can practically check are the section from the manifold to the muffler which is well before the water injection and is probably OK and the exhaust hose connected to the bottom of the muffler. The inside of the standpipe is a welded closed system. There is a good chance that when I had the restricted water flow from the bad elbow where the cooling water exits the engine, that the excess heat from the comparitively dry exhaust flow damaged the rubber exhaust hose exiting the muffler. I'll go for that first and replace the bad section if necessary with your suggested technique.

Dave

[rgoff]

My Ericson 27 has a similar standpipe/riser. Every 5 or 6 years I have to replace the system. What happens with mine is that carbon/rust from inside the riser falls to the bottom and clogs up the exhaust inlet to the riser. In my case, there is a pipe "el" joint at the bottom of the riser.

My symptom was that the engine would idle fine, but die when it was reved up. Yours may not have reached this point yet.

The first time this happened I replaced multiple things on the engine trying to fix the problem. Finally I called the factory and they suggested the exhaust system. I removed the exhaust piping at the engine and the engine ran fine (but made a heck of a lot of noise ). This confirmed the cause of my problem.

There was a post on this forum a couple of years back about installing a pressure gauge in the piping near the engine exhaust outlet to see if there was too much back pressure in the system.

[daveinrenton]

I think it has reached this point. When it is revved up, it coughs and sputters but does not die. But, it is thinking about it! The plugs are getting the brunt of the back-gassing and fouling up.

This is great stuff and I appreciate your sharing your experience. I'm on it this weekend.

Dave

[Don Moyer]

Rgoff,

Thanks for posting this valuable experience. I hope that it reaches a lot of Atomic 4 owners and promotes additional investigation and remedial work on exhaust systems. While it is unfortunately very difficult to measure exhaust pressure, I have estimated on several occasions, based on over 10 years of very focused technical service work on the Atomic 4, that 30% to 50% of the fleet is likely negatively impacted to some degree by partially restricted exhaust systems. Normal back pressure is 1 to 1 1/2 psi (which is unfortunately only published on MMI coffee mugs).

As little as 2 to 3 psi back pressure will result in some level of sooting of the plugs, 3 to 4 psi will lead to occasional caramelizing (and sticking) of intake valves, and 4 to 5 psi will result in chronic poor running. Above 5 psi, Atomic 4s will usually only run if one of the plug wires is removed. In other words, back pressure over 5 psi will only support a 3 cylinder Atomic 4.

By the way, in addition to the sources of elevated back pressure that you're mentioning, we are seeing an increasing number of failures of the inner lining of exhaust hose in the several feet immediately downstream of the water lift muffler, or wherever it may be that the engine cooling water is introduced. It appears that the heat still remaining in this section of rubber hose (even though water has been introduced) is still high enough to cause deterioration in this area and cause the inner liner to separate from the rest of the hose and crumble up like newspaper within the hose.

Don

[daveinrenton]

Wow and wow! I pulled the hose off of the muffler and, lo and behold, the inside was completely collapsed exactly 1 foot from the exhaust/water exit from the muffler! So much so that I cannot believe so much water could move through it making me think things were normal. Obviously, not enough exhaust was making it. The occlusion was a solid foot long and the volume reduced to no more than 20% of the hose diameter. I cannot believe the engine ran at all! I immediately went down to the hose supplier and got a complete replacement (about 80 inched worth) and installed it. The water no longer flows, it sprays out and with the proper amount of smog! I still have to replace the plugs that have many hours of use in those harsh conditions and so are probably not sparking optimally. Nonetheless, the engine still ran very well. Hopefully, the engine will clear itself of the offending carbon build-up. Is this a job for MMO?

Thanks again for everyone's contribution of information. Thinking in terms of total engine systems and their interrelated parts is a winner saving much expense replacing things that really had nothing to do with the problem. I attached a photo showing the collapsed section. Very scary!

Dave

[Don Moyer]

Dave,

Dave,

Wonderful news! Your statement, "Thinking in terms of total engine systems and their interrelated parts is a winner saving much expense replacing things that really had nothing to do with the problem" will be a main theme in our next workshop.

I'm not sure where you stand now with your adjustable main jet and plug replacement, but it would be interesting to see how quickly your old plugs would clean up if you did nothing for a while but clear the exhaust system. You may still decide to replace those items in a month or so after a little experiment to document the real beneficial effect of only repairing the exhaust system.

Don