Normal (?) Exhaust Smoke

[Dave O]

I have a late model Atomic 4 and am getting some smoke from the exhaust (please see photos). These were taken today from the stern rail ... about 5 feet above the exhaust. Water temp was 138F (about as hot as it gets) and oil pressure 30-40 psi depending upon idle speed which ranged between low and moderate (I do not have a tach).

The engine was new to me last season but aro. 30 years old. The smoke today was about the same as last season, so I'm not sure what "normal" looks like.

Plugs, wires, cap and condensor are new. I am installing one of Don's new carb's this weekend and will check the choke and mixture settings then. Compression was taken a few years ago and apparently aro. 120-125 across all cylinders.

Engine starts perfectly and runs very smoothly.

Thank you

Dave
C&C 29 Mark I
Toronto, ON.

[High Hopes]

Mine looks like this, worse when it is cold and choked.

On the carburetor... there is a tool which is used for measuring exhaust emissions. I forget what it is called, but it can be used to help adjust a carburetor for lowest hydocarbons, and therefore the best mixture (I think).

Don's kit has a fixed main jet. He also sells an adjustable needle valve. I may purchase one after I measure the hydrocarbons on my boat. I just rebuilt my carb.

S

[HerbertFriedman]

normal (?) exhuast smoke

I get similar smoke out of my A4 but usually is seems to increase with the humidity so maybe some of it is condensation. Monitor the oil consumption but I did not notice any.

[David Masury]

It could be just steam..... your hydro lift muffler may be full of sediment and thus it does not give enough time or room for the exhaust water to cool down. Next haul out, take out the hydro lift muffler and clean it... if it is an older metal one and rusty , you may just want to replace it with one the Don sells or purchase a fiberglass one elsewhere.

If you oil consumption is zero and you have good compression then there should be nothing to worry about.

David

[Kurt]

I'm glad you posted those pictures as there has been much discussion on the board about normal exhaust. I have a 1976 C&C 33 with an original late model A-4. The smoke out of my exhaust looks like yours and doesn't really change from cold engine to operating temp. A year ago the compression was 110 across all cylinders - haven't checked it since then. The engine uses a little oil - about half a quart every 25 or 30 hours of operation, but otherwise runs and starts well. Don't think it is anything to worry about as long as your performance is otherwise good as you report.

[Jim Booth]

MMO smoke color?

Good picture. I don't notice any smoke from my A4, at least no blue tinged smoke. I added some to a 12HP Kohler engine on my 40+ yr old garden tractor last season to attempt to reduce exhaust smoke. This season it seemed to be much less smoky, so I thought I was making progress on re-seating or cleaning rings. I added a new dose to the crankcase and gas. Maybe the dose was too generous because now it makes lots of blue smoke again. The oil level was at the bottom of the dipstick. So maybe it wasn't burning oil because there wasn't enough to burn!

If you add too much MMO to the gas, will it make the exhaust blue?

Jim

[Ken]

Looks just like mine has for the past 10 years on my Tartan 34c.

Ken

[Dave O]

More on smoke

I "lake tested" the boat for the first time last week. At idle and once the boat has reached a cruising speed smoke from the exhaust is as per the photos above or otherwise "normal". However, during aceleraton to cruising speed or in reverse exiting the slip there is much more smoke than that. A friend who was aboard (and also an A-4 owner) mentioned that the amount of smoke from the exhaust when acelerating was certainly not normal in his experience. Excess smoke is as per the photo ... just a whole lot more of it.

I pulled the plugs which are new and after 4 hours operation (2 hours idle for testing at the slip and 2 hours cruising) each plug is coated with a black sooty deposit. The deposit is equal on all 4 plugs. The deposit is not hard and cleans off easily. There is a lot of it.

I cleaned the plugs and then checked compression today. Engine was warmed up to 140F with a screw in compression gauge. Oil level full.

Cyl. # 1 121 psi
Cyl. # 2 118 psi
Cyl. # 3 120 psi
Cyl. # 4 119 psi

These reading are virtually identical to those taken in November '05 by the previous owner so compression seems great. In fact, a lot better than I would expect from a 30 year old engine.

New carb from Don. Idle, mix and choke are fine
New points, plugs, condensor, rotor and cap
New Racor separator and Don's polishing filter

Any thoughts on why the excess smoke during aceleration and the deposit on the plugs? Other than the smoke she runs like a dream. Starts instantly ... good strong acelereation given the small 2 blade prop ... dead smooth at idle. Have not yet been able to check oil consumption as not enough run hours.

Thank you

Dave

[Jim Booth]

I always thought dry black soot on the plugs indicates a rich mixture.

Jim

[gregt]

Mine looks like this as well (1971 C&C 27, late-model A4). I have also noticed that at low revs there is less smoke but at higher revs there is more. I have not checked the compression (have owned the boat for one season), but it burns some oil. Otherwise, starts and runs well.

[Kurt]

As I said in a previous response, my A4 is like this too. Interesting other C&C owners see this also. My motor runs great, good compression, uses a little oil - same smoke. Hmmmm - maybe it's a C&C thing (I have a C&C 33 MKI).

[Dave O]

Thanks everyone.

Jim ... yes ... the black soot on the plugs and the excess smoke suggest too rich a mixture to me also. I would expect less smoke even during aceleration, and a harder more brownish deposit on the plugs. Esp. after only about 4 hours operation. That is not much running time.

But I don't know how to make the mix. more lean. The mixture screw on the carb is set well (I am sure of that), and the choke plate is fully open. I don't have a tach but idle speed seems good, and I don't think that would result in these symptoms anyway.

Any ideas? My strong preference on several levels is to have this engine run really clean.

Dave
C&C 29 Mark I
Oakville, ON