Help! Water in carb throat!!

[raleighm]

I have been working with my A4 for a couple of years now and am still having issues. My original problem was contaminated fuel due to an old steel tank that had a lot of water/rust in it when I bought the boat. A year ago, I replaced the tank, fuel filter and carb with new ones and flushed the fuel system. I now have nice clean fuel but recently discovered a new problem.

I raced on New Year's Day and the engine started right up at the pier and ran beautifully. I motored to the pre-race meeting/breakfast, then started the engine again and motored around some more prior to the start. No roughness, low power, unusual smoke or any other contra-indicators. The race was in high winds and waves so we got knocked around a good bit and were heeled over nicely all day. After the finish, I tried to start the engine to go home and - nothing. It would turn over fine, checked to make sure there was spark, all the usual but never got it to run. It did catch once and ran VERY slowly and sluggishly in idle but soon died. This had happened on occasion in the past but had always started eventually and always started right up the next time I came to the boat and cranked up at the slip.

Now it won't start even after sitting for three weeks. I took off the carb and cleaned it thoroughly at home. Noticed some liquid in the throat when I pulled off the flame arrestor that smelled like gas. Put the clean carb back on and it still won't start. Freshly charged battery, good spark, no start. I looked into the front of the carb and it was full of dirty-looking liquid that was dripping out the front (arrestor was still off). I poured the liquid out into a glass jar that I had handy and after it settled out I found it appeared to be mostly water, with a little bit of gunky fuel on top. I took it home and dipped a q-tip into the water to confirm that it wasn't clear-looking fuel. The q-tip wouldn't burn so it's definitely water. I've attached a photo of the stuff. Also a photo of the manifold discharge riser setup.

I suspect that the only way water could be getting down the carb during cranking is through a bad exhaust or head gasket, or an internally cracked exhaust manifold (I sure hope it's not a cracked head since I bought the head new from Moyer two years ago!). I was cranking all this time with the water inlet valve closed so as not to fill up the exhaust hose. I even went so far as to de-couple the wet exhaust hose from the hot section, just below the water injection point, to be sure back pressure wasn't the cause of the starting problem. Still wouldn't start. A small amount of water came out of the hot section as I cranked.

Before I start removing the manifold, any good ideas as to troubleshooting ideas, sequence, etc. to eliminate any non-problems first? I'm at a loss. I've come to believe that the exhaust setup on my boat isn't very good but can't see how that would cause water in the intake manifold/carb. Any help would be greatly appreciated.

[Don Moyer]

The appearance of the water in the intake throat of the carburetor is disturbing, particularly after you took such good precautions to prevent water from backing up from the exhaust system. The water dripping out of the hot section is strong (but not conclusive) evidence that water may be coming out through one or more combustion chambers.

I would perform a compression check, a pressure check of the manifold, and look for evidence of water in one or more combustion chambers while performing the compression check.

Don

[raleighm]

Water in carb

Don, I took the spark plugs off and did not notice excessive moisture in any of the cylinders. I'll do a compression check on the cylinders and see what I come up with.

I'm not sure how water could be entering the carb throat from the cylinders since the intake valves are only open on the intake stroke where there is suction rather than pressure. There shouldn't be any connection between the exhaust ports and the carb should there? I suspect a crack in the water jacket in the manifold and think my next step will be to pressure test that.

Let me add that I pulled a real dummy move last spring when I forgot to open the water intake valve and overheated the engine. I panicked and opened the valve without letting the engine cool down. The steam blew a hole in the short section of exhaust hose right below the riser exit and that may have also cracked the manifold. That being said, after replacing the hose, the engine started and ran for several hours the next day and has run well since spring except after a hard sail as described below.

I also created a post showing the exhaust system setup that my boat came with. I suspect that a little water has occasionally gotten up into the exhaust manifold because I've often had difficulty getting the engine to start after a hard sail, even after it started, idled and ran perfectly when leaving the slip and motoring out. I've had no problems motoring in heavy seas and this doesn't seem to happen after a light air sail but after a brisk sail I sometimes have to crank the engine numerous times to get it to start and when it finally starts, it will run somewhat sluggishly for a few seconds and then normally. The next time out it has always started right up in the slip. Do you think that just enough moisture is getting in as a result of the boat being heeled over/tossed about for the dampness to inhibit starting?

This is the first occasion since I replaced the fuel system that it has refused to start at all after a sail and even after sitting in the slip for an extended time. It started very normally and ran perfectly prior to the New Year's race but not since. Very odd that it would suddenly get this bad.

[Don Moyer]

It's true that while an engine is running, or even cranking on the starter, water from within a combustion chamber will tend to flow out into the exhaust chamber of the manifold. However as soon as the engine stops turning over, and depending on the source and amount of the water entering into a combustion chamber, some of the water will very likely find its way to the nearest open (or partially open) intake valve and into the throat of the carburetor. Then, when you next turn the engine over (or if it happens to start), some of the water that started out in the combustion chamber will be drawn back up into the combustion chamber and be discharged into the exhaust system.

All that being said, a crack in the manifold could well explain where the water is coming from in the first place.

Don