No power this spring?

[J.MILES]

Hi my first time here, but I love it already. The issue is 25-30% power when prop is engaged. It will rev up normally in neutral. This is the odd thing, I had the same exact problem last summer. I removed the carb, had it completely cleaned and the only culprit appeared to be the spark arrestor. It was fairly clogged. With it cleaned, it ran like new. I put it away for the season and launched it yesterday in Kittery, Maine. A test run out of the harbor brought on the same symptoms of last year. I did the whole winterization routine. I put in new plugs and changed the oil over the weekend. Any ideas out there?

[smosher]

What does the engine do when you give it full power while in forward ?

Steve

[J.MILES]

Hi Steve,

It changes little. If left in full throttle position, it begins to run a bit rough and I expect may lead to a stall if left there, I didn't wait that long. It does not act this way when in neutral. Don did suggesst, water in fuel, moisture on points or critters in exhaust. How the hell critters could get in the exhaust is hard to believe but something is blocking. Last year it was starving from lack of air. A blockage in the exhaust will do the same thing?

Thanks for getting back to me. I'm heading up the coast to Rockland over Memorial so I want very much to get this resolved.

John Miles

[smosher]

So under load it starts to run rough and sounds like it will stall. Don recommended points, water in gas and exhaust pressure.

If this was mine I would replace the points, condensor, rotor, cap and I would also
look down into the dist to see if the advance springs are still there.

Gas is easy, use a portable gas can, what kind of fuel pump do you have ?

If using the mechanical pump you definately need the polishing filter and maybe it needs to be rebuilt or replaced.

Exhaust is tough, I guess you could disconnect it and see how it runs, But I would rebuilt it as its cheap parts from Home depot and getting the flange off
is the tough part. The other consideration is the water muffler, if you have one.

Any change in the engine if using the choke ?

Steve

[roadnsky]

I removed the carb, had it completely cleaned and the only culprit appeared to be the spark arrestor. It was fairly clogged. With it cleaned, it ran like new.

John-
If you take off the spark arrestor and run it now, what happens?

Steve already gave you a lot of places to look for clues, but the part about the spark arrestor is interesting.
-Jerry

[J.MILES]

When I take off the spark arrester, it runs the same way.

[J.MILES]

OK, Thank you for the advice thus far. Let me ask this... I appreciate the suggestions but many of them seem to be a "cumulative" remedy. This has happend suddenly. If last year, the exact same simptoms occured due to a lack of "air," how else is the air availability constricted. I don't know a lot about engines, I'm just learning, I'm a wood working guy, but I believe the total "air flow" meaning the exhaust may be part of the equation. Is that the case? Are there other air, (in/out) issues I may not be considering?

Thank you everybody. I will return the favor by reporting back what I found and becoming an active member. I love this site. Thank you for the Internet and MOYER!

J. Miles

[ghaegele]

I'm skeptical that the flame arrestor was clogged enough to be choking the air supply, since you have essentially the same problem, but I guess it's possible. What I think is that you either have a constriction in your fuel supply--easy enough to check--or a constriction in your exhaust. Perhaps the condition temporarily relieved itself after you cleaned the flame arrestor but then returned at the end of the season. I've never had the problem myself by have read on these pages how back pressure from the exhaust can cause just such a problem as you are describing. (Imagine a hand plane with a tiny throat blocking the wood shavings from exiting the plane!) Have you tried running with the exhaust disconnected? Or even just leaving one spark plug out will relieve the pressure.

Good luck.

[sastanley]

John,
I would check for an exhaust restriction next...it will definitely return a 'loss of power' symptom. Usually the point where the water is injected in front of the
muffler gets gunked up with stuff.

One quick test I've heard of trying to check for exhaust restriction without disassembly is to get the engine running and pull one of the spark plug wires. If the engine runs better on 3 cylinders it is an indicator the exhaust is restricted. The theory is the restricted exhaust is choking the motor with 4 cyls operating, but with only 3 pushing exhaust the restriction may not be as noticeable. Then you probably need to yank the hose & water injection elbow & clean it out. (edit - same test mentioned above..ghaegele was quicker to it than me..)

We've had to clean the exhaust elbow out every 4 - 5 years on my step-father's diesel. He has an odd recirculating raw water cooling system that only pumps water out of the exhaust pipe when the thermostat is open..I think this contributes to the problem. Although the build up in the piping is gradual, the power loss seems to happen suddenly..as if for a while the engine can handle the restriction, then suddenly there's too much. I can tell you from experience that during a week long cruise with the diesel, I didn't notice any power loss until the very last day of the cruise motoring home with no wind..my tell tell sign on that boat (2-cyl Universal diesel) was black soot in the exhaust when trying to get to what I normally considered cruising speed. It instantly clicked in my head what the problem was at that point.

[Don Moyer]

About two years ago, I had been pulling my hair out along with an owner whose engine would appear to starve itself for something after a short period of time.

It turned out that someone had set a briefcase in the lazarette so that it blocked the only air vent into the engine compartment. I don't know that we would ever have discovered this problem except for the fact that the owner himself mentioned that when he opened the engine compartment on one occasion he noticed a bit of suction had built up inside. After discovering and removing the briefcase the engine performed normally.

Don

[Kurt]

There are a lot of suggestions here, but, based on my experience with exhaust backpressure problems, I would save that area of exploration for last. I had a problem similar to yours - 25-30% power in forward and no difference in rpms when throttle was advanced. After much troubleshooting and even hiring a mechanic, we discovered a significant blockage in the exhaust elbow. This was discovered by a simple test - we removed the hot exhaust at the exhaust flange and fired up the motor - it ran great, although loudly.

Here's the difference between my situation and yours: my engine also lacked full rpms in neutral. You mentioned that your engine performs normally in neutral. Make sure of this by reving your engine up in neutral - it should rev somewhat "explosively". If it seems to gasp for air and only achieves something like 2,000 rpm (I think I could get 2,400 rpm) or less when reved, regardless of how much throttle you give it, you probably do have an exhaust restriction. If your problem only manifests itself in gear, I would steer away from exhaust backpressure as your cause. That has just been my experience.

[J.MILES]

Kurt,

Thank you very much. I will try to look for the problem where you suggest. Is it difficult to dissassemble?

J

[sastanley]

every one is different and unique to the boat. Mine in my Catalina 30 was not difficult. The galvanized pipe itself was seized together, but I had a small piece of rubber exhaust hose between my mixer & muffler that I could remove to inspect..this is a pic of my new exhaust section. The blockage usually happens in the area of the bronze water mixer.

Keep in mind I have new parts in the pic, and hadn't added the heat wrap, etc..

Hope this helps.

[roadnsky]

Kurt,

Thank you very much. I will try to look for the problem where you suggest. Is it difficult to dissassemble?

J

Remove the exhaust at the flange (2 bolts) where the exhaust meets the manifold. (See arrow in the pics)
Depending on the age and condition of the exhaust and the bolts, this might be easy or...
As Kurt said, it'll be loud but if it runs fine you know the exhaust is the source of your issue.