Can't make over 3kts

[JimHo]

I am stumped.
This is a new boat to me, and so I don't have history to compare her to.

The A4 starts on first or second revolution, and seems to run smoothly in idle. She will handle throttle well in neutral and seems to go up in the 2500-3000 rpm range though I do not have a tach.

In forward full throttle i can make about 3 to 3-1/2kts over water. However, after a bit she will suddenly drop in rpms and then I can only make 2 to 2-1/2 kts.

The carb has been cleaned and the floats adjusted. Opening the choke causes th ngine to stutter.

I thought it might be fuel, so tOday
I recleaned the carb and ran fresh fuel from an auxilary tank. I could only make 3kts again.

The water temp stays about 160-170 and the oil pressure stays at about 35. I don't feel any excessive vibrations, and am not blowing an Noticeable smoke. Water is coming out of the exhaust as it should be.

My next move was to change plugs, but I need to make tjis work soon as I have to get this boat up the river tomorrow against a 3-4 kt tide for haulout.

Is there anything more I should be looking at?

Thanks Jim

[Dave Neptune]

Jim, I would consider the slow speed as being due to needing a haulout. If it has been a while since the hull and prop have been cleaned I would chalk the performance up to bottom and prop fouling.

As it did drop RPM and the choke did not help don't worry about the fuel or carb just yet since she starts well. Lots of things non catastrophic can cause a drop in RPM's

Do you have points or an after market electronic ignition?

The temp seems a bit high unless you have a heat exchanger.

Dave Neptune

[JimHo]

Thank you Dave,

I am pretty sure this is electronic ignition.

The boat was put into the water in May, and the bottom isn't too bad. I can easily get her to hull speed under sail. The water is too cold for me to dive to check the prop.

[sastanley]

Jim...in Sept of 2008, I got my boat. The engine had the same symptoms you are reporting. A haulout makes a HUGE difference. Before it got too cold that fall of 2008, I had a buddy with a wetsuit scrape the prop and it made a world of difference, even with the bottom still dirty. It was the prop growth that was the problem.

Unfortunately for most boats that the A-4 pushes around, the power the engine makes at cruising speed (2,000-ish RPM) is simply not enough to overcome a dirty prop or bottom. I can tell after 3 or 4 weeks of prop growth a difference in the engine efficiency.

I recommend you get the prop cleaned (if you can) and report back. I agree with Dave, it is the main indicator based on your reports so far.

[JOHN COOKSON]

The carb has been cleaned and the floats adjusted. Opening the choke causes th ngine to stutter.
Thanks Jim

I think you are saying here is that the only way you can get the engine to keep running is to keep the choke closed a bit? Is so it implies that there is an air leak somewhere resulting in a lean condition - most likely between the two carburetor halves. There are a couple of ways to check this. (1) a flat surface (2)Put the two halves together (no gasket) and hold it against a light.
Do you have a PCV valve on the engine?
What this has to do with the drop off in performance I don't know - probably nothing.
As has been suggested you need to have bottom & prop cleaned so you know whether the drop off in performance it a boat or engine problem.

TRUE GRIT

[JimHo]

Thanks all. I will dive in the morning. I was hoping for a warmer solution! The water is a bit cold in New Hampshire right now...

The choke issue meant that the engine ran without choke as expected. Adding choke made the engine worse. The MMI manual mentions troubleshooting scenarios where running the engine with choke on helps. That was not the dase with me

[BunnyPlanet169]

Hi Jim -

I don't want to go swimming with you, but I'm probably near by (York) if you need an extra pair of eyes. Sounds like you're on the Piscataqua? You can PM me if you'd like.

[joe_db]

When I forgot to put my manifold pressure gauge hose back on I had similar symptoms.
If you were NOT having mixture issues I would suggest checking the prop and bottom and then the firing order.
Since you ARE having mixture issues, check the carb*, manifold, and PCV valve.

* I think a clogged main jet might have symptoms like this as would an air leak

[sastanley]

Joe, good idea..and a warmer solution.

Jim, double check the firing order is correct 1 - 2 - 4 -3. When there is no load, the engine may still rev up just fine if one of the wires is out of order/not firing, but no power under load.

Any easy check to make sure all cylinders are firing is to remove and re-connect one plug wire at a time while the motor is running (idle is fine)..you should notice a distinct change in the engine as you remove and re-connect each plug wire from the spark plugs. If they are all firing, then I think swimming is the next option.

[tenders]

Northeast location, September/October now, launched in May, not cleaned since, boat moving sluggishly through the water: this is a CLASSIC case of barnacled prop. A couple of barnacles on a prop, never mind a bunch, have a huge hindering effect on the prop's efficiency and they do not break off or wear off over time. I find that on Long Island Sound, from a May launch everything feels perfect until early September, at which point it is noticeable and then quickly gets worse. Barnacles do not seem to get the least bit dizzy.

Sudden drop in engine performance: this sounds like a classic sticking valve. I run my engine all the time with what I guess is about two cups of Marvel Mystery Oil in the gas to prevent this, and it works without requiring so much as a wrench. A similar amount of two-cycle engine oil will do the same thing, but with a bit more smoke.

[JimHo]

I was amazed at how bad the prop was, and the bottom paint lower down. I'm used to 45% copper ablative bottom paint which has very little growth.

I scraped the prop as best I could free-diving, and was able to make it to 3.8kts afterwards.

I ran up the river after low tide this morning. I was at a slow push when I came to the Memorial (lifting) bridge, and was able to keep her off the bridge until the span opened for me - after that the current pushed me along my way.

I did run the spark check, and noticed a definite change on pulling each one.

I will add the marvel mystery oil next year to clean fuel.

Again thank you all.

Jim

[sastanley]

good news

Jim, I think we can all come to the conclusion that the dirty prop and bottom were the main culprits...Now that you've confirmed it we can move on to the next order of business, whatever that is.

Even though it seems most of us were still leaning to a dirty prop, all the other things were quick easy tests to help maybe identify other issues. With a clean bottom and freshly cleaned prop the boat should perform much better. I've found the A-4 to be very picky about a dirty prop and the performance suffers quickly.

I have trouble getting under there to get the prop clean too, so I feel your pain. I can only spend several seconds down free diving, because for some reason I get claustrophobic under boats, but I'll hang in a bosun's chair all afternoon. My buddy has dive gear, so we make a deal that I do his mast work, and he does my dirty prop work.

[ndutton]

Guys, my diver costs me $35 for a bottom clean, some of the best money I've ever spent. With local conditions on fresh paint he does the service once every two or three months, then monthly as time goes on. I've used him coming up on 12 years now, ever since I bought the boat.

I did my own hull cleaning on the Westsail, never again.

[joe_db]

Wow - if I pay for a bottom cleaning it is well over $100.
I do it myself usually, but late in the year when the algae grows my wife gets paranoid I will get some awful disease. I gave in and hired the local dive company, who were somewhat delayed because the divers were out sick

BTW - how did a dirty prop relate to the choke

[capnward]

Jim,
Sounds like you gained almost a knot by scraping the prop in the water. (Shudder.) Good on ya. A clean bottom will add another knot at least.
But since you report that rpm suddenly decrease after a while, we should consider what could cause that. A sticky valve is a possibility. I heartily concur with the recommendation for Marvel Mystery Oil in the gas. I put in 2 oz. per gallon, and have not seen my valves since the rebuild 2,408 hours ago.
A fuel pressure gauge would be helpful here. You say you cleaned the carb, did that include the main jet? If yours is adjustable, turn it in until it seats, and back it off 1 and 1/2 turns, maybe 2 turns. Backing it out makes it richer. This procedure may dislodge a blockage in the jet, which could cause a sudden rpm decrease. If your main jet is nonadjustable, you may have to remove and clean it.
Besides the sudden rpm decrease problem, here are other things to think about. Did you try turning the distributor while running at speed under load, to see if rpm can be improved? Do the plugs look fouled, indicating a rich mixture? How old are the cap and rotor? If you have Electronic Ignition, wear of the points is not an issue, since there are none. There may be an air leak at the carb gaskets, making the mixture lean. If you have a PCV valve, try plugging its hose to the manifold with your thumb for a moment. If it runs better, you may be running too lean. When you add choke, you are closing it, not opening it. This richens the mixture. You report it stutters as choke is closed, that means your mixture is probably not too lean, or closing the choke a bit would smooth it out. Can you open the choke soon after it starts? If so, the mixture is not too lean.
Since she starts right up, you are not far from A-4 bliss. Good Luck!