Wont rev over 1800rpm under load

[Cruiser2B]

A bit of history first...Alberg 30 with A4, rebuilt completely by Moyer in 2008. I bought the boat this spring and have had zero issues until now.
following items on boat/engine.....

.has fresh water cooling
.electronic ignition
.indigo 3 blade prop
.new shaft
.fuel a week maybe 2 weeks old. i used a portable 3 gallon tank...no internal tank
. Racor 110 fuel filter assy
. boat was hauled and pressure washed in Feb. prop was clean
.removed and cleaned spark arrestor..no change in performance

anyway, i have always been able to achieve 2500-2700 rpms in foward. dont really cruise there but did have to run the motor that high going through some 6ft chop....that god for the extra power! and want it!

Anyway last weekend took her out and noticed at start up she was a bit hard to start, usually fires right up. no big deal..once started she kind of surged a bit, this was unusual. After she warmed up all seemed fine. backed her out and headed out. while heading out i decided to just run her up abit to clear things out. I only using run her between 1500-1800rpm. Well at about 1/3 throttle she got to 1800 and would not go past no matter how much throttle...just kinda got that hollow sound from carb. went back to 1/3 throttle and cruised out of the channel no missing a beat at 1800 rpm with ideas running thru my head. Once I cleared the channel i tried reverse....engine reved up to 25-2700 no problem. i did this thinking maybe prop was fouled. no change went back in forward. I decided to pull the choke abit to see if maybe she was starving for fuel....at about 1/2 choke she started to die...too much fuel. choke back in and cruised at 1800 for about 10 more min and finally went sailing. On the way back in she started right up and got me home. Today i went down and looked things over...nothing obvious. pulled the plugs, all looked good a slight tan, # 4 was a bit white when conpared to other 3 but overall fine. drain fuel/water separater, there was some debris but no water.
I asked around the docks and someone asked me how dirty the bottom was? would this have an effect on engine rpm. i can see not reaching same speed if bottom was dirty but engine should rev, correct? he told me his boat(alberg 30 with A4 -2 blade prop) wont go over 16-1700 rpm ever.

i ordered a new filter for Racor...nobody in Norfolk area stocked it...

Any ideas on where to look next? is it posssible the bottom is that dirty already? water here is very dirty, cant see 1inch below waterline. i might call a diver to check things out....will be about 75 to have it cleaned..Could it be timing?

any and all ideas welcomed

[sastanley]

Cruiser, welcome.

Yes..it definitely could be the bottom..if you have not cleaned the prop since February, I would clean the bottom & prop & get back to us.

I have found that my A-4 & Indigo prop are VERY picky about any growth on the prop..even tiny barnacles have an effect on performance. I've cleaned mine twice this summer already.

My advice is to eliminate the growth as a suspect before making changes to the engine. If it still runs at 1,800 RPM after cleaning, we'll have something to troubleshoot.

I do not think it is timing..it will run really bad if it is out of time (misfires, backfires, etc..)

[JOHN COOKSON]

If cleaning the bottom\prop doesn't help consider exhaust blockage in your differential diagnosis.

TRUE GRIT

[smosher]

I also have the indigo prop and it's noticeable when there's a wee bit growth.

When the bottom has growth it acts like drag and slows the boat reguardless of rpm.

If I remember correctly, reverse is geared down, which means you would need more rpm in reverse to spin the prop at the same speed in forward. I would say that since
the engine ran ok in reverse, thats the engine is ok.

[Bold Rascal]

Welcome Cruiser

I launched my freshly prepped boat (and clean prop) last november. It was late April this year before the water was warm enough (wet suit warm enough) for me to get in the water and clear away a temporary seal I had around the prop shaft and cutlass bearing.

I was amazed at how much marine growth there was on the prop. It doesn't take that long on the bay.

[Cruiser2B]

Thanks everyone, called a diver out. He will take a look in the morning, I will let you all know. I hve been using the boat 3 times a week up until mid July, then the wind has just been poor. i would say boat sat for 2 weeks before this last time out...prolly plenty of time for prop to get alot of growth on it. water here is very warm, diver said he was seeing a different kinda of growth this year...

i know the race guys here clean thier hulls every weds afternoon before heading out.

Thanks again

[Cruiser2B]

Diver came out this morning and cleaned prop and bottom. he said bottom looked good but prop had lots of barnicles. $60 bux to clean hull and prop. Not too bad

Took her out for a cruise a bit ago and engine went to to 2300rpm. she ran just fine, started right up. Boat was moving at 6.2 knots....making a wake! I am not too worried about it boat moves ok and this engine truely is just used as an auxillary, I will keep an eye on things.maybe this fall i will look at the carb.

just curious though, Does this seem like normal rpm for this boat and this prop?

thank for the help

[roadnsky]

Those are good numbers.
2200-2300 at 6+ knots is normal for 30' with 10,000 displacement.

I agree you should still give the carb and fuel system some attention as that is likely the reason you had the hard start and 'surging' issues.

[Cruiser2B]

Those are good numbers.
2200-2300 at 6+ knots is normal for 30' with 10,000 displacement.

I agree you should still give the carb and fuel system some attention as that is likely the reason you had the hard start and 'surging' issues.

Thanks roadnsky, is that all the RPM I should see? basically what i am asking is will the engine rev higher even though the boat wont move any faster? i guess prop slippage? will a 2hp outboard rev like crazy but not move the boat or will it just lug down and move it as fast at it can?

I did replace the racor 110 filter this morning too. today is started right up no surging, no wondering and idled nicely at 600rpm once warmed up.

thanks again

[roadnsky]

Thanks roadnsky, is that all the RPM I should see? basically what i am asking is will the engine rev higher even though the boat wont move any faster? i guess prop slippage? will a 2hp outboard rev like crazy but not move the boat or will it just lug down and move it as fast at it can?

You may get a few more RPM out of her but you're right there at hull speed.
After that, the drag gets pretty big. The A4 will either have to push the boat up the bow wave or usually it'll cavitate the propeller.
If the prop doesn't cavitate, the engine will lug.
If the prop cavitates, the revs go up, but the boat doesn't go any faster. In fact, I think you start slowing down.

After saying all that, the bottom line is that your numbers are good.


EDIT: You might find this thread interesting reading:

http://www.moyermarine.com/forums/showthread.php?t=4665

[Cruiser2B]

thank you for the explanation, makes sense. still learning here

[roadnsky]

That's what this forum is all about!

[Marian Claire]

Cruiser: I might have missed this but do you have the direct drive or the reduction gear? Dan S/V Marian Claire

[sastanley]

Cruiser2B, back when I was new to this forum, I had the exact same experience...I was asking all these questions about the engine running poorly, but after a clean prop I think I made the same exclamation (wow, a stern wake!!)

I've found you really need to keep the prop clean to accurately diagnose any other engine abnormalities...a dirty prop mimics all kinds of weird stuff & makes the engine work harder anyway.

That being said, Jerry's right...those numbers are great and about what you should expect..some people never see 2,300 RPM (unless you don't have a direct drive, per Dan's question)

Where are you? Do you have winter? If so, I'd enjoy the boat the rest of the season and now we can tackle individual problems as they come up, but for now, start your list of winter projects.

If you have a free evening, that is about how long it takes to pull the carb apart, clean it, and put it back together..I would highly recommend having spare gaskets for it (flange, where it connects to manifold & the carb bowl, where the two halves of the carb bolt together) in case you tear one pulling it apart (very likely.)

If you have a mechanical fuel pump, you may want to pull the bowl off that and drain any water that may have accumulated, but hopefully the Racor is taking care of that already.

When was the last time the oil was changed? Spark plugs, points, etc.. All these things can (& usually are) winter/winterization projects to insure trouble free start up in the spring!

[Dave Neptune]

Hmmm!

cruiser, good you found the problem. As Shawn & Jerry stated those are very good numbers with the Indigo prop.

Shawn, this is a classic case of a load increase on the engine and a decrease in rpm and performance~~something a Vac gage on the manifold would have indicated. The vac would be less (more load), the RPM's are down (decrease in output) and the speed is down~~IE the engine is fine and something else is bogging it down ~ HMMM ~ check bottom and prop.

Good diagnostics done here however the V/gage would save a bunch of head scratching .

Dave Neptune