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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Gas > Atomic 4
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Old 07-31-2011
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Question Engine wont rev past 1800rpm

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

Thanks SN
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Old 07-31-2011
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If not the bottom maybe starving for fuel? Reverse may have a different gear ratio allowing more revs? Assuming no changes in ignition timing and wiring in good shape and no air intake restrictions it may be debris in the carb. Suggest you drop the float bowl and look for debris or deposits which may have been sucked up partially blocking the main jet. If in cramped quarters it may be easier to take the carb home to a proper work bench. Suggest working on a large towel or cloth and laying out all parts in a sequential pattern and re-assemble in reverse order. Carb cleaner, thin wire and compressed air anything you can get at. let us know what you find. Assume filter is flowing freely? Next step check fuel pump for blockage and good flow/. Maybe try the new filter before opening the carb. Pinched or crimped fuel line? Portable tank not venting properly?
Pickup tube screen partially blocked?

Dabnis
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Old 07-31-2011
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thanks for suggestion, I did check the plastic tank for debris with a light this morning too....seemed very clean. when I applied the choke and it started to bog engine down, would that have indicated it was not a fuel problem? i am not saying its not a fuel issue....i am only asking. I am replacing the fuel filter, had to order one as no one in town had a replacement.

Do these engines go out of time often?
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Quote:
Originally Posted by Cruiser2B View Post
thanks for suggestion, I did check the plastic tank for debris with a light this morning too....seemed very clean. when I applied the choke and it started to bog engine down, would that have indicated it was not a fuel problem? i am not saying its not a fuel issue....i am only asking. I am replacing the fuel filter, had to order one as no one in town had a replacement.

Do these engines go out of time often?
With electronic ignition it is not likely, unlike the old points which could wear and retard the timing somewhat. My experience with electronic ignition in outboards, motorcycles and automotive use has been excellent. They either work or not, not much in between. Once set, unless the mounting screw comes loose, the timing should not vary. The choke may or may not cure a lean condition. The hollow sound you described is common with an overly lean condition. #4 plug being white may be an indication it is running somewhat lean. I doubt that a marine engine has any vacuum advance, one less thing to consider. A shop should be able to check the centrifugal advance or you can watch it with a timing light. As mentioned, you might want to wait for the new filter befare tearing into things. Let us know what you find. My guess is that it may be starving for fuel somewhat, not enough to kill it, but enough to keep it from running at higher speed

Dabnis
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Old 07-31-2011
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Had a similar issue a week or 2 ago where our engine would not accelerate past 1000 rpms and sounded strange. It turned out we had some small nylon line wrapped around our prop and shaft (crab pot?) that the bottom cleaning diver found.
Inspect your prop in the water by diving it or pay someone else to do it. We race our boat so we paid someone to do a thorough inspection and cleaning.
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Old 07-31-2011
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I agree with Caleb, probably the prop. Either it's fouled with barnacles or some kind of debris. My brothers boat wouldn't go past 2000 rpm in forward (reverse normal full rpm) so I dove it and it was a solid ball of barnacles so the blades couldn't pivot (Autoprop).
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Old 08-01-2011
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Thanks everyone, i have a diver coming tomorrow morning to see what going on under there. i will keep you posted
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Old 08-02-2011
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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? only went to 24-2600 that one time...maybe i was mistaken

thank for the help
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Old 08-02-2011
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I have the A4 with the standard A4 2 blade prop. I can get up to 2200-2300 at full throttle (and a clean prop), but I rarely go above 1800 for extended periods of time. Too much fuel burn and not enough speed to make it worth while.

The norm for the A4 with a properly matched prop is about 2000 rpm
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Old 10-19-2011
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I'm having similar problems and all things point to the prop/shaft/bottom.

30hp A4, C&C 27. After six weeks at the dock awaiting fuel pump, tune up, carb cleaning, and other uses for my money. The barnacles were so thick (LI Sound) the prop wouldnt even spin. I jumped in with a mask and gloves and a heavy duty marine scrub brush and handled the prop and part of the shaft (shows my ignorance not being more thorough).

Took her out and she was sluggish and stalled a couple of time. Once underway I could cruise at about 1/3 power (she revved and purred in neutral). No matter how much throttle in forward it just felt like she was fuel starved. Reverse vibrated unpleasantly.

Everyone I talk to instantly blames the build up.

Good luck!
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