Engine won't rev above 3,000

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Capt. Sam
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Engine won't rev above 3,000

I apologize if this has been discussed before, but my search didn't show it.
I just started out on a three day cruise Sunday but just out of the slip, the engine slowed without me moving the throttle, then wouldn't accelerate when I throttled up, then died when I tried to idle it. I got it started again and limped back to the slip. I thought maybe air in line was the cause as I had just changed the fuel/water separator. So, I bled the line, then started back out again. This time, she ran fine up to about 2800, but would not go above 2,900 - 3,000 with the throttle maxed out. I know I don't need to be running her that high but she would go there previously, with no hesitation, so I know something is different and not good different. So, back to the slip again, (We're getting real good a backing in) and this time I changed both the regular fuel filter (the spin off on the stb side) and the "hidden" one in back. bled the line again and took off. Same result, idles fine, accelerates fine, but won't exceed 3,000 rpm. Recent changes since last cruise: oil change, new bigger (80 amp) Balmar Alternator.
Any ideas will be much appreciated.
Thanks,
Sam
PS we went cruising anyway, the engine performed flawlessly the whole time except for this inability to exceed 3,000 rpm.
s

Capt. Sam Murphy
1994 Catalina 36, Hull 1327
Shoal draft, two cabin model.
Panama City, Florida

benethridge's picture
benethridge
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Maybe it's just the larger alternater putting a greater load on the engine?

Ben Ethridge
Miami, FL
1984 MK1 Hull# 263

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benethridge
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Probably not, now that I read your post more closely. Rope or some such wrapped around the prop shaft maybe?

Ben Ethridge
Miami, FL
1984 MK1 Hull# 263

BudStreet
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Posts: 1127

Sam, do you have the M35A? If so the manual says Max RPM is 3100-3200 rpm. How many RPM are you getting? When was the last time the bottom/prop was cleaned? Has the boat been sitting in the slip for a while? If you're only down a couple hundred RPM it could be as simple as that.

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Capt. Sam
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Thanks for quick response guys. Yes, its the M35B with very low hours.
I thought of the larger Alt being an issue, but I went for a test run right after I installed it, and it ran fine. Might be the prop intanglement but Ive got those cutter blades on the prop so I'm thinking that's not likely, But I need to go over the side and check it. I'll also use my laser hand held tachometer to be sure the rpm at the eng panel is right. Any other ideas much appreciated.
Sam

Capt. Sam Murphy
1994 Catalina 36, Hull 1327
Shoal draft, two cabin model.
Panama City, Florida

BudStreet
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If it's an M35B then the max RPM is even lower according to the manual I have it's 2900 to 3000. Was your boat re-powered? The M35B wasn't made in 1994.

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Capt. Sam
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Oops! You're right Bud, I have an m35a 30 hp engine. I went in the water today and checked the prop and shaft. No obstructions.
Also checked th
e tachometer with my optical tach. Its right on the money.
Still can't explain why it won't go above 2900 rpm. It did previously.
I'm sure its something that needs to be fixed. Hope someone else with have
an idea.
Thanks,
Sam

Capt. Sam Murphy
1994 Catalina 36, Hull 1327
Shoal draft, two cabin model.
Panama City, Florida

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stu jackson c34
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Posts: 1270

Sam, if it's the difference between 2900 and 3000, I simply wouldn't sweat it. My bottom needs to be cleaned (regular service is due soon on its quarterly cycle) and with a clean bottom I get 3000, dirty 2900. I don't know why, cuz the engine shouldn't "know" what condition the hull is in, it should just run, right? I just don't think with the quality of our tachs that 100 rpm should create an issue. Call me crazy (many do :)).

Stu Jackson, C34IA Secretary, C34 #224, 1986, SR/FK, M25 engine, Rocna 10 (22#)

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deising
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Sam, I don't know how likely it is that a larger alternator can rob you of 100 rpms, but you could eliminate that theory if you could measure your alternator's electrical output.

Assuming the mechanical installation is sound, if the alternator is putting out very low current (say, less than 20A or so), it should not drag down the engine speed appreciably. If you were to measure a high current, it "might" be a possibility.

I agree with Stu that it may not be a big deal, but 'something' changed and it would bug me, too, until I figured out what is was.

Duane Ising - Past Commodore (2011-2012)
s/v Diva Di
1999 Catalina 36 Hull #1777
Std rig; wing keel, M35B, Delta (45#)
Punta Gorda, FL
http://www.sailblogs.com/member/diva-di/

pierview
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Posts: 582

Sam...

You said you changed your filters thinking it was a fuel problem. Well, I had a problem where the RPM dropped and then would run up for a while until finally it stopped altogether.

The problem was at the fitting connecting the fuel line from the fuel tank to the water seperator filter. Its a 90 degree turn and that got clogged before the fuel got to any filters. Maybe this is restricting your fuel flow. Just a thought since nothing else seems to be working for you.

Chuck Parker
HelenRita 2072 Mk II
2002 Tall Rig - Winged Keel
Atlantic Highlands, NJ

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baysailor2000
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Here is how I would solve the problem. Re-install the original Alternator then test the RPM. This would show if the problem is due to the new 80AMP alternator. If the original alternator continues to produce lower RPM then look for another filter that is attached directly to the fuel pump. It is a screen and can be cleaned. Also could you clarify if the low RPM is also while in the slip and not in gear - or is it only when it is in gear.

Haro Bayandorian, 1999 C36 MKII, Sail La Vie #1787, M35B,
Coyote Point, San Mateo, CA.

shulme801
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Captain Sam,

I had similar issues with the 1995 C-36 MK II that I just acquired -- engine would not rev above 2600. I have the M-35 A with the std. alternator. My issue was that the previous owner had installed a prop with too much pitch. I reverted to the 15x9 3 blade from the factory and the problem was solved.

I'm scratching my head -- your problem sounded like a clogged fuel filter issue. But you've already thought of that and replaced both the spin off and the filter attached to the fuel pump.

Another possible culprit is the exhaust mixing elbow. Have you checked it? If plugged up that might explain the behavior you are seeing. If the elbow hasn't been replaced, it may be time.

Best regards,

Steve

Steve Hulme
S/V Coy Mistress #1467
North Carolina
1995 C 36 MKII TR/WK

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Capt. Sam
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Thanks to all for the thoughts and suggestions. I've done a few other checks since last posting: removed the air filter canister, cleaned out gooey residue from old melted filter. (could goo have gotten to fuel injectors?) replaced with new filter, (see separate post on this subject). More importantly, I checked the throttle linkage to see if it was hitting it's stop at 2900 rpm, then made slight adjustment to allow it go further. Although, it sure looked like it was nice and tight at the old throttle setting and it seems that a slip in the adjustment was not likely. With those items attended to, I ran the engine, in nuetral in the slip. Very, very briefly I ran it up to over 3000. I really hate to do that in nuetral and don't want to do it in gear at the slip as I'm worried about the effect on the silt under the boat. So maybe I fixed it??
Going on an overnight Saturday and I'll check it underway. Everyone is right about not really needing to run the engine above 3000. But the surveyor specifically checked that during sea trials when I bought her 16 months ago. And it went right up there without hesitation.
I'll report results on Monday.
Thanks all.
Sam

Capt. Sam Murphy
1994 Catalina 36, Hull 1327
Shoal draft, two cabin model.
Panama City, Florida

llunved
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Posts: 20

I ran into a similar issue recently. Boat had been sitting on the mooring for about two weeks. Suddenly engine would not go about ~2900 RPM. Plus vibration when under load. Checked everything. Finally dove under and on closer inspection foudn about an inch of barnacles covering the forward-looking side of the prop... Scraped them off and problem was gone.
 

1988 Catalina 36 MK I - Swept Away

kgatesman
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I'd start with the tachometers just aren't that good and could all benefit from calibration.  I replaced mine two years ago with the CD instrument cluster, it's more relative than accurate.  

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