Low Engine RPMs

[Bad Obsession]

I have a 1990 Catalina 30 with a Universal 23 hp diesel. I have had it since April and the most RPMs that I can get out of the engine is 2700 RPMs. I have changed the fuel filter and the RPMs haven't changed. The boat has always been consistant and I haven't lost any more RPMs. The engine runs great and I haven't had any problems with it. Someone has told me that there is a screen in the fuel tank that may be getting clogged up. I have also been told that that is a sign that the injectors may need work. What could this problem be? Could it be that someone has set the throttle so that 2700 is the max RPM allowed by the throttle? How do I fix or diagnose the potential problem? How expensive could it be?Any suggestions or help would greatly be appreciated.

 

[Ross]

Your propeller may be fouled.

Or the linkage on the throttle may have slipped.

 

[Phil]

couple questions

What is suppose to be its top rpms?Did you ever get higher rpms?Is the tac accurate, have you strobed the engine?Is it possible that the size if the prop is controling the max rpms?Do you hit hull speed at 2700 rpms?

 

[Landsend]

plugged exhaust elbow.

nm

 

[sailaway78]

Engine RPM

Have to wonder if you have checked the tach. Not sure what max rpm is for that engine, but 2700 is probably fairly close to the max. A slight error in the tach may be your only problem, since you have checked the most common maladies. Check the tach before you spend a lot of money guessing at something else.

 

[Stu Jackson]

M25XP

Before you go pulling your hair out and worry about all sorts of stuff:1. Run the engine out of gear. What's your max rpm? The engine in gear will usually NOT do the same RPM as out of gear. Normal for your engine: 3,000 out of gear, 2,700 in gear.2. The tach works off the alternator, not the engine. If your max rpm is not 3,000 out of gear, then you have two choices: interpolate the numbers and leave things as they are, or recalibrate the tach. Is it worth doing the recalibration? I doubt it, given your numbers.3. Yes, there's a screen in the bottom of the fuel pump. BUT, the secondary (usually Racor) filter should be plumbed BEFORE the fuel pump. Catalina kept doing it wrong for years. Turn the fuel off at the tank, remove the bottom of the fuel pump, clean out the filter, replace it and revise the flow from tank to Racor to pump. A replacement fuel pump, if and when you need it, can be found here: http://c34.org/bbs/index.php?topic=2515.0Since things have been working for you since you've had the boat, don't worry about anything drastic until you learn some more about it. It sounds fine to me.

 

[Franklin]

Or

The prop may be too big for the engine. I hear black smoke is a sign of this.

 

[Anchor Down]

M25XP

Rated max RPM: 3200-3300. But that's a bench figure, with no resistance. The engine is rated to run that fast, but I don't expect to get the rated RPM in the water.My '87 does the same thing. I'm about to check the throttle linkage stop screw to see if it's limiting the "throw" of the throttle lever on the engine, right after I see what the max RPMs are in neutral.Could also be that this boat is a bit over-propped from the factory, so is a congenital defect (maybe this happened when the C30 went to a three-blade prop?). But I'm not about to go through the expense of pulling my prop & having it re-pitched; in the big picture I'm content the way things are.

 

[Bad Obsession]

Interesting

I have been wondering about the prop since I do have the three blade prop.I am no getting haul speed. I am always with or against current but I usually see a range of 5-6 knots. Haul speed is 6.8 knots.I am not seeing black smoke and my transom doesn't have the soot on the back of it. There is a second fuel filter. The fuel goes to a Racor Filter and then to a second filter on the engine. The filter on the engine looks like it is the original, but it really shouldn't catch much because the Racor is a much finer filter and it would catch things before it got to the other filter. I just replaced my Racor.I have also thought about leaving things the heck alone and not being paranoid about them. That may be a good suggestion and I would mess with it if it gets worse. My Uncle has a Catalina 34, 1988, and he gets better engine performance than I do.....we have the same exact engine. That is fustrating.Oh well, I appreciate the information...thanks a lot...keep it coming!

 

[Bill Roosa]

Check the air cleaner

and do you have a clean bottom. Both can effect performance. 6.8 hull speed is just a gideline for the average fin keel boat of average lines and average surface roughness and average beam. I doubt your is that average so 6.0 may not be wrong. My Catalina 30, 1979 would only do 6.0 no mater how much sail I could get up.

 

[Franklin]

Bill

From my understand, hull speed has to do with the stern wave not being able to pass the bow wave. If this is true, then the shape of the hull doesn't matter...only the lwl.

 

[John]

2700 sounds ok to me

I have a 88C30 with am25xp and have been trying to get some more speed and better reverse stearing becouse of a tight docking spot .I tryed a CdI flex prop that made the boat fly allmost 7 knots and i could back up in a docking spot but i had a bad vibration between 1800 and 2200 rpm .The moter would max out at about 2700 rpms .With the old three blade prop the moter only runs up to 2700 rpms and i get about 51/2 knots. over 5.5 kts the back of the boat seems to suck way down my exoust is under water. At about 2300 i get about 5 kts.My boat is a wing keel with a 13" prop with a 10 pitch . John

 

[Anchor Down]

Join the Club

John, B.O. and I all have C30s that behave in exactly the same way, so there is evidence that this is typical. John, I get the same squatting and 5.5kts at ~2700 RPM when throttle is WFO, and the same 5kts when I throttle back a bit.When under sail, if the wind is stiff and I'm on a beam/close reach, I can just get over 6kts (GPS) if I can balance & trim the sails correctly, with surges to ~6.5kts. That hull speed value is an abtract theoretical number. I've had more fun sailing since I disregarded it.The C30 is a fat little boat with a beam of 10' 10" on a hull with a LOD of 29' 10". The beam/length ratio is high. This factor comes in to play to prevent it from ever approaching that theoretical hull speed, as well. So don't sweat it.B.O., the filter cannot be restricting fuel flow to limit your RPM. Notice the lift pump gurantees the injector pump on the engine always has all the fuel it can use and then some: the excess is returned to the tank via a recirculation line (that's the other line connected to your fuel tank). The secondary filter, new, allows this high flow rate, which is several times what the injectors can consume; routine maintenance would prevent it from ever getting so clogged that the injector pump would starve. Banish the thought from your mind.JeffP.S.— B.O., there is a small screen at the end of the pick-up tube in the fuel tank, and when it clogs after 20 years, you'll get inexplicable stalling. I've had my '87 since April, also, and had this problem from the moment I took possession. Stalling drove me nuts until I tracked it down. It's simple to remove the fuel line from the tank, unscrew the brass fitting, pull out the tube, and inspect/tear out the screen. But again, I don't think you're suffering restricted fuel flow: we three are all getting the same performance from sisterships with the same engine (allowing for John's after-market prop), so I think you're right where you're supposed to be.P.P.S.— John: yeah, she kickes up a heckuva prop walk in reverse, don't she? :^)

 

[Tim McCarty]

check the throttle cable...

I remember years ago having some problems with RPM's on my Yanmar 1GM, and found that the throttle cable was slipping...I now have a Universal M25XPB that operates well (albeit a bit loud), but it's only 2 years old. Back when I had the 1gm, I added a fastener to the cable to keep it from slipping...I have no idea what this was called or where you can get it, but it was supposed to stop the cable from slipping inside the cable housing...maybe some other sailors out there have some experience with this...good luck and fair winds...NOTE: this is only a suggestion...it may or may not be your problem...take it for what it's worth...

 

[Bad Obsession]

I feel better now

I feel better now. As far as haul speed...I have seen 6.8 knots....I have seen 7 knots. I have even seen 7.4 surfing a 4 foot wave. I have a tall rig bow sprit and that makes a difference. I have found that my boat LOVES to reach. In 10 - 15 knots of wind my uncle couldn't catch me in his 1988 Catalina 34 on a reach. My boat isn't too happy about pointing high and the upwind sailing isn't super....but man does she reach!