Falling short of max engine RPMs

[CLady]

Restriction of the fuel supply. Is it running warmish? Brown exhaust?

[Cadence]

Old fuel came up. I hadn't thought about it. I doubt that is it if your exhaust smoke isn't black. It is a thought to stick your pickup in a 2 gal. can of fresh fuel just to eliminate it. It isn't impossible if the boat has set up for awhile. Lord knows I'm no expert. Hopefully someone in the business will chime in. PS don't air lock your fuel line if you do it.

[blinkerfluid]

Thanks for all the suggestions everyone.. I'll try to go through an answer any questions, keep in mind that we've only had the boat for a couple weeks now and have only put about 3 hours on the motor while delivering her to her new slip.

I have no idea how old the fuel is. The boat wasn't used much over the past 14 months or so at least, fuel tank is currently only half full, so I know I need to top it off. No water has shown up in the Racor yet though.

The engine was running warm during delivery. Initially I was running at WOT (2400 rpms) and the engine heated up to ~210. I then backed the RPMs down to ~2k and the temp came down to 190. Still warmer than it should be. From what I've read, and the comments here, a clogged exhaust elbow could be causing both the low RPM and the high temp, so I will definitely be checking that out as soon as I can. Stupid job is keeping me from working on my boat!

The engine compartment is fairly well sealed up, however I had everything opened up when I ran the engine up to max RPM in neutral, so I don't believe that is the problem.

I'm going to take the airbox off the motor too and check that out. It's crushed in on the side at the moment, so it's possible that's causing some issues.

I'll double check the exhaust routing, but I don't remember there being any excess bends or kinks

I'll double check the tach as well, however, even if it is off, I don't think it's off by much just based on the boat speed vs rpm displayed. I'm getting boat speeds that I would expect with the given RPM.

I had similar thoughts on the drop in engine RPM. It was only for a few seconds and the engine continued to run smoothly the entire time. I thought perhaps I had a piece of kelp or something wrap up in the prop for a moment.

This is the literature with the rated RPM
http://www.westerbeke.com/productBrochures/w21_w21a.pdf

I'll probably check the governor last I think, after I verify that everything else is as it should be. I'm sure the guy I bought the boat from didn't adjust it, but the owner previous to him may have. The guy I bought the boat from didn't remember what the max engine RPMs were when he took it out, I think he probably never checked.

I got some Biobor JF fuel treatment that I'll be adding when I top off the tank. I'll be sure to get some injector cleaner too.

Thanks again everyone for the comments/suggestions. Now I just need to get down to the boat and work on it.

[Cheechako]

If you are substantially over propped I suppose it could heat up at high rpm. But I'm now leaning toward the exhaust elbow being plugged. I didnt see if you ever checked that above though..

[Stephen P]

Hi, I had exactly that same problem with a yanmar 30 and it went all the way down 'til it wouldn't rev above 1500. The solution was amazingly easy to fix.
It had started after an air leak from a slit under a jubilee clip on a water intake hose. That caused a lot of black exhaust smoke and therefore an unusual amount of coking building up. I fixed that but soon after noticed the revs weren't revving as high. This became the new problem and was incredibly easy to remedy. Before you change all the hoses take off the stainless steel exhaust manifold coming straight off the rear of the engine and into the hose that leads to the exhaust. It is an ss water jacket and has a slight downward kink in it, and 4 bolts holding it on. Remove the hose from it first then undo the four bolts. Chances are the tube in the manifold piece is blocked with carbon. Mine was down to a pencil thin hole allowing the exhaust out. Chip it off with a screwdriver to clear the passage. Bolt it back on. That should be the problem fixed. Maybe an oil change helps if it was all coked up. It's a chance to change the gasket but I got away with my old one. Engine revs freely.

[cwyckham]

I'm not sure how you know that the revs to boat speed are in the right range on a boat that's brand new to you.

My W27 tach was off by 150 rpm.

My W27 operated at 180-190 according to the temp gauge (I never calibrated it). I don't know if I was having some sort of issue, but I was making full revs at least.

[Cadence]

Originally Posted by blinkerfluid

Thanks for all the suggestions everyone.. I'll try to go through an answer any questions, keep in mind that we've only had the boat for a couple weeks now and have only put about 3 hours on the motor while delivering her to her new slip.

I have no idea how old the fuel is. The boat wasn't used much over the past 14 months or so at least, fuel tank is currently only half full, so I know I need to top it off. No water has shown up in the Racor yet though.

The engine was running warm during delivery. Initially I was running at WOT (2400 rpms) and the engine heated up to ~210. I then backed the RPMs down to ~2k and the temp came down to 190. Still warmer than it should be. From what I've read, and the comments here, a clogged exhaust elbow could be causing both the low RPM and the high temp, so I will definitely be checking that out as soon as I can. Stupid job is keeping me from working on my boat!

The engine compartment is fairly well sealed up, however I had everything opened up when I ran the engine up to max RPM in neutral, so I don't believe that is the problem.

I'm going to take the airbox off the motor too and check that out. It's crushed in on the side at the moment, so it's possible that's causing some issues.

I'll double check the exhaust routing, but I don't remember there being any excess bends or kinks

I'll double check the tach as well, however, even if it is off, I don't think it's off by much just based on the boat speed vs rpm displayed. I'm getting boat speeds that I would expect with the given RPM.

I had similar thoughts on the drop in engine RPM. It was only for a few seconds and the engine continued to run smoothly the entire time. I thought perhaps I had a piece of kelp or something wrap up in the prop for a moment.

This is the literature with the rated RPM
http://www.westerbeke.com/productBrochures/w21_w21a.pdf

I'll probably check the governor last I think, after I verify that everything else is as it should be. I'm sure the guy I bought the boat from didn't adjust it, but the owner previous to him may have. The guy I bought the boat from didn't remember what the max engine RPMs were when he took it out, I think he probably never checked.

I got some Biobor JF fuel treatment that I'll be adding when I top off the tank. I'll be sure to get some injector cleaner too.

Thanks again everyone for the comments/suggestions. Now I just need to get down to the boat and work on it.

I can probably thank you from all that had input. It appears you had read them all. Best of luck.

[blinkerfluid]

Originally Posted by cwyckham

I'm not sure how you know that the revs to boat speed are in the right range on a boat that's brand new to you.

My W27 tach was off by 150 rpm.

My W27 operated at 180-190 according to the temp gauge (I never calibrated it). I don't know if I was having some sort of issue, but I was making full revs at least.

Well, I know the pitch of the prop on the boat, and I have the (supposed) engine rpm. Transmission ratio is 2.1:1, so assuming a 35% prop slip I can calculate what the boat speed should be. At 2k rpms, I should see boat speeds around 4.6 knots (which is close to what I saw), and at 2400 rpms I should see boat speeds around 5.5 knots (again, close to what I saw).

I didn't mean that I knew exactly what the speed would be for a given RPM, I just meant that they were close to what I would expect.. Vs. the tach reading 2400 rpms but the boat traveling at 6.7 knots (hull speed, and equivalent to the engine turning ~3k rpms). That's what I meant when I said if it's off, it's probably not off by much (I would say 150rpm is not much, compared to 600 rpms)

Point being that I believe the engine really is turning slowly and I'm not JUST getting a false reading from the tach.

[blinkerfluid]

Originally Posted by Cadence

I can probably thank you from all that had input. It appears you had read them all. Best of luck.

Haha yea, I read them all, be silly to ask for advice and then ignore it

I'll get it figured out and then let everyone know what the problem ended up being.

thanks again!

[Cadence]

Originally Posted by blinkerfluid

Haha yea, I read them all, be silly to ask for advice and then ignore it

I'll get it figured out and then let everyone know what the problem ended up being.

thanks again!

Please do. I think only 35 % slippage is optimistic.








5

[blinkerfluid]

I think 30% is the norm based on what I've read.. Eitherway, if the prop is slipping more, then that means the engine is turning even slower than what the tach is reading.

[DeepFrz]

I would suggest that before you go topping up your fuel tanks that you clean them thoroughly.

[SkiprJohn]

Originally Posted by DeepFrz

I would suggest that before you go topping up your fuel tanks that you clean them thoroughly.

And, as has been suggested, new fuel and air filters as well as an open vent to the engine room. Some engines have a throttle stop on the fuel injection pump that is wired in place so that you can't mess with it. If yours can be adjusted then open it up a bit and see what happens. Throttle cables can stretch and come out of adjustment.

Good luck in sorting it out.

[zboss]

We had the same exact issue with our westerbeke 46. The westerbeke manual says that it should top out at 3100 to 3200 WOT.

Great... why am I not getting these RPM. Turns out that it was just the prop size... Cabo Rico intentionally installed slightly larger props on the boat with the intention of the user running the boat at 2400 RPM for a longer range. At the higher RPMs (2900) we would overheat after a short period. We eventually went with the correct size prop at the expense of a little range but I'm not sure that was a good choice.

[blinkerfluid]

UPDATE TIME!!

Well we've been going through the engine for a while now addressing issues that we see, so figured I'd post an update to this thread.

First off, I was mistaken about the "never used" fuel filter I mentioned earlier in the thread. Our boat has 2 racors set up in parallel, such that you just turn a lever to pick which filter you want to run. Anyway, the selector lever on our boat is backwards from most levers I've used. So, the filter I thought had never been used, was actually the filter being used. No big deal, but the reason I thought it was never used was that there wasn't any fuel in the fuel bowl; it was just so full of water you couldn't see the fuel anymore!

Having discovered that, we decided to just go ahead and pull the injectors to have them rebuilt. Injector company said the injector spray pressure was really low and spray pattern was poor, so they definitely needed it.

While we had the injectors out, we decided to go ahead and check the valve clearances. All the valves were WAY out of spec. Spec is 0.250mm (0.010"), the tightest one we had was 0.305mm but the majority of them were between 0.400 and 0.430mm (0.015"). All the valves I've had experience with in the past tend to get tight over time as the valve seats wear, so no idea why these were so loose. Best I can guess is that the spec for the W30 is 0.381mm (0.015"), so maybe someone in the past mistakenly looked at that spec and set this engine (W21) to it?

As of the moment, we've replaced all 3 fuel filters, rebuilt the injectors, set the valve clearance, checked the exhaust elbow, flushed the coolant system and changed the oil.

So now I have good news and not so good news. The Good news is that the engine seems to start much better than it used to and idles smoother at low rpms. The not so good news is that, while the engine definitely needed all the work we did to it, she is still only coming up to 2700 RPMs in neutral (verified with a hand held laser tach). I also have some conflicting data as to what max RPM is supposed to be; the link I posted earlier says max output is 22hp at 3k rpms, however the service manual I found on the boat says max output is 21hp at 3600 RPMs. Guess now I need to figure out if I'm only 300 rpms low, or if I'm 900 rpms low.

Once I figure that out, I think the governor is going to be my next check.