Enigine RPM's up & down

[AXEL]

I launched my C30 yesterday. It's about a 45 minute run from the marina to my slip. About 1/2 hour into the run the RPM's start going up and down on the Westerbeke 21. In the past when ever I've had this problem it was always the result of dirty fuel, be it water or microbes. Changing the filters would solve it. In extreme cases I have taken the fuel tank out and cleaned it which is what I did this spring. So with the boat in for the first time this season with all new fuel filters and a clean fuel tank I'm wondering why I still have the problem? I did put about 2 gallons of last years fuel back in the tank but I filtered it prior to putting it back it. I bought a fuel filter/funnel last fall that’s supposed to filter out the small stuff and water. I have to say I'm pretty sure fuel, filters, the tank and lines are clean. Right now I have about 2 gallons of last year’s fuel in the tank. I'm going to add 10 gallons of new fuel and try it again. Anyone have experience with this problem, what else could it be?

 

[RichH]

Check and recheck all the connection fittings.....

A surging engine is a possible sign of air being sucked into the fuel line. Most connection fittings on boats are 'compression' (with 'ferrule') fittings which are really good for ONE tightening; plus, they are easy to crack thus allowing air to become sucked in. Also (and assuming that you are using Racor Spin-on filters) ... did you lubricate the Racor gasket with oil before assembly? Start with the filters (also looking for a crack in filter body at the connection ports), then examine all the connections on the fuel system, etc. If you can pressurize the fuel line (not the tank) with low pressure air, it will usually show the leak quite readily.

 

[Alan]

RichH is...

...probably right, air being sucked into the fuel line can cause these symptoms. I would install a small length of clear fuel line just before the fuel supply pump. If any air is being draw in from the pump back to the tank you will be able to see the bubbles in the line. Then its just a matter of finding the faulty connection to eliminate the bubbles.

 

[Calif. Ted]

Did you only have the 2 gallons when you started,

seems like you might have even been sucking a little air thru the fuel pick-up, they are a little above the tank bottom.

 

[AXEL]

More detail

Thanks for the responses but I'm not sure and air leak is the problem. What's happening is about a 1/2 hour or so into the trip the RPM's start to drop. I'll push the throttle open and the RPM's do not respond or continue to drop. The engine may recover after about 15 or 30 seconds and the problem will reoccour a couple of minutes later. If I back down on the throttle the engine seems to rum better which makes sence. If I have the throttle open and am demanding fuel the engine RPM's drop or cycle up & down. If I reduce the throttle I'm calling for less fuel and the engine will run better but there us still a problem. If it's and air leak why would it take a 1/2 hour for the problem to occur? The Westerbeke has 3 fuel filters, 2 on the engine and one external fuel filter/water seperator. All 3 are new and the tank was just off and cleaned. I'm wondering if the fuel line itself has some lose material in it and I will change it this weekend. I will look for air leaks and the idea of hooking up a jury can full of fuel with clear lines might yeild some insight as to what happens when the RPM's start cycling. Other than that I'm at a loss.

 

[Stu Jackson]

Have you taken the intake screen off the

fuel line in the tank?

 

[Manny]

Was it choppy out?

Maryland and New Jersey had some rough weather yesterday, I assume NY probably had some also. I'm no expert but I agree with Calif. Ted, with only two gallons in your tank, good chance you were sucking air. Wouldn't take much of a wave to move all the fuel to one side of the tank or the other and cause what you were experiencing. I would add a couple more gallons of diesel and bleed the fuel system and go from there.Manny

 

[Rich (P303)]

Well...

we know it is air or fuel. So many places to look... so little time.I had a 63 Rambler Classic... (that is a car). It ran fine until it went up a hill... then it started to sputter. New fuel pump took care of that. Fuel Pump? Just ANOTHER place to look.

 

[AXEL]

Air, fuel, or mechanical

It was a little choppy over the weekend but no big deal. Normally I would agree that maybe with only 2 gallons I may have sucked up some air but mind you I wasn't sailing (heeling) just motoring. However, this is a problem that I had last fall and it occured with a full tank also. If it were an air leak why does it take ove 1/2 hour to occur? It might be the fuel pump. The Westerbeke has an electric fuel pump which I don't have a lot of experience with. I did have the injectors replaced 2 seasons ago. I'm actually hopping for a catastrophic failure. It would be easier to trace the problem. Stu, yes the screen was removed many years ago. One of the first things I do this weekend will be to either blow out or replace the fuel line. I might have something stuck up in there ( a little restriction).

 

[patrick]

It doesn't sound like its the problem

but you can always check your exhaust riser. Mine was plugged once and it acted weird and unpredictable like this.

 

[Mike B]

Filter in the fuel pump

It sounds like fuel starvation. Before you replace the fuel pump check the inlet side of the pump for a very small filter. You'll have to remove the fitting to get to it. Westerbeke places one in there to protect the pump. If it clogs you'll get the symptoms you mentioned. I had the same problem and replaced the pump($110)only to have a diesel mechanic tell me about the filter. Of course that was after I tossed the old pump Mike

 

[Stu Jackson]

Mike's point is well taken, but also

make sure the pump is downstream (after) the primary fuel filter. if not, simply re-plumb it. See the link

 

[AXEL]

I agree

I agree it is behaving like fuel starvation. The give away is that when I back down on the throttle like under 2000 rpms, the problem goes away. Mike, I did change that small filter on the pump. As I mentioned there are 2 fuel filters on the engine and a seperat fuel/water seperator, all filters are new and the fuel tank was just off the boat and cleaned. The exhaust riser was replaced about 5 - 7 yrs ago. It's something to think about though, I'm thinking;1. The fuel line itself has something funky in it. 2. I have an intermiten air leak. 3. The fuel pump is getting flakey.4. Bad fuel??The Westerbeke is self priming. A few weeks ago when I changed all the fuel filters, the electric pump did it's job, filled up all the filter housings and blew out all the air. That tells me it's probably doing it's job. I'll figue it out, it may take a couple of weeks though.Stu, there are 2 fuel filters before the fuel pump/filter on my boat. The primary fuel filter/water seperator and a second smaller fuel filter mounted on the engine.

 

[Mike B]

Check the filters again

Axel, when did you replace the filters, Spring or Fall? If it was in the Fall it's possible with the old fuel they grew some nice funky stuff in them over the winter. I delivered a trawler to the Annapolis show last year and apx 30 mins after leaving the marina it began to run just as you indicated. Actually it stalled on me twice before I backed off on the RPMs. Went back and had them change the filters and she ran fine for the next 8hrs. The original filters and engine only had 10hrs on them before I set off so it is possible for the fuel in them to go funky over time. They were black when they took them off. Good luck and let us know what you find.Mike

 

[AXEL]

Thanks Mike

Thanks Mike, but I just changed all the filters 2 weeks ago. In the fall I change the oil and oil filter prior to winter layup but I leave the fuel filters until spring for just the reasons you mentioned. Good call though.

 

[Anchor Down]

Go Simple

Axel, you're over-thinking this. You're preparing for surgery, when it might be just a splinter.I'm with Stu. This problem happened to me on my C30.A high fuel demand initiates symptoms.Happens full tank or empty tank.Yeah, it's fuel starvation. You have a restriction somewhere.I'll wager that the only filtering element that hasn't been changed in years (since manufacture?!) is the screen at the end of the pick-up tube in the bottom of the tank. It takes 1 minute to check. That was my problem, but I went through the whole system (and a lot of unnecessary filter changes) before I tracked it down.1 screwdriver and a pair of pliers to rip it out and toss it, and you're on your way. You'll feel foolish if you go and rebuild pumps, and then discover it was something simple and free to fix.Fair Winds,Jeff***** ***** *****Rich, I had a '63 Rambler. An American. Whole interior made down into a double bed, I think with the traveling salesman in mind. Of course, when I tell my teenage students about that, their eyes light up…

 

[sailaway78]

Think simple

The filters are new, and this happened in rough conditions. First thing to check is the screen on the tank pickup. Check all the simple stuff first, then work on the more complex issues. Many of us, myself included, tend to look for the most complex, hardest things first.

 

[Rich (P303)]

Yes... yes... Anchor Down!

Both front seats folded down to a bed! It was more of a chick magnet than my Triumph TR-6.The oil filter was the best. It was about as easy to change as turning up the volume on the AM radio.Wipers were a drag if it was raining hard... and you were going slow. Wish I still had it!

 

[Val]

Check tank fitting

I had same problem on my Yanmar, engine would quit but restarted OK. It's a clog somewhere. Try cleaning the fittings exiting the tank. Mine has an elbow and a small spigot, thats where the clog was. Good luck.

 

[Jimmy]

Another hidden spot for fuel prob's...

when starting my new to me Catalina 30, several weeks ago, I have a problem starting the engine...NO fuel was the apparent issue.. in fact the electric fuel pump wasn't trying to pump. it would click once in awhile..upon removal and taking the bottom fitting/pump cap off, NOT the hose fittings the actual bottom on the electric fuel pump, there-in lies yet another micro screen filter it was clogged fully... I cleaned it up and reinstalled it in the pump.. things went back to normal.. the engine fired and ran as usual..