WOT too low. Speed down significantly

[Oldlaxer1]

My new to me 1987 C34 is struggling to get above 2300 RPM underway.  It was hauled and bottom cleaned on June 24th for survey.  On delivery home I had some steam coming from the exhaust and it was running a bit hot at higher rpms so we throttled back. New impeller solved that problem. We've only had it out twice for short motoring trips since getting her home due to lousy weather. Took it out yesterday to knock some crud off the bottom and we were very slow across the bottom (GPS speed). I ran it up to full throttle and it only got to 2300 RPM and just over 4kts. I throttled back, shifted to neutral and ran up the throttle and it was well north of 2500 rpm and climbing so I throttled back thinking the issue isn't with the tach (even though it had acted up on the delivery home. Cleaning some terminals seems to have solved that issue).  Water temperatures are abnormally high so growth on the prop is possible. I'll check it with a GoPro today. Could anything else be contributing to the low RPM and speed?  I'll check the packing nut temp today while running it in the slip.
Thanks
John

[Jim Hardesty]

John,
My first thought is dirty fuel filters.  That's the symptoms I get when the filters need changing.  Engine runs fine but won't do full RPMs.  And a recently changed filter can be dirty.  Lots of information here on changing fuel filters and the filter of owners choice 2, 5 micron or even more course.  Easy job if all goes right.  I've even changed them underway.

Hope this helps,
Jim

[Oldlaxer1]

Thanks Jim. I'll check them out and replace. I have no idea when they were last replaced so this will get me on a regular schedule. 

[scgunner]

John,

You took it out to knock some crud off the bottom, don't you have a bottom guy? Jim's got the right idea with the filters, but I think I'd just go ahead and do a 100hr service which would set up a good performance baseline and then you can start looking for problems related to individual issues, like low RPM, overheating, etc.. Also when the impeller was replaced were all vanes in place or accounted for?

[Oldlaxer1]

Kevin, I do have a bottom guy but with my old boat twice a season was plenty. With a full pressure wash on the 24th of June I really wasn't expecting that much of a problem, but new boat to me so who knows.   We'll see what the GoPro shows shortly.  I did find all the vanes when changing impeller.  It is running at about 165 after almost an hour of motoring so I'm feeling good about that issue. Oil and filters were replaced just before I bought the boat.  I'll do a search for what else is on the 100 hr.

[Ron Hill]

John : If the new filters don't help increase the engine, look at the RACOR " Obscure check valve" as Stu posted above!!

Also there was a screen on the end of the fuel pickup tube in the fuel tank. I wrote about this over 25 years ago, but you might check it?
That screen can clog, and was eliminated in the 1993? C34 production.

If the boat has been sitting for the past 6 weeks you might check the prop for growth!!

A thought

[Robert Mann]

John, I am not familiar with the fuel system layout of the Mk-I, but my Mk-II will run quite nicely without the electric fuel pump operating.  However, it will not get close to full engine speed.  The wire to my fuel pump broke and it took me a couple of weeks to find the problem.  Check the fuel pump is ticking.

[Ron Hill]

John : That has been posted a number of times - as the fuel tank is higher than the engine (syphoning!!)

a thought

[Jon W]

In addition to the Racor, and on engine fuel filters, the original '87 fuel system tank pickup tube had a hose with a strainer on the end that can clog up. Unfortunately it's all inside the fuel tank. Before tackling that nightmare, is the Racor filter bowl full of fuel? If it is, the strainer inside the tank may not be the problem right now. Checking for and removing the strainer, is something you should plan for.

[Dave DeAre]

My 2002 MK 2 also would not run over 2,000 rpm. Replaced the electric lift pump and has been fine for 5 years. Check the pump.

[Oldlaxer1]

My 2002 MK 2 also would not run over 2,000 rpm. Replaced the electric lift pump and has been fine for 5 years. Check the pump.

I purchased a spare pump shortly after buying the boat. I'm kinda anal about spare parts.   I'll be checking the existing pump tonight.  Perhaps it isn't even working and I'm just getting gravity feed per Ron. 
BTW, my Racor is a 500FG Turbine series so Stu's clean out doesn't seem to apply to my situation unless the ball valve is somewhere else.  I'll be looking into that tonight too. 
New filters are on their way.  Hopefully I'll have good news to report. Thanks for all the insight. 
John

[Stu Jackson]

>>>>>>>>>>>>>>>
BTW, my Racor is a 500FG Turbine series so Stu's clean out doesn't seem to apply to my situation unless the ball valve is somewhere else.  >>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>

John is right.  I just Googled Racor 500FG Turbine and the Parker manual says a separate check valve should be installed if the fuel tank is below the filter/housing.

Just like I "discovered" this little gem:  RTFM.   

[rmjohns]

I had a similar problem in a prior boat that was Yanmar powered. It turned out the exhaust mixing elbow had rusted almost completely shut. It would also get steam since there were tiny holes in the elbow.  I haven't dug into the Universal enough to know if it's laid out the same way, but might be worth looking at.

[Oldlaxer1]

I'm definitely hoping it is a filter or pump issue....That exhaust manifold is almost $1,400.00.   

[Ron Hill]

John : Your exhaust riser mixing tube is stainless steel - not like the Yanmar that can rust.

A thought