RPM Loss on Port Engine

[Bargain Bill]

I can only get 2950 rpm at WOT on the port engine (75 hp 4JH3-TE) compared to 3450 on the stbd engine.
Visually checked the secondary (non-engine mounted) Racors and they seemed fine.
Both props were clean. The port side had a small ding, but I don't think it was enough to cause a 500 rpm drop.
Both throttles hit the max speed stop, so its not a problem there.
Someone suggested that it might be an injector problem.
Is this the next thing to examine?
Do injectors get pulled and cleaned or are they replaced?
I appreciate any advice before I start throwing money at this.

[duetto]

hi bill,

you didn't mention changing the yanmar on engine filter. probably should do this just to be sure, but probably not the problem since both engines draw from the same tank. also, pull the fuel pickups in the tank and make sure you don't have the screens on the pickups. i think this was a problem on earlier boats but not sure when it was corrected.

an air leak in fuel system could cause this. check around cover on racor (assumes you have 500 series racors). do you have a vacuum guage on racor?

bad fuel pump could have these symptoms. unfortunately on this engine it's part of the injection pump and not easy to check or replace.

did the drop in rpm happen over time or suddenly? if suddenly, after you did some maintenance?

you can have injectors pressure tested and cleaned and if necessary rebuilt/replaced. mack boring will do this in their fuel shop. we went to a local shop a couple of years ago and had a bad experience. i talked to mack boring after the fact and found out that they did it and very competitively priced versus local.

[Tanah-Keeta]

Hi Bill,
I have the 110 HP 4jh4-HTE (Hull #108) and have the same problem except on both engines. My engine WOT should be 3200. I went aground in a sand/shell area and the WOT speed has reduced to 2950. I have just sent my props off to Murphys in Norfolk for refurbishing. They look ok but these boats seem to be very prop sensitive... Only a few barnacles will reduce the speed. This will establish a base line.. if the props are ok then I will try some of the items mentioned by John. All my filters are new so I can eliminate that.

My port engine temp also reads close to 210 degrees at 2600 RPM (15 KTS) vs the starboard at 195. Drop it to 2400 (13 KTS) and the temps drop to 205/185. John had a thread earlier about his work with the heat exchanger... will try that next if the prop is ok. The mechanic I use feels that if the prop has a problem, then that engine may be working harder and cause the higher temp.

[duetto]

ron,

i'm willing to bet that you too have the "invisible" heat exchanger problem. take them to a radiator shop and i think your temps will return to the 185-190 range.

if you do it and they don't, i'll pay for a round at boat harbour

i'll be interested to see if prop work makes any difference. ours are getting pretty ratty.

[Tanah-Keeta]

Thanks John.. I will take you up on that drink..

Back to Bill's problem.. this last year on the way back from the Bahamas, my Stbd engine would not rev above 2200.. Turned out that bleeding the secondary fuel filter solved the problem.

[Bargain Bill]

Problem solved! Changed both filters on the port engine and it ran up to 3500 rpm just fine. Even though I had only 100 hours on them and the Racors looked clean, this was the problem. Promptly changed the stbd filters too. Thanks folks for the suggestions.

[duetto]

hi bill,

glad you solved your problem. something to think about. if you're using 30 micron racors you may want to think about changing the on engine yanmar filters. the fact that the filters were blocking flow that badly would make me think a lot of particles were getting to the yanmars. if you're using 2 or 10 racors i'd be less concerned.