H30 Yanmar 2GM RPM question

coleman · May 28, 2013

Is the tachometer known to be accurate? You could verify this with a stroboscope.

Darwin19229 · May 28, 2013

I have a 1984 H30 with a Yanmar 2GM and the manual states the engine is rated for a maximum of 3400 rpm for 1 hour and 3200 rpm for continuous operation. I normally cruise between 2600 - 2800 rpm and use about 1 gallon of diesel fuel every 3 hours. The prop is the standard 2 bladed that came with the boat. I hope this helps.

rocksculpter · May 28, 2013

Too much pitch

I've heard a lot of comments in other blogs about diesels running longer and cleaner if you keep the revs up. I have the 2GM20, if you are properly pitched you shoud be able to reach at least 3400. That's where you get the most horse power when you need it, like in seas or making the cut against the tide. Also if you have too much pitch it can get exciting around the marina not being able to thottle back. I'm running a three blade 14 X 11 with a 2.61 tranny. I had the prop repitched using the recommendations of the Prop shop in Lynnwood, Wa. Personally I like to cruise at about 2100 rpm others I know settle in at 2800.

Barry

rocksculpter · May 28, 2013

Another thought

If you are rev limited you should try cleaning out your mixing elbow. If it's the U bend one, they are known to carbon up. I chiseled mine out a few times.

Barru

Jake N Eggs · May 28, 2013

The first thing I would check is that the throttle cable is pulling the throttle linkage to the high stop. This can be checked without the engine running.

Steve Dion · May 28, 2013

Running these GM engines at low RPMs is not good for them or your pocket book. They should be operated at 80-90% of the max rated RPM. The GM engine is rated at 3600.

Check out Yanmar Help, it will explain the operation and why.

Www.yanmarhelp.com/index

I would have your tach and engine checked.

kloudie1 · May 28, 2013

"If it is gonna happen, It'll happen out there!"
Fuel filters and possibly the pick-up tube in the tank too. A diesel starving for fuel will sound fine, it just won't make power to rev..
Throttle cable is first, filters and fuel supply second, exhaust elbow next.. Sounds like your tachometer may be way off too so calibrate or have someone calibrate with a hand-held tachometer to get real RPM.. maybe that should be first so that you have a good idea of exactly what you are looking at.
Something like this is sufficient
http://www.amazon.com/s/ref=nb_sb_s...chometer&sprefix=hand+held+tachometer,aps,228

Bill Roosa · May 28, 2013

Check the tack first as you are close to hull speed at "max indicated" RPM, implying that the motor is actually reving to higher than indicated on the tack.

Dalliance · May 28, 2013

Same model & year, same engine and same prop -- At full out throttle, I get up to 3400rpm and 6.5 knots on flat water with a clean bottom. Hull speed is 6.84 knots. Check throttle adjustment first.

jphud · May 29, 2013

Sounds like a possible cable issue. As mentioned check for basic engine issues, fuel supply, air etc. You should be noticing other problems if it is engine related, such as smoking, and overheating. You can check your rpm at the engine with a device similar to a timing gun, then you will know exactly the rpm, not a bad thing to do even if you are not having a problem. Also has the gauge panel been changed or upgraded?

jphud · May 29, 2013

Watch when you put your hand in towards the throttle linkage on the side of the engine. The cable usually sticks out and wants to bite.

Alan Gomes · May 29, 2013

malyea said:
Thanks - It's not the prop pitch 'cause even in neutral I can only get 1800 rpm (ie, the prop ain't spinnin').

Looks like easiest first check is the throttle cable/linkage option...

then a tach check to verify actual speed...

then clean the mixing elbow...

Thanks

I wouldn't rule out the prop pitch as a problem--though it could be that it's not your only problem. If indeed you are pushing the boat at 4.5 knots at only 1100 rpm then that suggests to me that you are significantly overpropped--in addition to your other problem about only hitting 1800 rpm in neutral.

Of course, this assumes that your tach is giving you correct readings, which as others have suggested is something that should not be assumed but verified. Buy one of these for $40 and remove all doubt: http://www.harborfreight.com/digital-photo-sensor-tachometer-66632.html

Scott · May 29, 2013

Really, check the throttle cable first.

Blaise · May 31, 2013

I will bet a lot of money that it is the mixing elbow. Because it runs the same in nuetral, it is either the elbow or the governor. Five years ago I had an elbow made out of stainless steel. It is still perfect. If anyone is intrested, I will find out if they are still available.

lesrrt · May 31, 2013

Mixing elbow. If that checks, then ck the fuel delivery. If the diaphragm in the fuel pump starts to fail, max rpm is hindered. Start with the fuel filter first though.

Alan Gomes · May 31, 2013

Blaise said:
I will bet a lot of money that it is the mixing elbow. Because it runs the same in nuetral, it is either the elbow or the governor. Five years ago I had an elbow made out of stainless steel. It is still perfect. If anyone is intrested, I will find out if they are still available.

I bought a stainless elbow for my 1GM from here: http://exhaustelbow.com/

I was happy with the quality, the price, and the service.