H34 and Fuel return

Steverhnm · Feb 23, 2015

That's how my 1990 35.5 is configured. No idle problems.

Ralph Johnstone · Feb 23, 2015

PGIJon said:
It is important that the fuel return line is sloped down to the tank with no traps or obstructions in the line. If this is not done, the fuel system is prone to air-lock with consequent hard-starting.

Any chance you can give the source of your quote ? Sounds slightly flawed to say the least.

The return line takes fuel AWAY from the engine so the presence of air in the line is of little consequence.

Also, having the return line sloped down ensures there will very likely ALWAYS be air in the line. This sounds more like a wish list for the fuel SUPPLY line. To achieve this in any sailboat would be difficult.

kloudie1 · Feb 23, 2015

Same setup here.. No idle problems.. I would be looking at a vibration induced noise.. Our little three cyl engines really rock and roll at low speeds and idle.. Engine mounts contacting or muffler banging on structural grid or prop shaft hitting inside of stuffing box support ..
Have the valves been set in the last couple of years? Sometimes a too tight valve can make idle really rough.

Stu Jackson · Feb 23, 2015

In all too many cases of rough idle, the idle speed is set way too low. I've literally heard skippers run at 600-800 rpm and complain, when the engine smooths out completely at 900-1000. Most transmissions can handle shifting at 1100-1200.

Good luck.

Allan12210 · Feb 23, 2015

Stu Jackson said:
In all too many cases of rough idle, the idle speed is set way too low. I've literally heard skippers run at 600-800 rpm and complain, when the engine smooths out completely at 900-1000. Most transmissions can handle shifting at 1100-1200.

Good luck.

Yep. Mine idled rough until I bumped it up to about 950-950 rpm from 800. It was a combination of the engine rough idle and everything else in the boat resonating at that frequency that drove us crazy. First just ease the throttle up and see when it smooths out, then you can adjust the idle stop on the engine.

Richard Bryer · Feb 23, 2015

Nice to hear after 4 months of up on the hard! Sounds like you might up the rpm by 150 or so- until it smooths out. It will be rough at first start for a few seconds. It sounds to me as if that other sound is, as Kloudie suggested, either the muffler/exhaust banging , or the prop shaft on the log. I would check the muffler where it passes through the hole right behind the engine.

kloudie1 · Feb 23, 2015

H-34 Fuel return

Cool ! Watched it through .. Guy did a good job. Here is a shot of the idle screw..easy to get to and adjust; the little straight screw under the brass nut at the cable end in this shot .. The specification is 850 rpm, +- 25 rpm.. but I wouldn't trust the Yanmar tacho ..
Your video start sounds fine to me..

splax · Feb 23, 2015

It seems to me, from the symptoms you describe and the mechanics shown in the accompanying video, that in all probability you have partially gummed or blocked injectors.
I would ask, do you changed your fuel filters annually? Do you add biocide or fuel system cleaner when you fill your fuel tank. Personally, I would change the filters and go through a couple tanks of fuel with additive before changing settings on the engine. If you are confident that the fuel system and fuel are good, then I would remove and clean the injectors.
Changing the settings may work, and in some cases be necessary, but there is a delicate balance to be maintained to keep things working well. Changing one thing cascades into many changes to achieve the original performance that may not even be recoverable, even when the source of the problem is finally corrected.

splax · Feb 23, 2015

I listened to the engine running that you posted. The engine itself sounds good. However, there are a couple issues.
First, there is a bearing singing at the beginning until RPMs are increased. If this is a usual thing for you I might look into replacing the water pump bearing in the near future.
Second, the rattling bumping sound seems like it might be a hose hanger loose or something flopping against a bulkhead. Where I have a fuel pump mounted on the bulkhead has the same kind of noise when it runs.

Ralph Johnstone · Feb 23, 2015

PGIJon said:
Here's the link.... http://pdf.cat.com/cda/files/3375312/7/Diesel+Fuel+Diesel+Fuel+Systems+LEBW4976-04.pdf Page 23. I know it's not Yanmar, however the physics should be the same unless there is a pump on one end of the return.

No doubt about it .................... right there on page 15 (as shown at the bottom of the page). Absolutely beats me how a tank below the level of the engine would ensure that no air would be trapped in the return line

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I'll stick with the fact that most boat fuel return lines go uphill to the TOP of the fuel tank and have no problems ................. and very little air in them.

splax · Feb 23, 2015

For RPMs attach a piece of reflective tape to the shaft coupling. Use an adjustable strobe to light the tape on every pass in the same relative position. There is also contact instrumentation where you press a roller against the spinning shaft to get a reading, but this can be dangerous. The reflective tape option is much safer. I take no responsibility for untrained personnel using either option.
For tracking down the source of the vibration, plot the strength of the vibration and the path of the strongest readings will lead you to the source. You then might figure out the cause.

splax · Feb 23, 2015

Some smart phones can use an accelerometer app to get vibration strength.

H34 and Fuel return

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