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Timing Issue on 1988 OMC 140 HP Looper

J

jesmitter

New member
I have two OMC 140 HP Loopers on my 24' SeaRay. The fuel economy isn't good but, the timing is off a bit. I'm hopeful that it will improve by correctly adjusting the timing to factory spec.

The manual states an 18 degree BTDC timing spec. the best I can get it to is 12 Degrees BTDC. I have tested and checked the Power Pack, Voltage Regulator, Stator, Timing Ring, and the timing magnet installed on the Flywheel inner hub. All looks good. The engines run great. At 5,000 RPM, I cruise at 37 mph. However, as I mentioned, my fuel economy is lacking.

As far as I can tell, there are only two adjustments. One to set idle timing/speed and the other located under the flywheel which set timing ring movement range.

What am i missing???
 
How much fuel (approximately) are you burning?

********************
(Timing At Cranking Speed 4°)
(J. Reeves)

NOTE: If your engine has the "Fast Start" feature", you must disconnect/eliminate that feature in order to use the following method. The "Fast Start" automatically advances the spark electronically when the engine first starts, dropping it to normal when the engine reaches a certain temperature.

The full spark advance can be adjusted at cranking speed,"without" have the engine running as follows.

To set the timing on that engine, have the s/plugs out, and have the throttle at full, set that timer base under the flywheel tight against the rubber stop on the end of the full spark timer advance stop screw (wire it against that stop if necessary).

Rig up a spark tester on the #1 cylinder plug wire. Hook up the timing light to the #1 plug wire. Crank the engine over and set the spark advance to 4° less than what the engine calls for.

It's a good idea to ground the other plug wires to avoid sparks that could ignite fuel that may shoot out of the plug holes. I've personally never grounded them out and have never encountered a problem but it could happen.

I don't know the full spark advance setting your engine calls for, but to pick a figure, say your engine calls for 28°, set the timing at 24°. The reasoning for the 4° difference is that when the engine is actually running, due to the nature of the solid state ignition components, the engine gains the extra 4°.

If you set the engine to its true setting at cranking speed, when running it will advance beyond its limit by 4° which will set up pre-ignition causing guaranteed piston damage! You don't want that to take place.

No need to be concerned about the idle timing as that will take care of itself. The main concern is the full advance setting.

A fellow member from one of the various marine forums suggested having water supplied to the water pump (flushette or barrel) simply to provide lubrication to impeller. A worthwhile suggestion I thought, and entered here.

Be sure to use your own engines spark advance settings, not the one I picked out of the air here in my notes.

********************
 
flyingscott said:
what kind of fuel mileage are you getting. Those motors were not known for fuel mileage usually just the opposite.
Click to expand...

I am currently getting a pathetic 1.35 miles per gal with both motors running. But it should improve if I can get that last 6 degrees of timing, right?
 
Last edited:
joereeves said:
How much fuel (approximately) are you burning?

********************
(Timing At Cranking Speed 4°)
(J. Reeves)

NOTE: If your engine has the "Fast Start" feature", you must disconnect/eliminate that feature in order to use the following method. The "Fast Start" automatically advances the spark electronically when the engine first starts, dropping it to normal when the engine reaches a certain temperature.

The full spark advance can be adjusted at cranking speed,"without" have the engine running as follows.

To set the timing on that engine, have the s/plugs out, and have the throttle at full, set that timer base under the flywheel tight against the rubber stop on the end of the full spark timer advance stop screw (wire it against that stop if necessary).

Rig up a spark tester on the #1 cylinder plug wire. Hook up the timing light to the #1 plug wire. Crank the engine over and set the spark advance to 4° less than what the engine calls for.

It's a good idea to ground the other plug wires to avoid sparks that could ignite fuel that may shoot out of the plug holes. I've personally never grounded them out and have never encountered a problem but it could happen.

I don't know the full spark advance setting your engine calls for, but to pick a figure, say your engine calls for 28°, set the timing at 24°. The reasoning for the 4° difference is that when the engine is actually running, due to the nature of the solid state ignition components, the engine gains the extra 4°.

If you set the engine to its true setting at cranking speed, when running it will advance beyond its limit by 4° which will set up pre-ignition causing guaranteed piston damage! You don't want that to take place.

No need to be concerned about the idle timing as that will take care of itself. The main concern is the full advance setting.

A fellow member from one of the various marine forums suggested having water supplied to the water pump (flushette or barrel) simply to provide lubrication to impeller. A worthwhile suggestion I thought, and entered here.

Be sure to use your own engines spark advance settings, not the one I picked out of the air here in my notes.

********************
Click to expand...

The present fuel "non-economy" is 1.35 mpg
 
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I'm getting 1.35 mpg from both engines running together with the timing on both engines off by 6 degrees. The engines tune and run identically.
 
Last edited:
How are you checking timing? 18° is at WOT as these ignition systems will advance timing at RPM. You will not get good MPG with these engines, maybe 1.5 at best.
 
faztbullet said:
How are you checking timing? 18° is at WOT as these ignition systems will advance timing at RPM. You will not get good MPG with these engines, maybe 1.5 at best.
Click to expand...

I rev the engine to 4500 rpm then adjust timing while using a timing light. The best I can get is 12° BTDC. It should be 18° according to the OMC factory manual. The problem is that I am at the end of the adjustment range. Is there another adjustment somewhere besides on the throttle linkage?
 
Need a test prop and check the timing at WOT in gear with load or run with cowl off on water and have someone operate and check. You cannot just rev em up and test.
 
mechanicman said:
Remove the old vro system. And add a fuel pump. And mix the gas. You will see a big difference in gas consumption
Click to expand...
Explain how that will change the fuel mileage?
To the op there is nothing wrong with your motors.If you want better gas mileage buy a newer 4 strk or DI motor. If your timing was 6 degrees off you would be having running issues.
 
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Flying Scott.
Here's the scenario. The lake is approx 3 miles long. The boat a 17foot mirrocraft with a 60hp Evinrude 1990. The boat is rated for a 90hp.. it would take more than a 1/4 tank of fuel to go from one end to the other. With the old vro system.

With just a fuel pump and mix the gas . The same boat with the same motor. Took less than 1/8 of a tank on the same trip. Both times were wot.
 
That is not how that works. There was something wrong with the Vro or the carbs were leaking. Because changing from a properly functioning VRO to a regular pump will make NO difference in fuel mileage. I have done hundreds of those conversions on 2 cyl on up to V4s for people. Never once has anybody doubled there fuel mileage. Or there is.something wrong with your motor now that needs to be addressed.
 
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