Fuel consumption - Page 5

THEFERMANATOR · #41 10-19-2007, 12:47 AM

Those check valves being plugged will definately foul plugs at low RPM's. They are a common problem that is normally overlooked.

tsubaki · #42 10-27-2007, 09:17 PM

Got the carbs rebuilt (well, floats,needles, etc.) and reinstalled them.

Replaced the temp sensors and t-stat, the odd part is the difference between the new and old thermostats.

The new ones had no flow thru or bypass where the old ones were easy to permit cooler water to run right by them.

Gonna try it out in the AM and see if I can adjust the idle and timing in the water.
Oh and coating the 48 (no exaggeration) bolts with antiseize was as much fun as removing cactus needles.

Some leftover photo's.

tsubaki · #43 10-28-2007, 01:16 PM

Summary; after replacing the plugs, thermostats, temperature sensors, cleaning the carbs and replacing the floats, needles and seats, I think I finally got the boat useable. It idles great, throttles up immediately and does everything you would expect an engine to do.
These numbers are still not perfect because we didn’t have time or decent weather to perform good tests. 20 knot winds with 30kt gusts and 8" chop.*These are short distance speeds (just enough to get leveled out).
Got a 14 x 19 ss prop at, 5000rpm-42mph-19.5gph, 3800rpm-30mph-10.5gph,1250rpm-5mph-2.5gph. Boat was ¾ full of fuel.
Next time it hits the water there are to be fishing poles in it.

phester · #44 10-28-2007, 02:54 PM

T, those #'s sound good. I rebuilt my carbs last year and it made a noticeable difference. I thought it ran well before the rebuild, but the idle wasn't perfect, and it did have an occasional misfire at trolling speed. After the rebuild....much smoother idle, NO misfire, O stall-outs. All six plugs are burning perfect. Good luck on your next outing. [BTW, 1992 150 Johnson]

tsubaki · #45 10-29-2007, 08:26 AM

Thanks, phester.
5000rpm-42mph-19.5gph (2.15mpg),
3800rpm-30mph-10.5gph (2.85mpg),
1250rpm-5mph-2.5gph (2.0mpg).
There should have been a more fuel efficient speed but didn't have time to find it.
But I'm very happy with the performance now (or till I start experimenting with another prop to raise the rpm's *;D).

RobsTV · #46 10-29-2007, 03:20 PM

Is that 5000RPM the most you can get out of it when trimmed up? If so, you are lugging the motor, (at all speeds), and shortening it's life.

You should be running WOT about 5500RPM to 6000RPM's, and if not, then looks like a prop change is needed pretty quick. I think most run a 15x17 prop with the V20 and that type motor.

tsubaki · #47 10-29-2007, 03:35 PM

5500rpm is the max for this motor.
The best trimmed up was 5200rpm back before the repairs.
I know a different prop is in the near future, most likely an aluminum 15x17.

THEFERMANATOR · #48 10-29-2007, 04:10 PM

You don't want to be taking that engine to 6000 if you want it to live very long. I know the cross-flows suffer from an RPM induced vibration at either 5700 or 6100(can't remember which right now) from the rotating mass of the engine and flywheel. Many flywheels have become 2 piece flywheels from sustained runs at that RPM. Cross-flows red-line at 5500 like tsubaki said, I would shoot for maybe another 100 RPM's. These engines pull there best down low though.