[Public-list] Atomic 4 compression

[Brian Palmer]

Thanks everyone for all the tips and advice.  I tried a number of things,
and this evening, I hit the last of the items that was causing the poor
performance.  Here's a brief run-down:


   - I checked compression for all the cylinders: 110, 108, 105, 110
   - re-gapped the plugs to 0.035 (they were set to 0.030)
   - I took the carb apart and cleaned it out, changed the gaskets, and
   realized I didn't have a good seal on the larger of the two gaskets because
   the two cast aluminum halves are not machined perfectly flat... So with the
   gasket in and bolted tight, I could see some light through the other
   side.... I used some permatex on both halves to assure a good seal.  I was
   thinking this winter of taking each half, and running them over a flat
   surface with some wet/dry sand paper to try to true up the surfaces.  For
   now, the Permatex does the trick.
   - Cleaned the prop
   - And the last thing that seemed to make the big difference.. I
   disconnected the fuel line and pumped fuel into a clear container and
   realized I had a fair amount of water getting through my Racor filter, which
   I just emptied yesterday.  Turns out I had about a pint or 2 of water at the
   bottom of the tank, and my model Atomic 4 engine apparently needs gas to
   run, not water!
   - After pumping several gallons of gas in a container, letting the
   water settle, pouring the gas back in the tank through a water separating
   funnel, and then pouring the last bit with all the water into a disposal
   container... Finally I could pump fuel that was coming out water free.

I took the boat out for a spin, and she now does a solid 5+ knots at
1400RPMs.  I think I can't go higher RPMs because as I recall, I have a 12x7
2 blade prop, which I'm told is a bit too steep of a pitch for the engine,
and is bogging it down.

The engine just feels much more steady and powerful, and  the throttle feels
predictable, and I can run without the choke on at all.  What a difference!

Just curious, What size and pitch props do you all run?  It was suggested to
me to try a 3 blade 10x6 prop instead of my 2 blade 12x7.  I'm told I'll get
the RPMs up increasing my horsepower, and bogging the engine less, which
will make the engine run cleaner, and won't make the plugs get oily dirty
deposits.  I'm wondering if I repitch my 12x7 to 12x6, would that work as
well, but still keep the boat sailing faster for potential racing.  For now,
the 12x7 works just fine... I'm just thinking the engine might last me a
while longer if it's not working too hard all the time.


-Brian
L'Esprit #288

 1152496555.0