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Thread: Fuel/compression
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01-06-2022, 08:45 PM #46
about 7k
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01-06-2022, 09:27 PM #47Screaming And Flying!
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01-07-2022, 08:43 AM #48
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Merc 2.5 thanked for this post
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01-07-2022, 08:56 AM #49
Apples to oranges but,
When we lived in Fla I ran Av gas in all my hi comp motors.
In the areas popular w/the airboats, you can get it at local gas stations.
If not, local airports.
I was running OMCs though that are much larger bore than a 2.4/2.5 Merc so our junk won’t put up w/what your Mercs will.
At 170 lbs I was mixing 100 oct av w/93 pump w/no problem.
Lightly loaded.
As in, drag set up.
W/no other changes other than adding:
A passenger
20 gls fuel
A 30” lake wheel
It ran a 1/2 mile before detonating itself to pc’s!
On the smaller Merc bores, I’m sure it would have been fine.
Just remember to figure in loading, to your equations ; )
Remember too, compression on a 2 stroke is way different than a 4 stroke.
Due to firing twice as often, the combustion chamber builds/retains so much more heat than a 4 that you hit a point of diminishing returns way quicker.
For drag you see the positives way longer.
For lake, I think that 170 is as high as I would attempt for an OMC Looper.
For a Merc you can probably add at least +10 to this.I'd rather be competitive w/junk I built in my garage than win w/stuff I bought.
I refuse to allow common sense to interfere w/my boat buying decisions.
Checkmate 16' 140 Johnson
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01-10-2022, 03:35 PM #50
My thinking is I run 145/150 as norm setup but on weekend I just wanna ride , I can pull weight out of it , swap heads to 170lb ,throw some fuel in ,and let her ride. Is it a good idea to do a jet change goin from 93 to mix of 93 and 100 or 110 just less of it. ?
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01-10-2022, 05:27 PM #51
No jet change needed unless you were fat just to be fat.
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01-14-2022, 03:35 PM #52
I have been running 93-91 ethanol free fuel due to supply issues in my area mixed with ACES for years. I do run lighter weight, low pitch props but here is some better details on it.
https://www.screamandfly.com/showthr...highlight=ACES1992 STV River Rocket - bottle fed 260
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01-15-2022, 07:48 AM #535000 RPM
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Yesterday I ran my warmed up 2.5 225 hp mariner with 164 pounds of compression on 93 octane pump gas and 1 ounce of aces per 6 gallons of fuel. No problems whatsoever with this concoction.
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02-06-2022, 02:51 PM #54
Maybe I should start new thread but figured I'd try it here 1st
I put a holley red and regulator on my carbed 2.5 , only concern I have is long idle periods , after awhile of idle will it flood out or start leaking in places ? Mite b a dumb question, but I've always used a orileys 70$ ele holley pump. Like 3.5lbs to feed the pulse pump on motor , now that pulse pump gone , I'll have a steady 4.5 ,5lbs at all times. Thanks
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02-06-2022, 03:41 PM #55
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02-06-2022, 10:03 PM #565000 RPM
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On the inboard 3.0 volvo penta I worked on it had a regular car mechanical fuel pump but with a nipple like that. It attached to a hose going somewhere, carb I think. In the book it said it's there incase the diaphragm fails. Not 100% sure though.
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