crossflow fuel mix discrepancy?

[pcrussell50]

so, i have this '75 v4 crossflow 135hp mill on my stripped down 16 footer, [looks like a tahiti or sidewinder low-pro clone].

IIRC, the PO told me he runs it at 25:1. i have had it for a little over a year and it seems to run great. i do not have the original factory manual, but i do have the seloc manual, which also says to use 25:1. since these old crossflows are not particularly racy motors and have a big following amongst commercial "working class" users, i asked about it over at the iboats.com forum. they said the factory manual says 50:1, and that the seloc manuals have a fair amount of typo's. but one of them did come forth with this (http://www.evinrude.com/en-US/About.Us/FAQ/Oil.Fuel.htm?#Q2) little jewel straight from the OMC web site. sure enough, it says 50:1 unless you're "racing", in which case to use 25:1.

now, i'm pretty sure i use my boat like a lot of you. i cruise along nice and reasonably with the wife and our swim toys across the lake to our favorite cove. at the end of the day, i do my speed runs after i drop her off at the dock to go get the trailer... [yep, i trained her right. she can handle the trailer with the best of 'em*].

sooo, should i be using 50:1 or 25:1?

* i'm sure the fact that she grew up the daughter of a pro bass fisherman who had her backing up trailers since before she had a license has something to to with it :)

-peter

[FlowMaxx]

It is more important to worry about fuel. run 93 octane or better if it is available. 50 to 1 should be ok, but I run 40 to 1 XD100 if I am running hard in my crossflows.

[ChrisCarsonMarine]

The motor called for 50/1 from the factory,which changed recomendations from 25/1 in 1963.Since it is an older motor and being run hard a little,40/1 wouldn't be a bad idea,it is important to use high octane fuel,like flowmax suggested,and be sure your main jets are clean.25/1 is not necessary,and could actually cause your motor to run lean,due to the fuel replaced by oil and the thicker fuel[25/1]flows through the mains less easily,resulting in a leaner fuel/air mixture.Modern oils have come a long,long way since 30 wt.non-detergent in the old days,so you don't need as much in a full jewelled motor[no sliding or babbit bearings],Chris

[pcrussell50]

It is more important to worry about fuel. run 93 octane or better if it is available. 50 to 1 should be ok, but I run 40 to 1 XD100 if I am running hard in my crossflows.

hmmm...good point. i got that from another thread, too. i've been using 91, but this motor has an easy life pushing a light little boat with way too little prop. it never even sees full throttle except for the holeshot, which is almost instant. once on plane i have to pull way back to keep it below 6k. really, i try not to exceed 5800. but... i just got a prop with more bite that will surely allow me to open her up. before i try it, i'll have to do _something_ about fuel. maybe octane boost? since i don't even burn 6 gallons in a typical weekend, octane boost shouldn't put me in the poor house, i think.

peter