Merc 850 timing

[calvin]

Looking to splash my merc 850..1975 vintage..no not an xs but still an oldie but a goodie..my manual states 27 degrees for max timing...would backing off the timing be prubent on this motor??

[Riverdragon]

I've been running mine 25* and 93 oct with the mains up 2 sizes to success so far. Make sure you don't lug it and prop it for 58-6000 up top.

[calvin]

What boat are you running it on..and what prop i will start out with a 19 alum then ? What are the main sizes you are running?

[Riverdragon]

Small hydrostream. I think it had 90's for jets.. can't remember off hand but recall scrounging through my jet drills for a 92. Mine is a '76 so the jetting will be different, they had different carbs.

[calvin]

What make prop and rpm...I would like to start with a 19 alum and find a small 20 chooper!

[Riverdragon]

A bigger one... not gonna say too much about it.:p

[calvin]

What carbs do you have on your 76 85?

[Riverdragon]

Stock carbs. Center bowl types. Nothing special to the motor other than enough overbore to clean it up, reeds, and a gear ratio change.

[calvin]

What kind of speeds are you running?

[Riverdragon]

It goes alright. :D

[PIP]

Was Curious About This 850, Too. How Fast Does It Run On Your 'stream? What Model Stream (vixen, Vandal, Viper...)?

Have You Compared It To A 75 Omc?

[Riverdragon]

It hole shots much better, idles waaaaaaay better, runs smoother, and keeps it's rods where they are supposed to be. The top end is much better mainly due to the props I have for the merc, though it is noticibly harder on fuel.

My "good" powerhead for my Hustler spit the rods out, and my other is pretty whipped. I'm just going to freshen it up and have Tim Kurcz cut on it a little, then a resto and to the engine stand with it.

The boat is a 74 Vixen that is pretty light, stock Hustler will turn a 24 raker 6300, the Merc will turn a thin 28 inline chopper the same rpm with 2:1 gears on a coned case as high as water pressure will allow.

[Mark75H]

I think PIP wanted to know mph, not rpm

[PIP]

what are the gps numbers, and what were they with a 75 omc?

am curious as i have both motors to try.

[7500Blizzard]

Per his numbers if the slip isn't off the wall should be low to mid 70's.

[Mark75H]

Per his numbers if the slip isn't off the wall should be low to mid 70's.

And the prop is labeled correctly

[Riverdragon]

72-75 with the merc depending on fuel load, best I saw with a stock well worn Hustler powerhead was 59-60, the other one that flew the coop turned close to 8k and 72 mph.

The merc feel so easy and smooth at WOT and idles sweet, the OMC's are the complete opposite. I have some more fooling around to do on the shorty mid for the merc I'm making and then I'll go through the Hustler, I just hope it has some labrynth seals left to work with.

The boat just before leaving for Jasper, I had a helluva crazy summer and the night before leaving I threw it together to do the river run. It looks quite different now, ;) after some more preening I'll post some more pics.

[PIP]

that's a huge difference in top end. you know the weight difference between the 75omc and 85 inline?

does the 85 have a lot more punch throughout the powerband?

[Riverdragon]

The gear ratio kills the OMC top end wise. The Hustler/Stinger is a no low end, crappy idling pig. Due to the gear ratio it seems it might be a little snappier in the mid range to a point. I have'nt sat down and really looked into the differences between the 70 and the 75 OMC, but I work on a LOT of 70's around here and for the most part the low speed running quality is night and day between the 70 and 75.

I'm not sure on the weight but I think with the trim the 85 weighs around 240.