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Merc 800

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porter1

Contributing Member
"I recently bought a boat with

"I recently bought a boat with a 1970 merc 800,on the back of it there is a sticker that says direct charge. what is that mean? just curious."
 
"Mike you have me curious as w

"Mike you have me curious as well. I know the stator sends AC to the rectifier which converts it to DC to run the motor and charge the battery.The battery in this case acts as the regulator.Unless that's what it means.
I have googled it but didn't bring anything up,so if the experienced folk on the forum could explain I would be happy to store it with all the other bits and pieces that I have in whats left of the gray matter
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"
 
It refers to the weirdo shape

It refers to the weirdo shape of the pistons. Just Mercury advertising stuff.

Jeff
 
"It actually has nothing to do

"It actually has nothing to do with the "electrical" or "ignition".

In the 1960's OMC first developed their loop-charged induction system (loopers) - which was fairly revolutionary for getting gas/air/oil into the cylinders.

Merc's answer, at least for a few years until they relented and went with the loop charge design as well was "direct charge" which first hit the scene in 1969.

I have no specs or technical explaination but from what I gathered it was just a cross flow induction system with a fancy name...."
 
"Note the weird shape of the p

"Note the weird shape of the piston top. Combustion was so enhanced that compression ratios went up and timing was reduced with increased power.

Jeff



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"
 
"So Jeff, does the concave par

"So Jeff, does the concave part of that (fin) face the intake port? as a method to try and stop some of the gas/oil/air mix from heading right out the exhaust??"
 
"my mercury 800 will only rev

"my mercury 800 will only rev to 4200rpms according to the tach, is there any ajustments I can make to get it up to 5000 to 5300 like its supposed to run?"
 
"If your idle is set correctly

"If your idle is set correctly,throttles opening all the way,do a link 'n' sync anyway just to be sure,your timing is right,then all I can think of is you are using to big a pitch on your prop.What size are you using and on what type of boat?Oh and its not impossible that your tach is wrong? Been there and worn that particular t shirt
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"
 
"I checked the plugs and repla

"I checked the plugs and replaced them with normal plugs, had perma gap in there, all cyl. firing runs good idles fine. there are adj. screws for throttle stop and idle stop, but I don"t know how to adj. them, don"t want to mess anything up. I can"t se in the carbs to see if the plates are opening all the way."
 
"Hi Mike,
These motors are

"Hi Mike,
These motors are designed to take the perma gap plugs,and I can't see what difference it would make as long as the spark is strong enough to fire the gas.Jeff is about to jump on me
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.If you can get your hand in and manually open the carb it should move the throttle pick up lever 90 degrees.
If you want to see them move,you will need to remove the switch box bracket that is in front of it.A long 1/2" spanner required,a small hand, and remove the two bolts,don't forget you must remove the small plate under the handle to get at the nuts,1/4" self tappers.
Or take the handy way,get a buddy to help,shine a light in, insert a mirror and get buddy to move throttle.DO NOT ajust those screws if you can possibly avoid it,there is a good chance these stops are the original factory settings and they should be correct for use.
If you are getting 4200rpm,I think it boils down,to wrong prop,or carbs not opening fully.But then I've been known to be wrong before.
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,or the outside chance the tach is incorrect.And anyone who knows I'm wrong please let me know,I'm still learning,and would like to learn more,without the expensive mistakes.
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"
 
P.S. I forgot to add the throt

P.S. I forgot to add the throttle should stop not by going as far as it can but a hair short BY the throttle stop.
 
"..."So Jeff, does the con

"..."So Jeff, does the concave part of that (fin) face the intake port? as a method to try and stop some of the gas/oil/air mix from heading right out the exhaust??"

Yup.

Jeff"
 
"thanks, I think I will leave

"thanks, I think I will leave it alone until I learn more about it, The power trim sw. is bad and I think if I raise the motor a notch it may help get the bow up a little which would help get more speed. I don"t know the pitch of the prop but it"s pushing an 18ft glassmaster trihull that I think is on the heavy side of 2000lbs."
 
"Mike the pitch should be stam

"Mike the pitch should be stamped on it somewhere, 13 1/4-19 or something like that.That tells you that it is 13 1/4 inches in diameter and a 19 pitch.
I put your figures,and I added a couple of hundred extra lbs for good measure, through a couple of computer prop selectors and the general output for your setup is 13 1/4-19 for speed or 13 1/4-17 for load. Me? I would opt for the 17 pitch.But that's me
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.These selectors are not always accurate but never that far out."
 
"these are the numbers on the

"these are the numbers on the prop. 48 77344a-4 17p looks like 17 pitch I have no clue what the other numbers mean, any idea?"
 
"Mike, the "other" num

"Mike, the "other" numbers are just the Quicksilver "part number" for the prop - no usable info contained in it..."
 
"I am not sure how you measure

"I am not sure how you measure a prop but it measures 12 inches at the widest point across the blades. anyway I think my tac. is off, sometimes it reads idle at 500 rpms and sometimes 900. I raised my motor up 1 notch and today it was reading 4500rpms and 38 mph on the gps. the motor is really screaming back there, I"m not going to mess with it, it runs good, going to leave well enough alone."
 
"Word of advise, your engine d

"Word of advise, your engine detonated pistons easily...the surface gap plugs are very cold and the j gap ones dont go down as cold.

If you are running hard and the boat is loaded and maybe the fuel is a little old there is a risk of detonating a piston.

These engines were very loud and sounded liked they were over reving...if you have a 19 pitch prop it would be too big for your boat and a 17 pitch would be a better choice."
 
"jeff says he uses autolite 40

"jeff says he uses autolite 4092, I bought champion that crossed from them, the motor seems to runs a little stronger, but I don"t want to blow it up. I don"t plan on running it wide open very much or for long. I was just testing it out. I usually go out fishing and drift around."
 
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