safe timing on 1977 mercury 850?

[bryanwess2000]

I read the link and sync thread and it says 21* max timing but thats
6* less than my manual says and the motor is a dog when set at 21*.
The motor was at 30* before I changed it and has been run this way for >5years. I currently have it set at 25* and it runs ok, just down a little on power. So what is the safe timing on my motor since the link and sync covers all inlines which range from 18*-30* according to my manual? Should I be ok
2* lower than max advance (25* instead of 27*) ?

 

[bryanwess2000]

Re: safe timing on 1977 mercury 850?

Just read several pages into the link and sync thread and a couple people
had 850's and were told to run 21* so I guess i'm going to have to run it like that and deal with the major power loss. I guess going down to a 19p prop will be in order.

 

[corm]

Re: safe timing on 1977 mercury 850?

Hi,

I run mine at 27.
If your worried about yours or you live where they sell
that oxygenated fuel you could back it down to 25.
The 4 cyl were not prone to burning pistons like the L6 cyl were.

 

[Chris1956]

Re: safe timing on 1977 mercury 850?

Are you sure that is a 1977? The late 60s mercs used timing specs in the 30s. The 70s mercs used 23* as max timing. Has the timing pointer been verified to be accurate?

 

[bryanwess2000]

Re: safe timing on 1977 mercury 850?

Not sure if your asking me or corm. I'm pretty sure it's a 1977, it has
the #4596244 on the mounting bracket and the port side of block. According to my research it's a 1977. Plus it has trigger and coil ignition instead of a
distributor. From what i've read this type ignition was only on 1976 and 1977
model 85hp motors. My cover that goes in front of the carbs says 27* ATDC
max advance @ 5500 rpm as does my manual. Also this is an inline 4. I verified
TDC with a dial indicator and a depth micrometer as well as visually when I
pulled the exhaust cover, the pointer was within 1* Atdc and Tdc.

 

[trendsetter240]

Re: safe timing on 1977 mercury 850?

Not sure if your asking me or corm. I'm pretty sure it's a 1977, it has
the #4596244 on the mounting bracket and the port side of block. According to my research it's a 1977. Plus it has trigger and coil ignition instead of a
distributor. From what i've read this type ignition was only on 1976 and 1977
model 85hp motors. My cover that goes in front of the carbs says 27* ATDC
max advance @ 5500 rpm as does my manual. Also this is an inline 4. I verified
TDC with a dial indicator and a depth micrometer as well as visually when I
pulled the exhaust cover, the pointer was within 1* Atdc and Tdc.

Yes, your motor is a 1977. My engine spec sheet also says to set at 27* BTDC. Personally I would set it at 27*.

 

[Jeff_G]

Re: safe timing on 1977 mercury 850?

I would recommend dropping the timing to 25* and going up one main jet size. The problem isn't the engine but the fuel today. All of the inlines I recommend a 2* drop.
You will run fine at 27* until you get that one batch of junk they call gas today.
Timing is a matter of acceleration more than a power issue. You should not notice any difference between 27 and 25* in power, and on a small acceleration lag but only if you run a very light fast boat.
Inline 6 motors called for 23* most run 21* but even racing I usually took my timing all the way down to 19* at WOT.
Also keep in mind on the ADI ignitions your WOT timing will usually be 2* less than at cranking speed.

 

[ouchita]

Re: safe timing on 1977 mercury 850?

Mine is a 1976 and i run it at 27 with no problems which is what my manual says also

 

[Jeff_G]

Re: safe timing on 1977 mercury 850?

Can you get 1976 quality gas in your area?