'84 Merc 150 - how do I adjust timing?

[MAtkins]

1984 Mercury Black Max 150 XR2
Serial Number: 6532700

I'm reading conflicting information in 2 different manuals.
I can't figure out how to set the timing.

I'm supposed to find .462 BTDC using a dial indicator and set the timing pointer to a mark on the flywheel at .462 BTDC.
So, is .462 BTDC now considered TDC?

I'm supposed to set the Primary Pickup with a timing light until the timing light is 6? to 12? ATDC.
QUESTION: Does ATDC mean 12? past the pointer (really @ .462 BTDC) or does it mean from the actual TDC?

I'm supposed to set the Maximum Spark Advance so that it's @ 18? BTDC.
QUESTION: Again, does BTDC mean 18? before the pointer (really @ .462 BTDC) or does it mean before the actual TDC?

Finally, the spec for idle on this motor is between 600 & 700 RPM, in the water, in forward gear.
If after I've done all the above I find that the idle is incorrect, how should I adjust the idle?

 

[wired247]

Re: '84 Merc 150 - how do I adjust timing?

TDC is TDC. Top dead center of the pistons travel . The .462" thing is just a reference number to help you set the TDC mark because theres a few degrees that a dial indicator wont register as the piston doesnt move so its hard to nail TDC down exactly ( not really ) . .462 is a mark on the flywheel separate from TDC. When you go back to .462 after the indicator stops moving you set the register on .462 and your TDC will be set correctly when it does come around. Its something you do once and never touch again.

Cant help you with the rest. I don't set my timing like that.

 

[Chris1956]

Re: '84 Merc 150 - how do I adjust timing?

All timing is set in reference to TDC, not the .462. Remove spark plugs 2-6, and install them into their wires and ground their bases. Now put timing mark on #1 plug wire. Crank motor and advance throttle until you see the idle pickup spec. Now without moving throttle, adjust the primary pickup screw to just touch the carb lever. Advance throttle to full and adjust Max Spark Avance screw to max advance setting. Tighten lock nuts.

Install plugs and set idle speed to about 900RPM, using Idle Stop Screw to set idle speed and throttle cable to push throttle arm onto idle stop screw. After your water test and carb adjustments, you may want to adjust idle speed the same way to give 750RPM or so in gear.

 

[MAtkins]

Re: '84 Merc 150 - how do I adjust timing?

OK, I've got the .462 figured out and I'm convinced that the timing mark is set correctly.
Next I set the throttle cam and linkage so that the cam is not quite touching the throttle linkage roller.
This sets the exact location of the throttle arm at idle (according to at least 2 sources).

. . . set idle speed to about 900RPM, using Idle Stop Screw to set idle speed and throttle cable to push throttle arm onto idle stop screw.

If I do this after setting the primary pickup screw to the specified 'idle' which is 12? ATDC, changing the idle speed using the throttle linkage & idle stop screw will change that setting.
Is that what I'm supposed to do?

 

[wired247]

Re: '84 Merc 150 - how do I adjust timing?

It doesnt matter what the idle speed timing is. That 12 degrees thing is just a starting point. You want to adjust it once its in the water to allow the backpressure to put a load on the motor. You may have to adjust the idle mixture screws as well for a smooth transition off idle and the idle timing along with them to get to your target RPM in the water in gear.

 

[MAtkins]

Re: '84 Merc 150 - how do I adjust timing?

OK, thanks.

I've got the 12? ATDC set for the primary pickup screw, with the throttle arm set at 'starting point' idle.
I've got the 18? BTDC set for the maximum spark advance screw with the throttle arm set at full throttle.

When you say 'idle mixture screws' I'm not sure what you're talking about.
By 'the idle timing' I'm guessing you mean the primary pickup screw?

BTW thanks for all your help. I'm slowly getting through this.

 

[wired247]

Re: '84 Merc 150 - how do I adjust timing?

The idle mixture screws are on the carburetor and control...the idle mixture. Those get adjusted until you have a smooth transition off idle. The idle timing gets adjusted with the primary pickup screw until you get 750 or so RPM in the water in gear.

Pay no attention to me anyway. After I set the idle with the primary pickup screw, I just set the linkage so the lever is almost touching the carb roller at idle and then I disconnect the carbs from the linkage and rev it up on the muffs and set total timing at 2000 RPM to 23 degrees. That way the total timing is where it will be while its running WOT. That book method is whacked.

 

[Dukedog]

Re: '84 Merc 150 - how do I adjust timing?

There are no screws on his. They are WH's. Like ya said "set with idle timin'"........

 

[Chris1956]

Re: '84 Merc 150 - how do I adjust timing?

MAtkins, I have never heard of setting the timing as Wired has specified. Merc is pretty specific about idle pickup timing. Idle pickup is when the carbs first open. Adjusting the idle stop screw will change the idle timing, but not the idle pickup timing.

For the '93 Merc 150HP XRI V6, the timing is 0-9* ATDC for idle pickup and 22* BTDC for max advance, while cranking. Max advance will drop to 16* BTDC, when motor is actually running. I would think your motor is pretty close to that.

 

[Faztbullet]

Re: '84 Merc 150 - how do I adjust timing?

The specs for the 93 150 Xri are for a 2.5L block and fuel injected.so do not use them. The correct spec's for your 150 2.0 L is:
spark plugs...NGK BU10H
Primary pick up timing....11? ATDC
Max. Timing ....18? BTDC at cranking speed
Idle rpm in gear in water...550-650 rpm
Max WOT rpm.....5000-5500

 

[Dukedog]

Re: '84 Merc 150 - how do I adjust timing?

Sounds like ya'll are gettin' a coupla things confused. Settin' "idle" timin' will not involve tha "throttle" part of tha timin' arm.
1. Carburetors have a idle circuit already which is not to be determined by tha position of tha butterflies and/or throttle position. Idle speed is strickly done with tha timin'. If ya have ta move tha throttle ta make it idle where ya want it ya got a problem.....
2. Disconnet tha throttle completely.
3. Check tha carbs for sync. Makin' sure all three are completely closed at rest.
4. Replace throttle arm makin' sure you can at least "spin" tha roller freely without any pressure form tha cam. Make sure tha "line" on tha cam lines up with tha center of tha roller. Lock all this "in" usuin' barrel nut adjustment and throttle stop on tha block. I've had as much as 1/4" gap on some of tha hot rod motors but that's a different animal......
5. Set idle timin' at "0" ta start with. If it starts and seems happy there leave it. Now your done with tha timin' light. You may/may not need ta make changes ta get it to a happy spot on tha hose.
6. Put it in tha water, in gear and adjust tha IDLE TIMIN' SCREW" til YOUR HAPPY............

Make sure ta deep six tha timin' module before ya ever start if it hasn't been done already

Fb, Where did ya get tha plug number? Should be BU8H............

 

[wired247]

Re: '84 Merc 150 - how do I adjust timing?

MAtkins, I have never heard of setting the timing as Wired has specified. Merc is pretty specific about idle pickup timing. Idle pickup is when the carbs first open. Adjusting the idle stop screw will change the idle timing, but not the idle pickup timing.

For the '93 Merc 150HP XRI V6, the timing is 0-9* ATDC for idle pickup and 22* BTDC for max advance, while cranking. Max advance will drop to 16* BTDC, when motor is actually running. I would think your motor is pretty close to that.

I had never heard of it before I started doing it either. For a stock motor I suppose the Merc book method is OK but for modified motors it stinks and everything I get my hands on gets modified. The big problem with the merc method is that its not an actual check of the engines timing at either idle or WOT and depending on the cylinder and the age/state of the electronics involved and the tune of the motor, the Merc method can be a disaster in the waiting. As an engineer I have devoted large portions of my career maximizing high speed machinery to run faster than it was designed or rated to do so by the manufacturer. I look at outboards just like I look at packaging machinery. Its all about timing . For a lot of stock motors, the Merc method works fine but the Merc method does not account for timing variations due to crank throw variations and higher than stock compression ratios. For stock motors and modified motors it works better IMHO to set the max timing dynamically with the motor running at WOT which is (almost ) impossible to do in the water.

 

[Faztbullet]

Re: '84 Merc 150 - how do I adjust timing?

Fb, Where did ya get tha plug number? Should be BU8H.....

Service training manual..........

For stock motors and modified motors it works better IMHO to set the max timing dynamically with the motor running at WOT which is (almost ) impossible to do in the water.

Mercurys set at cranking speed as the way electronics are designed they retard at rpm vis versa on Junkrudes as they advance with rpm...thus a test wheel /prop.

 

[Dukedog]

Re: '84 Merc 150 - how do I adjust timing?

Service training manual..........

Alrighty then! Everything I've got, OEM manuals, MercNet and etc. show 8h or hw's. Tha bu8h's are dirt cheap at O'riley's........bu8h (7 grand and below)and buhw's (above 7 grand) is all I've I have ever ran till ya get to tha fancy 'lectronic stuff and 9500 + rpm motors........

 

[Faztbullet]

Re: '84 Merc 150 - how do I adjust timing?

You want a copy dog??

 

[Dukedog]

Re: '84 Merc 150 - how do I adjust timing?

Naw. I'll just keep "pluckin' da chickens tha same way I always have". Tanks anyway.............

 

[MAtkins]

Re: '84 Merc 150 - how do I adjust timing?

The carbs have no adjustment screws at all as Dukedog pointed out.
Also, the plugs are spec'ed at BU8H (Seloc) which is what I'm running.

I got to take it out on the water today.

I tweaked the primary pickup screw to set the idle.
The throttle cam is set so that I can see space between it and the carb linkage roller and it idles great.
I set the maximum spark advance screw on the water.
It wasn't so bad.
I'd tweak the screw while idling, run at WOT, then idle and tweak again, then run at WOT, etc. until it got it to accelerate smoothly.

So, the 12? (per the Seloc manual) ATDC for idle & the 18? BTDC for max ended up getting thrown out the window.
I had both set with a timing light but the motor wouldn't idle at all, even on a hose.

I did it by ear, on the water.
If I just bump the key to engage the starter, the motor starts.
It idles great, with the throttle arm against the idle stop screw, & with a gap between the throttle cam and the carb linkage roller.
When I nail it to WOT right of the idle it takes off and planes out beautifully.

The boat ran much better today than it has since I got it.
THANKS!!

 

[MAtkins]

Re: '84 Merc 150 - how do I adjust timing?

I've got another problem I thought I had fixed.

Sometimes I still have trouble starting it; a lot of trouble.
I have to play with the choke, give it gas, crank it with no choke, etc. to get it to start.
I have to try repeatedly. It'll fire, usually only once, and disengage the starter.

Once I coax the motor into starting and let it run for a bit, I can shut it off and it'll start right up.
I shut it off and restarted it today over and over by just barely bumping the starter with the key.

I thought the problem had to do with warming up but I think it's fuel mixture now.
I ran it in the evening and shut it off. The next morning I was able to start it with no trouble.

The problem seems to occur when I don't get the motor started right away and the carbs drain their fuel bowls (guessing) ??
The enricher works. I can smell the gas.
Again, I have to give it gas (sometimes with the choke button pushed in) to get it to start.

What's wrong with it?
Is there anything I can do to make it start more dependably?

 

[spookfreak]

Re: '84 Merc 150 - how do I adjust timing?

I've got another problem I thought I had fixed.

Sometimes I still have trouble starting it; a lot of trouble.
I have to play with the choke, give it gas, crank it with no choke, etc. to get it to start.
I have to try repeatedly. It'll fire, usually only once, and disengage the starter.

Once I coax the motor into starting and let it run for a bit, I can shut it off and it'll start right up.
I shut it off and restarted it today over and over by just barely bumping the starter with the key.

I thought the problem had to do with warming up but I think it's fuel mixture now.
I ran it in the evening and shut it off. The next morning I was able to start it with no trouble.

The problem seems to occur when I don't get the motor started right away and the carbs drain their fuel bowls (guessing) ??
The enricher works. I can smell the gas.
Again, I have to give it gas (sometimes with the choke button pushed in) to get it to start.

What's wrong with it?
Is there anything I can do to make it start more dependably?

Next time your out initially hold in the choke for like 30 sec. then turn it over. Works for me.
Also did you replace the fuel pump screen and diapham. Its a kit. Fixed my throttle problems.

 

[Chris1956]

Re: '84 Merc 150 - how do I adjust timing?

Gee, setting the timing by ear and feel. What a concept. Let's hope you do not experience a blown engine due to over advanced timing or improper synch. Well at least that will fix your cold start problem.