engine timing.. help understand..

[sti1471]

I have lots of questions and I am sorry for the long post. This is my first time timing an engine so I want to make sure I am doing it right.

I have a 1984 3.0L Mercruiser engine, with a points ignition. I have been reading the timing instructions and I want to see if I understand this.

#1- It says in the Mercruiser service manual #3 to use a jumper wire and connect the 2 white wires together. I look at my engine, and I do not have 2 white wires coming from the dist, but a single black wire running to the coil. I am thinking that my engine year was before they had the 2 white wires, so I don't need to do this?

#2- It says that I need to set my timing at 6 degrees BTDC. Once that is obtained, tighten down the clamp and I am done. However the 3.0L engines with the white wires says to set it at 6*, then when you disconnect the white wires, it should be at 12*. Since I do not have the white wires, should I set it at 12* or 6*?

#3- After watching an MSD timing video online, it says I need to set the idle timing, then rev the engine until it stops advancing, and then set it to "specification" if it is not already at specification. Which would be 35 degrees 29+6 according to the manual chart. Do I need to set the total timing on these engines, or do you just set the idle timing and stop?

#4- should the timing be set when the boat is in the water, or can it be done on the trailer?

#5- Last night I used a timing gun, and set the timing to 6* BTDC. The engine idles nice and seems to smooth out. However after setting that, when I rev the engine up using quick revs, it bogs and dies fairly quick. This is why I am wondering if I needed to set the total timing.

#6- After I set the timing where I want it to be, I kill the engine, and hold the Dist cap with my hand and tighten down the clamp. After tightening down the clamp and starting the motor again, the timing is now about 2 degrees off in either direction. is there a trick to tightening down the clamp while keeping the timing in the exact same place. I tried it almost 4-5 times, and every time, the timing was either 8, or 4 after I tightened the clamp.

Thanks for any help on this.

 

[Don S]

Re: engine timing.. help understand..

Sounds to me like you are reading information from manual 13, not 3. What you are describing is setting the timing of the EST electronic distributor.

Here is what manual 3 says.

 

[Don S]

Re: engine timing.. help understand..

#3 Set the timing as the manual says, not some aftermarket distributor you don't have.

#4- On the trailer is fine.

#5- Last night I used a timing gun, and set the timing to 6* BTDC. The engine idles nice and seems to smooth out. However after setting that, when I rev the engine up using quick revs, it bogs and dies fairly quick. This is why I am wondering if I needed to set the total timing.

Did you set your point dwell before setting your timing? You have to do that first.
You also need to adjust your idle mixture on the carb to get it right.

#6- After I set the timing where I want it to be, I kill the engine, and hold the Dist cap with my hand and tighten down the clamp. After tightening down the clamp and starting the motor again, the timing is now about 2 degrees off in either direction. is there a trick to tightening down the clamp while keeping the timing in the exact same place. I tried it almost 4-5 times, and every time, the timing was either 8, or 4 after I tightened the clamp.

Then you have to readjust it. Set it a couple of degrees off so it will be fine when you tighten it down.

 

[sti1471]

Re: engine timing.. help understand..

Don thanks for the reply.. I like seeing your replies since I know i am in good hands.

Tuning my carb idle mixture screw is difficult to do as I think the timing is off, so no matter what adjustments I make it still idles rough until I can get the timing on. I thought I would set the timing, and then set the air/fuel, but you are saying I need to set the air fuel and then the timing?

I set the gap points, but I have not adjusted the dwell. I don't have a dwell meter and I am not entirely sure how to adjust the dwell. From the manual it from what I could understand is adjusting the dwell was the same as adjusting the point gap.

the manual says to set the point gap to .022(.5). and to set the dwell to 28*-34*. Dwell can be set using a feeling gauge or dwell meter.
the manual says (dwell setting will be unsteady using this method).

I am sorry if this seems "beginner" but is setting the points gap the same thing as setting the dwell?

 

[Don S]

Re: engine timing.. help understand..

the manual says to set the point gap to .022(.5). and to set the dwell to 28*-34*. Dwell can be set using a feeling gauge or dwell meter.
the manual says (dwell setting will be unsteady using this method).

What manual do you have really? Seloc? Clymers?

 

[JerryIrons]

Re: engine timing.. help understand..

Get yourself a copy of the mercury manual for your engine, it will have the specs that you know will be right. (or at least righter than the clymers, etc) Someone here might even point you in the direction of one. All of this can be done on the trailer. I'm assuming you have new cap, rotor and condensor kit.

1) ensure that your spark plugs are correct, and that they are gapped properly.
2) make sure that your spark plug wires are in the correct firing order.
3) The condensor point gap and dwell are basically the same thing. Setting the point gap is basically a rough way of setting dwell. Go down to autozone, and buy a meter that measures dwell. It won't cost much and really gives you an accurate result. You can measure dwell without starting the engine at first to get close. Ground out the coil so you don't start the engine. Hook up your dwell meter, and just crank the engine over a little watching the dwell meter, it will give you an idea of dwell. Then adjust the condensor point gap some. It make take a few tries, you are basically tightening down a screw that holds a spring, and finetuning the gap. One way makes the dwell bigger and vice versa, you will figure it out shortly enough. Once you are close with your dwell, then hook up your coil and start your engine.
Measure your dwell again while running.
4) If you are worried about your idle mixture screw, just use a base setting of 2 turns out. Then you can do the trick of going either way until it runs rough and pick the middle.
5) Now you can play with your timing. Like Don said, the act of tightening down the distributor bolt changes the timing a little bit (on mine as well), so compensate for that. (ie set it at 4 degrees, planning on the bolt tightening to add 2 )

If you adjust your timing, check your dwell, just to be sure. It probably won't change, but if you change your dwell, it will change your timing. That's why you set dwell first.

To do this right, get a timing gun that measures advance timing as well. When you are on the water, you can rev up the engine to the specified rpms and measure the way the timing changes, there is a chart for that in the mercruiser manual.

You can play with the timing as well to see how the engine reacts. Go a couple of degrees and listen. Try out a little acceleration. If you advance it too far, you will hear pinging which = detonation which is not good for your engine at all. Pistons get ruined from that. I think though you want to be at the spec levels, if your engine runs better at a different timing base, you probably have something that needs to be addressed somewhere. (ie carb rebuild needed)

This is old school stuff, and actually pretty simple to do once you get it. Now you understand why people years ago took their cars in to be tuned up every year. Condensor points wear, dwell changes, timing gets off, etc.

Lastly, a bog on acceleration could be timing, or a whole other area of fun, the carburetor. Make your when you give it gas, you see streams of gas going in your engine from the carb accelerator pump. Also make sure you have new fuel filters, there may be two one near the pump and one in the carb fuel inlet. Depends on your engine.

Hope this helps, I was in your spot once as well. Lots of good info and help here.

-Jerry

 

[achris]

Re: engine timing.. help understand..

OK.. Here's how I do it... (since everybody is sticking a navel in I though I would too... )

1. Remove the old spark plugs. (Save them in a safe place). Gap the new plugs to 35 thou. Put them on a bench to one side, don't install them just yet.

2. Fit new condensor and points to the distributor. Set gap of points to 22 thou (that's with the rubbing heel of the points on the high point on the cam lobe). Leave dissy cap and rotor off, connect dissy cap end of coil HT lead to the engine somewhere. Doesn't matter where, it's just to stop you getting a belt.

3. Connect dwell meter and remote starter switch to engine (Usually the dwell meter will have 2 leads, read and black. Connect black to a good engine ground. Connect the red to the - terminal on the coil). Remote starter switch also has 2 leads. One goes on the battery +, the other on the small terminal on the starter slave solenoid which is NOT the ground wire... Doesn't matter which way round.

4. Turn ignition key to RUN position. Go back to the engine and push the remote starter switch and have the engine spin over. (And this is why we left the plugs out. The engine will spin faster with them out and give a better dwell reading). Read the 4 cylinder scale on the dwell meter (or set the switch to '4 Cyl' if it has a switch).

5. The dwell reading should be 28? to 34?. If it is, great. If not, you need to adjust the point gap again. If the dwell is high, the gap is too small, INCREASE it slightly. If the dwell is less than spec (gap too big), DECREASE the gap slightly. Adjust the gap until the dwell is within the range (28?-34?)

6. Fit rotor and cap to distributor, then install spark plugs, putting the right leads on the correct plug (actually quite important, and easy to get wrong :facepalm. Fit coil-dissy HT lead back on dissy cap..

7. Put timing light on spark plug lead #1 and start engine.

8. With engine running at around 650-700rpm (use the tacho section of the dwell meter) aim the timing light at the timing marks. Should be 6?BTDC. If not (and most likely it isn't since you replaced the points), loosen the clamp plate holding the distributor down and turn the distributor slowly until the timing is at 6?BTDC. Tighten dissy clamp. Recheck the timing, readjust if necessary. Shut off engine and remove all the tools. The next step should only be done on the water, with the engine in forward gear...

9. Set idle mixture for smoothest run at idle (in gear). If the engine hesitates on acceleration, richen the mixture screw(s) 1/4 turn and try again. If it still hesitate, the carb may need a clean out.

10. Set idle speed at 650-700rpm (in forward gear).

Chris............

 

[JerryIrons]

Re: engine timing.. help understand..

>>6. Fit rotor and cap to distributor, then install spark plugs, putting the right leads on the correct plug (actually quite important, and easy >>to get wrong ).

Yes good point. I don't think I've done that yet, but I have put the rotor back on not quite far enough down, with the end result being it not turning correctly and the engine backfiring and not even wanting to run, imagine that.

You will laugh, but I also sharpie the cylinder numbers right on the plug wires, then I even nail polish paint the cylinder numbers on my distributor cap. At home in your driveway it sounds silly, but on the lake with people staring at you there is no question, and just makes sure I don't miss the stupid stuff

OP does all of this help you understand points,dwell and timing better?

 

[sti1471]

Re: engine timing.. help understand..

You would not believe how much this information has helped me understand this. Just from reading these posts I think I know what I did wrong. I have an online manual that says "mercruiser service manual #3".

Since the idle speed was running rough and engine would die out during timing, I am pretty sure I gave the engine a couple revs by hand and let off to keep it running every now and then. I am betting when I let off the throttle it was idling around 1100-1500 when I set the timing to 6*. thus when I take it down to 600-750 it is most likely WAY to ATDC and won't run very good.

I think the key is to get it timed enough to get it to run at 650-700 rpm, then time from there, but I am positive I did not ensure it was at 650-700 when I set it, so the rpm could have been anywhere. I guess I was paying attention to so many things I forgot to make sure the RPM was right.

I took the carb off last weekend and removed every piece on it and cleaned it 100% and put everything back together. Nothing on the carb was suspect of needing to be replaced. I just changed the fuel pump filter last night. I noticed the fuel inlet does not have a filter in it at all, but until I get it running right I did not worry about putting it in since it was only a screen filter and since I just replaced my main filter. Unless that filter somehow effects how the entire carb runs I will hold off until I can get it running good and then drive to the marine shop and get one.

I will check the dwell, timing and everything as soon as I get home. I am hoping this is the issue I am so excited to get it on the water it is getting hard to sleep at night.

thanks everyone!

 

[sti1471]

Re: engine timing.. help understand..

So just to make sure I have this clear, my engine 1984 does not have a "base timing mode" I need to set it in?
my manual which reads the same as the link Don posted above mentions nothing of a base timing mode.

do I have this correct that my ignition does not have a base timing mode option?

 

[Maclin]

Re: engine timing.. help understand..

Base timing mode is a term used for electonic ignitons where the advance is controlled by a computer, that automatic advance needs to be disabled to set initial timing. You have mentioned more than once that your distributor has points so you have no computer controlled anything, thus no such thing for yours as base timing mode.

You just need to keep the rpm down to idle 600-700 when checking timing so your mechanical advance controlled by weights and springs is not kicking in. In essence that is your equivalent to "base mode".

 

[achris]

Re: engine timing.. help understand..

So just to make sure I have this clear, my engine 1984 does not have a "base timing mode" I need to set it in?
my manual which reads the same as the link Don posted above mentions nothing of a base timing mode.

do I have this correct that my ignition does not have a base timing mode option?

There is no 'base timing mode' with a points ignition system....

This might help you...

http://forums.iboats.com/mercruiser...ignition-system-works-329742.html#post2186518

 

[sti1471]

Re: engine timing.. help understand..

OK,

So I am not 100% sure if this makes a difference on the engine performance or idle, but as I was going over the boat and trying adjust idle, timing, and everything else when I noticed something on the carb. The "sight tube" was disconnected not hooked up to the carb during all my tuning / adjustments. So my question is, does the Sight tube not being hooked up to the carb affect idle, engine performance and other stuff? I was not sure if hole that the sight tube connects into was a Vacuum leak of some kind.

I hooked it up and started the engine and the idle that was once set at 650-700 was now at 400, so I had to readjust the idle and I was not sure if the idle drop was from the sight tube being hooked up or something else. I set the timing at 6* BTDC at 650 RPM, and was able to maintain the timing after tightening down the dist clamp.

Another questions is since I live in Utah and the lake I boat in is 4,855 ft above Sea level, is 6* timing good for me, or should I set it at 8* BTDC? I read in a Mercruiser service bulletin that for every 5000 ft it can be advanced 2*.

I ask this because when I turn the engine on while the boat is on the trailer on muffs, the engine seems to shake a little side to side as if the engine mounts are loose but they are tight. When the engine is cold the shake is shaking the boat as well. The boat sits on hinged rollers designed to absorb shock and bumps so maybe that is why it shakes the boat. Is this engine shake normal when cold and at low RPM when it is out of the water or should the engine be solid/still all the time? The shake of the engine gives me the impression that something is not tuned right, but after the engine is getting warm, the shake goes away and everything sounds and looks good.

I set the point gap to .022, and replaced the condenser with the new one I had in the boat for good measure. I took the spark plugs out and cleaned the black off them from when it was running rich. However I noticed that when in Neutral when I rev the engine "kind of" quickly it acts as though it hesitates and wants to die, I back off the throttle and it continues to run as normal, but when I rev the engine from idle slowly it revs up and runs just fine as high as I want to take the RPM's. I am wondering if this is bad gas perhaps. I plan to get it in the water on Friday to start the motor and try to adjust the idle and stuff then, but these are the issues I noticed as it sits on the trailer.

again, thanks for all your help guys. I know the boat requires a bit of work, but I love working on this boat and don't want to pay anyone to do it for me as I love learning this stuff.

 

[dswi]

Re: engine timing.. help understand..

Go back to the engine and push the remote starter switch and have the engine spin over. (And this is why we left the plugs out. The engine will spin faster with them out and give a better dwell reading). Read the 4 cylinder scale on the dwell meter (or set the switch to '4 Cyl' if it has a switch).

My dwell meter doesn't have a 4 cyl scale...What should I read, 6 or 8 and what math do I have to do??

 

[achris]

Re: engine timing.. help understand..

My dwell meter doesn't have a 4 cyl scale...What should I read, 6 or 8 and what math do I have to do??