1988 Mercury 25 xd Timing and sync problems

[JOHNNY-62]

I have a Mercury 25 xd. I changed all the Electrical. I have great spark, it jumps at least 3/8 of an inch. I rebuilt the carb. Checked the Flywheel key. It has started . Ran for a short time . When you go to start it again it won't turn over. I do not have a service manual . But the books I have cover some info on this motor. I have read as many forums as possible about people having issues with this motor. I feel like I am very close but I know I'm missing something. Any help would be greatly appreciated . Thanks John

 

[JDusza]

Not entirely clear on your symptoms. Why did you replace "all the electrical"? Were those ignition parts or wiring harnesses, rectifiers or starter solenoids? During carb rebuild, did you clean the low speed jets? When you say it doesn't "turn over" are you saying you cannot spin the crank with the recoil starter or the electric starter? Or it does spin (turn over) but doesn't fire? Is the engine not running now because it "won't turn over" or will it start and die?
Start with the basics. Sounds like you have.
Compression test. Probably okay but good to know for cylinder health.
Ignition. You have enough spark to jump 3/8. Test the plugs, verify that energy actually makes it through the spark plug. Air gap is a great test for power but plugs can fail. Now you need that spark at the right time. Put a timing light on the plug wires, repaint the flywheel marks for a good read if you have to and verify each cylinder fires at TDC only.
Fuel. With compression and ignition in place, inject a little premixed fuel into the carburetor or cylinders directly and try to start. With this you would expect the engine to try to fire. Might take a few pulls as manually injecting premix can momentarily "flood" the engine.
If it runs and starts to die, can you keep it running by squeezing the primer bulb in the fuel line, pumping the choke primer or by manually injecting premix into the carburetor?
If it runs, dies and doesn't restart, pull the plugs and see if they're wet. Do you have fuel dripping from the carburetor into the lower covers?
J

 

[JOHNNY-62]

Not entirely clear on your symptoms. Why did you replace "all the electrical"? Were those ignition parts or wiring harnesses, rectifiers or starter solenoids? During carb rebuild, did you clean the low speed jets? When you say it doesn't "turn over" are you saying you cannot spin the crank with the recoil starter or the electric starter? Or it does spin (turn over) but doesn't fire? Is the engine not running now because it "won't turn over" or will it start and die?
Start with the basics. Sounds like you have.
Compression test. Probably okay but good to know for cylinder health.
Ignition. You have enough spark to jump 3/8. Test the plugs, verify that energy actually makes it through the spark plug. Air gap is a great test for power but plugs can fail. Now you need that spark at the right time. Put a timing light on the plug wires, repaint the flywheel marks for a good read if you have to and verify each cylinder fires at TDC only.
Fuel. With compression and ignition in place, inject a little premixed fuel into the carburetor or cylinders directly and try to start. With this you would expect the engine to try to fire. Might take a few pulls as manually injecting premix can momentarily "flood" the engine.
If it runs and starts to die, can you keep it running by squeezing the primer bulb in the fuel line, pumping the choke primer or by manually injecting premix into the carburetor?
If it runs, dies and doesn't restart, pull the plugs and see if they're wet. Do you have fuel dripping from the carburetor into the lower covers?
J

 

[JOHNNY-62]

Hello I replaced the coils , Stator ,Trigger, Switch Box , New plugs. I just wanted to have everything new . My stator was bad when I first started to look at the engine . I was trying to say when you pull start it .It would not start. I have to pickup a timing light. I will check and follow what you wrote and see what happens . Thank you

 

[JDusza]

With those ignition components being new, you probably don't need the timing light although it would be a good add to your arsenal. Verify that your new spark plugs are delivering and then try to inject some premix.
This is a stretch, I know, but, ... "Ran for a short time . When you go to start it again it won't turn over. " ... Are you overheating and shutting down just prior to totally jamming up the pistons? If you're not cooling right, you only have a few minutes of run time. An overheat will happen fast. Check your tell tale for water. Does your XD have a thermostat? It will be in line with your tell tale at block exit so make sure it opens and you are peeing strong. If you think you have a water circulation problem, remove the thermostat and run without it. You should be putting out a strong water stream. If you have an infrared thermometer take a look at the running temp of your head near the spark plugs.
After sitting, will the engine restart? That could be a sign of cooling from overheating or evaporating off excessive fuel from flooding. If you're flooding you would expect to see wet spark plugs. Look at your plugs immediately following a stall.
J

 

[JOHNNY-62]

Hi J I put in a new water pump as well .When it ran It was peeing very strong . I'm going to try the premix. When it stopped after it ran .It would not start again. It did try to fire over but would not stay running. I will take all your advice and check everything over again.

 

[JDusza]

I see. It will try to start but not stay running. So ignition is firing.
Not sure of your set-up. Is the engine still on the boat or in a barrel? Are you working the controls from the helm or back at the engine? Work them back at the engine.
Do try the premix squirt, the squeeze ball and the primer push. Try to keep the engine running with a pump to the choke/primer and opening the throttle a little for more revs.
Your throttle linkages are good? Ignition advance is moving?
When doing the carburetor, did you remove the cover and low speed needle and clean out the low speed jets and needle seat? There're two jets to clear. Reset the low speed mixture by turning the adjusting screw clockwise all the way, closing it, then back out 1 1/2 turns. This should get you running, fine tune it later. Did you also rebuild the fuel pump side?
One way to test the float's needle valve and seat with an empty bowl before you reinstall is to gently blow into the fuel inlet, right side up and upside down. Do not use compressed air, just your breath. With the carb right side up, the needle down, the valve open, you should be able to gently blow into the carburetor. If you flip the carb upside down the needle valve should close and you should not be able to blow into it.
J

 

[JOHNNY-62]

Hello J .
Thank you for all your time and advice on this motor. I am taking it to a local mechanic that is very familiar with this model. I did all the things you mentioned . I usually never give up, but I think it got the best of me. When I find out what he knows I will respond to you and let you know.
Thank you, again, for all your assistance. It is greatly appreciated!
J