1973 9.8 Mercury won't start. Fuel, Spark & Compression all good

Double-

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This motor has about 110 pounds of compression in both cylinders. The spark is bright blue and has new plugs. Carb cleaned, but did not really need to be.

This motor still will not start, even with a squirt of fuel mix in the carb, or with a squirt in each cylinder.

The flywheel key is good.

Has anyone seen a hidden blown gasket issue, air leak or a drastic timing issue I am overlooking? Am I missing something else?

Thanks in advance-
 

hkeiner

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Re: 1973 9.8 Mercury won't start. Fuel, Spark & Compression all good

In principle, if the fuel, spark, and compression are good, then it should run. Perhaps the spark is not really as "good" as you think, due to bad timing, mis-adjusted linkage, etc.

You don't say if the motor used to run fine and just stopped on you or if you just got the motor and are trying to start it for the first time. If you never had it running before, I would suggest doing/checking all of the link and sync steps to make sure everything is correct. If the motor ran fine before and then it just stopped on you, then I would suggest that you describe how that happened to provide some more clues.

Just my thoughts...
 

Laddies

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Re: 1973 9.8 Mercury won't start. Fuel, Spark & Compression all good

Check for a bad flywheel key.
 

Double-

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Re: 1973 9.8 Mercury won't start. Fuel, Spark & Compression all good

Thanks for the responses.

The flywheel key is good.

This motor is new to me. The old owner "said" it was put away running, but now wont start.

The motor is in really nice shape and does not appear to have ever been "tinkered" on. All linkage is tight and in original location and in very good condition. I will have to get a book to check linkage adjustments to be certain however.
 

JB

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Re: 1973 9.8 Mercury won't start. Fuel, Spark & Compression all good

How long ago was it "put up"?

Sure sounds like a timing or synch problem.
 

This_lil_fishy

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Re: 1973 9.8 Mercury won't start. Fuel, Spark & Compression all good

Do a compression check....no compression no vrrroooom.


Actually that's about all that's left to check. Otherwise it's definately a spark issue. Even if it wasn't firing at the right time you'd eventually get some backfiring or sputtering.

Ian
 

Laddies

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Re: 1973 9.8 Mercury won't start. Fuel, Spark & Compression all good

Are the plug wires reversed
 

JB

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Re: 1973 9.8 Mercury won't start. Fuel, Spark & Compression all good

Does anybody really read the original post???

The flywheel key is good.

The compression is about 110psi in both cylinders.

He said that twice.

What does that leave?

Possibly timing waaaay off, but not enough to make her backfire.

Could poor or no scavenging not be providing enough air for combustion??
 

Double-

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Re: 1973 9.8 Mercury won't start. Fuel, Spark & Compression all good

Thanks for the responses.

The old owner says he put it away about 1-2 years ago. I tend to believe that due to the bad gas in the tank that was not totally "varnish".

The plug wires are not long enough to be reversed, but great thought!

I tend to agree that the timing would have to be VERY off not to get any kind of firing at all. I like the idea of poor scavenging. Are you thinking some kind of blockage somewhere internally?
 

JB

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Re: 1973 9.8 Mercury won't start. Fuel, Spark & Compression all good

Yes. I am thinking something jamming up the reeds or a dried out gasket not allowing crankcase compression.
 

allymoss

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Re: 1973 9.8 Mercury won't start. Fuel, Spark & Compression all good

make sure gap of plug is right, screwed in enough.

if its nothing else then it must be timing. As said before, go through link sync procedure even if it looks ok.
 

oldtruckface

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Apr 25, 2008
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Re: 1973 9.8 Mercury won't start. Fuel, Spark & Compression all good

to start your motor spray some deep creep into the carb.you can get it at napa
 

hkeiner

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Re: 1973 9.8 Mercury won't start. Fuel, Spark & Compression all good

The spark is bright blue and has new plugs. This motor still will not start, even with a squirt of fuel mix in the carb, or with a squirt in each cylinder.

Perhaps you can clarify what you are experiencing when you say you are spraying some fuel mix into the carbs/cylinders and it won't start.

1) Are you cranking the motor while you are spraying the fuel into the carbs or are you spraying and then cranking? You should be spaying while the motor is cranking to see what happens.

2) Does the motor not respond at all (while spraying the fuel into the carbs while cranking the motor) or does it respond a little but not "start" running on its own? These two different possible situations lead to totally different groups of probable causes.

Just thought this might help...

If you are correctly spraying the fuel while cranking the motor, you have a good spark, and the motor does not respond at all, I think that JB's opinion that "something is jamming up the reeds or a dried out gasket not allowing crankcase compression" is the most likely situation. I don't know how to test for this without disassembly of the motor. Perhaps someone else might suggest a quick and easy test for this, such as holding something in front of the carb throat while cranking to see if there is any suction?
 
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