LOTSA SPARK BUT NO FIRE - 1972 Merc 50/500

[timmeraw]

Even though I have lots of experience restoring these 4 cyl Mercs I am running out of ideas here on this 1972 Merc 50 with lightening energizer ignition. It has great spark on all 4? it has good compression(actually I have only checked the top two holes now that I think of it). Somebody had been playing with the timing stops and trigger throttle advance arm so using a timing light I did the link n sync per specs. Battery is good and cranking well. Fuel is fine(same tank I use for other motors I am working on). Carbs removed and cleaned (weren?t very dirty actually). Floats/needles/seats are working as I can pump till hard.

Problem is I cannot get it to fire up and run. With premix in the the holes I have had it pop once or twice but will not run. I am stumped. With spark this good it should at least consistently rumble for a second or two burning off the premix in the cyls. This is why I thought it might be a timing issue and set it all up correctly(including of course getting the distributer pulley arrow lined up with TDC mark on flywheel). One thing I should have checked?especially with the distributor off was if the plug wires were actually connected to the rotor cap correctly? I should have also checked the reeds when I had the carbs off come to think of it.

Any thoughts?

 

[Chris1956]

Re: LOTSA SPARK BUT NO FIRE - 1972 Merc 50/500

Do the spark plugs show water droplets? Do the plug wires arc to ground?

 

[timmeraw]

Re: LOTSA SPARK BUT NO FIRE - 1972 Merc 50/500

Chris,

I don't believe that there is any water on the plugs (just premix I have squirting in there). I will pull the plugs and turn it over some, clean the surface gap plugs, and try to fire it up and check them again. As for arching the plug wires to ground... I have not tested just the wires but with a spark tester it has very strong spark on all cycls and when I was setting the timing I had all four plugs out and attached to wires I bungied them to the block and they were cracking away.

 

[Chris1956]

Re: LOTSA SPARK BUT NO FIRE - 1972 Merc 50/500

Well, you need fuel and air to the cylinders, compression and spark to run. You have all these, so timing and water intrusion are obvious places to look.

You might stick a screwdriver into the top cylinder, and turn flywheel to make it top dead center. Now look at timing marks. They should indicate TDC or very nearly so. Now install top spark plug, put a timing light on the top spark plug and set the throttle until the carbs are still closed, but ready to open. Now crank the motor and see what the timing is.

Report back

 

[timmeraw]

Re: LOTSA SPARK BUT NO FIRE - 1972 Merc 50/500

Chris,

I have the timing all set. TDC agrees with the mark on flywheel and is lined up with arrow on distibutor sprocket. Have adjusted the out or wack spark timing to be between 4-4 degrees BTDC when throttle pickup just touches the cam.....and then set the max spark advance stop to 35 degrees BTDC. Using the timing light of course (plugs out connected to #1 high tension plug wire). I am pretty confident that timing is fine.

Im going out now to tear it down to get the carbs off and see how the reeds are. I wish I could recall but one time I read on here or somewhere that you can attempt to clean up gummed/dirty reeds by spraying something into the block with carbs off(maybe it was Kerosene ???).

I'll report back.

 

[Chris1956]

Re: LOTSA SPARK BUT NO FIRE - 1972 Merc 50/500

Gee, a wild thought. Are the transfer port covers tight? If they leak, you will get a lean mixture to the cylinders. same thing for crankcase cover and even carb base bolts.

 

[timmeraw]

Re: LOTSA SPARK BUT NO FIRE - 1972 Merc 50/500

Yep everything is tight. Pulling carbs now to check reeds....last thing I have not checked.

 

[Chris1956]

Re: LOTSA SPARK BUT NO FIRE - 1972 Merc 50/500

You probably need to pull powerhead and open crankcase to check reeds. Stock Reeds usually do not go faulty.