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Thunderbolt Ignition on 1974 7.5 hp Merc

M

majkmann

Contributing Member
I have a 1974 7.5hp. Question is, Thunderbolt Ignition will fire the NGK plugs with a bright blue spark but won't fire my spark tester. Is this normal or is my switch box going south? Motor's getting gas but won't fire up. Compression's 115lbs on both cyls.
 
Re: Thunderbolt Ignition on 7.5 Merc

It works on everything else and yes it's grounded. Is there a possibility of the spark being out of time via the switch box?? This thing won't even pop if I squirt gas in the spark plug holes.
 
Re: Thunderbolt Ignition on 7.5 Merc

It should jump at least a 3/8 inch gap. Can you put a timing light on the #1 plug and check for spark and timing. Put your hand over the carb and see if it is drawing in air/fuel. This engine has points right, no switchbox
 
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Re: Thunderbolt Ignition on 7.5 Merc

It has a switchbox, Not points. I already put my hand over carb throat and yes there's suction. Don't have a timing light, just a spark tester. It does seem to light up the NGK BUHW spark plugs pretty good. Pulled the flywheel and checked for broken wires or sheared key. All is fine. Except for the fact that it won't pop a lick. I even reversed the plug wire and gave her a tug. Large back fire!! I'm stumped!!!
 
Re: Thunderbolt Ignition on 7.5 Merc

Try spraying some ether (starting fluid) into the carb (with the throttle wide open). This is a drastic step, but it MUST do something or there's parts broken or missing inside (like reeds).

Jeff
 
Re: Thunderbolt Ignition on 7.5 Merc

Ether in a two stroke! No do not do this gasoline yes down the throat of the carb, Ether can blow a hole through your pistons....Merc
 
Re: Thunderbolt Ignition on 7.5 Merc

Nonsense! I've fired up lots of untold old Mercs this way that didn't want start--in fact, a Mark 55A just this morning. The ether lasts only a second or so before the normal fuel takes over.

Jeff
 
Re: Thunderbolt Ignition on 7.5 Merc

Just because you do it this way, doesn't make what your doing is the right way of doing it, until your told not to do it (Jeff):D ..Merc
 
Re: Thunderbolt Ignition on 7.5 Merc

Thanks for the suggestion about starting fluids, But I never spray anything stronger than WD-40 down the carb to start any motor. I'm thinking the problem resides in the switchbox. This is the only motor I've ever run across that will light the plugs but not the spark tester. I'm gonna rebuild the carb first. It's cheaper. Then I'll move on to the more expensive stuff if needed. Me & them black motors just don't get along so good!!!!!!
 
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