7.5 Honda early 80s, no spark.

[lmuss53]

I'm trying to get this Honda 7.5 running after it sat for 7 years. I changed the lower unit oil, crankcase oil, bled the fuel system out, and thought I'd see what it would do. I pulled it a few times expecting something to happen and got nothing. I pushed the kill switch a couple times and it fell apart, so I took the wire off the back to make sure it isn't shorted out killing the motor. I pulled the plugs out and put my spark tester on both wires and got no spark. I replaced the oil warning bulb thinking that might have to be there, no change. I have a good bit of experience with larger midrange OMC or Mercury outboards, but I've never had to troubleshoot one of these smaller motors. Can the forum help me chase this problem down.

 

[lmuss53]

 

[lmuss53]

 

[lmuss53]

What is this port in the second picture for?

 

[hondam]

Those motors had 3 completely different types of ignitions systems depending on when it was made, I think i know which one that is but a serial number would confirm that. That motor might have a set of points under the cam pulley that might need some attention.

Most of those engines came standard with a charging system, even the pull starts. That is plug that the charging harness would plug into.

You said you have worked on some Evinrude and Mercury engines, do you have a DVA meter?

 

[lmuss53]

Yes on the dva, I will post the serial # and check under the cover for dirty, stuck points. Thanks for the response.

 

[lmuss53]

BF75 1005012

 

[lmuss53]

 

[lmuss53]

Points are opening right as F mark reaches the dot on the belt hub. Points are open at T mark, .012 shim fits, .015 does not. I am not sure which wires to probe for what so I'm gonna stop here. Thanks again for looking in.

 

[hondam]

According to the service manual its a black wire, on that motor black wires are not ground.

 

[lmuss53]

Black wire coming from under flywheel, looking for peak AC? I need to find a manual. Thanks for the reply.

 

[lmuss53]

Ok I put the dva on the black primary coil wire after unplugging it from the connection that takes it to the top of the ignition coil. I got 10 to 12 volts just pulling the cord at an average pull. I did the same thing with the yellow charging coil wire and got 1500 mv?

I unhooked all the wires from the ignition coil post and probed it to ground, I got a consistent 1.3 ohm reading. I'm thinking that should be open until the points ground it, but I'm not sure.

Plug wire to plug wire reads 33Kohms, from what I can find this seems to be correct.

The points had 3.5 ohm resistance when closed, again not what I expected. I cleaned them with a point file and reset them to open as the F mark just reached alignment with the dot on cam pulley. After cleaning I got .5 ohm readings through the points with them closed.

I pulled the pull starter off and cranked it with my cordless drill (barely, but better than pulling 10,000 times). I finally went Grandpa on it and laid my finger on the tester lead. It would give me a half-hearted kick about every third rev. It would not jump the smallest gap I could get on the tester.

I've never had one of these apart to change points or condenser and I am hesitant to rip into pulling that belt and cover off. Is the resistance in the points circuit a sign of bad points?

Is the flow from the post on the coil to ground a sign that the coil is shot?

What would be your next step?

 

[lmuss53]

So I read posts on a couple different sights about these things being notorious for weak spark. I put it all back together and spun it up with my cordless drill. It cranked for about 10 seconds and tried to start, I gave it a little throttle and it started and ran smooth and strong. It won't idle down without quitting, but we can work that out hopefully. I went and got a fresh set of plugs and I'm going to gap them at .035 and see if they make any difference.

I'll probably pull the carb off tomorrow and clean it too. At least the old thing is running and I can work on getting it right now. Thanks for the help.

 

[lmuss53]

Plugs changed nothing, carb is in the juice soaking.

 

[lmuss53]

I downloaded an owners manual that calls for the plugs to be gapped at .024 to .028, I will take the new plugs out and re-gap them tomorrow.

 

[Alumarine]

I find the carbs on these motors respond well to a good cleaning if neglected.
It's critical to dismantle the carb to clean it properly.

Good luck.

 

[lmuss53]

Yep, got it down to the parts and pieces.

 

[lmuss53]

Well it is running, idling mostly, has a little stumble at idle but hopefully I can adjust that out. The idle screw is about a quarter turn out from where it was when I took it apart. I think it needs a water pump, that doesn't seem like enough water at idle does it. Everything is clear and clean as far as critter nests in the hoses go.

 

[lmuss53]

 

[lmuss53]

Took a half hour to get little video to post.