1970 Merc 7.5 will only start at 3/4 throttle in gear (Thunderbolt Ignition)

Hello everyone,

I am a newbie on this forum and I would greatly appreciate any help from all you knowledgeable folks! I have learned quite a bit from all of you as a guest in the past and I am struggling to get an old Merc. 7.5 out on the water.

My situation: My 7.5 will not start unless it is in gear and at 3/4 throttle. After starting, the engine will not idle and stalls once the throttle is returned to the "shift" position.

Engine history: I purchased the engine recently for $50 bucks at a garage sale. Seller was asking $200 but couldn't run it due to no fuel tank so he dropped the price. He told me it had belonged to his deceased father and had been sitting for 3 years. It is very clean so I took a chance. When I got it home, it would only start in gear at 3/4 throttle.

What I have done so far:
1. Seafoamed carb and replaced plugs.
2. Disassembled carb to inspect and clean (appeared to be clean to begin with).
3. Checked float adjustment, good.
4. Replaced old fuel lines.
5. Checked spark. Spark is weak on top cylinder and only at 3/4 throttle. Spark is very intermittent and only at 3/4 throttle on lower cylinder.
6. Visually inspected coils for cracks, burns (none). Inspected high tension leads for arcing (none). Swapped leads between coils, no difference.
7. Cleaned and re-tightened wires going to coils.
8. Inspected points, showing their age but not burnt and still opening and closing.
9. Visually inspected stater, no burned wires or marks.

I have ordered a manual but it will not be here for a few days. I am wondering if someone can help me properly diagnose the ignition system or if they have run across this exact situation in the past.

Thanks!

On these motors, I always remove and toss out the mechanism that prevents throttle up in N and R. (One bolt.) That makes a world of starting difference.

Have you adjusted the idle with the motor warmed up and in gear (boat tied to the dock or on a trailer)? If you can't get a decent idle that way, you might still need to mess with the needle and seat.

Jeff

I had a 71 7.5 I believe and it drove me crazy. It is well documented that the insulators under the flywheel (I am not sure about a 1970) crack and need replacing.
When I did replace mine, I replaced the HV wires in there as well. They were heavily corroded on the inside.
I had a no spark condition. It was perfect after that.
I will hunt down the old thread.

http://www.marineengine.com/boat-forum/showthread.php?393949-1971-7-5-HP-no-spark

Shame on me for not updating it with the final result.

I did.
http://www.marineengine.com/boat-forum/showthread.php?394857-Still-working-on-the-1971-7-5HP

Thanks Jeff,
I can adjust the idle to a decent level and it will run about 30 seconds then stall out or stalls immediately when put in the shift position. Engine will restart but only at 3/4 throttle. I have the engine on a stand and running it in a tank.

Thanks Jim,
Yes it's pretty much the same engine. I did check the insulators when I examined the points. There were no visual signs of cracks that i could see. I really didn't look at the wires too close, I will try that today.

Thanks for finding the old thread.

Only one of my insulators showed a minute crack on mine. I had ZERO spark. I didn't try advancing the throttle and checking. I changed them anyway as they were very cheap.
CDI makes them I think. They actually come with a new stator assy. I used some very good HV HT wire from McMaster.
I soldered everything I could.

fastjeff,
How do I get at the mechanism that prevents throttle up in neutral and reverse?

Well, I replaced the insulators and regapped the points today. I have spark on both coils but the engine will only start in forward at 3/4 throttle and then stall when trying to get to the shift position. I tried to adjust idle with no success. Stalls before you can get it where it should be. Guess I will keep playing with the carb tomorrow.

Does anyone know why this engine would start in gear?

The obnoxious little piece is just below and left of the carb. One bolt holds it on.

Jeff

I was thinking a ground at this point too. When the engine stalls, it just shuts off. It does not miss or sputter. I have already tried bi-passing the kill switch just to rule that out. It made no difference.

I replaced the ground wire from the stator to the throttle mount today. No change. It was a great theory though! I also got my new repair manual today. Mercury Outboard Repair Manual: 1965-1979. I eagerly opened to the section on ignition systems. Wouldn't you know it. There is no diagnosis or component spec information on 1969-1971 Phasemaker ignition systems. They only show how to take it apart and put it back together. Wow, $30 well spent.

Frustrated and willing to admit defeat, I loaded up the old Merc and headed to a local outboard shop that specializes in older motors. The man at the shop listened intently to my story and without hesitating informed me of my need for a stator. He then chuckled a little, pointed at a PILE of red stripe Mercs in the back of the shop and muttered "Those do too!" I had suspected this, but really don't want to part with $250 bucks for a new stator just yet. So my question is this: Has anyone ever tried to retrofit a different ignition system on one of these engines? Ok, call me nuts, but I'm the son of a poor farmer and my dad was really good at making things work from parts that were laying around.

My manual (for what it is worth) calls my ignition system a Phazemaker point type with an internal capacitor (1970 and 71). The Thunderbolt stator you have linked is the aftermarket replacement for my engine (according to CDI). The part number on my stator is 336-3996. It is my understanding from what I have read on the internet (not always the best source), there were two versions of the Phazemaker used in 1970 and 1971. One having an internal capacitor and one having an external capacitor. My stator has two ground wires. One from the stator to the throttle lever/bracket. The other goes from the stator to the lower housing next to the kill switch. There is green wire that leads from the stator to the positive side of the #1 coil and a salmon wire that runs from stator to the kill switch. Only remaining wires are both brown and run from points to negative side of coils.

The reason I was inquiring about a conversion is there seem to be more Mercs from the 60's and mid 70's laying around that can be had for next to nothing in my area. Not too many red stripes.

OK, I found a complete running 1968 Merc 200 (20 hp) that has a little knock. Started and ran well otherwise. Could I swap the Phelon ignition from this motor to mine?

Many changes on those two ignitions.

Jeff