TOPIC: Help with a non-starting 73' 150 Merc please

I've been working on a 150 Merc of mine for a couple of months. When it starts, it runs good. It may start every time for a couple of days, but then you try to start it, everything turns over but no fire to the plugs. I have gotten rid of all the old wiring harnesses, rewired everything direct to the engine (new wires thru the cowl), replaced key switch with a push button, and even put a small light bulb on the white wire going to the switch box to prove to myself that power is not the problem up to that point. I have changed the switch box and coil out with known working parts. At this point the light bulb tells me that power is good to the switch box, it cranks, but no fire. Sometimes I go back a few hours later, hit the start button and it fired right off!

What do you Merc mech's suggest? I am leaning towards a new trigger asm for the distributor. Would a new trigger from CDI be a good choice or is there a better choice? I really don't want to put another $300 into this old motor, but if it would fix it, I'm game.

Thanx for your help! Mike

Hi, Mike, the next time you get a no-spark condition, do the following test:

"1. Turn off ignition;

2. Disconnect all 3 distributor wires on the Port side of the switchbox (and the “mercury switch” if present);

3. Remove the HV lead from the ign coil to the center of the dist. cap (remember it unplugs from the coil and unscrews from the cap);

4. Reconnect the HV lead to the COIL only;

5. Position the free end of the HV lead approx. 3/8" from ground (block, shrouds etc), and find a way to hold it there;

6. Jumper the brown and white terminals on the dist. side of the switchbox to each other.

7. Check that you have +12V at the red terminal (even with the ign off);

8. Turn on ignition and verify +12V at the white terminal (same side as the red terminal);

9. Ground the black terminal on the distributor side of the switchbox - this should cause a spark each time you touch ground.

If you get spark with the distributor bypassed, and it won't fire with the distributor connected, the trigger is bad and the entire distributor housing assy must be replaced."

That being said, you've already done some of the steps like verifying power to the switchbox. Not that it couldn't hurt to verify again!

I would definitely mess with it until you get a "no-spark" condition, then immediately go into the testing mode. If you can get it to spark consistently by grounding the terminal, I'd bet the trigger is the problem.

My good buddy Dr. FrankenMerc recently had a pesky trigger problem, it would actually run the boat on a plane for a while, until it decided to quit. It kept repeating the symptoms, which can drive you crazy, since normally you'd expect the trigger to completely fail. These electronics are getting quite old now, and are starting to show a lot of strange behavior.

The CDI 134-3736 trigger is upgraded and known to be very reliable. You do have to use the supplied metal "chopper" disk since the OEM copper discs won't "fire" the upgraded sensor.

www.cdielectronics.com/product/triggers/mercury-mariner-trigger-134-3736-replaces-332-4177-393-3736-393-3736a23-393-3736a77-393-3736a79/

Here's a pretty cheap price on the CDI trigger kit:



HTH...........ed

Many thanx!

I will do this and report back later, or I might just eliminate the distributor and do the trigger. I'm told I might of fried a piston in a 140 Merc a couple of months ago from a bad trigger (double firing).

Thanx for the search on the triggers too. Any reason to purchase the one from CDI over the on ebay (kind of a no name, from Ohio or was it CDI, couldn't see a name)

Have you done business with Wuffle Marine out of Ohio?

And lastly, are there any "tricks" to replacing the trigger? I had a couple of old dist's, so I have torn one apart to see how it works. Seemed to be pretty straight forward, nut on end, spacers, washers, like an exploded view.

Thanx again for the help! Mike

Check out the "installation sheet" .pdf download at the above CDI link. It's pretty comprehensive and much better than any directions I could write! Since you've torn one down before, I don't expect you'll have any issues with it.

One good thing to do before tearing things apart, make a note of the belt timing marks, sometimes things don't line up as you'd expect, and it's good to know beforehand what you started with.

I've never done any business with that eBay vendor, but they do have a pretty good rating (99.9 percent). That part is from CDI, if you scroll down the the application chart you'll see where they refer to the CDI part number.

I don't think CDI sells directly from their website, as I could never find any prices or any way to buy from them. So, the parts have to go thru a dealer somewhere, and some dealers are more greedy than others

The vendor seems pretty straightforward, and stated in the auction that the part comes with 1-yr mfr's warranty; it wouldn't give me a bad feeling to buy from them. Some auctions I've seen ain't necessarily that way!

You know what the car dealers say, if you can find a better deal, buy it! And let us know where you found it too!!

HTH............ed

Yes Sir, I did read over the install sheet and didn't see anything that I hadn't already seen. Thanx for reminding me about getting things set up with the timing marks. I have a data sheet I made for myself on what to do before removing the belt,

Concerning the eBay vendor, at least they have a phone number and I did read all about the warranty. I'll give them a call on Monday and feel them out, maybe even get one on order right then.

I can't wait to report on how well all this goes down! Thanx again!

Thanx for the help! I got a trigger asm in, installed, took the rig over to a Merc Doctor in Tulsa to set the timing. It's been two weekends and two weekdays of running without a problem so far. Who would of thought a sealed electronic part would be intermittent in this way. Another L6 runs again!

That's a good deal TulsaPowerCat ! Congrats !