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1990 75hp Mariner missing .

B

billnorfolk

New member
Hi i have a 75hp Mariner ,3 cylinder clam shell hood see number 9483083.We have done extensive work on the fuel system and engine was running good ,a couple of weeks ago suddenly started missing on top cylinder ,its got new plugs and leads so thought it must be one of the three coils ,this morning have changed coil but made no difference still no firing on top cylinder swaped leads about but still no spark from lead on top cylinder ,any ideas where we go next not had a full days running since we bought it .:confused:
 
You just might be confusing a bad top seal with ignition problems. (You said "it's not firing", which means what? No spark, or not making power up there?).

If you swapped or changed the coils and that made no difference, then it's not them. The trigger might be causing it since that particular motor has 3 individual circuits. You can test them with and ohm meter (wires disconnected). If it's okay as well, then start looking for a switch box, but I'd think about that top seal first.

You can test it out by removing the front of the silencer box (so you can get to the carbs) and stuffing a rag in the top carb as the motor fast idles. If it's a bad seal, it will stop jumping around and smooth out. And when you remove the rag, it will pick back up and start jumping around again.

Jeff

PS: Just worked on a similar one and it did roughly the same thing. In its case, it's a bad top seal.
 
It is as i said in first post ,no spark from lead on top cylinder.Have new gaskets to carbs and reeds ,fuel pump refurbished, it started intermittent like firing then not then short bursts, now nothing ,holding lead away from plug you can hear and see there is no spark ,middle and bottom good spark ,top nothing .Been stood for several years so did expect a few problems as we went along but now thinking CDI switch box. Thanks Jeff but pretty sure its ignition fault.
 
Me too. Try an ohm meter on the trigger coil leads, from the black ground wire to each of the colored wires (disconnected!) If the readings look okay, it's switch box time. Lots of them on eBay (used) for under 70 bucks.

Jeff
 


Thanks Jeff ,going to run some tests later but am confused ,all wiring diagrams show 4 terminals on switch box in use ,on mine only 3 in use ,red wire to stator missing although by the look of the cap and the clean terminal never been used .Engine has run on 3 cylinders in the past so quite confused :confused: .No loose wires anywhere .
 
Whaaatt!! Those black/yellow wires are usually the kill wires! And what happened to the stator's red wire (the high speed coil)?

You got yourself a mystery here! Suggest you trace back those black/yellow wires and see where the hell they are going. And look at the wires coming right off the stator for that missing red wire. It's gotta be some place.

Wheeew! This is is a beauty.

Jeff
 
faztbullet said:
No mystery as blk/yel wires are proper position and it has a red stator with adapter...it only uses 2 wires.
Click to expand...

Thank you can see what it is now 2 yellow 1 green and white and 1 white and green from stator into a black adapter ,one blue from adapter to switch box ,mystery solved ,thanks again .Will change switch box hopefully will cure problem.
 
I see there's a place for the usual 'red' wire (high speed coil) on the switch box but it's not used. (This setup is not in any of my books.)

Apparently, this stator uses only one coil to run the ignition instead of the blue wire (low speed coil) and above mentioned red HS coil.

Learn something new every day.

Jeff
 
You need to get some new books as Merc as run this set up for several years on the 30-125hp !!!!. Sierra even makes their on version of this stator/adapter kit(18-5873).
 
fastjeff said:
I see there's a place for the usual 'red' wire (high speed coil) on the switch box but it's not used. (This setup is not in any of my books.)

Apparently, this stator uses only one coil to run the ignition instead of the blue wire (low speed coil) and above mentioned red HS coil.

Learn something new every day.



Jeff
Click to expand...

It is what threw me Jeff ,i even downloaded latest PDF file workshop manual ,it showed 4 terminals in use red to left hand outside ,sorted hopefully now just awaiting new switch box and fingers crossed we back on the water.
 
faztbullet said:
You need to get some new books as Merc as run this set up for several years on the 30-125hp !!!!. Sierra even makes their on version of this stator/adapter kit(18-5873).
Click to expand...

The latest manual i downloaded still had 4 terminals in use ,glad yours showed the new set up ,solved the puzzle well ,Thank you.
 
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