Mercury 90 HP 2 Stroke oddity

[Davids]

Hello all

Perhaps this forum is geared to racing and tuning, but reaching out for expertise- thanks in advance

Here is the issue, 2004 mercury 90 HP 3 cylinder two stroke not running on cyl number 1

The fuel system (http://shop.ebay.co.uk/?_nkw=fuel+system) and carbs are clean and the reed valves are good

Compression is 120 psi each cylinder to inc number 1 cylinder

coils with their ignition leads and plugs were swapped from other cylinders that are known to be good e,g running well and yet no difference, in essence number 1 is getting spark

cylinder 2 and 3 will run on their own (i.e ignition leads disconnected for the other cylinders) but not cylinder number 1

Thoughts

[nitro_rat]

Download the free troubleshooting guide from cdielectronics.com. It will walk you through the testing procedures for your symptoms...

[Davids]

Download the free troubleshooting guide from cdielectronics.com. It will walk you through the testing procedures for your symptoms...

Thanks for link and advice; I was ruling out electronics as i have swapped the coils and plugs and there is a very healthy spark as tested with a spark tester, unless the spark is at the wrong time if that is possible.

[RSWORDS]

Switch the green wires on the stator around and see if it follows.

[nitro_rat]

Thanks for link and advice; I was ruling out electronics as i have swapped the coils and plugs and there is a very healthy spark as tested with a spark tester, unless the spark is at the wrong time if that is possible.

Please read the troubleshooting manual. Your testing procedure is not valid so you're missing the solution...

[RSWORDS]

So I re-read this. Are you saying you have spark on all three?

[EMC 2870]

I chased the same issue on my 96 75. Its the same engine, different carbs. It was a coil. It fired fine at idle but failed to fire at RPM. I happen to have a 115 with the same coils and just swapped them. 75 ran like a top and the 115 Ran like ****. Kept swapping around until i figured out what coil was bad. Ended up buying 7 for both motors.

[half fast]

Are all carb butterflies in sink ?

[Davids]

So I re-read this. Are you saying you have spark on all three?
Yes spark on all three and swaped number 3 cup to number 1 and 3 runs fine with 1 still not firing. This is why I am leaning towards fuel

[Davids]

Yes sync completed and no sneezing

[Davids]

I swapped the coil from cylinders 2 and 3 and no difference with those cylinders going great, hence eliminating a coil issue, I will revisit the fuel side of things

[Motv18]

I want to say you have a clogged air or exhaust but compression seems legit.

how wet is the number one plug when you look at it after running, ( it should be soaked)

on the the other hand how are you tracking the miss. When you swapped coils did you pull the plug wires to verify the miss was still on number 1? Just feeling like it was still #1 missing doesn’t count.

If if you think it’s going back to fuel just cover the carb with your hand. It should kill or smoke that cylinder

another old old timer truck is move plug wire and coil to another cylinder since an ok plug ok wires and on coil can equal a miss but make one good and it works.

[half fast]

Peek in thru the spark plug hole and check to see if possibly the sleeve has turned . The inline four cylinders were more prone to do this . I usually just look at the exhaust port and see if it’s closed . Good luck . Hf...

[EMC 2870]

Has it backfired recently? COuld be a bad reed

[rhardwick]

Use your timing light to point down the venturi on the top carb. Throttle up the engine and you should see gas being drawn through the low speed circuit and fuel should come out the brass tube from the bowl. Use the running cylinders to match fuel flow. While you have the timing light out check for proper timing on the flywheel. The timing should be 120 degrees apart when you check all 3 cylinders. This will find if a double firing coil/stator could be giving issues. I don't think the magnets could come lose on the flywheel like OMC's did on their V4 and V6 loopers..........

[Markus]

Best way to figure out whether a problem is fuel or spark related is to look at the spark plug.

Do like this:

Put in 3 new plugs and run the engine so that the problem occurs.

Then look at the plugs.

Wetter plug = no spark
Drier plug = no fuel

[Krazymaan]

get the motor started and point a temperature gun right where the spark plug meets the head at take temperature readings.