Mercury 90 2 stroke (2003) Help!

[Robbohants]

Hello all,

Engine : 2003 Mercury 90hp 3 cylinder 2 stroke.

About 3 weeks ago I had a new lower carb fitted and the other 2 carbs rebuilt, also had a new inlet manifold gasket. The engine ran beautifully on muffs after this. It then had an oil pump delete and I then brought it home. I tried to run it up a week later and it started fine but I turned it off almost immediately as the hose pipe had frozen and I couldn’t get any water through to the muffs (was very cold that day).

A week later, (once everything had thawed) I tried again and I couldn’t get it to fire. I had a look around and found that a 20amp fuse (between the positive terminal on the starter solenoid and the voltage regulator) had blown, I replaced it. Still no joy however.

I noticed that the engine appeared to have flooded and when I tilted it all the way up fuel ran out the front of the carbs, just drips from the upper two but a lot from the lower carb.

I have tested the enricher valve and it is operating correctly (only open when the key is pushed in). I have tried starting it at all stages of throttle and with and without the key pushed in. I have let it dry out in between these attempts as it appears to flood each time, even when no enricher is used..

I have removed and cleaned the plugs and tested them for resistance, they are BUHW-2 plugs and read about 0.4 ohms. There is voltage at the HT leads when cranking, but I’ve not been able to definitively test for spark (need someone else to crank it so I can check - will do this tomorrow!)

I’m confused as the motor isn’t even attempting to fire, even when left overnight and cranked with no enricher it makes no attempt and after a few mins of trying appears to be flooded.

I am wondering if whatever caused the blown fuse could have had some impact on its sparking ability? Or if the timing could have been knocked out? Or maybe something completely different?
I’m reluctant to take it back to the engineer as it’s such a long drive and I’m fairly handy with the spanners so I’d like to fix it myself.
Any advice would be very much appreciated.

[whiskylee]

Kill switch on the control box in the on possible!

[Robbohants]

Originally Posted by whiskylee

Kill switch on the control box in the on possible!

It is in the right position, but I’ve not tested it, I’ll do that tomorrow

[A1an]

give it a wee blast of starting fluid.

[neil.mccrirrick]

It shouldn’t be leaking fuel. You need to check that first. If fuel comes out air will get in and throw the mixture out

[Robbohants]

Originally Posted by neil.mccrirrick

It shouldn’t be leaking fuel. You need to check that first. If fuel comes out air will get in and throw the mixture out

Would unburnt fuel (for example the fuel put in via the enricher valve) not flow back through the carb when the engine is tilted?

[neil.mccrirrick]

No once fuel is in the carb the only acceptable way out is through the manifold as designed. If the engine is upside down it will leak as you most likely have an overflow if the floats fail to cut the flow of fuel but not tilted unless your tilt is way past horizontal

[whiskylee]

Have someone keep squeezing the fuel primer bulb whilst you check for leaks/fuel

[whiskylee]

I would start with:

Compression test on all 3 cylinder's

Spark test on all 3 cylinder's

Fuel bulb primed whilst looking for any fuel leaks, carbs, fuel pump & hoses etc

[Robbohants]

Update:

It has a good strong spark, tested the kill switch too, no problems there.

I took the carbs and the oil tank off and discovered the bottom of the intake gasket is leaking (brand new gasket just fitted) AND…. The bolts holding the intake on were loose!!!, I’ve tightened them but still no joy, I think the gasket must be distorted or crushed as it is leaking fuel out the bottom. I assume it will also be sucking in air here which is probably why it won’t start? Although does leave a bit of a mystery as to why it started happily like that a couple of weeks ago.

Compression: I lent my compression tester out a few weeks ago so waiting on that to be returned and I’ll test the cylinders.

[Robbohants]

Further update……

…., so I took the reed valve/ intake manifolds off, the lower one was missing a gasket completely (only had one on the crank side of the reed valve not on the carb side), the middle one the gaskets looked new and the upper one had very perished gaskets, so I’ve ordered 6. I’m hoping this is my problem.

The upper two reed valves look good, however on the lower reed valve I can see a tiny slither of light through it on the outer edges of some of the reeds, do you think I need to replace it?

Thanks all for your help

[neil.mccrirrick]

Start with the gaskets and go from there. Take each issue one at a time or you will throw money at it and possibly create more problems

Poor gaskets and air leaks are most likely the reason you can’t start

[Robbohants]

Success!!, removed and cleaned the reed valves, replaced with new gaskets, and she fired straight up!

Thanks all for your help

[neil.mccrirrick]

Glad it’s worked out for you [emoji106]