2002 Mercury 90 Runs on Two Cylinders

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
wcurling
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2002 Mercury 90 Runs on Two Cylinders

Postby wcurling » Wed Oct 07, 2020 9:04 am

[A] 2002 Mercury 90-HP two-stroke-power-cycle engine I purchased and installed in 2005 on my 1984 Montauk 17 has less than 50 hours runtime. It appears the engine is running only on cylinders 2 and 3. I removed the carburetor for cylinder 1, disassembled it, and cleaned it with carburetor solution. I dried it with blown air, re-assembled it, and reinstalled it--twice.

Fresh NGK BUZHW-2 spark plugs where installed.

When the spark plug wire is removed from cylinder 1 there is no change in the engine speed, which would indicate that cylinder is not firing.

Yes, there is plenty of spark from the coil and the spark plug.

After running the engine for a short time and then removing the cylinder 1 spark plug, the spark plug is NOT hot to the touch, but the spark plugs from cylinders 2 and 3 are hot. This indicates to me no combustion in the cylinder 1.

Adjusting the carburetor mixture screw makes no difference. Fresh clean stabilized fuel and clean filters were used.

I also tested drawing fuel directly from a glass jar thus by-passing filters and additional fuel hoses. The idea was to eliminate any possible contamination from fuel filters, hoses or fuel tank.

GIve me suggestions what else might be done. They will be appreciated.

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Phil T
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Re: 2002 Mercury 90hp #1 carb concern

Postby Phil T » Wed Oct 07, 2020 9:32 am

If the cylinder is not firing you have an electrical fault.

How are you testing each component?

Test only one component at a time.

    • Swap the spark plug from #2 cylinder to #1 cylinder
    • Test
    • Reinstall as before
    • Swap the spark plug wire from #2 cylinder to #1 cylinder
    • Test
    • Reinstall as was before
    • Swap the coil from #2 cylinder to #1 cylinder
    • Test
    • Reinstall as was before

Report results.
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biggiefl
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Re: 2002 Mercury 90hp #1 carb concern

Postby biggiefl » Wed Oct 07, 2020 11:26 am

He said there is plenty of spark on cylinder 1.

My guess is the carburetor main jet is still clogged or your definition of plenty of spark is incorrect.

Try Phil's procedure said before tearing down the carburetor again.

Personally I would squirt some gasoline-oil mix into the top carburetor while running and see if the engine ignites first. If so then the problem is with the carburetor.

To overlook something in a carburetor rebuild is easy.

Is the cylinder 1 spark plug wet or dry when removed?
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

wcurling
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Re: 2002 Mercury 90hp #1 carb concern

Postby wcurling » Wed Oct 07, 2020 3:07 pm

Thank you Phil and biggiefl. Having already done Phil's suggestion I will redo as it is possible that I overlooked something in the process.
Plug was wet when removed. I will let you know the outcome when completed. wcc

Don SSDD
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Re: 2002 Mercury 90hp #1 carb concern

Postby Don SSDD » Thu Oct 08, 2020 6:53 am

If the plug was wet, you have fuel and the problem must be electrical

Did the wet spark plug smell like gasoline?
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jimh
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Re: 2002 Mercury 90 Runs on Two Cylinders

Postby jimh » Thu Oct 08, 2020 8:00 am

Check the pressure in cylinder 1.

To have combustion you need fuel, air, and spark. But you need the fuel-air ratio to be correct. Perhaps there is very poor compression in cylinder 1 and most of the fuel-air charge is being lost into the crankcase. Perhaps the carburetor for cylinder 1 is delivering too much fuel or not enough fuel to create a combustible mixture of air and gasoline.

Regarding testing of spark: the best method to test spark is to insert a SPARK GAP TESTER in the spark plug wire to the spark plug. The air gap in the spark gap tester should be easy for a proper spark voltage to jump across. A typical spark gap tester is made by Lisle and sold in automotive parts stores. The cost is modest, about $10.

Image
20610 LISLE In-line Ignition Spark Tester

biggiefl
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Re: 2002 Mercury 90 Runs on Two Cylinders

Postby biggiefl » Thu Oct 08, 2020 12:36 pm

I have seen spark but no fire with fuel because the spark was weak and the compression would literally blow out the spark.

I assumed a compression test was done, if not that would be a good idea. To not fire at all would usually mean there is little to no compression and that could be tested with your finger over the hole.

If plug was wet, probably not the carb.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

wcurling
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Re: 2002 Mercury 90 Runs on Two Cylinders

Postby wcurling » Thu Oct 08, 2020 4:35 pm

Thank you one and all for your thoughts, suggestions, and ideas; all are beneficial.

A [cylinder pressure] test showed 140 [PSI].

I did use an in-line Ignition Spark Tester exactly like the one shown. Strong spark was visible in the test.

I'm also going to dig in a little deeper and check the reed valve as suggested by the local Mercury marine mechanic.

Please know that I am very appreciative of everyones' input. I'll keep you up-to-date on the findings.

biggiefl
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Re: 2002 Mercury 90 Runs on Two Cylinders

Postby biggiefl » Fri Oct 09, 2020 10:47 am

I have seen reeds stick, especially in salt water. If you are taking the carb off, the reeds are right there. You can probably just stick a feeler gauge in the intake instead of removing the reeds.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

wcurling
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Re: 2002 Mercury 90 Runs on Two Cylinders

Postby wcurling » Sat Oct 24, 2020 4:40 pm

On October 26, 2020 I will pick up my Montauk from the marine mechanic who fixed the cylinder and carburetor problems that I thought were occuring in cylinder #1.

[The mechanic indicated the actual cause of the running problem was the] carburetors were out of synchronization. Carburetor #3 was the main problem. Carburetors #1 and #2 had their butterfly valve closed at idle, however carburetor #3 butterfly valve was slightly open. The mechanic synchronized the carburetors, checked [the spark ignition] timing, and confirmed the cylinder pressures. [The 2002 Mercury 90-HP engine is] now running on all three cylinders and ready to go.

jimh
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Re: 2002 Mercury 90 Runs on Two Cylinders

Postby jimh » Sun Oct 25, 2020 9:55 am

Did the mechanic test the engine on the boat on the water?

Perhaps, after you get the boat and engine back from the mechanic, you can get back on the water and make some tests to see if the running problem has been cured and boat performance is back to normal. If you can do that, please post a follow up so the readers of this thread will know the final outcome.

The mechanic performing a carburetor synchronization is probably beneficial, but I don't understand how a slightly out-of-synchronization carburetor at cylinder #3 was preventing cylinder #1 from working properly.

wcurling
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Re: 2002 Mercury 90 Runs on Two Cylinders

Postby wcurling » Wed Oct 28, 2020 12:50 pm

I just came off the Elizabeth River with my Montauk. The Mercury 90-HP ran exactly as expected. It started on a dime, accelerated rapidly,and idled smoothly. All three cylinders are performing as they should. At 2,700 RPM boat speed was 19-MPH, and at 3,800-RPM boat speed was 24-MPH.