90-HP Mariner 3-cylinder Surging

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Grumpy
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Joined: Wed Jan 11, 2017 4:40 am

90-HP Mariner 3-cylinder Surging

Postby Grumpy » Wed Jan 11, 2017 5:43 am

I'm a new guy on the block from South Africa and hello to all. Yours truly stay out in the countryside and have no boat repair shop nearby to contact and have to do repair things myself.

I have a Mariner 90-HP three-cylinder (mid 1980's model) with the following problems. When accelerating hard from standstill she would take off fast, then have a slight hiccup or surge (momentarily for a split second or two) and then take off like a bat out of hell. Next time she would take off fast and clean out of the hole for a few times, then have the hesitation again at another time.

Furthermore, after pulling away, she would continue to accelerate hard at WOT, run smooth and then start surging slightly in a "go/brake" fashion. When back at idle, and accelerating hard the same would happen again at WOT. However, running about half throttle the surging seems less and takes longer to take effect at speed; sometime she would run cleanly at mid throttle. What is causing this malady?

I serviced the engine and also fitted a new petrolpump kit which I suspected to be the culprit but now seemed not to be. All fuel hoses are good and not cracked.

The carburetors are properly cleaned, air screws out by one-and-three-quarter turns and carbs also properly synchronized. Timing is set with a timing light at 3-degrees BTDC at 800rpm idle and WOT 23-degrees at 2500 to 3000rpm. New gapless NGK - BUHW-2 spark plugs are fitted. Compression is fine at 800-kpa for all three cylinders.

I believe the tuning specs are okay because, as said before, sometimes she will jump away cleanly and accelertate hard to WOT before the surging action starts. Likewise with the pull away at WOT, sometimes clean and at another time with slight hesitation. If timing were off, surely the hesitation would be evident permanently--or am I missing something?

Can this problem be electrical? Or, perhaps something else?

Lastly, I noticed some fuel drops dripping from "Solenoid enricher valve". Can this be the cause as I understand this is only a choke device use in starting only.

Help would be greatly appreciated. Thank you

jimh
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Location: Michigan, Lower Peninsula
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Re: 90-HP Mariner 3-cylinder Surging

Postby jimh » Wed Jan 11, 2017 7:57 am

I don't have much advice to offer, but your mention of the solenoid enrichment valve may be indicative of the cause. Typically an engine with a solenoid-operated enrichment valve will allow a large amount of extra fuel to enter the air flow stream into the cylinders when the valve is opened. Typically the valve only is open during a cold start. At engine cranking speed the amount of fuel that can get added by the suction into the air stream is probably limited. The fuel:air mixture is enriched, and as soon as the engine starts the electrical solenoid should be released and the fuel supply stopped.

If that valve is leaking fuel into the engine while it is running, the extra fuel could account for the surging behavior you describe. On that basis, I would take a closer look at the fuel enrichment valve. Make sure that it is shutting off fuel when the solenoid is not operated.

Also, some of those fuel enrichment solenoid valves have an option for a manual valve opening. Make sure the manual valve is shut off.

ASIDE: I had a electric solenoid enrichment valve on an Evinrude engine. It had the manual bypass function, too. If that manual valve was accidentally left open, the engine would run very poorly after starting because it was always getting too much fuel.

Grumpy
Posts: 3
Joined: Wed Jan 11, 2017 4:40 am

Re: 90-HP Mariner 3-cylinder Surging

Postby Grumpy » Thu Jan 12, 2017 12:07 pm

Thank you for your advice on this. Trouble now is to lay hands on a new solenoid enrichment valve in my part of the woods.

jimh
Posts: 2312
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
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Re: 90-HP Mariner 3-cylinder Surging

Postby jimh » Sat Jan 14, 2017 12:37 pm

As a means of testing if fuel leaking from the solenoid enrichment valve is actually the cause of the problem, perhaps you can temporarily disconnect the output of the solenoid enrichment valve from the fuel hose that leads into the air intake, seal off both the valve and the hose just disconnected, and test the engine.

Grumpy
Posts: 3
Joined: Wed Jan 11, 2017 4:40 am

Re: 90-HP Mariner 3-cylinder Surging

Postby Grumpy » Wed Jan 18, 2017 1:29 pm

I have disconnected the two pipes from the leaking enrichment Soleniod valve and sealed them off properly by turning screws tightly into the rubber hoses, basically totally bypassed the soleniod valve altogether.
But to no avail - at WOT and mid throttle the surging still persists as described in the OP. I actually also set the floats level a millimeter or so higher because I suspected that the float levels drops under load and after a test run it is now worse. It even idles bad and bogs down out of the hole.
I going to set the floats back to spec again because as mentioned in OP she took off like a bat out of hell fom pull away and was only the top end surging going that troubled me at that state of tune.
I suspect that I may have an air leak between tank and the fuel filter/pump and going to replace the pipe from fuel tank with single piece of pipe directly to fuel pump with new primer bulb and see if this cures it from this malady. I never trusted those fuel line plug-in joints and chucking them out on tank and engine wont hurt my cause.


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