Mercury 2.5hp 2-stroke - why won't it start?

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Babylon

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Mercury 2.5hp 2-stroke - why won\'t it start?

2 year old Mercury 2.5 2-stroke mysteriously won't start. Professionally serviced last winter, run every few weeks through the summer, not dropped or dunked or abused, some use in salt water, some in fresh, last working in August. Have emptied tank of old fuel and filled with brand new (50:1 oil mix), still won't start.

I don't know much about 2-stroke petrol engines (except strimmer engine which doesn't like stale unleaded), but didn't think there was much that could go wrong with them.

Should I just change the spark-plug? How can I check whether its an electrical fault? Could it be that the engine flooded in transit and won't drain? Might it be old stale fuel down the end of the fuel line? Could it be that the bottle of 3-year old oil has also gone off?

The manual is (annoyingly) far away on board the boat - does anyone know of a PDF manual I can source.

I'm not panicking, its just I know I cannot row the rubber duck against the river's full ebb.
 
Re: Mercury 2.5hp 2-stroke - why won\'t it start?

Check/clean or replace plug is always the first thing to do. (you carry a spare dont you)

Check that you have a good fat bright blue spark. If not its an ignition problem OR the stop button/safety lanyard switch shorting. Check that switch

If spark good make sure you have a good flow of fuel to the carb.
Tank tap opening properly etc. vent open?

Possible that the float valve has stuck shut. Was the plug wet with fuel? Is the choke operating correctly?

Fuel wont go off in 3 months (he says with fingers crossed) I have had the dregs of a bottle of oil go off but only after quite a few years. It was obvious. It went all lumpy and would not mix with the petrol properly. Not normally a worry at all.

Manual can be downloaded from http://www.brunswickmarineemea.com/homepage/welcome

If you have good spark and the plug is good and you have a fuel supply to the carb then it is almost certainly a problem with the carb such as the needle valve / float stuck or the jet(s) blocked
 
Re: Mercury 2.5hp 2-stroke - why won\'t it start?

I recently had to deal with a customers non starting genny with a 2 stroke engine. Turned out to be a totally blocked carb main jet. So blocked that compressed air would not clear it despite soaking in carb cleaner. Eventually resorted to poking clear with wire from a wire brush. Not good practice but it did work and engine now runs.
 
Re: Mercury 2.5hp 2-stroke - why won\'t it start?

After trying to start the engine. Remove the plug. It will give an indication of the problem. ie if it is dry then it is a fuel problem. If it is wet with fuel and oil then clean the plug or replace it and try again but the problem is probably electrical. olewill
 
Re: Mercury 2.5hp 2-stroke - why won\'t it start?

>>> Check that you have a good fat bright blue spark.......... <<<<

Hi Vic,

That won't necessarily prove that the spark plug's ok. I posted here some time ago about the same thing because I had assumed precisely the same. We had a massive spark OUTSIDE the block and expected that the plug was therefore fine. It wasn't. Another friend with an identical engine simply said, 'Change the plug, that's your problem'.

'Yeh but, no but', we said, but he was right. New plug, instant starting, still perfect several months later, problem solved.

R's

Jerry
 
Re: Mercury 2.5hp 2-stroke - why won\'t it start?

I vote for the blocked jet.
My 2.2 Merc frequently misfires or is reluctant to start. I don't even bother with the plug, instead I just take off the float chamber and give the works a good blast with aerosol carb cleaner which does the trick.
If you are doing this on the boat make sure you put a basin under the carb... the float and needle will fall into the briny otherwise.
Prevention being better than cure I run the carb dry of petrol after use to stop gumming.
 
Re: Mercury 2.5hp 2-stroke - why won\'t it start?

>>> .... Prevention being better than cure I run the carb dry of petrol after use to stop gumming....<<

Totally agree! /forums/images/graemlins/smile.gif I've done that since buying my first two-stroke God knows how many years ago. It was the advice given to be by the company I bought it from, and has never caused a 'jet' problem on any of my engines in all those years.
 
Re: Mercury 2.5hp 2-stroke - why won\'t it start?

I had a similar problem last year after the engine was serviced when laying up.
The problem was corrosion/grit that had jammed the carburettor float from allowing fuel into the carburettor.
 
Re: Mercury 2.5hp 2-stroke - why won\'t it start?

[ QUOTE ]
Check that you have a good fat bright blue spark.......... <<<<

Hi Vic,

That won't necessarily prove that the spark plug's ok

[/ QUOTE ] What was the first thing I said? It was, "Check/clean or replace plug is always the first thing to do. (you carry a spare dont you)"
 
Re: Mercury 2.5hp 2-stroke - why won\'t it start?

/forums/images/graemlins/smile.gif
'Twas the spark plug! Covered in a gloopy film of yellow-brown, wiped it down, gently brass-wire-brushed it, and off it went first pull.

And yes, I do have a spare plug, but - err.. like the manual - the demmed thing is aboard the boat!

Thanks to all for the advice. Next time I need to troubleshoot, I've got the order of possible things firm in my mind: start with the spark-plug!
 
Re: Mercury 2.5hp 2-stroke - why won\'t it start?

A possible quick way of testing the whole ignition system is to squirt one of the ether based cold starting aerosols (e.g Bradex or Holts Cold Start ) into the air intake. Get it pretty covered in the stuff and then pull the starter a few times. If the engine fires and runs for a second or two then it's a pretty good indication that you're ignition system is OK so look for a fuel blockage /carburettor problem.
 
Re: Mercury 2.5hp 2-stroke - why won\'t it start?

Ether based starting aids are somewhat frowned upon because they contain no lubricant.

I have not tried it personally but a squirt of two stroke mixture into the carb throat is the prefered alternative. I did not think it would work but apparently it does.
 
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