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Jumpy · 24-08-2012, 14:36

I'm trying to solve a tricky problem with my outboard. It starts and runs reasonably well but lacks some power that it used to have at the high end. Two subtle clues are:

First, if I pull out the choke a small amount it makes more power; and

Second, if I forget to turn on the internal tank valve, it makes more power just before it runs out of gas.

It's a 2 stroke 5HP model. The carb is clean, gas is fresh, plug is good and compression is good.

Any ideas?

brantleychuck · 24-08-2012, 14:52

Sure sounds like it is going to be a carb issue. But your symptoms seem to conflict with each other. Pulling the choke should cause a richer mixture while the engine starving for fuel with the fuel valve closed would cause a lean mixture as the fuel bowl emptied out.

My experience with small 2 strokes is that problems are almost always the fuel/carb related. Get a good book with breakdown diagrams and clean and reassemble the carb according to the diagram. I messed with a 9.9 merc for weeks and finally figured out the carb had been reassembled incorrectly during some previous repair. My money is on the carb

S/V Antares · 24-08-2012, 15:07

Its the carb. If it has not beem messed with and suddenly or after prolonged lack of use you may have to take it apart.

I have had very good sucess taking the carb off and soaking the parts in Lemon juice for a few days. IF you are in the US tell the gov to stop putting ethenol in the gas.

simonmd · 24-08-2012, 15:22

Are the waterways clear and the thermostat opporating correctly? I had a Yamaha 5hp 2stroke which would loose power and it turned out to be overheating due to being clogged up with salt. The thermostsat was thrown away (waste of time in a warm climate) and waterwats scrapped and flushed through and it ran like a dream after that.

belizesailor · 24-08-2012, 16:23

I vote for carb.

Symptoms sure sound like it and about 95% of problems with small 2 strokes turn out to be dirty carb.

Note: to properly clean a carb you must remove it from the engine and tear it down and physically clean it...none of this supposed magic stuff you can put in the fuel will likely work.

Also, power surging a bit before an engine runs out of fuel is normal.

Acushla · 24-08-2012, 21:39

This is bound to be a fuel/carb issue. Remember the least amount of water in the fuel will cause such issues. Run some fuel out into a glass jar from the bottom of the tank and examine this for water. Do the same with the carb just to see if there is any water present in the carb bowl. Check that the float is OK and not deformed or punctured.

Acushla

SkiprJohn · 24-08-2012, 22:22

Definitely is a fuel problem if it runs better with the choke out a bit. Could be anywhere between the fuel pickup line in the tank to the carb itself. If it is an old carb and has a reed valve that could be gummed up just a bit. If you have ethanol additive in your fuel then unless you run the engine dry each time you'll develop that problem.
The engine will run strong and hard just before it dies from fuel starvation. Happens with all two-strokes. Weedwhackers, chainsaws and outboards all do it.
Good luck in finding the problem. Definitely is fuel related.
kind regards,

justwaiting · 24-08-2012, 22:56

I purchased a 6 hp late model evenrude in the 80,s that the owner had taken to the dealership 3 times where they changed the head gasket each time. I would start fine, ran smoth until a load was applied then it would die like it had a blown head gasket.

I replaced the exaust gasket, it ran without a problem for the next 3 years @ about 20 hours a week. Best motor i have ever owned - 2 strokes need back preasure more than 4 strokes, so if ever thing else fails may be worth trying.

SkiprJohn · 25-08-2012, 11:41

Might try checking the vent cap on your fuel tank just to make certain enough air is getting through. I know its a simple thing but sometimes it makes a big difference.
kind regards,