Trouble with outboard

[LindseyMay]

I have an old (1982) Mariner 4M outboard. It got dunked (half submerged for a couple of seconds) last weekend and is now playing up; it starts ok but immediately 'races' to full speed even though the throttle is at 'start'; if I turn the throttle down the engine fades and stalls. By flicking the throttle at the right time I can keep it running, but always alternating between racing to full revs and fading out.

I have changed the fuel, stripped and cleaned the carb, and the new plug produces a healthy looking spark.

Having searched this forum and iboats I can't find reference to anything similar so would be very greatfull for any suggestions.

Many thanks in advance,

 

[VicS]

Racing to high speed with the throttleat start is a bit of a puzzle otherwise I would say there was still water in the carb or fuel and suggest another look at that possibility especially the slow running jet/passages.

It cannot race if the throttle is not open significanly beyond idle so that prompts the question, are you sure you have put it all back together properly? Have you omitted or incorrectly fitted a spring that should close the throttle or fitted a link incorrectly? Or did it do that before you stripped it?

Thats me out of ideas! Have you actually put the question on the Mariner board on i Boats?

 

[alorwin]

Not familiar with this engine but if it has an airfilter and it is water contaminated with water then it will be the equivalent of running with the choke on hence lots of fuel to high rev and not enough air to low rev.

 

[Lakesailor]

Nah. Too much fuel will not cause revving without the proportional amount of air.
Air/fuel ratio is about 14:1, more volume creates more power and revs, modern lean-burn engines can run on much higher ratios up to 65:1 ,but it's always more air, not more fuel. Too much air will give a short racing effect until it strangles itself. Like when you shut the fuel tap off on a small outboard and it races as it runs out of fuel. Too much fuel and it will stutter to a halt. Pull your choke out and see.

 

[lw395]

I suspect the twist grip is not actually closing the throttle on the carb. There is a bowden cable running from the back of the tiller arm to the carb. Check that this is returning smoothly, and that its outer is properly seated. If you remove the air filter, you should be able o check that throttle and choke plates are moving properly with the controls.
Hope this helps!
Give everything a good rinse in fresh water and spray with wd 40 to dry it out, it should be fine.

 

[Birdseye]

[ QUOTE ]
I suspect the twist grip is not actually closing the throttle on the carb. There is a bowden cable running from the back of the tiller arm to the carb. Check that this is returning smoothly, and that its outer is properly seated. If you remove the air filter, you should be able o check that throttle and choke plates are moving properly with the controls.
Hope this helps!
Give everything a good rinse in fresh water and spray with wd 40 to dry it out, it should be fine.

[/ QUOTE ]

This sounds the most likely cause - certainly, an engine cant race without a corresponding amount of air.

Some engines (my lawnmower for example) have what is in effect a spring loaded governor to maintain a constant speed. If your outboard has one of these, it bypasses throttle control to a degree and could therefore be a cause of racing.

After that, we are onto less likely causes such as damage to the cylinder head / gasket on the air intake side.

 

[chamac]

Did you remove the carb. to clean it? If you did, check the gasket or seal arrangement to make sure you have a good seal. Air leaking in after the carb. would cause your problem.

 

[LindseyMay]

Thank you all for taking the trouble to reply...

The behaviour was the same before and after I stripped the carb so I don't think I've done any thing silly in the rebuild.

There is no air filter so it can't be blocked, in fact with the plastic air intake cover removed I can run it and see the throttle moving correctly as I twist the control.

I think I'm going to have the carb off again and check carefully for air leeks and possible spring loaded governors.

Once again my thanks to you all.

 

[misterg]

I'm with VicS - I think you have a blocked slow-running circuit - I think there's enough throttle at the 'start' position to allow the engine to run on the main jet, but without the little bit extra from the idle jet, so the engine runs lean, and races away, faster and more 'frantic' sounding than normal. As soon as you shut the throttle, the engine dies as there isn't anything coming from the idle jet.

That's where I'd look first, anyway.

Has the carb got an idle mixture adjusting screw? have you had it out? Is it set the same as it was before?

I'd strip the carb again, and blow out all the passages with an air line (even a bike pump). Take the jets and the idle screw out to do this (screw it in gently first, and make a note of how many turns 'till it seats so you can re-set it afterwards). Water alone can block a jet.

The other thing to check is that you've assembled the float arm & needle valve correctly: Some of these small carbs hold the end of the needle valve captive in a fork in the float arm. It's easy to re-assemble them with the needle valve sitting 'on top' of the fork, giving a seriously low float level and very weak mixture - this could conceivably give your symptoms.

0.02p

Andy

 

[mikejames]

Another one is the ignition contact breaker points being worn or dirty (if it is 25 years old) . Leads to an engine which is hard to start , and which screams away as the points open early, but starts only if the starter cord is pulled really hard and fast.
The points setting problem leads to over-advanced ignition timing which tends to make for poor speed control as well. Recoil starter based engines will also tend to 'grab' back at the starter cord, hurting your hand.


I went through these symptoms while trying to get an oldish Evinrude running.

 

[LindseyMay]

Many thanks to everyone again; I took the carb apart again, soaked it in loads of carb cleaner, blew everything through with compressed air (from one of those 12v pumps I keep in the car for flat tyres) and it now runs as good as new...