Motor not idling properly?

[fender22]

HI, I have a 135hp Mariner (Merc) 1987 model. Runs like a dream and everything but it seems to stall sometimes, mainly when motoring into ramps and such where you need to give a bit of forward, reverse, forward etc and finesse it in. Can be a bit dangerous sometimes if coming into a ramp and you need to slow her down with a bit of "backward". I'm not slamming it from forward to reverse or anythng, being gentle with it.

Would it be idling too high or perhaps idling too slow or am I just expecting too much? If it idles too high going to be more severe clunking it in to gear. Maybe the cables have a bit of sag in them and the time between the gear engaging and the the revs coming up may be too far apart?

[Roughasguts]

Mine does that when the plugs are fowled.
Replace them or clean them up with carby clean.

Of course as you say cables do stretch so it could well be that.

[peterbo3]

Mariner/Merc gearboxes do not like being "eased" into gear. You should not go from F to R in one movement but F to N should be done crisply then N to R. At what RPM does the motor idle?

[fender22]

I think I know what you mean, you do have to do it rather crisply or the dog clutch scutters. Trouble is, you need a fair bit of oomph to put it back into reverse to do it crisply and then quite often you give it more than you intended to. Like I said, hard to finesse it into a ramp or pontoon. Maybe I have to much tension on my shift?
I'll check the idle revs next time I'm out. Where abouts should they be?

[dnej]

Had this same problem with my old motor.Fixed it be tuning it on the water,while under pressure.Should idle at around 1000 rpm,I would think.
I know what you mean about being dangerous.
David

[fender22]

I know what you mean about on the water. Thing always starts first go and ticks over like a gem out of the water at home when I flush it! Don't know anything about tuning? Do you just mean adjust the idle? How do you mean "under pressure"?. Thanks for your help!

[Blackened]

G'day

Tuning: adjusting the fuel:air ratio by adjusting the mixture screws on the carburettor/s. If you're unsure, get a mechanic to do it, it can be a bitch if you don't know what you're doing.

Under pressure means under load, on muffs at home the engine isn't under any load, therefore may give a false impression of how its running.

Dave

[ozscott]

Mate - I bet you pounds to peanuts that you have shit in the float bowls of the carbs - strip them down and clean out the idle jets in particular. Put it all back together and chances are you will have a kitten at the ramp...very common with 2 stroke carb motors that are not used enough - especially when not running fuel out of the carbs (but thats not a good idea either because for a short time the motor runs on with little or no lubrication).

Cheers

[ozscott]

...ps. Classic symptoms are that it will start when cold and run well and then fire off onto the plane like a bought one, and runs well at revs, but bring her back in on the return trip and she starts to stall just as you bring her back to idle and take her through the gate from forward to neutral/reverse.

Cheers

[trueblue]

carbs... just need a clean out. New set of plugs just to make sure.

[sherkier]

Take your cowling off at ramp and see if it idles better,if so the chaces are you have a exhaust leak !Had this problem with a 60hp evinrude and when we striped it down the corosion was to far gone to repair!Had to buy a new motor.Just a thought.

[BM]

I'm hearing several issues here.

First, when idling at home on the muffs, does it idle smoothly or does it tend to "fart" or sort of missfire every so often?

You mentioned requiring effort to put the engine into reverse"crisply". If it takes some effort to put into gear then the cables may require replacing (they get tight over time).

Someone mentioned 1000rpm idle. No. 750 rpm max for your V6 (well, for all engines really). Thats 750rpm IN GEAR. Which will be around 800rpm out of gear (on a healthy engine).

There was a service bulletin issued a long time ago for the older Merc fuel pumps (say 1990 onwards). Called for the replacement of the fuel pump diaphrams (about a $25 kit) in order to combat a low fuel pressure problem at idle or low rpms. This often causes the "farting" or "popping" on the muffs. This is also caused by carbs set incorrectly and butterflies not fully closed which causes the engine to run lean at idle or low revs and "pop" or "fart" which is actually a mild backfire.

Some model V6 Mercs have adjustable carbs, others don't. If yours does then they should be set to approx 1.5turns out from lightly seated.

But you really need a base to start from. Need to know that the compression is good, timing is right and carbs are synchronised. Also need to know that the ignition system is good on all cylinders and that the plugs are good. If all that is fine then its fuel pump and probably carb stripdown and cleanout. Also need to make sure you are using good fresh fuel and good quality oil.

Cheers