Mariner 25 won't idle when warm

jwatson · 06 April 2015, 10:27

Had my sib yesterday. Ran fine for about half an hour, all throttle positions. Pulled my bro in the ringo, then it cut out. Got it going again but idles badly. Soon as I touched the throttle it starves and dies but if I give it full throttle immediately from idle it takes off like a rocket and stays flat out!! Got it back to the house and ran it on muffs to flush it out - ran as usual!!!! Bizzare! Need to get it sorted as the weather here in newquay is brilliant!! And sea is flat!

azzurro · 06 April 2015, 14:49

Quote:

Originally Posted by jwatson

Had my sib yesterday. Ran fine for about half an hour, all throttle positions. Pulled my bro in the ringo, then it cut out. Got it going again but idles badly. Soon as I touched the throttle it starves and dies but if I give it full throttle immediately from idle it takes off like a rocket and stays flat out!! Got it back to the house and ran it on muffs to flush it out - ran as usual!!!! Bizzare! Need to get it sorted as the weather here in newquay is brilliant!! And sea is flat!

Try changing sparks.
Other possibility is fuel line (as it becomes empty, the engine stops).

RIB-Teccie · 06 April 2015, 18:40

After doing the usual checks, I suspect some dirt in the slow running jet.

jwatson · 06 April 2015, 23:31

Stripped & cleaned the carb earlier & all seems to run ok. Also became apparent I wasn't getting full throttle.... Best hold on tight tomorrow!

RIB-Teccie · 07 April 2015, 07:41

You've not said if it's the yam mariner or the Merc one.

As the fault came on suddenly a burst fuel pump diapragm can also give those symptoms.

jwatson · 07 April 2015, 15:45

It's the merc one.
Seems to idle ok now. Would the diaphragm issue only cause the problem when hot?

jwatson · 07 April 2015, 16:08

The diaphragm would give that issue only when hot?

RIB-Teccie · 07 April 2015, 17:30

If the diaphragm gets holed fuel will get sucked straight into the bottom cylinder at idle (hot or cold) causing rough idling. It will be ok at full throttle until it bursts and there would be problems at all Rev ranges.

jwatson · 07 April 2015, 22:02

Right got you, because the pump runs off crankcase pressure from cyl 2?
As I said, ive cleaned the carb out & seems to idle well now, on muffs that is.
Could be worth whipping the pump off in the morning to double check though I guess ...

RIB-Teccie · 08 April 2015, 08:17

One trick you can try on the muffs is to warm the engine up and stop it. Then pull off the bottom ht lead and run and then the top one and run. That way you will find out if it off a pot. You will also know which one.

A1an · 08 April 2015, 08:20

Check the plug tips too, usually when the diaphram has holed the excess fuel in bottom cylinder washes the plug clean.

A certain way of telling is if you whip the pump off, block the "out" spigot with your finger and blow through the "in" one you should not feel/hear any air coming through the vacuum hole at the rear. If you do, the rear diaphragm is shagged.

kerny · 08 April 2015, 08:28

Now you have cleaned the carb and you say it's now working it will be fine. Any fuel left in the carb over winter gunks up into like a jelly. Should be okay now.

jwatson · 09 April 2015, 21:13

So I thought I'd check the fuel pump today, nothing wrong with it whatsoever as far as I can see. It's built into the carb though so doesn't have an inlet or outlet spigot and I'm not sure what it runs off! Went out round the bay for a few hours & idled fine. Was a bit hesitant / spluttery on pick up now & again mind.

RIB-Teccie · 09 April 2015, 21:20

Probably needs a blast to clear out the cobwebs.