mariner 75 "coughs" on tick over

[andy9466]

2002 mariner 75hp 2 stroke
when ticking over @ approx 500 rpm it occasionally coughs (like a little back fire) engine revs drop to virtually nothing then picks back up to 500 rpm.
the rest of the time it starts and runs fine.
i was wondering if any of you guys have ever come across this before.
any suggestions welcome.
many thanks
andy

[codprawn]

Maybe idle is too slow?

[andy9466]

Originally Posted by codprawn

Maybe idle is too slow?

thanks for the quick reply codprawn
i thought about this but it seems to be a definate cough maybe once every couple of minutes

[Nos4r2]

Are you running surface gap plugs?

[andy9466]

Originally Posted by Nos4r2

Are you running surface gap plugs?

no they are them what i call fancy ones
i think they are buhz w2

[Nos4r2]

Thats surface gaps.
They make the tickover raise a bit-it's quite possible it's been turned down too far to compensate.
Try the normal type plugs-from memory they should be BP8H-N-10 but best check them.


I prefer surface gaps though. They oil up less.

[andy9466]

Originally Posted by Nos4r2

Thats surface gaps.
They make the tickover raise a bit-it's quite possible it's been turned down too far to compensate.
Try the normal type plugs-from memory they should be BP8H-N-10 but best check them.


I prefer surface gaps though. They oil up less.

i will locate some of these plugs and see if it makes a difference
allthough due to work commitments cant try till the bank holiday weekend
thanks again for your prompt replys
andy

[Nos4r2]

Originally Posted by andy9466

i will locate some of these plugs and see if it makes a difference
allthough due to work commitments cant try till the bank holiday weekend
thanks again for your prompt replys
andy

Check the type though-I can't guarantee I'm right!

[AndrewH]

Andy

I had a similar problem with a Mariner 90 (albeit a slightly older one), that struggled on tick-over but was fine at revs. It turned out to be the diaphragm in the fuel pump that had given out. Should have been a rubber membrane over a wire mesh but the rubber had disintergrated completely. Net result was that engine was flooding slightly at tickover, but at revs when more fuel was needed then extra was used up.

Local service agent suggested the membrane should be replaced as part of service and he'd not seen one last much longer than 5yrs. Given yours is a 2002 this may be the cuase

(Apols for spelling ?? - too many peronis )

HTH

[andy9466]

THANKS ANDREW H
il' give the plugs ago first to see if this helps
then il' look at more technical things
cheers
andy