mariner 75 "coughs" on tick over

andy9466 · 14 August 2007, 22:21

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 · 14 August 2007, 22:36

Maybe idle is too slow?

andy9466 · 14 August 2007, 22:44

Quote:

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 · 14 August 2007, 22:50

Are you running surface gap plugs?

andy9466 · 14 August 2007, 22:53

Quote:

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 · 14 August 2007, 22:58

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 · 14 August 2007, 23:03

Quote:

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 · 14 August 2007, 23:07

Quote:

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 · 14 August 2007, 23:43

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 · 15 August 2007, 17:34

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

watersideman1 · 15 August 2007, 19:08

try using BUHW plugs they seam to run cooler & give a better tick over
also check the carb butterflys are all shut at tick over or it cause all two strokes to cough
this was a very comon problem on 1980-1999 engines

Turbodiesel · 15 August 2007, 19:51

Firstly, check the carbs are Synchronized, if not they backfire on tick over. Causes damage to your fuel pump diaphragms and will melt the plastic pulse pipe outlet from the block.

Each carb has a adjustment srew (philips head) with the engine at tick over or siwtched off, undo each screw so the butterfly is loose. Then push the link rod down so all the butterflys are shut, then do the three screws up tight again. Make sure the center carb has a very small gap between the roller and the cam, as this is your pick up timimg.
Easy as that.

andy9466 · 15 August 2007, 23:49

Quote:

Originally Posted by Turbodiesel

Firstly, check the carbs are Synchronized, if not they backfire on tick over. Causes damage to your fuel pump diaphragms and will melt the plastic pulse pipe outlet from the block.

Each carb has a adjustment srew (philips head) with the engine at tick over or siwtched off, undo each screw so the butterfly is loose. Then push the link rod down so all the butterflys are shut, then do the three screws up tight again. Make sure the center carb has a very small gap between the roller and the cam, as this is your pick up timimg.
Easy as that.

will check this as i think this maybe the problem as i had a cdm module fail on me at the end of last season and i thought it was a carb problem so i removed them and cleaned them all ,so maybe knocked the adjustment out a little bit.
thanks again for all your advice
andy