350ci-260hp mercrusier rev drops

[johnno351]

Hi, Bit of background first.
I have only just got this boat (1986 21 foot chapparral 215 xlc) and it was all running fine, till the other day when I took it off shore about 10 miles.

It ran fine all the way out and didn't miss a beat, we dropped anchor for a few hours and had a swim and some lunch then pulled the anchor and headed back.

This is when the fun started, after about 10 min's of sitting on about 25 knots 3000rpm it started to drop revs like it was going to stall so I backed off and it seemed ok but if I put the revs back to 3000 then it "popped" through the carb.

So I continued on at less revs then it started at those rev so I dropped it some more then it happened again, if I put the revs back up it would pick up for 10 or 20 sec's till popping and dying again.

In the end it was running us in at about 1400 rpm doing about 5 knots so I thought well at least we are moving so I left the rev's there but after another 10 min's it died, it would restart straight away and run again at 1400 rpm but die again in a min or so.

This went on for a while and nearly go me back to shore but then died and didnt want to restart, we did get it going a couple of times but then got a tow in from a passing boat (only half a mile out now).

So I get it home and thought i'll try to start it to run on the ears to clean the salt out and it ran fine.

I went out the next morning and bought a new fuel/water seperater filter and took it down the river to test it and it seemed fine for a few hours, pulled the kids around on the tube and had no issue till it dropped revs again so I took it out of the water down to get more fuel to rule that out, put in about 100 litres (20 gallons) and put it back in the water and it ran fine again for 40 min's till it started again, never to the same extent as the first time in the ocean but was not pushed on as I wasn't stuck out at sea.

My first thought was the fuel pump but I don't understand why its good then bad.

Any thoughts??

ps. sorry its a long post but I thought if I give as much info as possible it would help.

 

[johnno351]

Re: 350ci-260hp mercrusier rev drops

One more tid bit, I did just replace the belhousing on the outdrive, new bellows and shift cable and trim sensors.
The shift is smooth in or out of the water and the ignition interupter is working fine.

 

[rbh]

Re: 350ci-260hp mercrusier rev drops

Its either fuel or electrical, I am leaning toward electrical, points/cdi box, bad plug wires ETC. fuel I have noticed is all or none, its those electrical gremlins that get ya.

 

[sarantis]

Re: 350ci-260hp mercrusier rev drops

it seems to me more of a fuel problem than an electrical one.First thing you have to do is to empty your tank and inpect for crasp.It's possible that the dirt cloggs the grid that usually exists at the top of the tube that is adjusted upon the tank.As an alternative you can use an external tank directly to the pump.As another alternative you can use a clear hose from the fuel pump's output to the carb's inlet and check if during the rpm dropping down is full of fuel or has been filled with air bubbles.if up to here you are ok then check your filter at the carbs inlet and come back again to report.

 

[Don S]

Re: 350ci-260hp mercrusier rev drops

Checking timing when the prolem occurs and checking spark would be one way to check the ignition systme, but I would bet you have problems with the boats fuel system, not the engines.
Might read this thread and do some testing. http://forums.iboats.com/showthread.php?t=283269

 

[johnno351]

Re: 350ci-260hp mercrusier rev drops

OK, I have found the cause of my problems, had to cut away a bit of floor to access the fuel pickup stem into the tank, the filter in the stem was very blocked up.

Thats the good news, the bad news is as posted above the running lean has lead to a blown head gasket, so my job tommorrow is to strip the heads off.

Thanks for all the advice.

 

[johnno351]

Re: 350ci-260hp mercrusier rev drops

Will do, its just bleeding a little water to the oil so I hope we have got it early too.
It was still running today but I noticed it was hard to start and when I looked at the dipstick the oil was clean but under the valve cover caps was milky.

 

[johnno351]

Re: 350ci-260hp mercrusier rev drops

yes I know that car parts stay in cars

Only pain is i'm in Australia and they over charge parts here for mercruiser so bad that I will have to order from the US so will have to wait for them to get here.

Locally it was $400 just for the 3 bellows rubbers I dont mind paying a bit more but thats insane.

 

[Bondo]

Re: 350ci-260hp mercrusier rev drops

Will do, its just bleeding a little water to the oil so I hope we have got it early too.
It was still running today but I noticed it was hard to start and when I looked at the dipstick the oil was clean but under the valve cover caps was milky.

Ayuh,... I'd do a Compression Test before ya pull the Heads...
I Don't think the headgaskets are Bad...

Hard to turn over would more likely be leaking manifolds/ risers...
The little bit of Goo in the valve covers is merely Condensation, which'll burn off when it's run up to temperature...

 

[funk6294]

Re: 350ci-260hp mercrusier rev drops

You may check your local auto parts house and just see if they carry the gasket you need. The Fel Pro part number for a 5.7L marine head gasket is 17030. You might get lucky and they can order it for you at a resonable price.