Mercruiser 250 CID 165hp straight 6 problem

[cdnviking]

I am having an intermitent problem with this engine in my boat.<br /><br />When I run at around 2500-3000 rpm and do some modest "wave hopping" in <br />Southern Georgian Bay, occassionally my engine just "dies" (stalls). It usually decreases in idling speed and if I increase the throttle, it dies completely.<br /><br />When I restart it and give it some throttle, it behaves like it is either <br />"fuel starved" or being "flooded".<br /><br />Usually, the "fix" involves stopping the engine, opening the engine cover <br />and pumping the fuel bulb until line pressure is restored, then restarting <br />the engine and running up to 2000 rpm @ idle, THEN re-engaging the <br />transmission (which usually behaves normally then).<br /><br />My mechanic cannot figure it out (without much expensive "diagnosing"). <br />Besides, being the height of the season, I am likely to have to wait till <br />mid-september before he could run up my bill.<br /><br />Any ideas?

 

[Don S]

Re: Mercruiser 250 CID 165hp straight 6 problem

You shouldn't have a fuel bulb on an IO, so loose that. Then check for air leaks in the fuel system with a short piece of clear hose between the fuel pump and tank. Check it right at the fuel pump.<br />If there is air, check the connections. Also check the fuel pickup tube in the tank for blockage on the screen and check the antisiphon valve.

 

[cdnviking]

Re: Mercruiser 250 CID 165hp straight 6 problem

I have dual 18 US gallon fuel tanks with a tank selector valve (manual) inline between the tanks and the fuel pump on the engine.<br /><br />Should I still loose the bulbs? If I switch tanks, how do I prime the line?.<br /><br />I am wondering if it is time to change the fuel/water separator filter. If I hit a huge "bump", could it mix water already separated with the fuel?<br /><br />This ONLY happens when I am wave running in choppy water. On "smooth seas" the boat runs great (except for a bit of cavitation, but the prop could use a rebuild as the mouth of the river where the marina I dock at is a tad shallow).<br /><br />It is an old Safe-T-Mate Admiral II (1975).<br /><br />Someone suggested changing the shift lever cables but my mechanic (marina, not auto) said they are working fine and it isn't the cutoff switch on the cable causing the rough idle or inability to throttle up (most of the time, throttling up when this happens causes the engine to stall, but gradually, not an immediate cutoff).<br /><br />Sorry for any "silly" questions, but I have been out of boating for over 25 years and the memory isn't what it was.<br /><br />Regards

 

[John Carpenter]

Re: Mercruiser 250 CID 165hp straight 6 problem

Is it possible that you have some sediment or trash in the tank that is being stirred up by running in choppy water? Does it make any difference which tank you are running on?

 

[cdnviking]

Re: Mercruiser 250 CID 165hp straight 6 problem

no, not really! I used one of the two for the balance of last summer (bought the boat in august) and it did the same thing. The other tank had older fuel in it.<br /><br />I haven't checked for fuel tank ventilation yet. I guess I should ensure that there is enough inbound air into the tank to prevent vapour lock.<br />A suggestion has been made elsewhere that hitting a good sized wave might "swish" the fuel around, blocking the ventilation hose temporarily, causing a vapour lock.<br /><br />The engine seems to behave more like it is flooded. The more throttle I apply after the stall and restart, the lower the rpm's go and if I apply throttle too fast, the engine stalls right out. It is a really sickly sounding engine until whatever is causing this works itself out.<br /><br />This is not a permanent condition, it just happens sporadically (but frequently when wave "jumping")<br /><br />Anything above about a 1.5 ft (approx .5 metres) swell seems to cause this.

 

[rbezdon]

Re: Mercruiser 250 CID 165hp straight 6 problem

I would definately do what you suggested and change the seperators. Sounds like the engine is trying to run on water (or air).

 

[ziggy]

Re: Mercruiser 250 CID 165hp straight 6 problem

cdnviking, i got one of those engines too. sure is as easy as were gonna get for working on. are ya sure ya have a fuel water seperater? the fuel pump has a bowl on it too. when i first got my old old boat, it had issue with looseing rpm's too, and hard to start afterwards(though not nessesarily in rough seas). that problem, for me was the fuel filter. it looked horrible. ya could have some stuff in the tanks pluging up the fuel pick up or an air leak as suggested too. since ya got duel tanks and it happens on either or i wonder though, both fuel pickups pluged with crap?, air leak between the fuel diverter valve and fuel pump, perhaps? both fuel tank vents plugged? both anti siphon valves malfuntioning?. to me dual tanks is somewhat of a help for diagnoisis. ya could perhaps do the remote fuel tank thing thereby eliminateing anything prior to the fuel pump. i've never heard of a i/o with a primer bulb either. if dons says loose it, i would. i don't have one. since ya are able to prime it. and it works when ya do. i'd think back to the fuel filter (starvation) again to me. i agree with vatter41 too, if ya really do have a seperater, make sure the water is out and eliminate that possibility. <br />if ya got old fuel in one of yer tanks, i'd be useing it up too. it's already old and will be older next summer. maybe it's already to old even. <br />ya say ya like 2500-3k. me too. have ya tried a wot run? see if it chokes and dies, the fuel filter is cheap and easy to R&R. might be money well spent and eliminates that from the condition too. there's also a fuel screen right at the carb too. it's cleanable. <br />it hasn't been mentioned this time, but i read of a quick way to check yer fuel vents. open the gas cap after the problem and let some air in there, see if that fixes it.<br />have ya done anything to it maint. wise? tune up parts seem to always be good for a boat. though it don't sound like that's yer issue. <br />good luck on the 75 safetymate, my 72 is on going maint., all the time. and my pockets are runnin on empty. but i'm havein fun boating. hope ya find yer issue. this board will be VERY helpful for setting ya straight. there's much knowledge here to be had from many people here. might not be me as i'm just another joe boater though. i only happen to have the same engine as you is all. have fun and keep askin questions, bet you'll find the answer here on this fourm..........

 

[cdnviking]

Re: Mercruiser 250 CID 165hp straight 6 problem

Yes... had a full tune up done at the beginning of the season, points, cap, plugs, wires, rotor, etc. <br /><br />They setup the engine quite nicely (the marina mechanic that is). The mechanic has had a look at the carb since I told him of the problem and he can't find (on cursorary inspection) anything wrong. He even broke out the timing light and reset everything for me. The problem still pops up intermitantly.<br /><br />I am going to check all the filters and connections when I go up this weekend (as suggested by many, thank you). I am also going to disconnect the fuel lines from the engine and reverse feed air (low pressure) to ensure the vent ports are free from obstructions. <br /><br />I will also check the screens as well.<br /><br />The other thing I want to try is blocking one end of the line and evacuate the air from the other end to see of the bulb collapses (perhaps this is causing a major fluctuation in pressure in the line during high fuel demand times, starving the engine of fuel). I work in construction, so I can borrow a small vacuum pump for the job.<br /><br />Thanks again for all the valuable suggestions. My boat is a keeper, well worth troubleshooting these minor issues. I will post what seems to fix the problem so others can benefit (when I know for sure the problem is fixed).

 

[cdnviking]

Re: Mercruiser 250 CID 165hp straight 6 problem

Vatter:<br /><br />Like you said, air.<br /><br />The carb sounds like a jet sucking air when this problem occurs.<br /><br />Thanks for the memory jog! LOL!<br /><br />I will start with the inline seperator filter first, then on to the screens, etc.

 

[cdnviking]

Re: Mercruiser 250 CID 165hp straight 6 problem

Seems we identified the problem over the weekend.<br /><br />Seems the problem actually originates with a "loose spring" in the carb, <br />according to my mechanic.<br /><br />Hitting a good size wave basically knocks the choke partially closed and the <br />engine sucks to choke closed the rest of the way.<br /><br />I discovered this weekend that the way to remedy the situation is before <br />attempting to restart the engine, I put the shifter in neutral and move the <br />lever forwards a couple of times, then put the lever back where the button <br />releases and it is ready to put in gear. I restart the engine and voila, no <br />more hard idling, etc. Seems that priming the engine with the shift lever in <br />neutral resets the choke and I am "off to the races".<br /><br />Short of a complete carb overhaul to change out a somewhat tired old spring <br />(that works 99 % of the time), all I have to do to prevent this condition is <br />take greater care when approaching another boat's wake. Hitting it head on <br />and launching my boat over the wake is the principle cause of this engine <br />condition, but taking the wake at a more progressive angle eliminates the <br />hard jarring the choke gets and prevents the choke closing.<br /><br />I might rebuild the carb next year, not sure.<br /><br />Thanks for all the hints.<br /><br />Regards<br />Bill/Cdnviking