End of my rope HELP 43 power loss

"I have a 1990 4.3 that has be

"I have a 1990 4.3 that has been making me nutz. I asked last fall about stalling after the engine was up to temp. With your help I got that straighted out. Friday we were 14 miles from the marina on lake Erie and decided to go in. Earlier I thought the boat was lacking in power but we had an additional 300# person with us so I didn't think much of it. On the way back in it took forever to get on plane and ran ok for about 6 miles then it lost power and we limped the rest of the way in. I have changed the water separator and the coil and check the ESA for proper operation. Planning on rebuilding the carb and replacing the fuel pump. I'm just tired of chasing. What I could really use is a GOOD mechanic in Western PA. Not just someone like me, that charges $75 and hour and still can't find anything, but someone that can fix it. Any suggestions?"

Have you checked out your spar

Have you checked out your spark plugs & plug wires? Have you done a compression test?

"Yes, the compression was with

"Yes, the compression was within a pound or 2 of 155 on all cylinders, and I put new wires and plugs in as well. That's what is making me so nutz about this thing. I'm fairly mechanically inclined and grew up working on non electronic ignition engines.

I put it back in the water and ran it today, still the same problem. It seems to be at it's worst when the motor is warmed to 160 on the gauge. Once it cools down after sitting, it runs fairly well till it heats up again.

Thanks for the reply Chuck."

I'm leaning towards a fuel

I'm leaning towards a fuel delivery problem. Check the anti-syphon valve function and also the fuel tank vent line for a restriction. You may also want to consider installing a temporary fuel pressure gauge to see what the fuel pump is doing.

"a flapper (exhaust water

"a flapper (exhaust water shutter) might have fallen off into the Y pipe and be choking the exhaust..if not that, I might throw a coil on it if you haven't already"

"Sorry for the name difference

"Sorry for the name difference, I tried logging in from home and couldn't for some reason, just my luck. My wife calls me "Murphy".

Thanks guys, I did open the fuel cap while running to see if that helped, it made no difference. What's the best way to check for the flapper? Any idea why it would get worse when warmed up? Could it be a cracked head that tightens up when cool? I'm about ready to just order a new long block, but I don't have the time to do the install right now."

"visual inspection in the Y pi

"visual inspection in the Y pipe for the flapper. Long Block??? If you have 155 psi and good oil pressure, you'll have the same problem after you put in a long block. I don't follow the logic."

"At this point, I'm so fru

"At this point, I'm so frustrated that logic is losing to desparation. I'll look in to the Y pipe and let you know what I find. I did check and the point dwell is 35 degrees, timing is 8 BTDC and I unplugged the ESA which had no effect. It seems to be directly related to temp, although it doesn't seem to have the power it should from the begining."

"While you are check the respi

"While you are check the respiratory system, Have you checked your flame arestor for pluggage? Also the choke valve to be sure it is opening fully and staying there when warm? And what about that anti syphon valve? By the way what did you find before on the problem of "stalling after the engine was up to temp"?"

"I have checked and cleaned th

"I have checked and cleaned the flame arrestor, and the choke is working correctly and staying open. There doesn't appear to be any gas in the clear tubing. The new plugs, wires, coil and general tune up seemed to help the stalling although it will run very rough and stall now as well. What's the best way to check the "anti siphon" valve? Any possibility it could be a bad spark wire or two? They are new, but I've had bad new ones before."

Faulty wires can definatly bre

Faulty wires can definatly breakdown with heat. The AS valve is basically a spring loaded ball and seat valve that requires vacuum from the fuel pump to open. They can get gunked up and restrict fuel flow. You should be able to clean it with carb cleaner and check it for sticking / pluggage. This doesn't really fit in with the problem being temp related but worth a check.

"Where is the AS valve located

"Where is the AS valve located?

I will, tomorrow night, recheck compression both cold and hot and let you know if anything has changed there. It has also started backfiring while trying to accelerate when it's warmed up, could the spark advance have anything to do with these problems? Yet another random thought entering my mind."

"I hate to suggest random part

"I hate to suggest random parts changing, but if you have a lot of 18 year old parts on that boat... you might just cure the problem by taking care of a bit of 10 year overdue maintenance...that way you dont have to worry about wasting any money... That's why I suggest flappers and coil...those things rarely live 18 years.

What condition is the outdrive in? You wouldn't be the first person to complain about the engine lacking power as the outdrive is having a major bearing meltdown....and taking an extra 50HP just to turn"

"Well said. Could be coil but

"Well said. Could be coil but he did say he changed it in his original post. About the advance mechanism, if you have never checked it you definatly should. I also own a 1990 4.3 and when I rebuit it the centrifigal advance was bound up with rust and such. Took a little work to get it freed up and working smoothly. Yours is likley in simalar condition and may be binding worse with heat."

"That was in the back of my mi

"That was in the back of my mind as well. I had the boat serviced last spring and told them to go over everything. I even supplied new bellows and bearing but was told that everything was in great shape. Of course these are the same people that didn't mention the sparkplug boot that I had broken and they "supposedly" checked the compression as well. It would make sense if a bearing were tightening up as it warmed and then loosen up a bit when cooled. I guess, I'm off to pull the outdrive. It's just a shame that you can't find a "GOOD" place to have a boat serviced around here any more. No pride in workmanship. I suppose the whole 18 year old thing is what had me looking a new motors."

"thing is, the "long block

"thing is, the "long block" or main part of the motor is one chunk that has no problem surviving 18 years in a boat if it basically gets it's oil changed seasonally and is winterized, so I think you'll probably find it's ok.

Another thing that could be happenning (and I have lost track of what was checked and not checked) is water from a failing exhaust manifold or riser could be flooding the cylinders slightly, wetting spark plugs....then once it sits and dries, away you go again....A flapper stuck in the exhaust can certainly cause the water to back up into the cylinders also contributing...but again...18 year old manifolds are quite overdue for inspection and likely replacement....and we've heard of several brand new long blocks being destroyed by old exhaust manifolds this year around this board so that's part of what sets the alarm bells off when someone wants to replace the only good part and bolt all the old ones back up to it...If you want to abandon trouble and repower, buy a complete drop in motor that has all new components- everything on it. There was aplace selling complete 2008 Mercruiser 4.3's for around $3800 with manifolds and starter, ignition, alt, whole ball o wax on evilbay recently"

"I saw those on ebay, if I wen

"I saw those on ebay, if I went that far I may just do the entire drive as well. Only problem is, I just don't have 8K lying around with nothing better to do with it. Guess I'll just have to get this figured out. Which bearings are most prone to seizing on the outdrive? I just changed oil in the outdrive a few weeks ago and it was clean, so I'm hoping it's nothing internal."

"wel, just recheck the level,

"wel, just recheck the level, and then drain a bit of oil out - if the oil is still clean and not gathering shiny bits, you should be fine...the outdrive is way down the list from flappers and exhaust components in probability...
There is also a lot of threads on these boards about people getting an air bubble when filling Cobras and wiping out the upper gears do to low oil level...quite a specific method some say for filling properly"

I will recheck level and check

I will recheck level and check for metal flake tonight. Won't have time till tomorrow to check the flapper though.

"Long story short, I screwed u

"Long story short, I screwed up somewhere along the line. When I checked compression this spring I must have still had fogging oil in the cylinders or something. I decided to recheck the compression and found two cylinders down drastically, so it looks like I'm off to rebuild or replace. Any recommendation on buying Reman or rebuilding this one? I can buy a Jasper reman for about 2K, with a 3 year warranty.

Thanks for all the help."