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1987 four winns 260 mercruiser sudden power problems

F

frank_winns

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"Purchased this boat in May of

"Purchased this boat in May of this year. The person before me had the carb rebuilt, tune up, cap rotor, wires, coil. All look to have been replaced. Fuel filter is newer. Drove boat all summer. Last week a buddy and I went out and the boat was running great. About 45mph, when suddenly the motor bogged out and stalled. The tach has been inop since boat was purchased. We started the boat up and was fine on take off but if opened all the way up the boaT would fall on its face like there was no gas. Limped it back to dock. Thought we found a faulty supply hose. We fixed that and went back out. 20 minutes later it started doing it again. Mind you this boat has only missed 3 weekends of not going out. GPS I have driven 500 miles. So saturday I remove tank cover, check vent for tank. No unstructions, remove pickup, nothing on screen, remove antisiphon valve and just put straight tee for testing purposes. Replace fuel filter/seperator. Drain old fluid into glass container. No contminets or water. Take boat out for over a hour. Boats running 48 mph running great planning great. All of sudden boat starts to gradually slow down. Temp outside is under 70 this day. Was cooler other day also. Go to plain, boat can barrely get out of own way. Has no backfiring, or running out of fuel like the ohter day. Boat would barel hit 35mph. Did notice that if I went from full throttle to neutral motor would die. Gas gauge would go to e and boat would stahl. I beleive the tank to have enough gas. Do not want to fill it all the way up incase I need to remove the tank. Plus Oct 15 rack and launch closes. I am a auto mechanic so working on things is not a problem. Just puzzled that all summer no problem. I didn't pull plugs, or take a compression reading. It does have a mechanical fuel pump. I figured if it was the pump it would run like crap all the time. Just need some guidance."
 
Does it have a condenser in th

Does it have a condenser in the distributor?
 
""boaT would fall on its f

""boaT would fall on its face like there was no gas"

Does the fuel pump have a dome held in place with a inverted "V" clamp? Yes? There is a filter inside of it made of stone material or paper. Carb has a screen filter. There should be a semi-clear hose running from the pump to the carb. Disconnect it at the pump and probe the nipple it was attached to; it should be open and clean so it warns you when the pump diaphragm is leaking but can't if it is plugged.

If you find brown varnish from years of use plugging it, that may be part of your problem. Lift the top off the carb and see what is in the bowl. Brown granules of varnish may be in the bowl. You can clean out the carb but the pump will need replaced to get rid of it. BTDT."
 
"Well check all filters in fue

"Well check all filters in fuel. No contamintents found. Found coil to have carbon tracking. Replaced coil. Take boat out and still had lack of power. Had very big exhaust bubbles in water. On trip in noticed spark knock. All of sudden boat made loud noise stalled, caught self and had a very bad backfire. The motor was running with key off. Finally blew # 5 spark plug out. Cannot tell yet if plug was stripped, but had porcelin were plug wire connects. Not sure if electrod is in motor yet. When all this went down you could hear what sounded to be a nice fire in the intake. Just 1 minute before I had flame arrestor off. Thank god it was back on. I'm about ready to buy a jet ski."
 
See if you can find the remnan

See if you can find the remnants of the #5 spark plug and pull all the others. You're a mechanic so you should know how to read their condition and determine how each cylinder is operating.

It sounds like you have electrical/ignition problems. I would examine the entire ignition system and perform tests on all. Perhaps a burned exhaust valve caused the backfire and ensuing fire. The engine run-on w/key off can be a mechanical carb./fuel issue. Is there fuel in the sight tube from the fuel pump. Yes? Pump is gone. That would cause excessive fuel to be dumped into the engine causing the explosion. You have your work cut out for you. Good luck.
 
"There was no fuel in the hose

"There was no fuel in the hose from pump to carb clear. Not for sure yet, gasket by accelerator pump looked wet. Thinking maybe carb is dumping fuel. Most of ignition is fairly new. Saturday I will pull all the plugs and run compression test. Did notice condensation on 4bbl plates last night.Also will run timing check also. Just seems odd ran farily well all summer. Over night tarted running like crap. Thanks for pointers"
 
"" Did notice condensation

"" Did notice condensation on 4bbl plates last night."

Water in the fuel? Or, engine?

Don't trust what someone told you when you bought the boat. Re-examine the entire ignition. Look under the cap for carbon tracking; remove the rotor and look at the optic sensor (unless points ign.) for rust on the sensor. I replaced mine (rusted) and did away with missfire.

You should probably pull the carb. top and look for water and crap in the bowl, check the float drop, etc. A good dose of water may have killed the ignition until some fuel got in the cylinders and casued the backfire. I've heard of plugs being blown right out like yours. I have a 4.3L in an SUV that #2 & #6 plugs just work there way loose after a few thous. miles. Use a plug thread chaser with some heavy grease on it and clean the plug hole threads when the engine is cold. If that #5 hole is stripped you may be able to get a helicoil into it.


If you find water in the bowl, it is in the fuel tank. If you have alot of fuel in the tank, DISCONNECT BATTERIES, remove the vent line at the tank and use a stiff siphon hose to touch the bottom of the tank and siphon the water off the bottom until clean gas starts coming out. Then add 2 cans of SEA FOAM to the tank and fill it with pure gas, at least 91 octane to stop any pre-ign. or run-on. The SEA FOAM will clean out the carb passages of varnish buildup and help to de-carbonize some of the intake.

If only a 1/4 tank of fuel, dump in the SEA FOAM and fill it up. Sea Foam is also a fuel storage stabilizer."
 
"Well I was able to get the bo

"Well I was able to get the boat out of rack and store and on a trailer last night. Brought boat home and started to investigate. #5 had blown porcelin out not the metal. Was able to get the ac r43ts out. Began to remove the other plugs on the port side. 2 of the remainders basically broke the minute I put a socket on them. 1 was a autolite 26, the other was another brand. The #7 had stress cracks on porcelin when removed. On starboard side 2 plugs were actually marine plugs. They were in the best shape. Egg on my face, believed the lady before me that owned boat had people that had a clue. I did find most of reminents of # 5 in bilge. With plugs out and coil disconnected motor spun freely. Will do a compression check and hopefully get it in the water saturday. Keep you posted. I guess that coil could have been some of my problem."
 
"Sounds like the previous owne

"Sounds like the previous owner may have been taken when it was serviced. Somebody cracked the ceramic of the plugs when installed; didn't know what they were doing!!!

I think you will come out better than thought with new plugs, etc."
 
"Did a compression test. Found

"Did a compression test. Found compression ranging from 150 to 130 in #5 and # 7. Carbon probaly is cause. Put all 8 plugs in and engine fired up. Ran for over 20 minutes on trailer. Took down to water drove from the river to the rack and launch on the lake. About 30 miles. Boat ran like a champ. Believe I have a prop issue, the engine was severely over powering prop now. It was a spare prop. Had hit a log earlier this summer due to storms. At 40 I was able to hear the 4bbls open up. This wasen't happening before. Fuel consumption seems to be down now that its running better. Believe I remedy condition. Keep you posted."
 
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