Old boat help

Our club bought a 1990 Supra Sunsport in March. When we test drove it, it ran great (go figure). For the couple weeks after it ran great too. Then it started to go downhill. It hesitates under acceleration and eventually surges from 2000 to 3000 rpm, no in between. Itll run terrible then get over 3000 rpm and run fine again. The problem gets worse the longer you run the boat. Eventually it will hesitate longer and longer to the point where it wont get above 2000 rpm and just stay stuck at a half plane under full throttle bogged down. Also the idle gets worse and worse the longer you run it until it surges more and more at idle and eventually starts stalling.

First we tried a carburator cleaner and sea foam. That didnt work. Then we tried rebuilding the carb. That didnt work. Then I took it to a shop where they pumped out 4-5 gallons of water and redid the totally rusted points, that HAS to have fixed it right? Nope. Still exact same problem. We have replaced the fuel filter twice. The vent line on the tank isnt clogged. What the heck could it be?! The boat was old and sat for a couple years, which is not good...but it ran fine at first. And we have put gas in the boat a few times, so its not old gas.

We NEED this boat fixed for our club to ride and we dont have unlimited money to throw at it so I need to find the cause of the problem. Ive talked to 2 mechanics and both cant figure it out. Supraforums have been down, but I put a post up there a while back and noone came up with the answer. Someone on the these forums has to know something, please help us out!

Timing? Did you give it a full tune up? I would change plugs, wires, cap, rotor and swap the points style ignition with a pertronix ignitor kit and coil. That and make sure the timing is correct.

That sounds like a exhaust manifold/head or a corroded block issue.

I would pull off the exhaust manifolds and check out the heads to see if there is some break-through in the castings. You could also have a issue with the coolant channels in the block. When a motor sits for a long time without a rust preventative, you can get internal corrosion.

Check for vacuum in the block first. If it is leaking, you should be able to measure it by briefly interrupting water flow to the strainer. Water would show up in the oil fairly quickly.

Brett, we replaced the plugs, and then the mechanic worked on the points. Havent checked timing, but wouldnt bad timing cause it to run rough consistently (at all rpms and regardless of engine temp/how long it has been running)?

Karl, that sounds like a doomsday verdict...by "break through" do you mean cracks in the heads? And not sure exactly what you mean by the strainer interruption test putting water in the oil, but we checked for water in the oil when we bought the boat and it seemed perfectly golden. Not milky or black. We have changed it once and every time it has been checked the oil has looked good...so I dont think there is water in it. The shop did a compression test and to my knowledge didnt find anything abnormal, if that is related to what you are talking about.

Thanks for the quick replies!

When I started reading this post I was hoping you were at LSU and I could come help check it out. Someone in the club here has an old Supra that I've seen out on the water. A quick search revealed that you were at VT. Boooo! Ha!

Did they replace the condenser when they did the points? A bad one could potentially cause intermittent weak spark and also damage to the points.

I'm not to sharp with non-electronic ignition systems but I would check the timing, as previously mentioned, to cover all of your bases.

4 or 5 gallons of water was in the tank?

I keep going back to fuel delivery and/or the carb. Had friends boat similarly. Ended up being trash in the fuel pickup inside the tank. similar symptoms to what you're describing.

How bad was the carb with that much water in there??

First, be certain the fuel system is clean. Check the fuel bowls and needles and seat for trash. Clean the air bleeds by spraying carb cleaner in them with the little hose on the can held tight to the air bleed. Also check for vacuum leaks. Check float level, ensure no flooding out the boosters while idling or after turning it off.

Verify points are clean and gap is good, if you have a dwell meter even better. Check your ignition timing. 10* initial is good and should advance smoothly to 32*-36* by 2500-3000 RPM.

Does sound a lot like fuel starvation for the not getting to speed/not having power, and junkin carb or vacuum leak for the rough/wandering idle.

^^^^^^^^^^^ DO what this guy says. I had a similar problem on ly 85. Take out the points and check the swing weights that advance the timing in the dizzy. If they move freely, you are probably good, if not, get some good penetrating lubricant and get them to move freely. If they stick, it will do what you are describing.

I had a similar issue on my boat. No power in the low RPM range and the engine sounded really rough when you would give it gas but if I could get it to plane out it would work fine. I started with the same things recommended below (points, plugs, fuel filter, carb) but nothing worked. Turns out two of the valves had gone bad. I would try a compression test again if none of the other suggestions work out. My one and three cylinders both registered 0 when I checked them. I got the heads machines and I'm back in business.

Sounds like a dead cylinder. A fouled plug can cause these symptoms too. Start it and take your plug wires on and off one at a time. If one of the plugs is bad, when you pull the wire the engine will start to run better. Of course then you have to find what fouled the plug.

It can be doomsday. Typically, there is a bad channel in a head. The way to tell is to run the engine on the fake-a-lake and listen to it. Turn off the water for several seconds and see if it changes tone dramatically without water flow. Also, let it set for a day and take out the oil plug. See if water comes out first. That will indicate a corroded engine block or head.

If you have a metal fuel tank, the new gas has alcohol in it and will severely corrode the interior - causing all kinds of runability issues. The solution is to change to plastic and re-plumb all the fuel system with new hose. The alcohol will gum up the old hoses and render the carb useless. I had to completely rehab the entire fuel system on a 1969 boat before it would run well enough for a large lake.

TOUCHDOWNNN! Its fixed.

Turns out after the marina sucked the water out of the gas tank and redid the points that it was basically fixed. The problem was when I took it out after that, there was probably 1 gallon of gas in it. Since its nearly impossible to get all water out of the tank without draining and cleaning it, Im guessing some water managed to get in again causing the same problems. After adding 30 gallons of gas to the boat it ran flawlessly last night and again today. Not 1 stalling, no hesitation/bogging down. Even ran about 800 lbs of ballast.

Knock on wood that was all...I dont want to jinx it but right now its running great overall. Maybe itll act up again when the gas gets too low but Im beyond relieved/pumped.

If there is a lesson to be learned here it is that boats run better on gas then water.