7.5 honda BF75L wont stay running

Hey hoping someone here can help me I have a older 7.5 honda BF75L (maybe 1984 or 85) I have done a carb bath put on new seals, new fuel line, primer ball, and connector. Checked spark and have a fuel water separating filter. After all that the motor will run and idle fine but while in gear (in a barrel or under a load) will die after about 15 to 20 minutes of running?!.... After it dies it doesn't want to start afterwards. If I leave it alone for a day or two and come back to it. It will fire right up with 3 pumps on the primer ball and choke out 5/8 to 3/4 the way out (normal starting procedure for it) I don't have a lot of money so am doing there repairs myself. Had a mechanic give me instructions on how to set the carb adjustments, was nice enough not to charge me. If anyone can help it would be greatly appreciated.

Hi flyin_sweed...(clevr hndle!)
Sorry she's giving you trouble.
This problem could a sign of a couple of things.
The first, and most alarming, is that your outboard may be overheating. These old girls are meant to run fairly cool. Around 160 to 170 degrees Fahrenheit TOPS. If it is overheating, each time you allow it to get to the point it shuts itself off, a little more damage is incurred and the longevity of the engine is at stake. So, ensuring that overheat is NOT occurring is of the utmost importance. As it approaches the temperatures I just listed, if the temp continues to climb, you must be prepared to shut it down before it gets much higher and figure out why. If the pee stream is strong, then it is likely a thermostat issue. Or. it could be a buildup of deposits in the coolant passages. Sometimes a flush of pressurized water BACKWARDS through the head and engine block can do wonders. Many people use vinegar or a product called "Salt Away" to aid in the process. Of course, this is done with the thermostat removed to gain access to the passages so it is an opportunity to re gasket and replace the stat. The use of compressed air AND water can work well when "backflushing" too.
Also, I don't recommend running an outboard in a closed container for more than 2 or 3 minutes at a time unless there is a steady resupply of fresh, cool water constantly flowing to keep the engine cool.

If you find the engine is cooling properly but still shuts off after a time, try running it wth the cover removed to see if that makes a difference. If that has positive results, then it's likely the engine has an exhaust leak and is "choking" itself out under the cover. This is a common occurrence on these old Hondas ( and others) and requires that the powerhead be removed from the oil case and new exhaust gaskets fitted. When this happens, it afford one the opportunity to clean the oil sump and filter and many choose this time to assess and repair/replace internal engine components like main and rod bearings.

There's a couple of ideas to check out. And, while it could still be a carburetor problem, I see these as more likely given the symptoms you've listed.

Let us know what you find and
GOOD LUCK!

Thanks for the info and I will definitely check into that. The water stream is very strong (but doesn't seem to get warm) and I replaced the thermostat and gasket beginning of last season so I will definitely be doing the back flush. A little description on how to do that would be very helpful as I have never done that before. Btw "flyin sweed" is what I named my boat since it has a good strong Volvo Penta that flys across the water thanks again for the quick response.

Also , when you place the hood on your ignition wires may come to contact with a ground or short between themselves. You can not tell what kind of spark you have with the hood on.

Ok so it wasn't over heating. Never got over 120℉ pee stream 63-70℉ water in barrel was @ 58℉ ambient temp @ 65℉ will take it to the lake and run it with the hood on and see what happens. Thanks again for your help.

Not getting over 120 deg. is an indication that the thermostat is not closing. If it's not closing....then it might not be opening either. What I mean by that is that sometimes a thermostat gets "sticky" and will sometimes stick closed but then, suddenly, open up and then stick in the open position. Yours is stuck open at present with that engine temp reading and that should be addressed asap. A stuck open stat causes poor combustion and carbon deposits to rapidly build up on the pistons, valves and valve stems. This build up can cause piston rings to stick and crack and cause valves to hang open and burn. That is why it's just not a good idea to "fix" a overheating issue by removing the stat and leaving it out. And, of course, we all know a stuck closed stat will burn her down quick!

Well I tool the thermostat out and tested it in pot of water on the stove. The thermostat started to open at 135℉ and seemed to be all the way open at around 155℉ and everything looked pretty clean inside the housing. So if the stat is working why would it not come up to temp? I ran it for about 10 minutes....

I still think the thermostat is bad. Yes it opens...5 degrees too soon in this case. And then fully opens.....ok. But....Does it "modulate" in an efficient manner?

The way it has to work is that it begins to open and there is a FLOOD of cooler water entering the engine and then reacting with the stat's wax sensor...whereupon it starts to close up again. Then, there is hotter water acting on the sensor, causing the wax to expand and it opens again.....open-close-open-close-open....in a fairly rapid "modulated" manner. And that's what it does up to "operating temperature". When the engine reaches that "setting"....the stat STILL has to modulate...close-open-close...to maintain that temp.

What is probably happening is that it is "sluggish" in getting the movement done. So....the engine will run too cool for quite a long time...but then....as the fire continues to burn and a slooooow heat up occurs.....the engine will likely tend to overheat as the stat is still not keeping up the steady "fluctuation" needed and the margin for error is now on the OTHER end of the spectrum.

So, I still recommend a new stat.
It's the only way to prove me wrong ;~)

You make an excellent point. I would have never thought of that. Good thing is I can get the stat and gaskets for $40 I will get that and let you know what the outcome is.

I hope that gets it done. Because, if it isn't the stat, then that would mean there is a bad seal between the block passage and the head passage. That would HAVE to be in the thermostat housing somewhere. It could either be caused by some missing metal on a passage wall...as in a hole of some sort. Or, it could be that the thermostat "mounting" surface is irregular and not keeping the cool water out of the cylinder head when it is supposed to. The only way I know to repair these when you find that corrosion has taken a toll is to epoxy and then hand shape with a file and sand paper or a Dremel tool. JB Weld Aluminum formula works pretty good.

With it having been run that cold for probably the last few years of it's life, you may want to consider a decarbon treatment or two. There is a product called Berryman's Chemtool that does a good job as well as some others such as 3M induction cleaner. For those of us on a budget....water works pretty good too. Any of these liquids "spritzed" into the carb throat with a spray can or bottle while the engine is throttled up, will tend to soften and loosen the carbon deposits built up in the combustion chamber. You have to be careful not to introduce too much too fast and keep it to as fine a mist as is possible. Doing 3 or 4 10 minute treatments once for every few days of running is better than doing a 1 hour treatment only once.

I don't think you can go wrong with a new thermostat but you should test the new one right out of the box. There has been a BIG problem with aftermarket parts being sold in the U.S. lately and I've gotten to where I've lost faith in the replacement parts stream. But, hopefully, if you're buying from Honda or boats.net (which sells genuine Honda parts) it will be a quality replacement.

Good luck.