I actually changed the thermostat.
For anyone reading this who is considering something similar, the list of everything I did process wise, and how I would do it again chronologically, to get the engine going, without me having to worry about on water reliability, is:
Note, I did not do everything in this order, but having done it one time, this is how I would do it again.
Also note I have not yet changed the timing belt or tensioner or spring. I keep meaning to, and I keep finding other things to do instead. Frankly, the existing timing belt looks brand new, there are zero cracks, and I have inspected every inch of it on the inside and out. The tensioner makes no noise at all. The belt still has all of the factory printing on it, and there appears to be very little wear on that printing. I do plan on swapping the timing belt this winter.
I did set the idle higher than the factory recommendation, it is idling somewhere around 1000 RPM. When I balanced the carbs, I did not have a functional tach, and I though the carb balance was lousy, but it turned out my original idle was just over 500 RPM after warm up, so of course it was running lousy.
Having done it once, I would have no real fear of doing it again, nor would I shy away from buying another Honda engine. Overall the engine has been pretty easy to work on, most of the issues I had I created on my own and they were easily resolved (broken water pump bolt from over tightening, messed up the gear selector location while the lower unit was off, did not use enough grease when installing the impeller the first time, I probably ruined the original fuel pumps buy cleaning the diaphragms with lacquer thinner).
Overall the only real disappointment I have with the Honda is that is it not 150hp. The boat would be much fast with an extra 60hp.
For anyone reading this who is considering something similar, the list of everything I did process wise, and how I would do it again chronologically, to get the engine going, without me having to worry about on water reliability, is:
- Drained oil from engine
- Flushed oil tank with diesel fuel to soften up old oil sludge, let the diesel sit in the oil tank for a couple days
- Drained diesel fuel and again let engine sit for a couple days
- Sprayed oil into cylinders through spark plug holes
- New oil filter and new oil
- Removed lower unit (the old impeller in the lower unit made spinning the engine by hand nearly impossible)
- Turned engine over by hand as many revolutions as my forearms could take, to oil the piston rings and oil control rings, spray extra oil, too much oil will always be better
- Spun the engine over on the starter with the spark plugs removed to prime the oil system (I did not do the remote oil filter idea I had)
- Removed thermostat and cleaned everything I could reach through thermostat port
- Disassembled and cleaned the check valve for the water flush port in thermostat housing casting
- New flush port check valve orings and re-assembled
- Replaced thermostat housing without thermostat (thermostat not installed)
- Cut the hose bib end off a 5/8" garden hose and connected that hose from house faucet directly to stainless steel water tube in the engine mid section, this eliminates the water pump impeller as a variable.
- Flushed engine with water in the forward direction (water flow from mid section stainless tube). Before you do this, make sure your intake manifold is bolted on, or the intake ports are taped shut.
- Flushed water through engine backwards, with no lower unit attached, to clean out whatever junk was in there (water flows through flush port and goes through thermostat housing since no thermostat is installed). Before you do this, make sure your intake manifold is bolted on, or the intake ports are taped shut.
- Installed new thermostat
- Used a portable fuel tank and test ran engine on un-rebuilt carbs with no lower unit, just to make sure there is no rod-throwing event, in which case the project is over...
- (here is where I would replace the timing belt and tensioner and spring, but alas I have still not)
- After first test run, replaced the new oil filter and engine oil
- Cleaned all carburetor valves and orifices but did not replace hard parts
- Rebuilt carburetors with new orings and gaskets
- Cleaned all the metal fuel lines with lacquer thinner, let them soak before re-assembling
- New fuel pumps and orings
- New engine block mounted fuel filter
- All new fuel hoses inside power head
- New fuel quick disconnect coupler in power head (from newer BF90D, the old version was discontinued, and the new version bolts right in)
- Test ran engine a second time, again with no lower unit, on the temp fuel tank, and on the garden hose, let it idle for a long time to warm up as best as possible
- Balanced carburetors
- Cleaned the pee hole hose (it shot out a bunch of junk)
- Ran engine probably once a day for about 15-30 minutes like this, just to keep the engine oil flowing and washing sludge
- Changed engine oil and filter again
- Replaced impeller in lower unit, make sure to use lots of grease so the impeller does not drag excessively. My engine has the Mercury lower unit, I used the $28 Mariner impeller kit from Sierra, it comes with parts that will not be used, and it works great so far (couple months).
- Replaced oil/water seals in the lower unit input shaft which mount in the impeller base housing
- Replaced the bronze bushing / rubber seal in the mid section extension (25” engine)
- Replaced the c-clip which retains the washer that covers the bronze bushing / seal.
- Re-installed lower unit
- Ran engine in a tub of water to check impeller function (impeller moves water significantly faster than my house faucet)
- Changed lower unit oil
- Tightened prop bolt
- Now that the engine operates “self-sufficient” I spent a little more time on idle and carb settings
- New fuel lines and bulb and water separator in the hull (not really a Honda thing)
- Removed and cleaned fuel tank (not really a Honda thing)
- Pressure tested fuel tank (not really a Honda thing)
- Replaced fuel pickup fittings (not really a Honda thing)
- Painted fuel tank (not really a Honda thing)
Note, I did not do everything in this order, but having done it one time, this is how I would do it again.
Also note I have not yet changed the timing belt or tensioner or spring. I keep meaning to, and I keep finding other things to do instead. Frankly, the existing timing belt looks brand new, there are zero cracks, and I have inspected every inch of it on the inside and out. The tensioner makes no noise at all. The belt still has all of the factory printing on it, and there appears to be very little wear on that printing. I do plan on swapping the timing belt this winter.
I did set the idle higher than the factory recommendation, it is idling somewhere around 1000 RPM. When I balanced the carbs, I did not have a functional tach, and I though the carb balance was lousy, but it turned out my original idle was just over 500 RPM after warm up, so of course it was running lousy.
Having done it once, I would have no real fear of doing it again, nor would I shy away from buying another Honda engine. Overall the engine has been pretty easy to work on, most of the issues I had I created on my own and they were easily resolved (broken water pump bolt from over tightening, messed up the gear selector location while the lower unit was off, did not use enough grease when installing the impeller the first time, I probably ruined the original fuel pumps buy cleaning the diaphragms with lacquer thinner).
Overall the only real disappointment I have with the Honda is that is it not 150hp. The boat would be much fast with an extra 60hp.