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Honda bf 75 alarm

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Pinboy122

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hi all, I’m having some trouble with my dads 2000 bf75
at full throttle after a few minutes an alarm goes off and it goes into limp mode. The alarm sound is constant and neither of the 2 lights on the control come on. If you put the shifter in neutral the alarm will go off and you can continue to full rpm for 30sec to a minute and it will do it again. If you just putt around or even half throttle it’s fine.
It has been reasonably maintained. It started this last year so I put a new thermostat in, no change. This spring I put a new water pump/impeller assembly in, no change.
I’m thinking maybe the temp or oil pressure sender but don’t want to just throw parts at it.

Any ideas???
Thanks,Al.
 
Normally, when the engine is running, there should be a green light....which indicates good oil pressure.

Since you have NO lights, that tells me that there is an issue with the oil pressure.

Check the oil. Make sure it is clean and recently changed....with a new oil filter.

Make sure you are not using Synthetic oil....use only mineral base oil and the oil level should only come up to about 1/4" below the full mark.

You can make sure that the green light is working, by running the engine and then removing the lead going to the oil pressure sender. That will simulate good oil pressure.

If the light lights and the oil is fresh , then it would be best to test the oil pressure. One thing to do before that, would be to remove the oil pressure sender and clean the small opening with a solvent like breakleen. Make sure there are no obstructions in the hole of the sender and the hole that the sender screws into. Poke the hole using a wire or similar item.

Run the engine and see if the green light comes on. If so, then you are probably good to go. If not, then check the oil pressure. Harbor Freight has a very inexpensive kit. Not the best, but will suffice for what you are trying to do. https://www.harborfreight.com/engine-oil-pressure-test-kit-62621.html

If oil pr
Mike
 
Suggest it's possible both lights are not working and possible overheat issue, would have thought oil pressure would be more of an issue at low RPM, the fact that it only alarms at WOT could mean insufficient cooling at that engine speed resulting from blocked passages or build of salt, silt etc around the cylinders in the block. Just my interpretation of your sympoms.
 
Those are a couple of great responses. I will definitely check the oil pressure sender and at a minimum try to get that green light back on.
As far as the temp goes would a good test be to unplug the temp sender while it is alarming? If it stops it would tell me overheat or possible bad temp sender?
Thanks,Al
 
***update***
had some time to look it over today and this is what I found. I took the thermostat out and is was a little plugged up with some type of scale. I cleared it out and put it in hot water to test. It is stamped to open at 72c and did not even start until 78c, that’s like 161 to 173 Fahrenheit. I took a run after putting it back in and had the same alarm and limp mode on a full throttle run. Took the stat out and made a run and got no alarm but it doesn’t run as good without it. So I’m going to get a new thermostat and give it a try. I was hoping to find one that runs a little cooler but it seems that they only offer 1 temperature. Is there anything else I should be looking at or is that stat opening late
 
***update***
had some time to look it over today and this is what I found. I took the thermostat out and is was a little plugged up with some type of scale. I cleared it out and put it in hot water to test. It is stamped to open at 72c and did not even start until 78c, that’s like 161 to 173 Fahrenheit. I took a run after putting it back in and had the same alarm and limp mode on a full throttle run. Took the stat out and made a run and got no alarm but it doesn’t run as good without it. So I’m going to get a new thermostat and give it a try. I was hoping to find one that runs a little cooler but it seems that they only offer 1 temperature. Is there anything else I should be looking at or is that stat opening late enough to cause an issue?
Btw the lights on the control seem to be working fine now.
Thanks for your responses,Al
 
You can get a 60 degree 19300 ZW9 003. I still think you may have to take the head off and clean out the water passages around the cylinders.
 
Thanks for that link, I’m gonna order 1 up. While taking the head off isn’t beyond my capability, that’ll be a last resort. I’m going to look around and see if I can find a flush that will be effective, maybe something like they use for salt water engines..
 
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