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Honda bf50a doesn't pee at higher speeds..

A

ArGuy

New member
Hello everyone. This is my first post and I apologize for starting with a question but I've been lurking here for quite some time. This site really helped me get my tohatsu 40d running like a top. That being said, I bought a nice used 1993 Bass Tracker Tx17 with a gorgeous 2002 honda bf50a that purrs like a kitten. I got my first chance to take it out this memorial day weekend and ran into issues pretty quick. I replaced the impeller and it pees water like a champ until you get it around 15 mph at which point it stops peeing and the temp light and buzzer comes on. Backing off the throttle causes it to start pumping water again. Strangest thing I've encountered. It is a long shaft on a 20 inch transom and the cavitation plate is level with the bottom of the boat so I don't know what's going on. Any help would be greatly appreciated. Thanks in advance.
 
Might be bits of the previous broken impellor plugging up the water passages.
Try removing the thermostat and back flushing to blow out the bits and pieces ?
 
dark_star said:
Might be bits of the previous broken impellor plugging up the water passages.
Try removing the thermostat and back flushing to blow out the bits and pieces ?
Click to expand...

Great advice but I've done all that. Like I said..it pees water fine at idle and low speeds. I'm not a boat mechanic by any stretch of the imagination but I did backflush it and the impeller I changed was alright. I couldn't get it to pee when I bought it while in a bucket until after I raised the water level over where the the lower unit bolts up to the main unit. I was thinking that the boat was displacing so much water that it was no longer drawing up water. I just don't know. I did check the thermostat and it opens in hot water. Oil is not milky so I think the head gasket is fine. I just hate dealing with outboard mechanics because I've had a bad experience in the past. Yeah..I got screwed. I'm at my wits end because what good is a 50hp honda when my 9.8 evinrude on a 1448 is just as fast?
 
did you open up the plastic intake screens and see if there's anything in there blocking the system ?
I understand it pees at idle, but maybe under throttle something changes that ?
 
dark_star said:
did you open up the plastic intake screens and see if there's anything in there blocking the system ?
I understand it pees at idle, but maybe under throttle something changes that ?
Click to expand...

I haven't checked them since I got back but it was clean before going to the lake. I cleaned everything before we took off for the weekend. It's strange..pees fine until a certain rpm basically and then it stops and overheat light and buzzer comes on until I throttle down and it pees again. I'll remove the vents and backflush by removing the thermostat and running a water hose through it. I'd think head gasket but there's no loss of power and the oil is perfect. I'll do a compression check if time allows me tonight to definitely rule that out.
 
Check to be sure that there is no buildup of salt, corrosion, or mineral deposits inside the thermostat housing. If there is a buildup there, it is the same throughout the engine.

When you changed the water pump, did you replace housing and plate also? If not were the cup and plate smooth and free of any grooves? Any grooves can limit the water supply.

Lastly, there may be a slight blockage of sand or debris in the block around the cylinders. The only way to get this out (since you have already tried to backflush) is to remove the head and dig the stuff out.

If you only knew where and how the previous owner boated, it might give you some hints on what might be going on.

The water flows from the waterpump, to the base of the engine block and branches off to the pee hole and also up through the block and the head. Then to the thermostat and once it opens, it dumps out the exhaust.

If there is not enough water flow out through the exhaust, at higher speeds, the exhaust overrides the water flow and then you see no water coming out the telltale...in fact you probably see exhaust.

One way to see if you are getting enough water to the thermostat is to remove the thermostat cover and watch what water comes out of the housing when you accelerate. You should only do this for a very short time, so you do not hurt the engine. Water should come shooting out of the housing.

Another check to be sure that the engine is in the water far enough, is to have someone look over the back at the engine lower unit and take a video (for your review) to see if the boat is causing some sort of issue.

Just as couple of thoughts.

Mike
 
hondadude said:
Check to be sure that there is no buildup of salt, corrosion, or mineral deposits inside the thermostat housing. If there is a buildup there, it is the same throughout the engine.

When you changed the water pump, did you replace housing and plate also? If not were the cup and plate smooth and free of any grooves? Any grooves can limit the water supply.

Lastly, there may be a slight blockage of sand or debris in the block around the cylinders. The only way to get this out (since you have already tried to backflush) is to remove the head and dig the stuff out.

If you only knew where and how the previous owner boated, it might give you some hints on what might be going on.

The water flows from the waterpump, to the base of the engine block and branches off to the pee hole and also up through the block and the head. Then to the thermostat and once it opens, it dumps out the exhaust.

If there is not enough water flow out through the exhaust, at higher speeds, the exhaust overrides the water flow and then you see no water coming out the telltale...in fact you probably see exhaust.

One way to see if you are getting enough water to the thermostat is to remove the thermostat cover and watch what water comes out of the housing when you accelerate. You should only do this for a very short time, so you do not hurt the engine. Water should come shooting out of the housing.

Another check to be sure that the engine is in the water far enough, is to have someone look over the back at the engine lower unit and take a video (for your review) to see if the boat is causing some sort of issue.

Just as couple of thoughts.

Mike
Click to expand...

Thanks Mike. Yeah, being in front of the engine doesn't help when diagnosing things. I'll take the old lady out with me and let her video the motor for me at speed. The cup was okay when I replaced the impeller. The top of the housing wasn't perfect. There was definitely daylight showing between it and the shaft. Maybe that's where the problem lies. Thermostat housing is clean as a whistle.

The boat has been registered in Arkansas since new so no saltwater but I'm sure it's been in some nasty water for fishing. Is there a good online place to buy honda parts? The local honda (and only one) shop is a large dealership that has a marine center but only for yamaha and mercury. All my parts have to come from their motorcycle / atv building and the people there aren't competent with outboards so I end up going from building to building having one explain to the other what I need.
 
There is a gap at the top of the waterpump housing, so I would not be too concerned about that unless there is something really unusual.

boats.net seems to be the place a lot of the people here go.

Mike
 
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