![]() Good rule of thumb though if you are running in a bucket to get the whole lower unit below the water. I have found this to be true most of the time but not always. The water level has to be higher than the pump, otherwise it won't prime and will melt itself in the air its in before it has a chance to suck water. People say all the time on here when this comes up that the wp housing must be submerged when you are running in a bucket/bag. I have, however, had problems with running engines in bags/buckets. If when you start the motor up it doesn't suck the water out of the hose itself then its probably sucking air from around the muffs: not good. You just need to be smarter than your flushing device. I have customers that fry their impellers using muffs. I run multiple engines a day 5 to 6 days a week on muffs and never hurt impellers. The pump and bearings are meant to float so there is a good. This is your bearings making all this noise. You may notice that the jet boat’s pump is much louder and sounds like a bunch of coins raddling in a metal can when out of the water. Round ones that are soft rubber seal good. When a jet boat is not in the water, the pump and bearings are not being cooled and lubricated. Square muffs don't seal on a lot of motors and burn the pump via sucking air. I don't see how a garden hose could hurt the pump. I think the impeller blades are folded forward and dong nothing once you're at speed. I have also heard whacky stories about barrel test tank tuning where the exhaust gases would replace air in the agitated water mix? Do engines breathe? (LOL) Aside from powerhead combustion.Today's new motors are rigged with flush hose connections but are not recommended for running engines.only salt flushing.Īlso. I think muffs were made for flushin but not load test tuning. In my mind, once the exhaust is out of the tuner, no back pressure is needed or maybe even wanted. But asside from that is there any real reason not to run a motor out of the water? The motors obvioulsy have an idle relief, a lot have above water exhaust, and how much back pressure could there be with water running past the bullet at 60mph+. Obvioulsy loading the motor on the water, with a boat loaded the way it would normally be would be the best. People always talk about a lack of backpressure when running motors on muffs, potentially causing damage etc. I hear people talk about this all the time so I wanted to start a little discussion on it. That being said I have a hard time believing you could damage an engine idling it out of the water for hours even running a tad lean. They would run much better with back pressure. Dump em in the water and the back pressure DID make a big difference. Old J/E engines from the 60s, 70s and 80s did not like to idle out of the water. Once on plane there is no back pressure aside from what is cause by pressure differentials and harmonics in the exhaust tuner itself. This proves that back pressure (from being submerged in water) doesn't do much. I adjust carb motors without back pressure and then water test them and they run exactly the same. The proof of this is revealed in adjusting carbureted engines: if back pressure affected how outboards ran then the a/f mixture would be different with and without back pressure and we would not be able to adjust carbs out of the water. And in those area its hard to "damage" a motor. The only thing back pressure affects is idle and some midrange. ![]()
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