Test Running Merc 7.5 OB muffs/barrel?

[Somerowl]

Good day gents,
Cadet here, need to know if there are muffs available for my 1982 Mercury 7.5HP Outboard or if I need to submerge it in water to test run?
There's a drought out here in Cali and dumping 30 gallons in a barrel to run the motor is not something I want to do if at all possible to avoid.
The local shop sold me a set of muffs, but I can't figure out where to put them?
Confused.
Nick

 

[tpenfield]

The water intake is under the ventilation plate, so a regular set of muffs is a no-go. I am not sure a water intake adapter exists that would put the water where you want it. Muffs tend to waste water anyway as they do not seal tight and spew excess, so I do not think 20-30 gallons of water in a bucket is going to be any different.

Just use as narrow a bucket as possible, making sure the lower unit is well submersed.

 

[Somerowl]

Thanks, that makes way more sense to me now.
Can you describe where the ventilation plate is on the housing?
I'm assuming just above the contact point for the lower unit"?
Nick

 

[tpenfield]

The ventilation plate is part of the lower unit just above the propeller . . . keeps the propeller from grabbing air (sometimes mis-labeled the cavitation plate)

 

[Somerowl]

Got it, much thanks. That's telling me that, with this unit, I can probably get away with a 5 Gallon bucket as the lower unit is relatively short. I do have a 30 Gal that I could fill half way which would appear more than adequate.
Thanks a bunch for the info, can't wait to fire it up and splash the reworked fishing boat Saturday!

 

[gm280]

Somerowl, just make sure you fill enough water to get to the internal water pump and keep it pumping while running. Too little water is a way to wear the impellor fast... JMHO!

 

[Somerowl]

Understood, just rebuilt the lower end on a 70HP Evinrude and now I REALLY understand what drives and lubricates the impeller operation. No water = certain death in no time. That was truly my biggest concern about the test running process as the 2 stroke system (as long as you mix correctly) ensures the presence of oil for the engine operation.
Thanks very much.

 

[Scott Danforth]

I run my 9.8 in a 5-gallon bucket. just pull the prop off. water level is higher than the raw water pump so I know I am primed. then you only need a trickle of water out of a hose to keep the bucket full

 

[Sea Rider]

Just don't throttle past idle if in need to gear forward or will see in front of your eyes how fast a test barrel depletes itself in just seconds.

Happy Boating

 

[Somerowl]

Awesome info, never thought about removing the prop, great advice. The whole point of this is to make sure the motor runs and shifts and has nothing to do with anything else, great advice, much appreciated.

 

[Sea Rider]

If with an issue being the prop on, just test on barrel at NEUTRAL and idle speed.

Happy Boating

 

[Somerowl]

Didn't quite get her running last night (been sitting for a year), but will give another shot today after new plugs etc. bucket on a stand seems like it will work pretty well. I did take the prop off, but appreciate the neutral, idle suggestion as well.

 

[UncleWillie]

One you get it running, remember that in the lake, the water only goes through the engine Once!
The muffs simulate normal operation as the exhaust water never returns.

Notice that the water coming out of your Tell-Tale, (the Pisser) is noticeably warmer than the water from the hose.
Even at idle, a 7hp engine will heat up a 5 gallon bucket of water in just a few minutes.
You will need to keep a garden hose overflowing the bucket to provide cool water if you run the engine more than a few minutes.

The design of the engine assumes that the water coming in is well below 80 degrees, not over 100!
There is no way to conserve water when running an engine at home. It is your cooling system and you will need lots of it.

 

[Mi duckdown]

Well. merc makes a hose type of muff for those type of water intakes but you MUST remove the prop to use it.

 

[Sea Rider]

That's a very bad design, imagine removing prop everytime the engine will be flushed after saltwater use. In that case use a barrel and don't need to remove prop. Uncle Willy is quite correct, you can't possibly flush right an engine on a barrel with hot water, will end overheating engine.

Barrel flushing is just good for short time testing, won't tell if an engine works ok when at load while pushing a boat which is a different boating story.

Happy Boating

 

[Somerowl]

Got her running and ensured the "pisser" is working well, that's all I needed to know and shut her down quickly. Thanks for all the input, suggestions and direction. Will give her the lake Test Friday. Much appreciated.
NIck

 

[ondarvr]

I run my 8hp Merc on muffs all the time, you just clamp them on so the water feed cup is covering the water intake on the AV plate, no need to remove the prop.

 

[Somerowl]

Could you send me a picture?

 

[ondarvr]

A pic won't be available anytime soon, but just take the muffs an stick them on. The muffs don't care if they're clamped on the lower unit water pickup inlets or the ones on the AV plate.

 

[Sea Rider]

Just to give the idea...



Happy Boating