No Jet Tin Experience Needed... Ok I need help!

[panFried]

I found a 1998 1648 Polar Kraft Jon and trailer for sale, which I need another tin like I need a hole in my head. What caught my eye was the Mercury 30 Jet w/ steering console. I looked the boat and motor over but I have no idea what to look for on a Jet. I checked the impeller area which looked great and did not show signs of damage in grating. The motor has been winterized and sat since 2011. I would like to fire it up and owner is more than happy to let me, however this is one of those deals where the boat operator (husband) has left this world and owner has no idea how to operate. Any tips would be great! Obviously I want to know it works and is worth buying but I don't want to ruin it either.

 

[JoshKeller]

a few things - I'd do a compression test.

i'd get a simple $12 spark plug wire tachometer. back the boat into the water, and leave it on the trailer. start it up, run it WOT and see what the RPM are and if they fall into the recommended range on the tag on the side of the motor. Verify its pumping water. You'll instantly know the jet is functioning by the huge amount of jet spray.

After you pull it out of the water, squeeze some grease into the purge hose and see if any water comes out. Other than that, the jets are pretty simple.

 

[panFried]

Thanks for the quick reply Josh. Bad with acronyms so what is WOT?

EDIT : Ha I looked it up, "Wide Open Throttle"

 

[panFried]

So I was trying to wrap my brain around how to run this Jet WOT on the trailer without damaging anything. So I googled... Are you suggesting to run the tach test on the motor while shooting an awesome water cannon like this video?

[youtube]P84soNxL5XI[/youtube]

 

[Ranchero50]

Just treat the engine like any other outboard. Look for corrosion or other signs of abuse / neglect. If the bottom of the hull is nice as is the grate then you shouldn't have to worry about stress cracks or other damage to the pump. You can fire it up out of the water but don't let it run for more than a couple seconds or the water pump impeller will overheat and not be happy. As Josh said, do a compression test and make sure they are both within spec. You can also run it in a barrel but not above idle because the pump is always pumping.

I really don't like running above idle on the trailer is the pump is a giant vacuum and will suck up all sorts of junk and crap. I would also do some ignition chops at different RPM's and check the plugs to see how the carbs are fueling.

 

[panFried]

Thanks Ranchero! I did a good visual of the hull and other than minor scratches from gravel it was clean. Sounds like I just need to do a comp test and fill with fresh fluids for a test fire. Can you run jets on idle with muffs? I suppose not since the jet is always pumping even in idle.

 

[BigTerp]

I think Outboard Jets makes some sort of adapter/fitting that plumbs into the water pump so you can run the engine at idle with a water hose hooked up to it. Not sure if they are stock on some motors or if it's something you have to install aftermarket. But if it were me, I'd want to see it run at WOT under load, not on the trailer. Will she let you take it for a test run? Josh and Ranchero pretty much summed it up. Definitely do a compression test to confirm all cylinders are where they are suppose to be. The throttle chop test(s) are a good idea as well. I also like the idea that Josh had of getting an RPM reading. At WOT there is a recommended range the motor should run at. If the motor is running good and the impeller clearance is where it's suppose to be, it should fall within that range. I'd also check the fuel lines and carbs while you have the hood off since it has sat for 4 years.

When we rebuilt my motor we test ran it in a barrel. Give it any sort of throttle and the water from the barrel is depleted in seconds.

What happened to your other boat you were working on?

 

[panFried]

Thanks Terp! It's been a while. So I'm really interested in the bigger boat/motor, but I'd have to start a new project all over again. Ugh! Since I literally live in between 3 awesome rivers the jet motor is really appealing, I just don't have the experience with them.

Yeah she will let me test it out and I'm sure she would let me drop it in the water. I'm not sure there is enough straight river by her to get up to top speed and test RPM, not to mention trying to hit anything since I don't own. I bet I can leave some cash as good faith and take it to a lake near by or large body of water. Thanks for all the input. What do yall think the value of just that motor would be? (1998 Mercury 30 Jet) If everything checks out OK.

Found a nice YouTube on running Comp and spark test for those of you that have never done one before.

[youtube]eSmNMWTDtZE[/youtube]

 

[panFried]

What happened to your other boat you were working on?

I still have it and use once in while when I get down to farm. Last year was busy summer for me. Unfortunately I live by more rivers than lakes so Ive been shopping the jets. I see they are 2500-5500 depending on the size brand new. So when I heard about this boat with 30 jet for sale I went to look since price seemed good. Much bigger then the 1636 Lowe liner and will support bigger motor than the 1636.

If I buy this one I'll definitely flip the other, and recoup some cash.

 

[JoshKeller]

keep in mind that with an outboard jet, theres no load on the impeller like there is on a prop - you can run it to WOT rpm on the trailer. After I do any motor work, i drive to a local ramp below a dam that I dont normally run in, back up my boat in the water enough to submerse the jet, and fire it up. When going WOT, i get the same rpm on the trailer, in the water, or powerloading. as long as there isnt a ton of grass/mud/sand/etc to suck up into the pump, you can run it on the trailer for as long as you need to to verify its running well. I've ran mine WOT up to 5 - 6 minutes.

as for value, in this area (which jets are at a premium), id start it at $3500, and take any offer over 2500.

 

[panFried]

keep in mind that with an outboard jet, theres no load on the impeller like there is on a prop - you can run it to WOT rpm on the trailer. After I do any motor work, i drive to a local ramp below a dam that I dont normally run in, back up my boat in the water enough to submerse the jet, and fire it up. When going WOT, i get the same rpm on the trailer, in the water, or powerloading.....

Thanks Josh for the info, but I'm not familiar with how Outboard jets operate but it seems to me, if I have the engine wide open and water propelling out the back there will be force. I guess you're just suggesting to idle it WO, for a few minutes and not to engage the motor in drive. I guess if I have the boat in the water at that point, I might as well take it for spin. [emoji15]

 

[Captain Ahab]

There is an adapter hose to run a jet out of water

 

[Ranchero50]

This is how jet pumps work...

On the back is a gate. In neutral the gate dumps half the output in 'reverse' and half in 'forward' (shown in the pic). For forward the gate moves out of the way. For reverse the gate shifts further up (or down) so all the output is dumped under the motor

The engine exhaust is ported into the output stream.

 

[duckfish]

keep in mind that with an outboard jet, theres no load on the impeller like there is on a prop - you can run it to WOT rpm on the trailer. After I do any motor work, i drive to a local ramp below a dam that I dont normally run in, back up my boat in the water enough to submerse the jet, and fire it up. When going WOT, i get the same rpm on the trailer, in the water, or powerloading.....

Thanks Josh for the info, but I'm not familiar with how Outboard jets operate but it seems to me, if I have the engine wide open and water propelling out the back there will be force. I guess you're just suggesting to idle it WO, for a few minutes and not to engage the motor in drive. I guess if I have the boat in the water at that point, I might as well take it for spin. [emoji15]

With a jet, the motor is always in "drive" and the impeller always spins in the same direction. So if the engine is running, there is always force, regardless of throttle setting. You can run the engine at higher rpms with "neutral" force (based on the gate position shown very well in the pic above) if the binnacle has a neutral detent button in the center, but it is still pushing lots of water around at high rpms. If testing on the trailer, just be sure all that water flow isn't stirring up tons of mud and gravel that will be sucked thru the impeller.

2 other oddities about jets... you can actually "brake" a jet boat very quickly. Since impeller rotation never changes, you can theoretically go from full throttle forward to full throttle reverse instantly. You are only moving the gate so there is no gear damage from rotation change to be concerned with. Still wouldn't recommend full-full for other reasons, like a huge wash over the transom, but quick thrust changes have saved my butt plenty of times when a boat-eating boulder just under the surface snuck up on me. Second is the near lack of steering at low rpms, essentially none in neutral (you don't have the lower unit to act as a rudder) and very poor steering in reverse at any rpms. It's something that you get used to and learn to deal with.

 

[duckfish]

2 other things to check I haven't seen mentioned. Look thru the intake grates at the volute liner. If it is heavily scored, it will need replaced. And ideally, if she'll let you, remove the intake shoe to inspect the liner and impeller and count how many washers are under the impeller nut and lock washer (one with the bent up ears). Try to find what the factory number of total washers for that motor is. If most of the shim washers are still under the nut, you still have wear left in the impeller & liner. If none, both should be replaced. This shouldn't be a deal breaker, just keep in mind you'll have several $100's in immediate maintenance to figure in to the deal.

 

[panFried]

2 other things to check I haven't seen mentioned. Look thru the intake grates at the volute liner. If it is heavily scored, it will need replaced. And ideally, if she'll let you, remove the intake shoe to inspect the liner and impeller and count how many washers are under the impeller nut and lock washer (one with the bent up ears). Try to find what the factory number of total washers for that motor is. If most of the shim washers are still under the nut, you still have wear left in the impeller & liner. If none, both should be replaced. This shouldn't be a deal breaker, just keep in mind you'll have several $100's in immediate maintenance to figure in to the deal.

Thanks Duckfish! Between you and Josh, I'm almost thinking I need a buyers agent. LOL

 

[dhoganjr]

Sounds like the guys have got you pretty well lined out.

I would also check the pump bearing grease. Look in the boat for a tube of 2-4-C grease with a push pump, I keep mine in the boat, if not there pick one up. Take a zip lock bag or empty clear bottle, a rag or paper towel will work also, and pull the hose on the left side of the pump and put the zip lock bag around the hose. Pump grease in the grease zerk and pump until fresh grease comes out, the fresh will be cream or off white color. If it has been well maintained grease should come out after 1 or 2 pumps but continue pumping till you see fresh. Look at the old grease, should be light gray to gray color. If it is real dark or black you will probably be changing pump bearing in the very near future.