Other 61X Powered Mini Jet Boat

[RBS145]

Love the pics and the details. I really want to build one of these in the near future so I’m taking lots of notes.

How does the hull track with such a smooth bottom? I’d think a small chime of some sort improve steering although I guess the point is to be able to slide up and over almost anything.

Everyone says the 61x has more than enough power but I’m still thinking a small 4 stroke would be ideal based on improved mileage and sound levels. Comments about sound level anytime the engine is running and only a 25 mile range with an 11 gallon tank have me thinking a four stroke would be more than worth the added investment. Would it be too much power in such a small hull though?

It is a very loose feeling as far as handling goes, the back end sort of drifts around corners. Which is actually not a bad thing depending how the river is, because you can keep the pump intake over the deepest part of the river easily. I have ordered a different style of trim nozzle that is supposed to help a lot with more thrust in corners from Minijet Inc here in Canada. I post some pics once installed. The easier it is to slide over obstacles the better for sure.

Definitely more than enough power in the 61x engine. It feels really fast on a shallow/narrow river already. If you watch any videos of the 4 stroke engines in these, they have all been trying to deaden the sound with Kilmat or similar. They also all seem to wear some kind of headset/hearing protection, these aluminum hulls resonate sounds like crazy. I installed a ton of Kilmat and closed cell foam to absorb sound. It helped, but it's still quite loud. That soundbar for tunes is coming out. I found a comms setup from SENA that you can play tunes and chat with the passenger at the same time. I also installed a 21 gallon tank which nets me about a 65mile range. I've never burned an entire tank yet in a full day of running around. Also, I would not even consider a boat hull without the taller windshield too. We get soaked even with the big window.

If you are looking to build up a boat and you live in the US. You should definitely be looking to buy soon, the exchange rate gets you a big discount right now. I just got back home from Vegas and $500USD cost me $750CAD. Ridiculous considering it's been at par before.

 

[fastgtfairlane]

Impros could fix up your impeller and probably repitch it to 10/16 for you at the same time. The stator veins look ok on the pump nothing a little bending and file work wouldn't fix. Sweet setup. Any mph numbers for the addition of the dual carbs and pipe?

 

[OCD Solutions]

If you are looking to build up a boat and you live in the US. You should definitely be looking to buy soon, the exchange rate gets you a big discount right now. I just got back home from Vegas and $500USD cost me $750CAD. Ridiculous considering it's been at par before.

I was looking at pricing on a 12ft kit this morning and I was doing the cost saving in my head. A low exchange rate is good for exports.

I bought a Limitless Tonneau Cover/Sled Deck out of Kelowna, BC earlier this year and had it shipped to me here in the US and basically got 40% off due to the exchange rate at the time.

 

[kevbo]

Make sure to tune the carbs a little rich of peak RPM or else your pistons may end up looking like your pump.

 

[RBS145]

Impros could fix up your impeller and probably repitch it to 10/16 for you at the same time. The stator veins look ok on the pump nothing a little bending and file work wouldn't fix. Sweet setup. Any mph numbers for the addition of the dual carbs and pipe?

Yeah, that's where I bought it all. I'm heading down south later this winter, I'll reach out to them before I head that way. I haven't had a chance to run GPS yet on it and the snow is flying up here now. I'll update next year, although it didn't feel much difference. It needs lots of tuning and that impeller was pretty thrashed already.

Make sure to tune the carbs a little rich of peak RPM or else your pistons may end up looking like your pump.

Care to elaborate? I'm not real familiar with these ski engines. I was seeing 6500rpm peak, builder told me to tune for 7200 ish. A new impeller and potentially a 10/16 instead of 9/15 will likely change that too. Might buy one of each pitch and go from there.

 

[RBS145]

I was looking at pricing on a 12ft kit this morning and I was doing the cost saving in my head. A low exchange rate is good for exports.

I bought a Limitless Tonneau Cover/Sled Deck out of Kelowna, BC earlier this year and had it shipped to me here in the US and basically got 40% off due to the exchange rate at the time.

Depending what type of rivers you run, a 12ft could be great. The lighter the better if you run out of water and have to push it. The rivers here change throughout the year and some channels are open one day, but closed the next due to flow changes. If you aren't worried about that, I would also like the extra space for camping gear and what not.

 

[kevbo]

Yeah, that's where I bought it all. I'm heading down south later this winter, I'll reach out to them before I head that way. I haven't had a chance to run GPS yet on it and the snow is flying up here now. I'll update next year, although it didn't feel much difference. It needs lots of tuning and that impeller was pretty thrashed already.



Care to elaborate? I'm not real familiar with these ski engines. I was seeing 6500rpm peak, builder told me to tune for 7200 ish. A new impeller and potentially a 10/16 instead of 9/15 will likely change that too. Might buy one of each pitch and go from there.

Depending on how tall the exhaust port is, it needs to turn at least 6800 with that pipe. If it is "race" ported then adjust the pump load so it gets on the pipe quickly. A freestyle pitched impeller is ideal. What I mean by "rich of peak RPM" is adjusting the top screws at full throttle while watching a tachometer. It is much safer to open them so the engine turns 20-40 rpm slower than the maximum rpm mixture setting. It is easy to burn a piston if the mixture is allowed to go lean of peak power.

 

[RBS145]

Depending on how tall the exhaust port is, it needs to turn at least 6800 with that pipe. If it is "race" ported then adjust the pump load so it gets on the pipe quickly. A freestyle pitched impeller is ideal. What I mean by "rich of peak RPM" is adjusting the top screws at full throttle while watching a tachometer. It is much safer to open them so the engine turns 20-40 rpm slower than the maximum rpm mixture setting. It is easy to burn a piston if the mixture is allowed to go lean of peak power.

Intake and exhaust ports were left stock, no additional porting. The builder said it's more reliable that way, which I cannot validate. I will keep that in mind when I get out in the spring to tune again. I'm going to start from scratch with the impeller change.

 

[RBS145]

Finally got the boat out again, what a blast this river was. Haha.

 

[OCD Solutions]

That looks like such a blast.

This video came up in the "watch next" options.
Ya'll are crazy!

 

[RBS145]

That looks like such a blast.

This video came up in the "watch next" options.
Ya'll are crazy!

I think New Zealand is where these little boats originated from, they have tons of crazy rivers out there.

 

[WFO Speedracer]

I tried to post one up this morning but the link would not post correctly. This is not the vid I saw but it was the same guy.

https://www.tiktok.com/video/7148139275580706090

 

[Cmm314]

Awesome ride! Saw a similar boat (but not as nice) at my local river a while back and looks like a ton of fun. Love the pictures…keep ‘em coming

 

[RBS145]

Another river system close to Calgary.

 

[RBS145]

Rivers are starting to flood out around here. Makes for a lot of fun little side channels. Also found out I don't have the power to push up the high flow in spots, so speed and momentum is the only way through. Scared my buddy pretty good going through some bushes back to the main channel too.

 

[JC-SuperJet]

Go Yamaha!

 

[RBS145]

Made a few changes to the boat for this season.

Added a Southern jet Posi-nozzle trim system with an electric actuator to adjust on the fly. It has a level indicator gauge as well. The boat has way better thrust in the corners and tracks better too. It also shoots a 60 foot rooster tail when trimmed up all the way too which is fun to play with.

Added some hearing protection that let's me talk to the passenger and listen to tunes at the same time. It's Bluetooth to my phone and can take phone calls as well. Pretty slick setup. Click here if interested

Had a new intake grate built with some gussets on the back side to reinforce the tines. So far so good, no broken tines and the pump loads the same as before.



Started to tune the dual 38's, what a frustrating endeavor this has been! I've tuned lots of motorcycles and cars, but man this is finicky. Last year it was running extremely rich at the end of the season, which was probably great for breaking in the new engine. But, it was likely down on power from it. The plugs were coming out really black and oily, I'm shocked they never fouled. This year I started trying to lean it out a bit and the slight adjustment was making it REALLY lean, the plugs came out white and looked HOT. I've been trying to richen it up all season so far with a bit of luck, but it is still a bit lean to me. Here's jetting that I've used.

End of last season jetting:
135M
72.5P
2.0N/S
80G

Where I'm at now with jetting:
150M
80P
2.0N/S
95G

Tested pop off at 26psi on both carbs. The front cylinder is leaner than the rear which seams really weird to me. I'm looking at buying a tach to continue tuning, I have a motorcycle hour meter that has a tach. But the RPM numbers on this one are really wrong though, 15000RPM at WOT haha. Should be doing 60mph at that RPM. I've looked at the PET tach on the Watcon site, but having a hard time justifying $300 for it. Here's some pictures of the piston wash and plugs after the last tuning session yesterday. Any suggestions on where to go from here are appreciated, things to check too. I'd hate to burn up a piston or worse.

 

[RBS145]

 

[JC-SuperJet]

Because of the heavy loading of the Boat + 2 Passengers, Upstream River Current, and hard Turning, you're better off keeping it on the rich side.

With all those loads, the Engine is straining, and the Crank is twisting at the hard turns which changes the Piston/Port Timing resulting in higher operating temperatures.

The Stock Yamaha 760 came with staggered Ignition Timing (Rear has 2 degrees less Spark Advance) and Compression (Rear is lower) in both Cylinders to address this. Must tune each Cylinder as Single Piston Engine. Each Carb will end up with different Screw Adjustments. The Rear 44 mm Carb has a larger Main Jet.

Are you using 38 mm Mikunis? Seems like 38's by the Pilot Jet sizes. Is the Engine a 701 or a 760? Thought it was a 760... 61X = 701...

 

[RBS145]

Because of the heavy loading of the Boat + 2 Passengers, Upstream River Current, and hard Turning, you're better off keeping it on the rich side.

With all those loads, the Engine is straining, and the Crank is twisting at the hard turns which changes the Piston/Port Timing resulting in higher operating temperatures.

The Stock Yamaha 760 came with staggered Ignition Timing (Rear has 2 degrees less Spark Advance) and Compression (Rear is lower) in both Cylinders to address this. Must tune each Cylinder as Single Piston Engine. Each Carb will end up with different Screw Adjustments. The Rear 44 mm Carb has a larger Main Jet.

Are you using 38 mm Mikunis? Seems like 38's by the Pilot Jet sizes. Is the Engine a 701 or a 760? Thought it was a 760... 61X = 701...

That makes sense, it's a lot of load on it. I just thought the rear cylinder would have been the one acting up more than the front. The other odd thing to me is that nothing mechanical has changed in regards to the engine since the end of last season and now the jetting is much leaner with richer settings. I've double checked all the hoses and primer connections to make sure they are sealed. The carbs have been cleaned and rebuilt this season as well.

It is now a 62T bottom end and 61X top end. I am still using the original 61X electronics though, flywheel and stator as well. I have a MSD enhancer installed now too. I made sure to set the stator timing to the center marking on it. Both cylinders compression tested at 180psi.

Yes, it is twin carb Mikuni 38mm now.