Other 61X Powered Mini Jet Boat

[RBS145]

Hello, first post here. I've been browsing the forum since I bought this boat this seems to be the best place for Yamaha engine info that I've seen on the web. Wasn't exactly sure where to post this, so please move it if I got this wrong.



The boat is a 10ft aluminum hull with 1/2" UHMW (Teflon) on the bottom like a skid plate and weighs in around 1000lbs loaded fuel/two people. These are great for running rivers around Calgary where I live and is a ton of fun. It has a 701 61x engine, but has low compression (125/130). Assuming it's down quite a bit on power, stock hp is 62 from what I've seen, guessing it's sitting closer to 50 at this compression. I reached out to Impros and installed a Solas 144 Stator, Solas SS wear ring and Hooker 9/15, which made a huge difference from the worn out stock setup. It could still use some more punch though, I was going to just rebuild the engine back to stock specs but after browsing around and seeing tons of different options. I'd love some advice on which direction to go.

Has to be reliable as some rivers here, if you lose power you are going to have a bad time and could be in some dangerous situations if you are dead in the water. I've read that a pipe really wakes the engine up, but it's not an option as the front of the OEM Yamaha pipe is maybe a 1/8th inch off the firewall (see pictures). Anyways, here are the options I've researched on the site and others.



1. Rebuild to stock (maybe add some bolt ons)
2. Have a Jetmaniac engine built
3. Swap to 760

Keeping reliability in mind, what would you do?
Here's a video of what the boat drives like currently, top speed up river is 30mph and down is 35mph which feels plenty fast. I wouldn't complain about a touch more top end so I don't have to be at WOT to maintain some speed.

 

[WFO Speedracer]

Swap to 760 is my vote

 

[Mdavies_02]

Rebuild the 701, a/m cdi like an MSD enhancer, and maybe get a SBT Wear ring to protect your pump. Having a replaceable wear ring in those conditions would be extremely beneficial.

Has anyone ever measured how much further a Waveblaster B Pipe or similar fits to stock? A pipe would make that thing scream.

.

 

[JC-SuperJet]

Keep it 100% Stock for maximum Reliability.

Install a Fresh Top End and Rebuild the Carburetor with a Genuine Mikuni Kit.

Best to install all new Engine Gaskets and Crankshaft Seals, then Air Leak-down Test to confirm air tightness.

ProX Pistons are probably the best choice. WSM Pistons are good too. Stay away from Forged Pistons so you don't have to deal with cold seizures. NO SBT ENGINE!

The 61X Cylinder Block has more Bottom End than the 760 62T Cylinder Block due to the lower Transfer Port Heights. I'm thinking you need Bottom End Torque more than Top End Speed to handle the Currents.

You could port match and blend the Exhaust Ports for improved flow and performance.

 

[Quinc]

If you are fine with power stick with what you have bore it and toss in some pro-x pistons. Wouldn't hurt to shave the head or get an a/m head that brings compression up from 150 to 175.

For a large increase in power at the cost of significantly more fuel consumption (dual 44 carbs) go with the 760 and get a Zeeltronic ignition for it.

 

[Quinc]

Also that thing looks like a blast! But how do you keep gravel/rocks from jamming into the impeller and stopping the boat?

 

[RBS145]

Rebuild the 701, a/m cdi like an MSD enhancer, and maybe get a SBT Wear ring to protect your pump. Having a replaceable wear ring in those conditions would be extremely beneficial.

Has anyone ever measured how much further a Waveblaster B Pipe or similar fits to stock? A pipe would make that thing scream.

View attachment 426175.

Thanks for the input! The boat has a fairly tight grate on the bottom to stop any larger than 1/2" rocks and junk from entering the pump housing. So far, maybe 10 hours on the river since the SS wear ring and it still looks pretty good. Might be worth keeping a spare rebuildable one in the boat though in case something catastrophic happens. Here's a pic of the grate, ugly but it works well.

Keep it 100% Stock for maximum Reliability.

Install a Fresh Top End and Rebuild the Carburetor with a Genuine Mikuni Kit.

Best to install all new Engine Gaskets and Crankshaft Seals, then Air Leak-down Test to confirm air tightness.

ProX Pistons are probably the best choice. WSM Pistons are good too. Stay away from Forged Pistons so you don't have to deal with cold seizures. NO SBT ENGINE!

The 61X Cylinder Block has more Bottom End than the 760 62T Cylinder Block due to the lower Transfer Port Heights. I'm thinking you need Bottom End Torque more than Top End Speed to handle the Currents.

You could port match and blend the Exhaust Ports for improved flow and performance.

I've had this kit bookmarked for a while now. Any experience using these guys? It doesn't say anything about brands, but pictures look similar to the ProX pistons.

Click here

Good to know about the SBT engines, I had my eye on those as well. I will delete them from my memory.

Bottom end is definitely the most important part of the powerband in these, getting "On Step" quick in some spots is very critical. But, having a bit more top end range would be nice to be lower in the RPM when cruising some times.

If you are fine with power stick with what you have bore it and toss in some pro-x pistons. Wouldn't hurt to shave the head or get an a/m head that brings compression up from 150 to 175.

For a large increase in power at the cost of significantly more fuel consumption (dual 44 carbs) go with the 760 and get a Zeeltronic ignition for it.

A/M head was on the radar for sure. If I bring it to 175, is 91 octane is good? That's the highest octane readily available fuel.

As for fuel consumption, the boat has a range of about 25 miles upstream before I need to turn around and come back or add fuel. I have a 19 gallon tank on order though and that will be a big improvement from the 11 gallon tank in there now. Fuel consumption would be less of a concern at that point, aside from the current price of $7.56 per gallon cost for 91 right now.

 

[JC-SuperJet]

For Reference, two of my Friends (Business Partners) build Two Stroke Aluminum Mini Jet Boats.

Having each owned Aluminum Mini Jet Boats with Triples in them (YAM 1100 and KAW 1100), both Guys arrived at the same conclusion that Triple Power is NOT worth the extra Noise, Weight and Fuel Consumption.

They both say that 100% Stock Yamaha 701, or Stock 760 with it's 62T Exhaust are the perfect match.

They are selling these Aluminum Mini-Boats like Hot Cakes!

 

[JC-SuperJet]

Atlantic Jet Sports sells good Parts. And the AJS Sales Rep Jim is very knowledgeable regarding PWC. Give Him a call.

That looks like a WSM Kit which is okay.

Shortblock Rebuild Kit - Yamaha 701 61X - 2-Stroke1.00 Over Size Pistons - 82.00mm

Yamaha 701 61X Complete Standard Shortblock Rebuild Kit. Carbureted 2-Stroke Motor. Kit Includes: New Crankshaft, All Pistons, Top End Bearings, Complete Gasket Kit & Crankcase Sealant. Fits The Following Models: 1993 Yamaha VXR Pro 700 Shortblock Rebuild Kitit1993 Yamaha Wave Blaster 700...

www.atlanticjetsports.com

 

[Scorn800]

Your little boat is sick!
If I lived on a river, I would definitely have 1.

 

[RBS145]

Atlantic Jet Sports sells good Parts. And the AJS Sales Rep Jim is very knowledgeable regarding PWC. Give Him a call.

That looks like a WSM Kit which is okay.

Shortblock Rebuild Kit - Yamaha 701 61X - 2-Stroke1.00 Over Size Pistons - 82.00mm

Yamaha 701 61X Complete Standard Shortblock Rebuild Kit. Carbureted 2-Stroke Motor. Kit Includes: New Crankshaft, All Pistons, Top End Bearings, Complete Gasket Kit & Crankcase Sealant. Fits The Following Models: 1993 Yamaha VXR Pro 700 Shortblock Rebuild Kitit1993 Yamaha Wave Blaster 700...

www.atlanticjetsports.com

Sounds good, I'll give him a call.

Your little boat is sick!
If I lived on a river, I would definitely have 1.

It's a ton of fun! I've had a bunch of different toys over the years and this one offers the most smile per gallon so far.

 

[Cryptonick]

Your little boat is sweet! I cant think of a more reliable motor than a yamaha 701!

 

[OCD Solutions]

Having each owned Aluminum Mini Jet Boats with Triples in them (YAM 1100 and KAW 1100), both Guys arrived at the same conclusion that Triple Power is NOT worth the extra Noise, Weight and Fuel Consumption.

They both say that 100% Stock Yamaha 701, or Stock 760 with it's 62T Exhaust are the perfect match.

What about the 4-strokes?

 

[Cryptonick]

There are a ton of incredible and fairly reliable options depending on how deep your pockets are…… But id say dollar for dollar a yamaha 61x/62t platform is pretty reasonably priced reliable and hard to beat. Whats it top out at with the 701 currently? Do you have a link to what hull it has?

 

[JC-SuperJet]

What about the 4-strokes?

My Friends only use 2-Strokes for simplicity, weight and cost reasons.

Doesn't mean a modern Fuel Injected 4-Stroke won't perform better. They are doing good business with the reliable Yamaha Two Strokes. So they are sticking with the 2-Stroke Platform.

If a Customer shows up with a 4-Stroke Engine he wants installed in a Jet Boat, I'm sure they will do the job for the right price.

 

[kevbo]

You can get good low speed thrust with the Superjet style exhaust if a larger nozzle is used. It just won't go as fast as it would with a tuned pipe. For untuned exhausts, keep the ports low! You can widen the exhaust port a little and up the compression a little. Make sure the nozzle is at least 85mm and the rpm is over 6500. Using a 155mm pump is a better option for lower speed boats.. These jet boats have a lot of hull drag so upping the power doesn't help top speed very much, as many owners have learned through experience..

 

[waterfreak]

I think you could definetly fit a b pipe in there! that's 20 HP right there with no loss in reliability .
I would say contact @JetManiac for all of your yamaha parts needs.

 

[RBS145]

There are a ton of incredible and fairly reliable options depending on how deep your pockets are…… But id say dollar for dollar a yamaha 61x/62t platform is pretty reasonably priced reliable and hard to beat. Whats it top out at with the 701 currently? Do you have a link to what hull it has?

That's the way I ended up going, I'm working on an update with some pictures, this boat was overhauled this summer after a rocky trip earlier in the season. Topped out at 30 upstream and 35 downstream. Although, I think that number is bit higher now. I'm not 100% certain, but is similar to this kit.Click here

I think you could definetly fit a b pipe in there! that's 20 HP right there with no loss in reliability .
I would say contact @JetManiac for all of your yamaha parts needs.

I ended up getting a R&D pipe modded to fit in there. The B pipes were too long past the flywheel side.

 

[RBS145]

I had a good crash mid season and cracked some welds on the hill. Long story short, we spun out and slid backwards into a log jam. Which cracked the steering nozzle, we didn't notice that when we looked. Headed downstream and it blew apart when I tried to turn right. It resulted in the boat not turning at all and going right into a big cut bank at speed.



Used a ton of electrical tape and big zip ties to piece the remaining parts back together. The limped the boat 10 miles downstream to the truck. I had a couple more trouble free, but rough trips which caused some large leaks in the hull. So it was time to strip it down to nothing for a bunch of welding.

Lots of reinforcements to the hull and repairs to cracked welds.


Added a well needed foothold to keep us in place.


Added pump protection bars.

 

[OCD Solutions]

The pump protection bars seem like a no-brainer plus they add a nice little boarding step.
I'd be curious to see a list of typical repairs and areas to beef up on these.

Is that a teflon hull liner?