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Offline Mokai Dreamin'

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Growing pains
« on: September 19, 2019, 03:16:56 PM »
I thought I would do a 10 hour update on my 2.0 as I'm starting to see speculation creep into some of the messages and posts here, so wanted to update everyone on what's happening as of September 19, 2019.

First off a confession. When I did my initial review a few months ago, I did not have my Humminbird GPS hooked up in my boat. I just downloaded a couple of speedometer apps, not realizing they were in kilometers per hour, not miles per hour. So while I achieved up to 19, it was 19 km/h not 19 mph. 19 km/h is roughly 12 mph. This was not a sustained speed either, as it typically dropped down to about 9 or 10.

I started working with Rick at Mokai about the problem, and had been in communication with Tom about this issue, as  well as a few other individuals who owned the 2.0. I had been reluctant to post anything as that was only going to fuel negativity about the boat. I also didn't think it was fair to Mokai to start bashing them,  while they were in the process of working with me to resolve the issue.  Hitting somebody while they are down is never a nice thing.

The first issue was the stock gear ratio. The boat had a 3.1 inch diameter gear sprocket on the clutch, and a 2.6 inch diameter gear sprocket on the overdrive. That combination produce roughly a 20% overdrive. Mokai determined through some testing that while the boat seem to be working with lighter weight people, when you started getting up towards 200 pounds the engine would crap out before it would get to speed. You can kind of think about this as being in fourth gear and being on flat ground. Keeping in mind that you're starting out in fourth gear, and it's going to take a while before the engine is not taxed and you can realize the full potential of that fourth gear ratio. If you take this example a little bit further and introduce an additional load (like an extra 30 or 40 pounds or say going uphill) the engine would not have enough power in reserve to ever get up to speed.  This is what was happening with the stock gear ratio.

So, Mokai switched over to a 2.9 inch diameter gear sprocket on the crankshaft (clutch was removed) and went to a 2.8 inch gear sprocket on the overdrive. This combination reduce the overdrive from 20% to 3%. Think downshifting into third. Now, the RPMs of the engine went up, from 3650 or so to 4430, and the engine had some more power to actually achieve its full potential.

While this was very helpful, another problem cropped up. People could briefly see some faster speeds (over 20 miles an hour in some cases), but then the boat would crap out and either significantly slow down or stall in some cases. The situation was worse under load.  So If you were on nice flat even water you might get up to speed, but then again you may never get up to speed on a river with current. The boat would have enough power to maintain a slower speed, but that was it.

Another forum member here discovered or questioned that the issue might be with the fuel delivery. He ran some tests along with Rick at Mokai and discovered that the gas tank in the 2.0 was only capable of delivering about a half gallon per hour, and the boat seem to need about 1 gallon per hour at full throttle. The problem was the draw tube, which goes inside the tank. This is a little brass tube with some screening on the bottom that quite literally sucks up the gas, which then goes into the fuel line to the carburetor.

While everyone involved thought this was the eureka moment, and the boat was finally going to come up to speed consistently, it still was having issues. The culprit this time, the pulse pump. There was some question as to whether a vapor lock was forming, as the pulse pump is sitting very close to the engine and gets quite hot. This turned out to not be the case. The problem seem to be with the signal itself, which was being taken from the crankcase side of the engine. I noticed on mine, that oil was getting into the pulse line, which obviously was interfering with the signal. I even went so far as to buy a new pulse pump and relocated the pump much further away from its original location.

Well,  my results were mixed. In some cases I was getting up to 17 miles an hour upstream, but then after about a quarter mile the boat would lose power and I would drop down to about 8 or 9 miles per hour. I tried moving my gas tank up front, tried lighter weight gas tanks with larger gas intakes in the rear, etc.  I could not get over this hurdle.

One other form member here was getting a sustained speed, and came to find out he was using an electric fuel pump. His test seem to indicate that right around 4000 RPMs the pulse pump could not keep up with demand. These small engines were not designed to run past 3650 rpm's, so that's part of the problem, but the same pulse pumps have also been used successfully with engines at rev at much higher rpm's.  So, the location of the signal is still in question. The electric fuel pump bypasses all of this and just delivers up to 15 gallons per hour.  He is getting sustained speeds at 175 pounds.

I installed an electric fuel pump on my boat and just recently did a test, and I could not get past 14 miles an hour. Since I had previously gotten up to 17 this just added to the confusion. I had spent so much time working on this problem that autumn creeped in here in Alaska, and the river started to get covered with fall foliage. The Mokai is very susceptible to small amounts of debris, and I suspect that what was going on in my case is I was picking up debris on the intake grate, before I was able to get the boat up to full speed. So, while I think the problem is solved with the electric fuel pump, I still have not seen a sustained 17+ miles an hour personally on the river. The 17 btw was upstream. 

I say on the river, as I took my boat out to a local lake and I saw up to 18 miles an hour on a flat stretch, and this was before the electric fuel pump and any change to fuel line. Load seem to be a catalyst for the problem.

So, once again I think the problem is solved, but will have to wait for a few more people to purchase these and do some testing to confirm that. So far I only know one person who was able to get sustained speeds.

So, what is Mokai currently working on?  Well, they designed a new one piece hood to allow for a true cold air intake for the carburetor. This is going into production and will be available right around October 1 or so. They are working with Kohler and trying different pulse pump signal locations on the engine. They will also be experimenting with an electric fuel pump, and may even play around with some additional gear ratios. I'm not so sure any change to the ratios will be likely, as the 3% ratio seems to be one of the best banks for the buck.

I can say in my experience this boat is extremely sensitive to load, and it really likes flat, calm water. If you will appreciate the boat is essentially in third or fourth gear, then you can appreciate it doesn't take much before the engine will start to lug, and you lose all your power, and you can't downshift to 2nd or 3rd. 

My experience also seems to indicate that right around 14 miles an hour, this boat takes on a different personality as it comes up on plane. If it cannot reach this initial 14 miles an hour, then it will never get up to top speed. I think this is similar to other boats that take on a different personality as they come up on plane. Resistance is reduced, and the engine almost breathes a sigh of relief, and then has enough power to push the boat even faster. 

If you think you're going to go out in current, and get 16 or 17 miles an hour I'd say forget it. There's just not enough reserve power here in my opinion. Get yourself out in a nice calm river or perhaps head downstream and you could really make some tracks. In short the Mokai is still no jetski.

The speed increase is quite significant though compared to previous models, as long as you understand the limitations. I hope this helps to clear things up a bit. 
Best,
Troy

Offline happul3

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Re: Growing pains
« Reply #1 on: September 19, 2019, 04:58:38 PM »
That's great investigating, Troy! In combination with previous posts, it reads like a thriller :) Even though I have no intention of buying v2, it is a very interesting story and answers many questions, even may have some hints as to increasing v1 performance. There however something I am a bit confused about: your analogy with car gears. Maybe I read too much it that - it is just an analogy after all - but the reason a car does so badly at 5 mph in 4th gear is that the engine's rpms far below what they are designed to be. As a result the an engine may be putting out 10% of the rated HPs or just stalling altogether. There is no way around that in a car with a manual transmission because the ratio between engine rpms and  car speed is strictly fixed by gear. But that not the case with a Mokai. Even if one anchors the boat, the engine is perfectly capable of rotating pump at whichever rpms governor and/or water flow resistance allows.     So the Mokai should be able to reach what speed it supposed to reach regardless of whether it starts from stand still or being temporarily helped by an external force (a catapult, perhaps :)  Am I missing something here? 

Offline Mokai Dreamin'

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Re: Growing pains
« Reply #2 on: September 19, 2019, 06:16:10 PM »
I was just attempting to compare the experience in the Mokai to something most people could relate to. The car analogy seem like a good one, even though you are correct it's not something you can directly compare.  Writing is a bit of an art form too, and I think I'm better than most in my descriptive writing, but by no means perfect. I'm just trying to help people make an informed decision.

The whole overdrive thing can be a bit tough to wrap your head around, or at least it was for me. With infinite power and torque you could create whatever ratio you wanted to and have it work, but with 9.5 hp and 13 +  foot-pounds of torque,  you obviously have limitations at certain loads. To compound or complicate things,  the resistance or load does not stay constant.  This boat performs differently on flatwater than it does in current for example. It performs different at 170 pounds than it does at 200 pounds. It even performs differently with weight distribution, but only up to a point.  For example, once the boat gets up on plane, then adding too much additional weight up front can actually slow the boat down as it creates more drag. At slower speeds, that same scenario can help the stern from digging in too much. I think once you start getting into this you appreciate what a difficult task it is to design a boat!

It's funny you mentioned the implications for version 1, as the person who discovered the fuel issue to begin with on version 2, is trying out an electric fuel pump on the version 1. He believes the reason version 1 is running hot was due to it running lean. He has a stock boat, so we will see shortly if his theory holds water. I will not mention his name here as I think that's an infringement of privacy. Up to him if he wants to post the results or not, but suffice to say there are some additional theories being tested by others.

I just wish I wasn't the sole guinea pig at the beginning of all of this! It's been a very trying and frustrating experience.

And, I don't want to really get into bashing Mokai here as I think there's plenty here to digest already, I really feel quite strongly that Mokai should have recruited about a half dozen beta testers to test this boat before they went to production. Enough said there.

Overall I think they have a fine product here, but it certainly was not without its growing pains.
Best,
Troy

Offline Painlesstom

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Re: Growing pains
« Reply #3 on: September 19, 2019, 06:36:13 PM »
Thanks for the great posts Troy, very helpful to anyone interested in the 2.0.

FYI The heat issues with the 1.0 has already been found to be the air plenum. I've done extensive testing and shared all my results here. These fuel pumps have no issue feeding the Subaru's.  http://www.improvingyourmokai.com/index.php/topic,1237.0.html
Tom

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Offline happul3

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Re: Growing pains
« Reply #4 on: September 19, 2019, 11:10:20 PM »
There is no question that better cooling helps v1. But it does not preclude the possibility that v1 is also fuel-starved at full throttle and run lean/hotter than it could otherwise. Is there good evidence that pump and pick up are adequate during full throttle operation? I recall that I saw surprisingly variable fuel pressure when I connected gauge after the fuel pump. I discounted those observation thinking that the cheap gauge must just be crap, but perhaps there is more to it. And that was not even full throttle / under load operation.   

Offline Painlesstom

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Re: Growing pains
« Reply #5 on: September 19, 2019, 11:21:07 PM »
1.0 used the same motor as the previous one piece Subaru models, and the same fuel pump. My 2011 with the high compression EX17 head is fed just fine with this fuel pump with oil temps always 220 at the highest. Stock cooling configuration without my water cooled muffler or intercooler on a stock engine has shown oil temp up at 280+. With improved cooling flow and my water cooled muffler on the 1.0 the performance stays the same the entire trip, I start out at 4180 rpm on that boat and it will stay there all day.
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Offline happul3

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Re: Growing pains
« Reply #6 on: September 20, 2019, 08:11:28 AM »
Consider this as a possibility: If a lean-running motor is cooled well, it's oil temperature can be as you describe and the performance will be stable. But the lean condition is unchanged and motor is underperforming ...   

Comparing V1 to previous model does not exactly prove that v1 is running fine. Again, it is possible that all the Subaru models have  undersized/underengineered fuel delivery systems. What we need is to check fuel pressure after the pump during full throttle / full load operation. Perhaps splice a gauge into fuel line such that it is visible from the operator sit?

Offline Hillbilly

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Re: Growing pains
« Reply #7 on: September 20, 2019, 08:50:38 AM »
Troy, your threads are just great.  Lots to learn here that can apply to all the boats.  It seems that the hull design of the newer boats can actually achieve the "on plane" state, which is terrific for speed, especially in calm water.  Your description of the accelerate in high gear and gearing change needed for different weights makes me wonder if a torque converter may eventually be the answer. 

But let me ask about the electric fuel pump.  Do you use a pressure regulator?  These carburetors and the sliding barrel Mikuni's that I use are sensitive to pressure in the bowl. How do you obtain adequate flow at open throttle and not over pressurize at low speed/idle?  Could someone share the correct setup here on the forum?


Offline Painlesstom

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Re: Growing pains
« Reply #8 on: September 20, 2019, 09:03:23 AM »
The fuel pump is 1-2 psi @ 15 gph. It wouldn't present a problem with the float needle as the plastic Mikuni pulse pumps can generate up to 5 psi. So no regulator is needed. The only concern I would have with electric is a means of ensuring the pump shuts off if the engine stops, not just when you shut the engine off. If there was a leak and the engine shut off from lack of fuel, the pump continuing to run would be bad. So some kind of controller that saw a tach signal to keep the pump energized would be safest.
Tom

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Offline Mokai Dreamin'

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Re: Growing pains
« Reply #9 on: September 20, 2019, 09:23:06 AM »
George:

I'm just using a one psi, 15 gallon per hour electric fuel pump. So far, no issues. If you got into the 2 to 4 psi then yes, I think a regulator would be a good idea or you could create a loop back to the tank to relieve excess pressure. Tom would know more about this than me, but that's what I've seen guys do when I researched this on YouTube. Running a return back to the tank with a check valve I think would be an easy solution. And of course not sitting there and letting the pump run without the engine being started would be a good precaution as well. The Stik boat uses the Mikuni carbs and their electric pump is over 2 psi, more like 3-4 psi. As far as I know there is no issue there either. 

Lastly, I don't know if this is the permanent solution as Mokai is still working with Kohler on alternatives.  Grabbing the pulse source from another location may very well prove to be just fine. The crankcase has been cited as not being a very good location. Have you played with this at all?

Looks like Tom beat me to the punch, so what he said :) Take care.
Best,
Troy

Offline happul3

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Re: Growing pains
« Reply #10 on: September 20, 2019, 09:52:42 AM »
The fuel pump is 1-2 psi @ 15 gph. It wouldn't present a problem with the float needle as the plastic Mikuni pulse pumps can generate up to 5 psi. So no regulator is needed. The only concern I would have with electric is a means of ensuring the pump shuts off if the engine stops, not just when you shut the engine off. If there was a leak and the engine shut off from lack of fuel, the pump continuing to run would be bad. So some kind of controller that saw a tach signal to keep the pump energized would be safest.

Can the pump be fed by alternator only? Simplest solution could be to add a bridge rectifier between original voltage regulator and battery and feed pump from that connection. Battery will see a very slightly reduced max voltage and the pump will shut off as soon as motor stops. The only possible drawback is that starting with empty carb bowl could be problematic. Not sure how significant that  that is. Easy to check though.

Offline Mokai Dreamin'

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Re: Growing pains
« Reply #11 on: September 20, 2019, 10:18:23 AM »
Can the pump be fed by alternator only? Simplest solution could be to add a bridge rectifier between original voltage regulator and battery and feed pump from that connection. Battery will see a very slightly reduced max voltage and the pump will shut off as soon as motor stops. The only possible drawback is that starting with empty carb bowl could be problematic. Not sure how significant that  that is. Easy to check though.
The manufacturer doesn't specify the range at which the electric fuel pump can operate. I doubt it would be an issue running up at 13.5 to 14 V though, but not certain about that.  I also don't think it would be a problem to start the engine without the fuel pump engaged. In fact, that's exactly how I do it right now or it floods very easily. The carburetor bowl is far from empty.
Best,
Troy

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Re: Growing pains
« Reply #12 on: September 20, 2019, 11:01:26 AM »
Troy,

I did play with the pulse origin years back.  Lots of karts took the pulse from the crank case but oil fouling was a problem, as it was for me.  Taking the pulse from the head, on the carb intake solved that problem and gave a reliable pulse for the fuel pump.

I may experiment with the electric pump.  Automatic shutoff is a safety concern but someone will figure that out if the electric pump works out.  The pulse pump should be adequate, as karts use them and they use lots of fuel.  I run some bigger carbs on my KX's and was rejetting this summer just to see what power could be obtained and got to the point where the motor seemed fuel starved when running at open throttle with bigger main jet.  I assumed that I over jetted but it could be that the pump couldn't keep up.

Offline happul3

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Re: Growing pains
« Reply #13 on: September 20, 2019, 12:18:55 PM »
The manufacturer doesn't specify the range at which the electric fuel pump can operate. I doubt it would be an issue running up at 13.5 to 14 V though, but not certain about that.  I also don't think it would be a problem to start the engine without the fuel pump engaged. In fact, that's exactly how I do it right now or it floods very easily. The carburetor bowl is far from empty.

To clarify, the additional rectifier (it is really only a single diode that would used, but for some people acquiring a full bridge component may be easier, I suppose) would not increase voltage fed to the pump relative to feeding it from main battery. When engine operates, charged battery is at >14V anyway. The extra rectifier diode just prevents pump being fed by battery alone...

Offline Mokai Dreamin'

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Re: Growing pains
« Reply #14 on: September 20, 2019, 12:47:11 PM »
To clarify, the additional rectifier (it is really only a single diode that would used, but for some people acquiring a full bridge component may be easier, I suppose) would not increase voltage fed to the pump relative to feeding it from main battery. When engine operates, charged battery is at >14V anyway. The extra rectifier diode just prevents pump being fed by battery alone...
Yes, your explanation makes sense. I overlooked that. Fishfinder is operating up there at about 14 V too, although I recall getting warnings from that thing. I don't see why your idea would not be viable. The only issue I could see is if you don't get the engine started relatively quickly, you don't have any way to get additional fuel to the carb.

Unfortunately, most new engines now are adjusted to be on the lean side, so they are much more difficult to start and with EPA restrictions, you can't get access to the jets easily to remedy that.
Best,
Troy