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Author Topic: Fuel Delivery  (Read 379 times)

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Offline Painlesstom

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Fuel Delivery
« on: September 09, 2019, 08:59:51 AM »
Historically the Mokai has come with various problems to solve, each model with their own issues and some issues carried across to each one. People bounce ideas around and eventually a solution is found and sometimes the culprit is different than initially guessed. That's what forums do, people talk, they guess, we wait for someone to share results. Every past model has lost performance when hot due to cooling issues, and when I hear multiple reports of performance loss with the 2.0 when hot, I automatically expect cooling problems to be the case here too; from looking at pictures of the boat I saw how that might be the case. It's come to light that fuel delivery issues are causing problems for some people which causes a lean condition, a lack of power, and running hot; so for now the cooling system is off the hook. lol   ;D

Additionally I would just like to add that while I don't care for the new design of the 2.0 as it would not suit my needs in the conditions I would use it, it is a pretty cool concept with lots of potential for many people. It is definitely faster than any previous model if everything is working correctly, and I sincerely hope Mokai can refine it to the perfect craft they and their customers wish it to be. There are people out there who think I am trying to put Mokai out of business, and that's ridiculous. I'm just filling a space in the equation to make these cool boats better, everything has an aftermarket and that's a good thing for everyone. It's no secret that we don't see eye to eye, but I've driven the sales of their boats with my support and advertising for many years and I hope that one day they see that. And who knows, maybe someone will bring a 2.0 to me and I'll actually like it?  :D
Tom

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Offline Craig5251

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Re: Fuel Pump
« Reply #1 on: September 10, 2019, 09:15:02 AM »
That was a very good post Tom. Iíve sensed some tension from a ď newbie ď lately about the 2.0, but this explains your position perfectly.
And anyone thinking you want Mokai out of business is nuts. They produce the product you enhance.

Offline Painlesstom

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Re: Fuel Delivery
« Reply #2 on: September 18, 2019, 07:17:59 PM »
Thanks Craig. Those tensions have been resolved so no worries.  \./8

From what Mokai has told a couple people, the 2.0 has fuel tank pickup and fuel pump pulse issues, which starves the engine of fuel at full throttle and causes it to run hot and not reach full speed. I've seen video of one running with a 1.0 fuel tank and a 2 psi electric fuel pump and it was flying.
 
From what I've heard so far, Mokai has no solution yet. I bet they are wishing they had done more testing now..
Tom

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Offline mokamo

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Re: Fuel Delivery
« Reply #3 on: September 19, 2019, 03:21:54 AM »
flying? Any video like that will definitely increase Mokai 2.0 sales.

Until now no video? Whats going on here?

Offline Painlesstom

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Re: Fuel Delivery
« Reply #4 on: September 19, 2019, 09:18:52 AM »
It was definitely past 20 mph without a doubt. But the video is not mine to share publicly and was asked only to share it privately. I can PM you the link with the same stipulation.
Tom

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Offline mokamo

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Re: Fuel Delivery
« Reply #5 on: September 19, 2019, 11:46:07 AM »
Thank you Tom.
Saw the video and i'm convinced to buy one.  I think i still have a place in my garage where i can hide it from my wife :)
My 2017 Hobie Adventure Island is now for sale :)

I may need to contact the owner of that video to find out the procedure and parts to fix the fuel starvation.
I will also call Marie to hear what she would say about reported issues and latest update on fixes...

Offline Painlesstom

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Re: Fuel Delivery
« Reply #6 on: September 19, 2019, 01:31:20 PM »
Glad I could help.  Good luck!
Tom

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Offline voipwell

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Re: Fuel Delivery
« Reply #7 on: October 09, 2019, 11:51:13 PM »
I'm the owner of the video and I'm glad it was helpful to you.
If you are considering purchasing a Mokai there were two issues i encountered.
1)Oil from the crankcase was getting into the pulse fuel pump that relies on the positive and negative pulses that come from the crankcase via a small tube.  It was causing the engine to starve for gas during high rpm.  This is a common problem with multiple solutions.  I chose to put on an electric fuel pump.  And,  the pulse fuel pump can be simply used as a bilge pump.

The second issue was that the pickup tube in the gas tank was screwed in to tightly to the quick connect on the gas tank.  I simply removed the quick connect and turn the tube 3 turns counter clockwise. 

Then the boat was perfect for me and my wife.

There are reports that at around 200 lbs driver,  the boat may not plane.  I believe it is true.  I also believe that Mokai is working on it.  I also believe that at the current 1.02 to 1 gear ratio that Mokai left a lot of impeller rpm off the table.  This whole release of 2.0  was so difficult because a couple of issues happened at the same time making it very difficult for them to figure it out.  I mean you have the tank pickup tube restricted and then you have the fuel pump issue at the same time.  I think they thought they were working the engine too hard at 1.3 to 1.  I don't think there were.  To take advantage of the torque and hp curve for kholer they need to only turn the engine at around 3600 to turn the prop at 4680.  I believe they can go over 1.3 to approaching 1.4.  to hit 5k rpm of the impeller.   1.3 is what they introduced the 2.0 at.  But the fuel problems made them pull back to 1.03 and when that didn't work they left it there until they figured out the fuel system which i believe they have.  That just leaves one more problem for Mokai.  200 lbs.  My guess is that they are going back to 1.3 and that will plane the 200 pounders.  That would bring the impeller speed to 4680 rpm.  1.4 will bring it to 5040 rpm and i believe it could reach that.  I purposely have not asked them about what they are doing.  I've purchased another boat from them and expect to pick it up within a week.  Although i was willing to take one just like the one i have,  they are not that kind of company.  Hey,  an easy $5600 as is.  No way,  they told me that when they solve the issues they would be glad to.  I've been told my boat is being assembled so rather than ask how they fixed it I'm going to let myself be surprised. 

I've only been aware of these 2.0 problems since i took delivery end of August.  Since then i have seen Mokai make very big efforts and big progress in making it perfect.   Does Mokai care about the roll out problems they had with 2.0?  I do believe so.  That's how i judge.  If they care they will get it done and i do believe they are finally there.  I think they executed the release poorly.  But, if i had to choose between a good release execution and a great boat,  I'll take the boat. 

Offline voipwell

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Re: Fuel Delivery
« Reply #8 on: October 10, 2019, 12:15:30 AM »
I think Mokai intended this boat to go 27 mph.  I think it did in their testing(1.3 to 1).  I think they even did get 200 lbs of driver to plane.  But the fuel system sent everything into a tailspin.  But they don't give up and when the first successful video shows up 5 months after you start shipping things aren't going so good.  That's a bad enough situation to crush a lot of people.  I've seen people fold for less.  Mokai is tough and i don't think i would ever underestimate Rick Murray.  I have a better insight into why he is the only player in the game.  They really believe in what they are doing but i bet this was the worse year they every imagined of experiencing.  But,  on the other side of this i'm happy to see a man put 20 years of his life into something and finally get it to where he wanted it(and i wanted it).  The intensity of the struggle to get it there only enhances the victory. 

Offline Mokai Dreamin'

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Re: Fuel Delivery
« Reply #9 on: October 10, 2019, 03:14:04 AM »
I've already commented elsewhere on the forum,  but I'll add to this particular post about the gear ratios to clear up a little confusion.

The version of the boat that shipped in July used a 3.1 inch gear sprocket on the engine, and a 2.6 gear sprocket on the overdrive. At that particular ratio, the engine was spinning at around 3650 rpm. If you run the math on this, it will theoretically produce  4351.92 RPM's.There is friction happening inside the gearbox, there is friction happening at the hull bearings, so actual number would be lower. But for comparison this is a good number.

As Nick pointed out, Mokai thought that the engine could not produce enough power at that particular ratio, so they switched the gears to make it easier on the engine.  They went to a 2.9 inch diameter gear sprocket on the engine to a 2.8 inch diameter gear sprocket on the overdrive. This combination produced 4588.21 rpm. The engine RPM went up to 4430. I have many videos I shot myself that show the tach at this speed, as well as the tach at 3650 or less at the original ratio.

One way I found to make this easier to wrap your head around this is think about the original ratio as being in fifth gear and then downshifting into fourth gear. The RPM of the engine will go up, as you change the gear ratio, all else being equal.

So, you can see by the numbers the stock gear ratio will not produce faster speed. It will however reduce engine RPMs and improve fuel economy. That is the main reason in an automobile we have overdrive to began with.

If you went to something like a 6% ratio, you would end up with 4583 rpm's at the impeller. Engine RPM would drop from 4430 at the 3% ratio to around 4300 at 6%. Engine rpm does NOT remain constant. I made this mistake at the beginning.

I think what's useful about this discussion is what the speed is at the impeller, but I also want to point out or emphasize that the engine RPM does not stay constant. At a reduced ratio the RPMs go up, and at a higher ratio the RPMs go down at the engine. If the engine had infinite power then higher ratios would spin the impeller faster, but this is not the case. The engine has finite power, and power will balance itself between impeller speed and engine speed based on load. This is real world and what I experienced when I changed ratios.

Personally I think the engine craps out on torque at the higher ratio. The Kohler reaches its maximum torque at under 2500 RPM if I'm not mistaken. So, I don't think going back to the stock ratio is going to produce more speed or help with  heavier  individuals.   The 3% ratio seems to be about the best bang for the buck IMO.  The other thing is there's a finite amount of combinations due to the belt length.  I'm currently working on an idler pulley for my engine. so  I can go from the 3.1 inch clutch  diameter to a 2.9 inch diameter gear sprocket on the overdrive. This will produce this 3% ratio and give me the clutch back. A 6% gear ratio will Improve fuel economy ever so slightly, but is still going to reduce RPMs  at the impeller where it counts.

As to the draw tube, I had a different experience than Nick.  The quick connect valve for the gas consist of a spring with a ball that seals the opening when the fuel hose is removed.  When I examined this connector and  inserted the nipple from the fuel hose to  compress the spring  and push the ball down to allow fuel to flow,  it did not extend below the threads of the draw tube. So, with that said no matter how far I attempted to thread or screw in the draw tube,  it would not interfere with the fuel delivery. In fact if it did touch the ball that seals the opening in the valve,  you would not be able to insert the nipple to begin with as the ball would hit the top of the tube and prevent  the  mechanism from engaging that lock it in.

That's not to say what Nick is experiencing is incorrect, but rather there are some quality control issues going on here.  if I was to unscrew my drawl tube three turns, it would fall out. There's not enough threads there to hold it in. So, it would seem on the fitting that Nick got somebody got a little ambitious with the tap and when too far.  I actually don't think this is a fault of Mokai, as I don't believe they manufacture the valves in house.
Rick from Mokai said the drawl tube diameter is too small. It's also possible by relocating the pulse signal to another location the electric fuel pump will not be needed.  Last I talked with them they were working on this.

I can also say that Nick  is the only one who's gotten the speeds over 20 miles an hour sustained.  I'm right about 200 pounds (202) and  I was able to get up to 17 miles an hour on flat water, but  could not sustain that in the river.  I attributed that to picking up debris. Last time I went out with the electric fuel pump I never got over 14, but again  I think this was because I was picking up debris. On totally flat water in a lake I got  more sustained speeds, but it took a LONG time to get to that speed. Like 1/4 mile or more of distance.

To me it did not seem like there was anything in reserve, so I seriously doubt a different ratio is going to help this boat. The numbers don't support this either.  I'd also bet that for people going upstream in rapids, you're going to slow under 10 miles an hour at 200lbs.  Probably more like 7-8 mph. At 175 pounds, maybe 10-11 would be my guess. 

The Mokai is still no jet ski, but the 2.0 is still the fastest stock Mokai out there.
Best,
Troy

Offline voipwell

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Re: Fuel Delivery
« Reply #10 on: October 11, 2019, 09:01:28 PM »
May be possible multiple draw tube problems but i think what Rick meant about the draw tube size was in relationship to compensating for the pulse pump issue.  They found that a larger diameter tube than stock helped it and were considering that as a solution i believe.  But i have a feeling that pulse pump is off the table now.  Now i believe they probably reviewing ratios that they have a stable fuel system.  It seems like they are very methodical.  Troy,  i know Rick wants to plane 210 lbs with 2.0.  I want to with 1.0.  All i know is weight is very important so he's going to have to thread the needle and he won't give up until he does.  Troy,  by the time Alaska thaws out next spring,  Rick will be working on his 2 seater Mokai and you should be planing.  Wouldn't hurt to stay away from sugar and carbohydrates just in case he can't.  Worked for me.

Offline voipwell

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Re: Fuel Delivery
« Reply #11 on: October 11, 2019, 09:25:26 PM »
I cringe when you post you got 17 mph with a bad fuel pump.  Clean grates will get you 19 but that is still 1 mph from planing.   He's very close.  He's just got to find the absolute sweet spot.  It must be between 1.03 and 1.3.  But think about it.  Fuel system first to get the most power.  Gear Ratio second.  I think he's on number 2 now.  As hard as this is for Moakai right now,  I think Marie is withering from it but i think Rick is a Geek head and is loving the challenge.  Just my guess.  It is his life's work.  And possibly 1-2 mph from reaching his goal.  He'll make it.

If you removed your gov. then i don't think anything i have to say about my stock settings would pertain to you.

Offline Mokai Dreamin'

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Re: Fuel Delivery
« Reply #12 on: October 12, 2019, 02:29:32 AM »
 Well, there may be something to revisiting the old ratios now that the fuel issue is solved.
 The data in my last message was based solely on  the stock fuel supply, and that variable has been changed. If you could keep the engine RPM over 4000 and use a 6, 10 or 20% ratio, then  you would most definitely increase speed.

Mokai may have to go to some kind of a belt tensioner though, as there is a finite amount of gear sprocket pulleys available, and it's impossible with the stock set up to maintain the  right belt tension without some kind of a tensioner.

I've already rigged up a little system myself, but have not tested it as I ran out of time.  I am confident that with Rick's perfectionistic personality,  he will exhaust  every conceivable option. So,  he's the right person for the job. Too bad  for the customers who purchased the boat before these issues got resolved though. I really think Mokai should be compensating the original users, but happy to see they are on the case at least.
Best,
Troy