Custom/Hybrid Melmack's very unique 300sx build

[Melmack]

Rode the ski today. Got some good footage of how well it rides. Thanks to BBYamaha for filming.

We had some major issues. It Ran great on the trailer. The second we dropped it in the water, it died immediately. I messed with the pop off to no avail. Might be an issue with the reed valves. One of them was suspect from the get go.

Keep in mind what you see here is the ski running at 2/3 closed choke. That's the only way it would run in the water. Despite that, the ski runs night and day better than the stock pump setup. It felt like about as responsive as a stock 550sx. Here's one of two short clips of the test ride today. Next one up in a few minutes. And dont let the black wetsuit fool ya. I'm pushin' 200lbs!

 

[McDog]

The motor sounds weird.

 

[Melmack]

Second video is up. It sounds weird for several reasons. First it's a 300 single cylindar. Second, it has a loud Kerker pipe. Third, its running on 2/3 choke with a major carburation or reed vale issue. I can't imagine how it's going to run with a tuned motor and 2/3 more throttle.

 

[McDog]

I thought you were going to run some sort of 4 stroke motor?

 

[Melmack]

Read back a bit around post #8.

Yes, it will eventually have a very unique 4stroke. But it's not finished. The manufacturer is still working on it. This new motor will be as light as the 300 motor and makes about 50 hp stock but can add another 45hp with a simple bolt on device. The idea here is to develop a light hull and drive line that can handle a varied amount of HP. That way we can sell the initial craft as an EPA and CARB legal ski in all 50 states. My vision is to offer an affordable all around ski with ample hp to have fun but you can buy additional hp for 'Competition use only.' This will be a simple bolt up modification that most of us could handle with a torque wrench. Details are being worked out to obtain the engine by December and have it ready for Daytona. (Sorry, I can't go into it too much detail about the engine)

This ski is set up to test the abilities of this craft with about 45-50hp. Once tuned, I will test it and get feedback from riders in all types of riding situations. Then, I will install a much more powerful motor at around 80hp and see how the pump handles the hp increase. So far, it looks promising. It ran very well today with very low power. I'm going to make some changes and test again tomorrow. Hope to have it rippin' by then.

 

[Liquid Graffix]

is that the Guadalupe??? If so, we used to go tubin there! (went to school in San Marcos)

Thats a nice clean ski so far.

 

[Melmack]

Thanks. It is the Guad. Just south of the I-35 bridge. Great place to ride because of all the pro level Wakeboarders and glassy water. It's like a highway for boats in the summer. Wake after wake after wake. Lots of fun. This light ski is going to launch off those wakes. I'm kinda scared how it will react to a large surf wave.

BTW, Texas State or SWT?

 

[Liquid Graffix]

SWT ...before they changed the name

 

[BBYamaha]

Get a real motor so we can get this project going, stop beating around the bush.

 

[Melmack]

Shut up cameraman! :smile:

so, what years did you go there stunts?

 

[Sanoman]

l agree with some tuning this ski should run great! IDK how big you are,but it carries you well,the way it's running.

 

[Liquid Graffix]

I was there from 97-99, back when Playboy ranked us the 5th largest party school in America. Hence the name change

 

[Melmack]

Sanoman: I weigh almost 200lbs. Plus I replaced the pop off spring and the reed valves and it ran waaaaay better today. Still needs a ton of tuning. I'll try to get get another video tomorrow afternoon.

Stiunts: I didn't actually go to SWT but I did go to a ton of parties there. Still a big party school. I Lived there in SM with some friends that went there at the same time you where there. You probably knew some of them.

 

[WFO Speedracer]

Where are you at on the jetting, your starting point should be 77.5 low, 80 high 1.5 needle and seat 165 gram spring 1 1/4 turns out on the low sped 3/4 turns out on the high speed

 

[Melmack]

What size carb are those specs from? I thought you used the 34mm from the 500. Mine is a 38.

I'm too tired to remember where I left off tuning yesterday but I had the small silver spring, it was way too low. Wouldn't idle or run in the water unless choked. Then I put in the large brass spring, ran OK w/out the choke but has a dead spot in transition I can't tune out. I think the top is at 1 on top and the bottom around 1.5-2. I'm going to try the middle spring tomorrow (I can't remember my spring sizes.) I haven't pulled the jets, I just cleaned the carb and replaced the gaskets. This carb is 1 of a 3 carb external fuel pump set off a Yamaha 1100 that I modified for an attached pump.

 

[WFO Speedracer]

Interesting, so you have a 75 pilot and either a 95 or 107.5 main jet, the 1100 carbs had different jetting the center carb is jetted leaner than #1 and #3, either way I think your main jet is too big

 

[Melmack]

So your thinking just a tad low on the bottom and too high on the top by 20+points?

I'm using the #1 carb. It's the one with the throttle linkage off the front cylinder. I'll assume the pilot is close enough at 75 for now. I can get it to idle correctly within 1.5-2 turns out. I probably need to change the top then. The top seemed pretty close though. Once up to speed it ran very fast and clean and didn't get hot. I ran Wot for about ten seconds and the water was still pretty cool.

Dose the hesitation mean it's loading up or lean in the transition? It's not a bog that takes several seconds to clear out. It's just a split second hesitation between .5 throttle and full. It feels so close. I'm still thinking it could be pop off because I can pop the choke just a little bit and it transitions much better. I think I'll try this other spring just for grins and see what happens. If that doesn't work, Ill try the 95 jet off the center carb or look and see if I have an 80ish one too.

Thanks for the info WFO

 

[Melmack]

Also, don't I want the bottom as close as possible? Couldn't I go to a 77.5 or even an 80 on the bottom to have the adjustment screw almost closed? That would make for better bottom end response correct? In theory, you're screws would just have to be cracked slightly if it was jetted perfectly correct? Of coarse then I would have to go down even more on the top. Not sure how small the top jets get.

 

[jeepNski]

just out of curiosity, why do you guys build the 300 sx's... are they lighter. why not the 650 or 750?

 

[WFO Speedracer]

I see no way that thing can run properly with a 107.5 main jet, I could be seriously wrong but I doubt it.