JetManiac/Blue 781 - backflip capable

Joined
Apr 29, 2016
Likes
77
Location
Malvern pa
#1
Been meaning to post this for a while. I bought my first aftermarket hull this year. It’s a RCW Havoc and the first AM hull I’ve ever ridden. It came with a very fresh 781 from jetmaniac. The ski ripped, but I had no skill and wanted more power so I bought a 1015. Long story short, found metal in the 1015 shortly after I got it dialed in, so I switched back to the 781 “temporarily” (or so I thought).

Many unforeseen machine shop issues have made the 1015 rebuild a 10-12 week process. In that time, I decided I was going to learn to flip the 781. I’d say I attempted 100 or so flips before I got them all the way around. Most of those attempts were with the big motor prop (8/16 thing blade) so the setup was not ideal. I finally got it and can now land 1 out of 5 or so.

This jetmaniac motor is insane for its size. Everyone who rides it is blown away. It’s had probably 100 gallons though it this season or more and water from time to time and it’s never had an issue.

@JetManiac and @Blue do an incredible job for an incredible price. Not to mention Chris is extremely helpful and gets stuff shipped suuuuuper fast. I’ve dealt with a lot of jet ski companies and these guys are by far the best!!! Highly recommended.

Setup details:
RCW carbon havoc
781 by jetmaniac
38mm carbs
Zeeltronic ignition, slightly more aggressive curve than wax curve
PFP pipe ran wet. 67.5 spray bar jet, 90 in the stinger
Stock 155 pump
6/12 prop Repitched to 7/14 -5mm cut back
Limited slip tank
Thrust trim

 

Spyder

Site Supporter
Joined
Jun 28, 2017
Likes
29
Location
Michigan
#3
I've got a JM781 in my chan and love it. I've never ridden a +1000cc ski but I love the power I get from the 781 in combo with the torrent 148 setback pump I have. I'm currently only getting about 3/4 of the way around in my best attempts. Not the ski's fault, I'm just a chicken. The ski did make it all the way around on it's own once when my feet came out. I prefer riding barefoot but had to break down and buy some wrestling shoes, I'll post a video if I ever get it all the way around.

Thanks guys for the inspiration to keep trying!
 

Blue

Port for the Sport
Joined
Oct 2, 2008
Likes
504
Location
St Cloud Florida
#4
Thank you for this post. Im glad to hear that you are happy with the motor. It would probably be even better with a smaller prop but by the looks of the video you are getting it done...

I was just tell Chris this weekend that i wish more people would try bigger carbs, more compression and maybe a little race gas rather than going to a bigger billet motor. The motors I build are very dependable, run great and have a lot of power with 38 carbs and pump gas. But with the bigger carbs and some other add ons like total loss theres no need for a bigger engine. There is still more power to be made in the 781 with the proper setup.

Thanks again.
Blue

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Joined
Apr 29, 2016
Likes
77
Location
Malvern pa
#6
Thank you for this post. Im glad to hear that you are happy with the motor. It would probably be even better with a smaller prop but by the looks of the video you are getting it done...

I was just tell Chris this weekend that i wish more people would try bigger carbs, more compression and maybe a little race gas rather than going to a bigger billet motor. The motors I build are very dependable, run great and have a lot of power with 38 carbs and pump gas. But with the bigger carbs and some other add ons like total loss theres no need for a bigger engine. There is still more power to be made in the 781 with the proper setup.

Thanks again.
Blue

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I do have Novi 48s and a PHP intake laying around. Maybe i'll give it a go!

PS, I did run the 6/12 for a bit and felt it was under propped. Maybe its just because i was so used to having the wrong prop but i felt like i was taching the motor out before i was halfway through the setup wake and just couldn't get the thing around. I didn't give it very long though. probably needed some more technique change.
 
Joined
Apr 29, 2016
Likes
77
Location
Malvern pa
#7
I too can vouch for the JM781. It’s very cool to see completely different setups around the heart of the machine. This video is of a JM 781 in a heavy glass hull, 38s, MSD enhancer, PFP, and an oem 155.

@Jcary85 , how is yours on fuel? My woman can burn 5 gallons in just over an hour. Seems like it eats a ton with only 38s.

Mine SIPS fuel. Its amazing. Everything is relative, but compared to the 1015 with 48s, it burns probably half the fuel. On a weeknight, I'm out for about 2 hrs, probably 1.5hrs of actual riding and don't make it through 5 gallons. Maybe 4ish.
 
Joined
Feb 19, 2013
Likes
4,819
Location
Chico California
#8
Thank you for this post. Im glad to hear that you are happy with the motor. It would probably be even better with a smaller prop but by the looks of the video you are getting it done...

I was just tell Chris this weekend that i wish more people would try bigger carbs, more compression and maybe a little race gas rather than going to a bigger billet motor. The motors I build are very dependable, run great and have a lot of power with 38 carbs and pump gas. But with the bigger carbs and some other add ons like total loss theres no need for a bigger engine. There is still more power to be made in the 781 with the proper setup.

Thanks again.
Blue

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What would your ideal setup be to get the full potential out of the 781?
 

Blue

Port for the Sport
Joined
Oct 2, 2008
Likes
504
Location
St Cloud Florida
#9
I think a 781BB with a
PFP or RRP style pipe WET. With a Ported exhaust manifold.
Novi 48s maybe even 49s
V Force Reeds 2 or 3s.
A good intake manifold
Compression in the 220 to 235 range
Total loss with an aggresive curve would ripp pretty hard.
If someone was planning a build with the intentions of doing a setup like this I could possibly even do a little more on my end to ensure it gives max potential.


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Joined
Feb 7, 2006
Likes
393
Location
Limerick, PA
#10
Congrats again buddy. The ski is a good machine but I know its your dedication and effort that made it come around for you. You can see how hard your working for it!
 

SXIPro

JM781 Big Bore
Joined
Mar 17, 2006
Likes
1,461
Location
Here on the 'X' mostly
#11
I'll chime in on the JM/Blue 781BB as well. Mine is in a plain old 2004 SJ with all the typical goodies B Pipe, MSD , Lightened flywheel, etc. etc. and it absolutely rips thru the entire powerband. If I don't consciously remember to hold on with a death grip when I pin it, it pretty much leaves without me. And the funny/surprising thing is that not only is the acceleration like flipping a light switch, but the top end is white knuckle scary now. I greatly enjoy when the clowns on their Sparks come around to 'play' and I just leave them behind choking on two stroke smoke. :)
 

Blue

Port for the Sport
Joined
Oct 2, 2008
Likes
504
Location
St Cloud Florida
#12
I'll chime in on the JM/Blue 781BB as well. Mine is in a plain old 2004 SJ with all the typical goodies B Pipe, MSD , Lightened flywheel, etc. etc. and it absolutely rips thru the entire powerband. If I don't consciously remember to hold on with a death grip when I pin it, it pretty much leaves without me. And the funny/surprising thing is that not only is the acceleration like flipping a light switch, but the top end is white knuckle scary now. I greatly enjoy when the clowns on their Sparks come around to 'play' and I just leave them behind choking on two stroke smoke. :)
My new favorite term.. is it fast bro. No its White Knuckle Scary ...

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