Just got back from testing on the river after installing a Jetworks mod on my GPR-WHY DID I NOT DO THIS SOONER! Actually I have had one on my XLT for nearly a year and it has been great, but I didn't find time to do the GPR till last week. It used to be a pooch out of the hole and now it takes off like a scalded cat! We also dumped the catalyst and switched to a R+D D plate at the same time. It seems that the pipe needs to build some heat now before you get top rpms. I used to get max revs the first pass with the cat in (on a cold motor), now the second pass seems better than the first. I was getting 7080 the first run and 7140 the next four times?? Does the pipe warm up quicker with a cat than a D-Plate. A hot pipe will pull more revs than a cold pipe-it acts like it is shorter. Maybe a cat equipped boat builds heat in the pipe sooner so you get the best of both worlds for one pass. Cold motor combined with a hot pipe? Maybe the exhaust system was not full of water the first ride (from being apart)? I will have a better idea after the next ride. Best run was 75.9 mph going with a 2.5 mph current and about 71 against the current. Fuel had just switched from 4 bars to 2 during testing. We set the valve to open at 3000 rpm (with full flow coming in about 3500) by using all three washers. Gotta love it when a plan comes together.

NICE, are you using it with or without the free flow?

Voo
My boat is an Island Stage 3 (1200) without a free flow. It has:
Porting
A Protec head
Gas valves
Avent CDI
Oil injection deleted
Accelerator pump deleted
Prok F/A's
Reed stuffers
Everything Carl could think of in the pump and ride plate


Best speed at low altitude (Havasu) 76 mph.
Best speed at home (2400' ASL) 73.5.

How does this mod work on a ski with the sound suppression in place? You see, I'm already planning mods for next season

Seems to work well. I am not sure what you are asking me when you say "How does it work?" So far no problems. I have about 1 hour on the GPR, but I have like 30 on my XLT with the same setup (Island Stage 3 also).

quote:

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Originally posted by 75 + Single:
Seems to work well. I am not sure what you are asking me when you say "How does it work?" So far no problems. I have about 1 hour on the GPR, but I have like 30 on my XLT with the same setup (Island Stage 3 also).

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What I was asking is does it work as well on a ski with the sound suppression on as it does on the ski's with the free flow???

Sorry I did not "get it" sooner. Here is the best answer I can give you since the only free flow equipped GPR around here was my 01 that I sold to a buddy a couple years ago and he has since parted with it and now there are none that I am aware of. I recall the free flow on my old craft doing NOTHING for the performance of my boat, just making it very loud. Loud enough to **** off my neighbors at the lake and make me the subject of rude comments on the deck during Happy Hour on Saturday afternoons. The Jetworks mod however turned my boat from a slug (on the low end) into a rocket. I have so much power now that I can break the prop loose at will, even at 10-15 mph. Remember I am at 2400' and this kills performance, just ask Woody in Nevada. My boat used to take off like a 22' Scarab with a 350 and now it just jumps off the line. Would it be better with a free flow? Maybe, maybe not. Fercho would best answer that, he has the experience. Could I use more low end power, not really, I have all I can use now, because I have no desire to change to a prop that will hook harder and go slower. I am presently using either a depitched 14/20 I Cut or a Nujet (both from Carl at Island Racing)-both are excellent by the way. Here's my 2 cents worth. Forget the noisy free flow and just do the jetworks mod alone-you will be happy with the results. Hope I answered your question this time. Where are you located BTW?

Thanks, I didn't know you are running with the sound suppression on also. I don't want to remove it and this answers my question. I'm in Michigan and keep my ski in the northern lower peninsula on a large freshwater lake, Lake Charlevoix.

Voodoo, be prepared to change your prop pitch. I was running the same pitch as you before adding the Jetworks mod. Now, I'm running the Nu-Jet 6.5 Pro at 13/17.

Is it difficult installing Jetworks yourself?

For 50 bucks, and it improves your bottum end that much, all I have to say is ****.

Is this the mod that you are talking about

http://www.rivayamaha.com/RivaStore/product_page.asp?Category=Flow%20Control%20Valve#

Fercho, you should patent this so that Yamaha will have to pay you big bucks in the future. Granted everyhting is switching to Fuel injection and stuff.

Heck liquid. This mod has been around for years in other ski's. I wish that someone had applied it to the GPR early enough or even Yamaha incorporated it in their ski's. I would probably had made the GPR's Holeshot King of the two strokers.

There is more to the mod than just a valve.

http://www.hydrotoys.com/gpr/fernando/flowcontrol/Flow%20Control.pdf

What exactly do you do to the jetwork mod?

Stage2
The purpose of the Jetworks mod is to change the way water is introduced into the muffler (waterbox). On a stock boat it flows through the water jacket surrounding the exhaust pipe (it is double walled) unimpeded-the flow is unrestricted and water is being fed into the muffler any time the motor is running. The problem is that you end up with a muffler full of water all the time and when you take off you must "blow the water out of the muffler" before you get full power. Hence sluggish takeoffs. The jetworks mod reroutes the water from the pipe overboard and supplys the muffler water from a controlled source thru the jetworks valve to the muffler. The jetworks valve is adjustable and is normally set to start allowing water to flow to the muffler at 3000-3500 rpm. Thus the muffler is much drier at idle and acceleration is greatly improved. Did I get that right?

yes, but just dont idle the boat for long periods of time without blipping the throttle to allow water to cool the rubber couplers........i melted one before on my tripple pipe boat going through a 1 mile no wake zone about 3 years ago.

Thanks Dana I overlooked that. We were blipping the throttle quite a bit at Havasu last fall at the Worlds. Gawd that is a long no wake zone from the race site thru London Bridge and past the marina on the other side. I thought I was going to have to change plugs get on plane. Are you riding the Firecat this winter or did you get a new ride?

Terry

Some guys claim there's no overheating issue at idle. But, since I already had one expensive waterbox meltdown, I decided not to take any chances and installed a bypass valve for the no-wake zones. It's much more quiet, too. Check out this topic: http://rivaforums.com/eve/forums?a=tpc&s=6446095904&f=4886094314&m=663101425&r=663101425#663101425

BTW, I've since upgraded all the hose to Riva's synflex double-walled hose. The clear stuff was wearing easily against other surfaces and was too rigid to maintain a good seal.

So that is what it does stock, with out Fercho modifying the jetworks mod?