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  1. #1
    Pistonwash's Avatar
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    97-99 GP (65u) mods



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    Flying Scotsman's Avatar
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    Are you still alive and kicking Mike ?

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    Moderator OsideBill's Avatar
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    Talked to him couple weeks ago, alive but busy.

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    ....back from the dead.... J-ME's Avatar
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    PW in da hizzle

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    Dave Sharp dav_dman's Avatar
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    Mike's forgotten more than i'll ever know about jetski's

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    Mpeavler's Avatar
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    who is this guy? He think's he knows something?


    He's washed up and on the has been pile in love with some woman from Ft Walton Beach...


  8. #8
    Echo's Avatar
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    Quote Originally Posted by Pistonwash View Post
    Page is dead.

  9. #9
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    GP engine & handling mods & upgrades- By Mike Thorne- Certified Yamaha Tech.

    First of all, I hope I can help simplify the process of learning more about your GP and possible upgrades that actually WORK! I have worked on Yamahas for 8 years and I hope to share as much info on the GP with you as possible.

    There have been design changes in the GP's original format over the 3 years of GP1200 production. The changes were in the hull, nozzle and exhaust chamber. This is basically all that has changed in the OEM GP design. The aftermarket modifications and other equipment mods I will suggest WILL help your ski perform better. They were not just tried and tested by me but, other engine techs and tuners that I have gleaned from over the years.

    The first "negative" attribute of the ski when you first ride a GP is something called "porpoising". This is the what happens when the ski begins to bounce up and down when riding, which affects speed and handling. Not to mention it is an annoyance. It can be cured. I will suggest the proper mods later. The more speed you develop with your GP, will be enhanced to a point of VIOLENT porpoising if this phenomena is not addressed.

    Your GP engine is a powerful unit in it's stock form but, it can be made better with a few suggestions. It can be made into a fire-breathing, arm-pulling beast with porting, carburetion and pipe mods.

    What to do first?

    The first modification you should do is address the "porpoising" effect.

    Next you will want to change your ski to handle and "hook-up" better. Then you will begin changes in your engine configuration.

    Here is a suggested list of handling mods in order of importance:
    1.) Bullet Marine/RIVA limited ride plate [helps eliminate porpoising]
    2.) R&D intake grate [helps in "hook-up" of ski]
    3.) Blueprinted (Solas) prop J prop or XO [will increase top-end speed w/ mods]
    4.) RIVA sponsons (Pro series) or (WORX) sponsons [helps turn and make ski handle better]
    5.) O degree '97 GP exit nozzle [helps in reducing porpoising but slows ski down, suggested for those who seek maximum porpoise reduction]
    6.) UMI steering system [helps with steering and handling]
    7.) If not the XO or J prop then get the Skat Trak pump. [This is the ultimate in "hook-up" enhancement]
    8.) Truing the hull [more on this later. helps with handling and tracking of ski]

    Engine mods-for limited ski builders in order of importance:

    1.) Aftermarket air cleaner- (R&D Plenum, RIVA single cone units, Tau Ceti and others) [a must in helping your GP "breathe" better]
    2.) OEM head milled or aftermarket Head [increases engine cranking pressure and helps with quickness]
    3.) Aftermarket cdi unit (RIVA) [increases your rev-limit and lets you change timing of the engine]
    4.) Aftermarket reed stuffers [helps increase the speed of your carb induction system]
    5.) Taper-bore OEM carburetors-qualified tuner modification, "I have a suggested tuner list later". [increases over-all flow of fuel/air to the engine]

    ****These are the first mods that should be done on your GP. ****

    This is a compiled ,tried and true list, of what HAS worked and is the least expensive to make your GP better. There are a ton of aftermarket companies and TONS of aftermarket goods available for your ski. But, you will waste money and time finding out what actually works and what does not. I have just simplified and saved you hundreds of dollars if you will follow my suggestions.

    Acquiring data to ensure proper tuning and upgrades- By Mike Thorne- Certified Yamaha Tech
    Now, that you have provided yourself with a list of modifications on your GP. Here's some more suggestions to help you "tune" your ski. Get a composition book and take notes. That's right, you're back in school. BEFORE you start your mod list, you must first write down your existing "baseline" of what are the current performance readings of your ski.

    As follows:

    1.Tachometer readings.

    2.Cranking pressure
    3.Top-end "flat water" speed
    4.Carburetion settings
    5.Oil/fuel mix ratios, something I forgot to suggest in the engine mods list. Take the OEM oil injection off and go to Pre-mix with your fuel. It is not mandatory, but HIGHLY suggested. Why? Because Pre-mix lubricates better and it doesn't depend upon an oil pump to work. If your oil pump ever fails, your engine is fried!!!!
    6.Record all conditions of testing i.e. , air temperature, water condition, impellor choice, ride plate and intake grate used etc.

    Equipment used for testing:

    Aftermarket tachometer- It is important to be able to accurately find your "target" rpm's with your mods and the OEM tachometer will not suffice. I suggest a (Tiny-Tach) or other aftermarket "JETSKI" tachs. This is an important tool in tuning your GP. Get one.

    GPS- This is another useful tool in finding your "target" top-end speed. You are wanting to develop a baseline on what your ski does with and without mods. Then you will be able to see where you are going and where you have been.

    Snap-On compression gauge- Again, another tool to help determine baseline on what your GP is doing or should be doing. Cheap gauges are worth what you pay for them and are mostly unreliable.

    Spark plug gapper- Important to have your plugs gapped right. I am very anal about my plugs being gapped right and clean.

    Mikuni pop-off chart- You should know what pop-off your carbs have along with the specific jets, needle and seat and springs. If you make changes in your fuel induction you will NEED to know what your baseline is and be able to re-jet from there.

    Yamaha GP 1200 factory manual- Duh! You need this in the greatest way. It has everything that is vital on your GP. Get one!

    There are other tools you can buy that will help you in tuning your ski, seek out and find what others use to monitor their skis. I use a laser temp gauge to help check temps of the head pipe and head. I have a "ballpark" range of temps for the pipe and head. This helps me get a snapshot of what is going on in the engine. Also, I have a water temperature gauge/sensor connected to my outgoing water. This gives an indication of what temperature the engine is running at various points of the power-band. I am looking at what temperature the engine is running at wide-open-throttle. Then I will know if it is too hot or too cold and change jetting or water to reach my baseline.

    One of the most important factors in your upgrades is knowing what your ski is doing before and after mods. Heat is the number one enemy to your engine. When you begin the process of "dialing" in your ski after engine mods, you will want to beat this enemy called HEAT. Fuel and water are the only things that actually cool your engine. So, when you are monitoring your ski after mods, focus on these 2 aspects.

    Fuel: Your ski has a specific need for a certain amount of fuel. When you begin to change your carburetion/air flow and head, the fuel demands of your engine will change also. Generally with a "limited" package of mods, you will only change the turns to your existing jetting specs on your OEM carburetors.

    Water: There are "by-pass" fittings that will help in directing flow and help with allowing more flow. You can also change exhaust manifold gaskets to help with flow. I suggest that when you begin to do (porting) to the engine, you change exhaust manifold gasket to a Raider 1100 gasket. It has bigger holes going into the cylinder thus increases water flow.

    Again, using your composition book, you will log in all readings and settings of your ski. This will help you determine what your ski needs in carburetion and cooling. Suppose you change the air cleaner without changing your carb jetting. Your ski was turning 6850 rpm's BEFORE you changed the air cleaner, now it is only turning 6750..what happened? Checking your comp book will show this differential. And you will then see that you need to change the jetting to get the rpm's to go up.
    Aftermarket cylinder head and carb phenomenon's- By Mike Thorne- Certified Yamaha Tech

    About your Head: This was taken from Group K's website, Harry and Gerhard Klemm are 2 very respected tuner/ builders in the jetski industry. I respect their opinions and concur with them. Their website is Group K and provides invaluable material.

    AFTERMARKET CYLINDER HEADS-

    While these parts are very attractive, we consider them to be questionably worthwhile. The claimed benefits of the billet heads are improved cooling and improved gasket sealing abilities. We agree that these would be very desirable qualities on a high compression engine format. However the stock engines push only 110 -120 psi of compression. The Group K Sleeper kits for both 1100 & 1200 machines pushes no more than 150 psi. Our testing showed that higher compression ratios were not a measurable performance benefit on our kits for these triples. Many of the billet heads we have seen are made to yield compression ratios that we consider too high to be compatible with 92 octane pump gas. Our testing showed the end result of this choice is a huge increase in operating temperature, with a questionable increase in performance.

    The modified stock heads have no cooling or sealing problems that we have observed. Good cooling is a function of efficiently exchanging the heat away, not just a function of the water jacket size. The water jacket surfaces of the stock cast heads are faceted and finished in a way that offers more than sufficient "water contact surface area". The greater the water contact surface, the more efficiently the head exchanges heat to the coolant. To date, we have seen no aftermarket heads that have more water jacket contact surface area than the stockers.

    Another claimed benefit of the aftermarket heads is a greater resistance to "warpage". Warpage, for the most part, is more a mechanic's "old wives tale" than a technical reality. No head, on an engine receiving a reasonable supply of coolant, can "warp". If an engine were run at length with little or no coolant, any head will eventually sustain a distorted head gasket-sealing surface. It is likely that a billet aluminum head would distort slightly less than a cast head. This is because the aluminum mass around the domes is typically so much thicker. Unfortunately this thicker mass also represents a longer heat path that reduces cooling efficiency. In situations where gasket surface distortion is an ongoing problem, the thicker mass head would be preferable.

    That pretty much sums up how I feel about heads.

    Now about carburetion-

    Now before you go out and spend $1500-$2000 on a set of *new* aftermarket carbs (Novi's, Buckshot's, SRM's and others) please hear me first.

    There is NOTHING wrong with your OEM carbs. Especially if you get them modified (read taper-bored). They will work smoother and even better than aftermarket carbs. Why you ask? Because they were designed by engineers who spent millions of dollars in r&d to make them. When you taper bore your OEM carbs you are increasing the air/fuel flow to your carbs without drastically changing the power-band. What usually happens to a person buying aftermarket carbs is they will be frustrated for months after buying them. Why? Because when you change the entire carburetion system on your ski without knowledge of SPECIFIC needs to your GP, it will not perform to it's peak. Most guys will go out and buy these monster 50 mm carbs, slap them on the ski and spend months trying to get the ski to run correctly. Without knowledge on jetting and ski NEEDS you will be frustrated.

    So, I suggest getting the OEM carbs taper-bored and they will perform wonderfully. Don't trade tuning headaches for 1.5 mph.. It's just not worth it. I'd rather have my ski blast out of the hole with NO gurgles or hesitations than going another 1.5 mph. Besides, you will save about $1500 in the process.. No brainer, right? You can send your OEM carbs off to a carb specialist and get them back with his jetting specs and voila'! Your ski now hauls butt and is quicker than you imagined.

    I will provide a list of carb specialist later.

    Hull truing 333- By Mike Thorne- Certified Yamaha Tech.

    First, you need to know this isn't a great "technical" process.. If you have time, you can do this right. You're not going to get the same results as going to a professional hull tech but, this will help make your hull work a little better.

    OK, enough disclaimers...

    You will have to remove the engine from the ski, then you will have to siphon or drain fuel/oil from the tanks. If the engine is in the ski when you flip it, it will cause the hull to flex inward and you won't get a "true" result.

    Be careful when you flip the ski over, make sure the handlebars are cushioned or have no weight on them. You don't won't to break the steering assembly. You can remove the rideplate and intake grate, this will give you a little more room to lean against the ski. This part of the process will take some time and ingenuity. There various ways to "hang" the ski or make a makeshift sawhorse stand. Figure out what works for you or ask others for help.

    What sanding material and tooling to use:

    There are a few different choices. I personally will take a 1 ft. piece of 2X4 piece of wood, cut it to about a 2X3 piece. I will use the cloth-backed 60 or 80 grit, wrap it onto the 2X3 and staple it on one side. This is for the first sanding run. The second run is the same piece of board with drywall sandpaper, 2nd run is the final touch-up. DO NOT USE AN ELECTRICAL SANDER or any type of mechanical sander... You cannot get the exact & accurate results attained by hand.

    After the ski is tits-up and secure enough to put adequate pressure...I take a big metal T-square and place it on the rear section of the hull. Make sure your straight edge is long enough to go from rear to about 30+ inches forward. From the rear of the hull "before trim tabs", I will inspect the hull forward. What I'm looking for is where the hull begins to "curve" toward the front.. This is where your water contact surface is at high speed. Where the hull begins to "curve" on back toward the rear...is where you want to focus your attention. I will take an erasable marker and mark the spot on the side of the hull where the "curving" begins.

    Now, I will take a can of gray primer and spray the bottom of the hull from a couple of inches forward from the marker mark, back towards the rear. Don't worry, you can take some acetone or mineral spirits and clean-up gray spots later. The primer will help me identify where the "peaks" and "valleys" are on the hull.

    I will begin to sand the HULL not the chines.. Slowly find out what dips and hooks are present. Remember, your focusing on the hull from a few inches in front of marker rearward to the trim tabs. What you will notice is there are dips and peaks...and a HOOK at the very end of the hull. As soon as your eyes and mind get a good picture of what is wrong with the hull... Begin to sand with FRONT TO REAR strokes...No cross strokes...just back and forth from front to rear.

    Work on the space between chines, one at a time... Start from one side and go across the hull to the other side. You will find some of the peaks disappear...and you might have a valley or dip to deep to sand out. Leave this for the 2nd run. When the rear of the hull does NOT have a hook in it, you are close. I used to sand the rear even with the trim tabs, I found that I had sanded a heck of allot material out, so much the yellowish fiber was showing through ALLOT! I now will just make sure the hook is gone...and I'm happy.

    Be careful NOT to take out too much material... USE YOUR HEAD!!! When the primer disappears, pay attention to how much of the peak or pit is gone. You might even want to re-spray areas to make sure they are straight. From time to time, take your straight edge and inspect the trueness of the hull. "Peaks" have to be sanded flat. If a "pit" or "dip" will not sand out, you will have to use a good filler to fill it. Wet systems has a good sand-able filler you can use... Of course you'll have to let it dry for the 2nd run.

    OK the rear hook is gone and you've filled the "pits" and "dips" let them dry... Now look forward of the marker, towards the nose of the hull. Since your 2X3 piece is straight and rigid, you'll have to really be careful since the hull is curving at a high degree of pitch. Don't mess with the keel yet. Focus on the marker curve forward and begin to sand the same front to rear stroking motion...you don't want to be consumed with this portion of the hull. Just sand the major peak areas and do not take a lot of material out.. I hope you can understand this.

    Make sure there is a good smooth transition from either side of the marker point. Remember your hull rides on the last 30+ inches of hull at wide open throttle... This is where you lose or gain performance.

    Now the Keel... There are few ways to approach this. You can make a template from a small block of wood with a widened V cut in the block of wood. This is a little hard to explain and probably best that most of you don't try it. I will super glue the 60 grit cloth sand paper to the cut out V and begin to work it front to rear and sharpen the V a LITTLE!!! I usually have couple of blocks that I have experimented with... I wouldn't advise most of you to try this because of the change in the Keel, from flat to V to a rounded V. It's a weird transition and you don't want to screw with it too much. You could end up hurting your ski. So I suggest you just leave it alone, it's not that important for what you are trying to accomplish.

    Now the 2nd run begins. You now will slowly and gently sand the chines...YOU DO NOT WANT TO TAKE OUT TOO MUCH MATERIAL FROM THE CHINES! So be careful! You will focus on the hook in the rear. The chines have it too. You can make a smaller 1X1 piece of wood, wrapped with sandpaper and work on the sides of the chines gently, sharpening them SLIGHTLY! You are mainly trying to get the dips out, that's all. Now back to the hull filler... Fresh 60-80 grit on the block and begin to sand filler flat. You've finished that and now you switch to the drywall sand-paper.. I like this type for finishing because I can see and blow it off better to reach my final finish.

    Take straight edge out and re-inspect... Is the hook gone? Is it pretty straight to the marker? Good transition past the marker?

    Also, be careful around the pump intake area...you just want it to be flat but don't take too much material out. You could change water flow into the pump if you take too much out of the forward intake area.

    I hope this will get you started...I know it will help to get the hooks and dips out...time and time again it has proven to help in tracking and hook-up. Just be careful not to take out too much material. Front to rear...front to rear...long strokes. I know I've left out some instruction. I am sorry, but it's hard to cyber-tune without being there.

    Water logged seats a nuisance well here is a trick to save you the headaches in the future!!!- By Mike Thorne- Certified Yamaha Tech.

    As you racers know, during the race, a million gallons of water is dumped all over your ski. And if you've noticed, after moto 1 your seat will retain a lot of that water. This phenomena is not as prevalent with newer models. But, for the sake of the GP's, it is. You may gain 20+ lbs. in a race. And in the venerable stock class...that is a lot!

    We noticed that in the ocean races this happens quite often.... So here's what you have to do.

    You will take the staples and other fasteners off of the seat to remove the seat cover. Letting the existing foam dry thoroughly or replace it altogether (not advisable) if damaged and rotten. It is shaped to your seat so this would be difficult for someone to try and reproduce. You can get a good upholstery person to do this for you, if you can't do it yourself.

    After foam has dried, you then will get a can of Scotch Guard waterproofing spray. Spray (read soak) the foam completely and let dry. You will then repeat this again after it has dried. Next step is to size and cut the heaviest duty commercial plastic you can find. Cut to fit seat. Then with your handy tube of silicone, put a bead of silicone along the "staple" lines area and begin to staple the plastic to the seat. You start stapling the right side then put a few staples, then go to the left side, couple of staples, then top, then bottom. Then begin to rotate like you were torquing your head. making sure the silicone is properly sealing and seating.. Do you understand? If not email us and we will get back to you....

    Next comes the seat cover, you will need the longer stainless steel staples when re-stapling the seat cover.

    Again I hope you get the jest of the mod.

    If it is too hard, take it to an upholstery shop and tell them how you want it done.

    After it has dried for a couple of days, voila'!! You have a water resistant seat that will not retain 1/10 of the water it did before, if any.

    Light is always better...quickness kills.

  10. #10
    African-American
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    Stock and dual cooling water routing

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