Factory pipe hx

[Bigredram87]

I have a factory pipe system off of a 720xp and wanted to put it on my hx. It looks like the only difference between the 2 pipe systems is some different clearance dents? Is that accurate ? Also the water restrictor claims it's a .5"od x.281 restrictor according to specs , is there something special about this piece I have never seen one or can I machine a piece with a .281" hole in it

 

[Bigredram87]

Also I read some older posts that people put 800 carbs on them instead , is it also safe to just jet the stock 720 carbs to factory pipes recommendations (everything else completely stock) or has that proven to be incorrect

 

[glsmohio]

I have a 96 spx (720). it has the factory pipe on it with 800 carbs and r d nozzle with trim tabs and I also put a 96 xp prop on it. they ski is awesome. tons of power. I also have a scoop gate on it. the ski has around 60hrs on it with no problems. I built the ski for my wife....

 

[Bigredram87]

That's cool!! I'm hoping for now I can just as safely re jet the 720 carbs to fp recommendations for cost reasons and later buy a set of 800 carbs

 

[Bigredram87]

But I would love some input on that and the hx vs standard 720xp pipe they have a digit different part number

 

[glsmohio]

It's how the pipe comes off the block. They're different manifolds if I remember correctly. Not saying you can't rejet the carbs of a 720 but if you're not spot on it could end up costing you a motor just putting that out there with 800 carb setup like 96 XPS they are spot-on

 

[Bigredram87]

Sounds good it seems like the manifold is the same part number at least

 

[Matt Braley]

The chambers are completely different. You will need a HX chamber. You must also measure the outlet of the chamber and make sure it's 38mm. The first ones were 34mm and they would burn up the rear piston no matter what you did.

No you should not run stock 38mil carbs even if you rejet them. They just cannot do a good job of feeding the monster your 720 will become with that pipe on it. Many people have burned up they're engines following that old advice.

 

[Bigredram87]

Thanks for advise as always matt. I am going to try search for someone to trade this pipe section to, am I correct that the manifold and everything else is the same ? Also matt what jets am I looking for in 800 carbs . Thanks Matt

 

[Matt Braley]

Yes the rest is the same.

40mil carbs without an accel pump- 70 lows and 142.5 highs. That's how they will come if they are from a 96 787.

 

[Bigredram87]

And I want a 38mm ID pipe outlet?

 

[Matt Braley]

And I want a 38mm ID pipe outlet?

You MUST have one. FPP would swap the original chambers for the upgraded ones with the 38mm hole back in the day. There are still 34mm chambers floating around out there though so folks need to be careful.

 

[Bigredram87]

Wow glad I talked to you first, I have never seen one of these water restrictor listed in parts list , if I can't find one is it as simple as just getting a coupler made with a .281" hole in it or is there more to it than that

 

[Bigredram87]

Matt before I go any further I should probably ask if this is even an spx pipe or if it is hx maybe they had it on wrong ski(piston is blown)

 

[Bigredram87]

So I measured the ID of the inner outlet pipe(not the outer lip) and I get between 37.3- 37.9mm depending on where I take measurement if that helps identify this pipe

 

[Matt Braley]

It's the later version of the chamber so that is good but if it lined up with the waterbox on a SPX then it won't on a HX. You can mock it up and see how far off it is. Maybe you can get away with a longer coupler or something, The HX chambers have the outlet in a lower spot.

To get the inside bolts of the manifold tight you will have to cut down the short end of a 6mm Allen wrench.

 

[Bigredram87]

Ok great , if i can make it fit tuning wise am I safe to just go with the gsx carbs? I didn't know if tuning would be different on this pipe vs hx

 

[Bigredram87]

From looking at pictures of people selling there's on eBay just curious if the pipe is supposed to have this pronounced inner tube (ID 38mm) others don't seem to have this

 

[Matt Braley]

Yes that looks normal to me. Sellers on ebay are clueless. I don't think I've ever seen one on there that's not missing pieces.

 

[Bigredram87]

Haha speaking of missing pieces my last issue is the instruction stating I need a .5"x.281" restrictor on the outlet line going out the hull, can I just make that piece I assume it's literally just to slow flow

 

[Matt Braley]

Yes you should be able to. I have not messed with that and have been just fine.

 

[Bigredram87]

When I do get this pipe installed I'm going to tune the pipe in a test tank , the fpp directions say to start at 3/8 turns out from closed on the adjuster and tune by testing the chamber temp 2 inches from j pipe. Does anyone know a good temp range for this besides there suggestion of a slow sizzle of water lol maybe like 200 F?

 

[glsmohio]

I'm telling you just set the carbs to what an 800 motor should be on an XP the 96 version you will not have a problem no need whatsoever to do anything else

 

[Bigredram87]

I'm telling you just set the carbs to what an 800 motor should be on an XP the 96 version you will not have a problem no need whatsoever to do anything else

Sounds good and your water adjustment on the factory pipe is at the 3/8 starting point ?

 

[glsmohio]

I can't remember but I'm still giving it plenty of water to keep it cool if I remember correctly this pipe gets you 20 or 25 horsepower you only want 15 or 18 of it to make it reliable