Building modified 787, tuning and order of operations.

[IDoSeaDoo]

Hey guys. I'm finally to the point of engine building on my dream XP project. It's been 8 years coming. Here is the list of goodies going in there:
42mm Novi carbs (look stock, but are bored with NOVI bombsights and no choke plates)
port-matched OE rotary valve cover
Spec1 Factory Pipe
PSI Adjustable dome head (as well as a good stock head)
MSD Water Injection
97 SPX water box
MSD ignition control
1mm bored cylinders running weight-matched ProX (ART) pistons
R&D Power Plenum Flame Arrestor

I'm not sure how to go about breaking in and tuning this thing. I am afraid of running this thing lean and burning up the pistons on break-in. I am not too sure about this PSI head, so I was thinking of experimenting with it later, after I have the motor broken in. Initially, I was going to just install the stock head and stock ignition, and maybe even leave off the water injection. Break it in, then install the other goodies. The carbs come with 162.5 mains and 77 pilots with a silver spring and 1.5 seats. What should my pop-off be? I'm not sure if this spring is OE (probably is). How many turns out should my screws be? I plan on not running the water regulator, but instead hard-jetting it with a 150 main jet. Should I use the front or rear of my Factory Pipe?

I'll definitely be using premium gas and Klots PWC oil for assembly and break-in. Once I break in, I'll switch to Amsoil Interceptor. I clearanced the RAVE valves and chamfered all the ports on the cylinders. Some were downright NASTY. I did not raise the exhaust ports as I was recommended. I was a bit nervous to do it.

This is my first time delving into such big mods. All hints greatly appreciated.

 

[mikidymac]

Matt Braley is the one you want to talk to about jetting.

There is no reason to use the Klotz, just use the Interceptor from the start.

 

[IDoSeaDoo]

With aftermarket flame arrestors, how does one secure the carbs to the pipe? I've had a rotary valve crack once because they were unsecured. Don't want to repeat that...

 

[mikidymac]

You should have a bracket that goes from the aircleaner base to the pipe.

 

[IDoSeaDoo]

Mine has no bracket or place to attach one that I can see

 

[GGuillot]

I'll definitely be using premium gas and Klots PWC oil for assembly and break-in. Once I break in, I'll switch to Amsoil Interceptor.

Why not just run what oil you're gonna run from break in going forward? Seems like an unnecessary risk to make the switch between different oils. During break in, once you get it out on the water and get it under load I'm sure the rings will seat regardless which oil you use.

If you're unsure of it leaning during break in, just run it less than half throttle first tank and ck the spark plugs frequently for the indications of it being lean or rich.

 

[IDoSeaDoo]

I was recommended Klotz PWC oil for break-in. It apparently makes better films. Anyway, the guy that recommended this builds performance engines for a living. He said to use it as assembly lube and to break it in. I trust his judgement. I will definitely check plugs often. I'll also have an EGT gauge with me, and will make sure temps don'g go beyond 1100F.

I spoke with Matt Braley last night and he suggested that my jetting is okay. I am running 162.5 mains and 77.5 lows with a 1.5 seat. I will make sure that my pop-off is between 15-20psi. I plan to run water injection on my pipe, but stick with the stock head, at least through the break-in period. I'll also leave off the MSD enhancer. I'm very curious to see the difference that makes.

I'm still concerned for my rotary valve. Maybe in time, I'll fab some sort of bracket for it. I really like this plenum, seems like it'll breathe very well.

 

[mikidymac]

Klotz isn’t any better than other oils for breakin. Also keep in mind it isn’t the correct spec oil for your engine. There’s s also the group of thinking that you don’t want any synthetic oil for breakin to allow the rings to seat.
I personally would not use or recommend Klotz in a Seadoo or for breakin period. And I use Klotz in my superjets.

 

[IDoSeaDoo]

I mounted my hi-flow mikuni fuel pump on the hull, with about a 12" hose to the pulse line. I keep hearing about a fuel line restrictor and realized there was one in the oem fuel strainer. I'm not running one anymore and wonder if I should put a jet in somewhere.

Removing the carb pump, I realized that there is another restrictor in the return line of the PTO carb, but not the MAG carb. I'm not sure why that restrictor was there. I can only theorize that it's due to the fact that the MAG had the pump.

I also was hinted to get my Pop-Off around 18psi for all the mods I have. Indeed, with the free-flowing intake and larger carb throat, there will be less vacuum in the carb, and no doubt need less pop-off. However, my carbs came with a 2.0N/S and the lowest I can achieve is about 30psi. I guess I need a 2.0N/S but then it just seems like my jets are too high: 162.5 high and 80 lows on 2.0NS.

 

[Matt Braley]

The jetting you have came in the carbs and it's too early to split hairs with that stuff until you see how it runs. There is always a little fine tuning involved so I'd wait until you see what the ski asks for.

Aftermarket carbs do sometimes need a #65 jet in the return line. A high speed Mikuni jet will screw into the single side of the stock plastic "Y" piece. If those carb bodies didn't have the original restrictions drilled then they will not need that since they were once stock carbs.

 

[IDoSeaDoo]

The rear carb has the restrictor, but the front doesn't. I don't really want to modify them in case I ever want to sell them, so I think I'll just put a 65 jet into the front return orifice. I believe it'll screw right into the hose barb and both carbs will have the same restrictor. Someone in the future may want to return to a carb-mounted pump. Heck, I may want to.

 

[IDoSeaDoo]

The jetting you have came in the carbs and it's too early to split hairs with that stuff until you see how it runs. There is always a little fine tuning involved so I'd wait until you see what the ski asks for.
.

I ordered the 2.0 N/S and some other jets already. Matt, I believe you mentioned that popoff should be closer to 18psi. The lowest I can get with the 1.5 is around 30, which sounds high for the wider carbs. I saw an old thread where a guy got 62.5mph with an X1 prop running a similar setup. He had 2.0N/S, Rossier Pipe, and OceanPro FA. Sounds pretty similar to my setup. Said his carbs were dead on, but rich up top. He used 167 Mains, while I have 162.5 I think I can use the needles if I need more fuel up top. Will dial that in with the help of my EGT probes tapped into my exhaust manifold.

This thread was relevant as well, especially for these carbs: Help with Novi 42I carb jetting. - Page 4

 

[IDoSeaDoo]

Needle and Seat came in. Had to use a black spring to get it to 18psi. Since my NOVI carbs were in series, one had a restrictor in the return line, and one didn't. Since I'm using the External mikuni dual-pump, my carbs will now run in parallel (getting their own fuel feed). Hence the other carb will need its own restrictor. I used my pop-off tester to determine the restrictor size by seeing how much pressure it builds when I blow air through it. It's about an 80 or 82.5 jet. I ordered more jets to use as the largerst I have is 77.5. Someone on fb suggested I just add one to the main return line, thereby restricting both, but I'm not sure if that would somehow compound the restriction on the one already restricted. Anyway, you must have equal restriction on both return lines in order for the carbs to act the same.

 

[Matt Braley]

I mentioned adding a jet to the return line three posts ago. I also included the size and location. I looked on the 2010 thread you linked and a guy had just gotten off the phone with Novi and received the exact same advice.

 

[IDoSeaDoo]

I wonder why NOVI told him to use a smaller restrictor.

 

[Matt Braley]

I saw them say 60-65. I recommended 65 because I've always used that one and been fine except for one set of odd carbs that kept flooding out at idle so I went a little larger on that one. It's a matter of maintaining good fuel pressure without having too much.

 

[mandriva]

I used psi dial a dome many years! check the O ring who seal the dome and chamber combustion! She leak easy if you increase or decrease the psi and you risk hydro lock, the O ring broke and water leak into the chamber combustion!

 

[IDoSeaDoo]

I used psi dial a dome many years! check the O ring who seal the dome and chamber combustion! She leak easy if you increase or decrease the psi and you risk hydro lock, the O ring broke and water leak into the chamber combustion!

I traded that head for a nice R&D. Even on stock head, I'm getting 175psi compression. Hope that settles out once I run it some