787 carb tuning/jetting for R&D exhaust. Carbs are all stock from past owner. Help!

[TurnerBFC]

Hi there,

I recently purchased a 96 XP and I bought it running rough. The previous owner said it would bog and run poorly up top.

The ski has flame arrestors and is fitted with a R&D exhaust setup.

So, furthermore, I went into the carbs today to find that the typical grey fuel lines did their part on the filters (I am doing a full rebuild soon on the carbs and replace fuel lines), but what concerned me more was that everything within the carbs I think was stock, here's the data:


MAG Side:
Needle & Seat: 1.50
Main Jet: 147.5
Pilot Jet: 75

PTO Side:
Needle & Seat: 1.50
Main Jet: 147.5
Pilot Jet: 75

and the springs almost looked like they were a faint green.

With this exhaust, should the carbs not be running some different parts inside than stock?

Can you guys tell me what I need to order and how to tune these carbs (HS, LS, etc).

 

[Matt Braley]

Yes I can. I have set up a couple of these pipes and they work good. If the jetting is stock the highs would be 142.5'2 and the lows 70's. It sounds like someone has set it up to compensate for the pipe. I think your complete fuel system service might bring this back.

 

[TurnerBFC]

Yes I can. I have set up a couple of these pipes and they work good. If the jetting is stock the highs would be 142.5'2 and the lows 70's. It sounds like someone has set it up to compensate for the pipe. I think your complete fuel system service might bring this back.

Ok awesome. Thanks for the fast reply.

What should I order? I have read 65 gram springs, and a 2.0 needle and seat. What do you think?

 

[Matt Braley]

I think you should leave the previous set up alone until you try it with a fresh fuel system. Springs change pop-off and that affects the low end. He previous owners description of how it ran matches the clogged internal filters you found.

I would get the O-ring and filter kit along with the new fuel lines. I always replace the fuel valve because they often fail and they are only $20 new. If has not had genuine Mikuni kits in the last few years then it will likely need them and fresh needle and seats.

 

[Seadoobuddy]

I think you should leave the previous set up alone until you try it with a fresh fuel system. Springs change pop-off and that affects the low end. He previous owners description of how it ran matches the clogged internal filters you found.

I would get the O-ring and filter kit along with the new fuel lines. I always replace the fuel valve because they often fail and they are only $20 new. If has not had genuine Mikuni kits in the last few years then it will likely need them and fresh needle and seats.

Happy Birthday Matt!!!!

 

[TurnerBFC]

I think you should leave the previous set up alone until you try it with a fresh fuel system. Springs change pop-off and that affects the low end. He previous owners description of how it ran matches the clogged internal filters you found.

I would get the O-ring and filter kit along with the new fuel lines. I always replace the fuel valve because they often fail and they are only $20 new. If has not had genuine Mikuni kits in the last few years then it will likely need them and fresh needle and seats.

OK. I am purchasing a kit of genuine mikuni parts to rebuild the carbs. So should I buy the 1.5 needle valves again and continue to use the current spring for pop off?

 

[TurnerBFC]

Also, what about the High speed and Low speed adjustments on the carbs? This is new to me as my other skis have never had carb issues.

 

[1983]

Use the current spring for testing with pop off gauge after inspecting and going through carbs. Only change spring as last resort if you cannot get pop off psi within acceptable range as these guys suggest.



Rob

 

[TurnerBFC]

Use the current spring for testing with pop off gauge after inspecting and going through carbs. Only change spring as last resort if you cannot get pop off psi within acceptable range as these guys suggest.



Rob

Gotcha! Thanks, Rob!