Do 787 carbs need to be cleaned after fuel line replacement?

[Shane0524]

I'm about to change out some gray lines on a 1996 GTX 787 with 49 hours on it. This machine sat up from 2007 until December of 2014 and is in great condition. It had 41 hours on it when it was brought back out after nearly 8 years. The machine runs perfectly now but my question is, do I need to clean the carbs along with the fuel line replacement, or just filter or what? Any tips on fuel lines, cleaning filters or removing carbs. Also can anyone point me towards how to remove the carbs and the difficulty level. thanks

 

[Sportster-2001-951C-Stock]

I say if the engine runs flawlessly, you probably don't need to disassemble and clean the inside fuel chambers of the carbs. If you are removing the carbs in order to replace the fuel lines as preventative maintenance and it's running flawlessly already but while the carbs are off I would take the opportunity to remove the fuel feed side plate off the carb and check the fuel filters, remove and blow them out to make sure they're clean.

If you find trash in these tiny mesh filters and/or green corrosion inside the fuel lines, you might also want to disassemble the metering side of the carbs for a thorough cleaning of all passages as well. In this case the minimum parts I think you might need are replacement metering needles, these come with the brass seats and new o-rings for the seats. The rubber tip on the end of these needles tends to take on a groove over decades and can sometimes begin sticking in the seat. This needle sticking in the seat can cause hard starting and/ fuel flooding, with rough idling and inconsistent idle. The needle/seat sets are calibrated for your carbs so make sure to purchase the correct ones and leak check the fuel feed side gaskets by pressurizing with a few psi of air to confirm those old recycled gaskets aren't leaking fuel.

I recommend the Mikuni SBN carburetor manual for reference and advise not to change the metering spring, keep the original, and avoid bending the metering arm.

http://www.mikuni.com/pdf/sbn_manual.pdf

 

[Shane0524]

Thanks for the advice

 

[CReynoldsMIZ]

Here's what I would do. I would disassemble the carbs, blow out the tiny carb filters, and put it all back together. Being $20 years old I would probably replace the needle and seats as well. If you just do those things it shouldn't really mess with the way it runs being that you didn't mess with the low and high speed screws.

 

[Shane0524]

Can you shoot me a part number for the needles and seats, or tell me which number they are on the carb diagram. Do the intake gaskets between the carbs and engine need to be replaced if through carbs are taken off? May the filters need to be replaced or just cleaned out?

 

[Sportster-2001-951C-Stock]

The 787 motors all use the 1.5 seats I believe. This site lists the 1.5 seat as well:

http://www.seadoosource.com/carbreference.html

If you want to be certain, the factory service manual should have the correct info as well, www (dot) seadoomanuals (dot) com has a nice library of factory manuals, grab one if you waven't already, there's tons of important info in the manuals.

The seat/needle set you would want could be either of these two types, 1 each/carb, I use the normal type which has worked flawlessly for decades, inspect the seat internally(with magnifier lens) and polish the surface with lapping compound if you see burrs on the seat (sometimes low quality aftermarket parts finish is poor) or reuse the original brass seats.

786-35018-1.5 (high alcohol resistance tip)
786-35015-1.5 (normal tip)

After removing the internal filters for cleaning then you should be able to blow them clean with a few gentle shots of air, or you can spray through them with acetone based carburetor cleaner to reverse flush them if you like.

The carburetor to manifold gaskets might rip or tear when you remove the carbs, you might want to have a spare set on hand. I often am guilty of reusing them unless I have a set handy or the originals are too beat up. A little heavy grease can hold them in place while fitting the carbs.

 

[Minnetonka4me]

If any rubber parts feel dry....just rebuild the carbs with new genuine kits. Its not that expensive.

I carry OEM kits and needles and seats in stock at all times.

 

[Shane0524]

So if I remove the carbs and clean the filters, and replace seats and needles, will I be able to put the carbs back on and have it work just like it does now, or will it have to be re-tuned to some degree?

 

[CReynoldsMIZ]

Correct. It should run just fine.

 

[Sportster-2001-951C-Stock]

You shouldn't need to do any carburetor tuning other than perhaps adjust idle speed slightly if anything. I would say aside from that if it doesn't run exactly the same, you must've made an error during reassembly.

However, once it's all back together you'll need to confirm the oil injection pump control lever is adjusted correctly by confirming the mechanical position and probably will need to adjust it some, considering it's controlled by a cable connected to the throttle linkage.

The factory service manual describes how to check and adjust all of the linkages, so if you don't have a copy of the BRP service manual for your model you should download that for review before beginning work.

One further word of advice, if it's not running properly and flawlessly as it is now, that means there's a problem that should be addressed ASAP, instead of "riding it for the day" while "hoping it fixes itself" without addressing the issue. It's not a good idea to run a 2-stroke engine that's not fueling properly b/c the pistons can be overheated if it's running too lean. For example, say for instance you forgot to install a gasket at the carb/intake there would be an air leak at that flange which would cause that particular cylinder to run lean. In that case the engine would not be running correctly like it should and you should easily be able to notice the loss of performance.

 

[Shane0524]

With 49 hours on a 1996 that runs perfectly with gray fuel lines, after the line replacement, what's some opinions on whether or not a full carb rebuild is necessary?

 

[Sportster-2001-951C-Stock]

I would only service the carbs if you plan to remove them. When removed, check the filters on the fuel feed side of carbs and if trash is found there in the filters then disassemble metering side for cleaning.