Need help with carbs on 96 GTX

[jforest]

I have a 96 GTX with a 787. I've pretty much rebuilt everything from the engine to the jet pump, including the carbs. The carbs will pump fuel and both of them pop off around 26-27 PSI. It seems as if the carbs will not let fuel past the needle when I have them on and trying to crank it. When I take the carbs off, there is no fuel in the fuel chamber. I feel like I've tried everything prior to posting a thread but at this point I'm not sure what to try next. When I rebuilt the carbs, I sprayed all the ports and jets with carb spray to clean them out. Any suggestions would be greatly appreciated!

 

[soccerdad]

Will it start with a prime? You say it pumps fuel. How do you know? Does it pump it all the way into the return line?

 

[jforest]

I can put fuel in the cylinders and it'll start but then dies. I removed the return line and cranked it and it comes out the return fitting.

 

[racerxxx]

Are your fuel lines hooked up like this? Have your replaced your fuel lines? Just trying to rule out some stuff.

Sent from my SGH-T889 using Tapatalk

 

[jforest]

Yes they are hooked up like your photo. All fuel lines in the ski have been replaced and hooked up. I did them one at a time to make sure they were routed correctly.

 

[racerxxx]

When you dis assemble the carb, is there fuel in the fuel pump body of the carb? Is the pulse line hooked up? That is the black line on the left in my pic? It goes to the crank case.

 

[jforest]

Pulse line is hooked up. Doesn't seem to have any issues pumping fuel. When I crank the engine, plenty of fuel comes out the return fitting. Im thinking there must be a blockage I'm not finding after the needle and before it goes into the carb.

 

[IDoSeaDoo]

You sure your fuel is turned on? Try running a separate hose to a can of clean fuel.

 

[jforest]

The selector is set to on. I installed the carbs with no fuel in the fuel pump and turned it over until fuel comes out of the return fitting so I'm thinking that the fuel is on. The fuel is fresh as I filled the tank up a few weeks ago.

 

[TurnerBFC]

I had the same issue. Turns out that I though I had my new fuel lines on correctly, but I actually messed two of them up. Double check your routing. On the top and sides on the fuel baffle it says ON, RET, RES, VENT. Verify those are correct.

Good luck!

 

[jforest]

I'll double check when I get home today but would I get fuel if they were not correct? I know I'm getting fuel as the carb has pumped it out and I also used a syringe to make sure there was fuel in the line.

 

[jforest]

Is there a check valve or something on the side of the valve body that leads to the low speed jet? It looks like it would bring fuel in from the side then go through the low speed jet. I tried spraying carb cleaner through it but it did not let any of the cleaner through. It looks like there is a brass ball or something in the port. Both carbs are like this. With the gasket, it seems like its the only way it gets fuel.

 

[jforest]

Got to looking at it more and it was just a through hole that was used to drill a hole to the center hole where the check valve is on the bottom of the valve body. It is plugged on purpose.

 

[soccerdad]

http://www.mikuni.com/pdf/sbn_manual.pdf is the manual for the carb. Has an awesome description of the fuel flow in the carb. Could something be holding your needles down and keeping them from opening? Can you try a pop off test with the carb fully assembled?

 

[jforest]

I did a pop off test with the carbs assembled. I did a top end rebuild and had to split the case in order to clean it out. I'm wondering if all the cranking I've done has messed up the piston rings and/or the case is not completely sealed and not pulling sufficient air through the carbs. I'm trying to think past the carbs as everything with the carbs seems like they should be functioning properly. I tried to do a compression test but my harbor freight tester does not take good measurement. I'm working on getting a second tester from a friend to see if that helps.

On a side note, would the pulse line being open affect the compression test on the mag cylinder?

Thanks for everyone's input! I really appreciate it.

 

[IDoSeaDoo]

On a side note, would the pulse line being open affect the compression test on the mag cylinder?

Thanks for everyone's input! I really appreciate it.

Good question. Compression happens after the piston goes past all the ports, but if it could suck in a little more air via the pulse line, would that make the compression a little higher? Anyone have an answer?

 

[racerxxx]

Nope no difference. You do a compression test with the throttle wide open, it all goes into the crank case.

Sent from my SGH-T889 using Tapatalk

 

[mikidymac]

What carb kits did you use. Some of the cheap ones the diaphragm are very stiff and can hold the needle open but I guess they could hold it closed too.

 

[jforest]

I got the kit from SBT. I'm really starting to think that for some reason I'm not moving enough air across the carb to pull in fuel. I'm going to do a compression test when I get home and see what the results are.

 

[mikidymac]

The SBT kits might not be your problem but they are not the same quality as OEM Mikuni.

 

[mikidymac]

I think you have a carb issue. Even with low compression you should still have fuel coming out of the carbs.

 

[Seadoobuddy]

SBT do not use OEM needle & seats. Once they told me that I ordered OEM from Parkeryamaha.com

They may have the same "specs" but may not operate the same as OEM...just my 2 cents.

 

[IDoSeaDoo]

I didin't think the SBT kits came with needle and seat... am I wrong?

 

[mikidymac]

SBT do not use OEM needle & seats. Once they told me that I ordered OEM from Parkeryamaha.com

They may have the same "specs" but may not operate the same as OEM...just my 2 cents.

I think you are saying do not use SBT? Only use OEM.

 

[mikidymac]

I didin't think the SBT kits came with needle and seat... am I wrong?

None of the kits come with needle and seats but you need to replace them when you do a carb rebuild.