750sx Carb Rebuild Issue...

[Gunner_626]

My buddy and I just got done rebuilding my set of dual Keihin 38mm carbs as well as the fuel pump and after hooking up all of the hoses correctly the carbs pull fuel through the sending line but only right up to the carb inlet. There isn't enough suction to actually make the fuel go into the carb. Even when I pour some premix directly in and crank it, I can see the fuel sitting in the sending line probably an inch before it hits the carb. I also made sure that my pulse line was clear and it is blowing out air from the crankcase. What did I do wrong??? Any info is greatly appreciated! Scott.

P.S. I took off the sending line and blew threw it and the fuel filter on the line and bubbles came out at the bottom of the tank, so it is clear as well. Could my fuel filter be screwing up the sending of the fuel? The day before we rebuilt the carbs fuel was flowing just fine to the carbs and the ski idled great.

Before removing the carbs I had the ski running in the driveway the day before for 30 minutes. The ski idled great, it was just the higher rpm's where the carbs went nuts, so thats why we decided to rebuild. The pulse line is blowing on every rotation. Already tried both the on position and reserve. Gaskets were put on the exact same way they came off per exploded diagram. I've included some high res photos on the fuel pump and the carb as well.

Oh, and when I run the ski on the premix poured directly in, the carbs work wonderfully.

 

[Waternut]

P.S. I took off the sending line and blew threw it and the fuel filter on the line and bubbles came out at the bottom of the tank, so it is clear as well. Could my fuel filter be screwing up the sending of the fuel? The day before we rebuilt the carbs fuel was flowing just fine to the carbs and the ski idled great.

Are you sure it's hooked up correctly? This statement alone makes me believe you hooked up the supply and return lines incorrectly. If you blow into the supply line (the hose that sends fuel to the carb from the tank) nothing should happen because the fuel filter prevents anything from flowing backwards in that line.

The supply line on the carb is the lower fitting pointing to the right. The supply line on the tank is the aft fitting pointing to the right.

 

[Waternut]

One more thing. Your main jet looks like it's sitting really high. All of my main jets sit almost flush with the carb body. That wouldn't affect idle and may not affect anything but looks different to me.

 

[cmeripper26]

Did you check to make sure the needle valves are not siezed inside of the seats. This is kind of an uncommon problem but its happened to me twice which will cause no fuel getting to the intake. Or is the fuel not making it to the carbs itself like losing suction?

 

[Gunner_626]

I can blow straight through the fuel filter into the bottom of the tank. It's a generic fuel filter from autozone. I am 100% sure that all of the hoses are hooked up correctly.

Are you sure it's hooked up correctly? This statement alone makes me believe you hooked up the supply and return lines incorrectly. If you blow into the supply line (the hose that sends fuel to the carb from the tank) nothing should happen because the fuel filter prevents anything from flowing backwards in that line.

The supply line on the carb is the lower fitting pointing to the right. The supply line on the tank is the aft fitting pointing to the right.

 

[Gunner_626]

The fuel itself is not making it to the carbs, suction loss...

Did you check to make sure the needle valves are not siezed inside of the seats. This is kind of an uncommon problem but its happened to me twice which will cause no fuel getting to the intake. Or is the fuel not making it to the carbs itself like losing suction?

 

[tor*p*do]

Gaskets were put on the exact same way they came off per exploded diagram.

I think this is where you went wrong.
Get a good rebuild kit and replace all gaskets, diaphrams, etc
check needle and seat- replace if necessary

 

[Waternut]

Alright then, let's start with the simple stuff then...

Do you have the plastic film that goes between the fuel pump and carb? It sounds simple but I ran my ski for a while without it and couldn't figure out why it ran so crappy and so rich.

On the metering side, is the diaphram installed with the large metal side down? Does the order go in this order: metal backing plate, gasket, diaphram, metering plate? Does the needle move up and down smoothly? Did you check the pop off pressure with the new spring or reuse the old springs?

We'll try to get to the bottom of this but the bottom line is...keihins don't like it when the fuel pumps get rebuilt.

 

[Gunner_626]

Yes, all the gaskets are in the correct order on the fuel pump and the plastic film is on in the correct order. I didn't reuse the old spring and I kinda wish we didn't mess with the fuel pump in the first place. I'm going to try and reuse the old spring because i'm thinking that the new spring i'm using has increased the pop off pressure which might be causing my problem.

Alright then, let's start with the simple stuff then...

Do you have the plastic film that goes between the fuel pump and carb? It sounds simple but I ran my ski for a while without it and couldn't figure out why it ran so crappy and so rich.

On the metering side, is the diaphram installed with the large metal side down? Does the order go in this order: metal backing plate, gasket, diaphram, metering plate? Does the needle move up and down smoothly? Did you check the pop off pressure with the new spring or reuse the old springs?

We'll try to get to the bottom of this but the bottom line is...keihins don't like it when the fuel pumps get rebuilt.

 

[Kennay]

Just bring them by tomorrow after 6... I will fix them for you, and you can go home and install them and fire the ski up when I am done. Shouldn't take long....

 

[Gunner_626]

Problemo solved. Simple fix.

 

[Kennay]

Damn right it was. You are lucky you are only an hour away :bananapowerslide:

 

[cmeripper26]

Out of curiosity what was the problem?

 

[Gunner_626]

Since it was a universal type aftermarket kit, I didn't punch out a little tab on the clear fuel gasket which happened to be covering up the fuel inlet to the pump...