The gas lines to the primer bulb of my Ryobi 790r string trimmer primer bulb have literally rotted away and I must replace them. There are 2 connections to the bulb,2 to the gas tank and 2 to the carburetor. I need a diagram to tell me how these should be interconnected and nobody seems to know. Help!

For all intents and purposes, it really should not matter.

The primer bulb has to fill with gas, so that's the reason for the tank hose.
It has to inject into the carb (prime the fuel line, so that's the reason for the carb connection

If there is a difference in size, then the larger one goes to the carb.

Primer bulbs work a little differently in diaphram carbs.

Although it would not seem to matter, the correct hookup will make sure the in-bound fuel goes through the filter. If hooked up backwards, the fuel would be sucked through the return tube (which, by the way, is shorter than the up-take line). I just replaced my lines too, however, now I have to replace the bulb itself. My plan, since the lines are different colors than the factory ones were, is to hook them up, and press the primer bulb. Watch the fuel. If it is going from the filtered line to the bulb, its correct. If its flowing from the return line, then they're backwards... switch them.

Ok guys. For all of you that can't get the gas trimmers going, can't keep them running or have to replace fuel lines... here is all you need to do.

First of all most of these problems can be taken care of by removing the carburetor/air cleaner cover. Remove the choke lever plate from the back of the carb. Remove the cover plate from the back of the carb. At the 6 oclock position the is a hole that is about 1/4inch wide. Inside this hole is a screen that prevents debris and particles from going into the carb and the jets. Most of the time this screen is clogged with bits of the primary fuel filter that is found inside the fuel tank on the fuel line that feeds the carb. This primary fuel filter deteriorates because most fuels contain ethanol. Ethanol is hard on the primer bulb, all fuel lines, and the fuel filter. If all your fuel lines and bulb are yellowed its time to replace them.

Get on "outdoordistributors.com and order 1) fuel tank assembly which includes a new fuel filter 2) Two fuel return lines (keep one as a spare) 3) primer and hose assembly and 4) a muffler spark arrestor screen. Install these parts. To hook up fuel lines: connect the top of carb hose to the short primer bulb stem. The bottom carb hose to the fuel line that has the filter on it inside the tank. Finally, connect the remaining fuel line that comes out of the fuel tank to the center or the longer stem of the primer bulb. Change out the spark arrestor on the bottom of the muffler... the old one is probably all gummed and is restricting exhaust

How to replace your Ryobi 990r trimmer Primer Bulb: I just got done doing this having never done it before and found most web illustrations and instructions extremely lacking. After fumbling though the various instruction here is what I did that worked. Sine my lines had all but disintegrated and I did not pay close attention to the installation I was depending on the internet to help me out:

1) Purchase 1 bulb (2 ports) $9, 1ft of medium tygon fuel line $3, and 1ft of small tygon fuel line $3.

2)Cut the tip of one side of the medium fuel line at an angle to make it sharp so that you can push it though the tight hole in the tank. In my case the filter had fallen of the fuel line and was rolling around the tank. You will need to fish it out; for me, it was easiest to remove the tank altogether.

3) Shove the sharp fuel line though one of the two holes in the tank, probably makes no difference which hole, they looked the same to me. Keep pushing the hose though until you can fish the end though the tank filer throat. Now cut the sharp tip off to attach the filter securely. If your filter came apart place the stack of washers on the barbed stem of the filter and then attach the fuel line to that stem.

4)Pull the line back though the hole you originally started to shove it through. To position correctly, keep in mind where it is going to be sitting in the tank to get the best immersion when you are using the trimmer.

5)Connect the opposite end of the med fuel line to the top of the carburetor. You may want to cut the line as you probably needed the extra length to get though the fuel tank.

6)Attach the IN side of the bulb to the bottom of the carburetor and the out side to the remaining hole in the tank using the small fuel line.

NOTE: The primmer bulb works by drawing a vacuum on the carburetor and then passing the fuel back to the tank. Keeping that in mind helps me understand how to hook it up. I also cut the small fuel line a little long so I could remove and install the bulb more easily.

Hope this helps somebody else

I am actually trying to do the same thing. I bought a new primer bulb and replaced the fuel lines. I am having trouble identifying which lines go where. Also, how do you identify the top and bottom of the carburetor? If someone else could outline this process it would be much appreciated. Thank you.