I get asked about installation of replacement fuel lines and filters on the KZ750 Twins alot. Such a simple thing, but the topic has many fine points, and I wanted to provide as much detail as possible about my preferred method of installation.
But first, a few points:
- I know many people like clear fuel lines because you can see through them for troubleshooting fuel flow; I even used to like them for the same reason. But now I never use them because over time they get hard and brittle, and easily loose their seal when jostled, sometimes at the side of the road, sometimes just while riding. Even if you take the extra insurance step to use mini clamps, the seal can fail in time. On the other hand, if you use a reputable brand rubber fuel line you will not have these problems, and you won’t need clamps.
- I change my fuel lines and filters every year when I return the bikes to use for the riding season. But even if I lived in a year-round riding climate, I’d still change them yearly. It only costs about $10 to replace it all, and you don’t have to worry about clogged filters, rotting lines, etc.
- Never use paper-element fuel filters. It’s not a lawn mower.
- Plastic inline fuel filters get softened by fuel over time, and can bend to the point of restricting fuel flow if you’re not careful. So be careful.
- 1 early model KZ750 Twin
- 1 package of 1/4″ x 24″ fuel line (Good Year, Prestone, or whatever is at your local auto parts store)
- 2 inline 1/4″ brass-element mini fuel filters (I get them from z1Enterprises.com whenever I’m ordering something else, but you can probably get them at any bike shop)
When the KZ750 was designed, apparently the engineers never thought we’d have to worry about fine rust particles in the tank or inline fuel filters to compensate. Silly engineers. As a result, if you run without inline filters, installing fuel lines is an easy, intuitive breeze.
However, since this is the real world, most of us do have to worry about rust, and we do have to use inline filters. And because of this, we have to do crazy, creative things in order to have room to accommodate the filters… and not cause them to bend and shut down fuel flow as they soften from extended contact with fuel… or melt from contact with the back of the engine.
And this is why I’ve written this post; My goal was to find the best way to run the best fuel lines with the best fuel filters. Oh, and for me, “best” means “best possible at the least reasonable expense”. 😉
So we start with my garage plan chicken-scratch drawing on the back of a dirty envelope to help convey my design layout:
So, we start with one package of reasonable brand fuel line. I’ve always used Good Year line in the past, but this time AutoZone had Prestone. Whatever, it’s 24 inches of 1/4 inch inner-diameter standard fuel line.
As the design drawing above indicates, cut the line into four pieces as follows: 4″, 4.5″, 5″, and 10.5″ (or whatever is left). UPDATE, 2015: For the last couple years, I’ve actually modified the lengths a bit, and have been using 4″, 5″, 5″, and 9″ with great success.
Assemble the parts so that the natural curves in the hose works in your favor, so that when assembled, the filter will be stressed as little as possible. I’m not sure if you can tell from the pic, but the curves are opposite. Here is the assembly order:
Left: Petcock -> 10.5″ hose -> filter -> 4″ hose -> Left Carb
Right: Petcock -> 4.5″ hose -> filter -> 5″ hose -> Right Carb
Assembly Step 1: Connect the right line to the right carb. I hope you have small hands, it’s tight in there. You may have noticed in the pics that I have the tank sitting up on a wooden block for space.
Assembly Step 2: Complete the right line connection to the right output of the petcock.
Assembly Step 3: Now feed the left side line assembly in from the right side, around the throttle cables and connect.
Assembly Step 4: Finally, bring the line around and behind the other right side line, to connect to the left carb.
Here’s a finished view. Note that the filters are spaced offset from each other, they are not bent or stressed, and the lines and filters are not touching the engine. And hey, don’t hassle me about how dirty the engine/carbs are, or that there are old hornets nests that I’ve never cleaned out… It’s a working man’s bike and that’s how I like it to look… 😉
One additional caveat though… If you use the original stock ’76 – ’78 side covers, you will have to cut away a bit of the cover to accommodate the fuel line running where it was not intended to be. But if you do it with a nice, smooth arc, it doesn’t look out of place.
I hope that helps!