TOPIC:

A recent question to me in a "private message" brass floats query was: "Should I also install a fuel pump to make starting easier?". Apparently they had read something about this.
The article says:"It primes the carbs for you and you just have to blip the starter when its cold and away you go. No cranking endlessly (assuming everything else is OK). It also eliminates the vapor lock that so plagues the 1300".
My answer (IMHO) was NO. Firstly: A fuel-pump can prime a fuel-injection system but it can not "prime" a carb'd system. If the bowls are dry (for example) the only thing a fuel pump would achieve is to fill the bowls more quickly relative to letting gravity do the same thing. It is engine vacuum that "sucks" the fuel through the idle-circuits thus "priming" the carbs. The fuel-pump can't do this. It simply fills the fuel bowls. Once the bowl is full the needle shuts off the fuel flow. It's also noted that a low pressure fuel-pump must be used to avoid flooding. The reason: The float/needle assembly can exert only so much "closing" pressure to shut off the fuel flow into the bowls. A fuel pump with too high a delivery pressure will over come the float pressure on the needle and continuously pump fuel until you have filled up the open cylinders and air-box.
If you have an efficient fuel-line routing with minimal bends, loops and other gravity defying air-traps the fuel will flow easily and fill the bowls quickly . If there is a concern about the bowls being low or dry: turn the fuel valve on before you start gearing up. Another down-side is the additional fuel connections (2 at least)creating the potential for 2 more fuel leaks.
The carbs on the 1300's dry-out quickly when left for a few days. Merely hours if in the hot sun. This is the reason I modified the fuel lines to feed from the two outside carbs simultaneously. *See "fuel line routing"* It fills the bowls very fast. The first couple of starting revolutions will "prime" the circuits if dry and "(assuming everything else is OK)" it starts immediately. Again: Just my personal opinion based on my own experience and logic owning the same 1300 for 34+ years.
Save your time,money and frustration and do the fuel-line correctly.

Hi Scotch....checked out your fuel line routing pics ...very nice job..totally agree with you that a fuel pump is not needed and why ...yes, a hot kz1300 will dry out/evaporate the float bowls by just leaving it setting a little while and they need time to refill with fuel when you're ready to go and before you start ..ok, this is the part where everyone is going to jump on me..what drives me nuts is saying the gravity fed, carburetted kz1300 "vapor locks"..someone may have already addressed this, in that case I'm just blowing in the wind ...if I'm using the wrong terminology just let me know ...vapor lock: the inability of fuel to flow past a substantially heated area of the fuel line/fuel delivery system ...the fuel, because of this heated area, evaporates/boils at a faster rate than the fuel system can recover ...ergo a gaseous vapor/bubble is formed causing a blockage ..i.e. "vapor lock" ....if you had an old ford or chevy with a diaphragm fuel pump and you mounted the exhaust to close to your fuel lines on the frame rail, then YES, you can have vapor lock ..a drop of gas will expand to a large gaseous volume and the fuel pump, diaphragm or electric can't keep up ...on the pressure side, it ain't happening ..why? ..2 reasons: physics, the evaporative effects of a liquid to remove heat ..design, a good fuel pump can move a couple gallons a minute of fuel ..that's a a lot of heat removed ..you can have vapor lock on the pressure side with a torch, laying the (metal) fuel line on the exhaust manifold and driving across country, the exhaust heating the fuel almost to the boiling point before it gets to the pump, limiting its evaporative cooling effect because it can absorbe no more energy, i.e. heat (most likely scenario) ....if the kz1300 were boiling fuel, you'd hear it bubbling in the tank and carb bowls ..prolonged hissing out the tank vent and carb jets and bowl vents ...you'd smell gas everywhere ..you couldn't touch the carbs if the heat were there ..your fuel line would be brittle and melted ....the answer to the problem is the same two things, physics and design ...what no one will believe is that those big 'ol tanks, coupled with the engines heat, condense moisture "inside" the tank just driving down the road ..parking it too! ..a tank vent, vents both ways ..driving, the tank empties, cool air enters and meets the hot fuel caused by the engine ..condensation is formed ....you park the bike, the engine heats the fuel and it expands ..later it contracts pulling in cool (moisture laden) air, which meets the still warm gas and condensation forms ...now here is where it gets good ...those little micro droplets form little 1/4 droplets and so on and follow the fuel line to the stock, electric fuel shutoff ..lowest part of the fuel system (design) ..water being heavier than fuel begins to build up and after awhile begins to restrict fuel flow ...so how does the 'ol 13 run with your newly built fuel regulator? ...LIKE CRAP!! ...how many times have you pulled over to the side of road for 10-30sec then she'd start right up for another 5-20mi run before you'd have to pull over and do it all again? ..down shift and keep increasing rpm's till you sucked all the fuel from bottom of the float bowls ...takes about 30sec for that new fuel regulator to fill up the bowls once you pull over..you can sit and idle all day huh! ...eliminating the fuel shutoff relay won't fix it! ..as long as your fuel line goes below the carburetor fuel intake spigot (you must spin it to point up or at least level, instead of down) you will always have a lower area that will collect water and act as a restriction...you say "won't water form in the carb bowls?"...not in the same way ..the micro droplets don't have enough time to form larger droplets because of the turbulence and fuel turnover, they will be managed out of the system ...not the same as letting it sit for extended times (winter, etc) where a lot of condensation can accumulate.....you say "you have pulled the fuel line off and there was no fuel right there, so you know it's vapor locking because of the bubble there"...I can't help it if you ran "up hill" from the tank petcock spigot with your fuel line giving a place for a restrictive bubble to form, or that you brought it in hot (pretty much the normal thing for a 13) and the fuel evaporated out....you must run your fuel line level or down (hill) from the tank petcock spigot until you reach the carb fuel spigot (the one you spun) ...no chance for a bubble above, or a water plug below ........I'll say it again! ..It Ain't VAPOR LOCK'IN!!

..ok..the rest here is history and fluff ...got the bike in the mid eighties, me, mid 20's..1980 B2...1000mi later and a rod knock ..shop manual, man did I read that thing...scary but I did it ..all fixed and going ...then the "vapor lock"..geez! now what ..musta taken those carbs apart 15-20 times ..interstate, other state, side road, parking lot, bench ..knew it was fuel something??? ...stored it with a full tank of gas up to the rim
..went out after winter, same thing ..later, taking it apart I noticed the fuel shutoff relay had rust in it "a lot" off rust ..???...filled it to the rim for winter??? ...realized water had been standing there...got me thinking ..ran the fuel line straight to the carbs ..never another problem with "vapor lock"...didn't mean to jump on Scotch's post like this ..guess I just needed to vent! ..lol..I looked up his post on fuel line routing and his design is much superior to mine ..I just ran straight to it and man! that tank was a pain to hook and unhook ...you guys take care and keep'em going ..I miss mine, even though I'm still mad at it for all the times it made me take those carbs apart ...ha.

Great discussion guys. I've always dismissed any talk or write ups on the old site that ascribed fuel problems on a 1300 to vapor lock.

A condition where a bubble of vapor is filling a gravity fed fuel line is never a vapor lock. Any bubble of vapor will always weigh less than the liquid from which was formed. Any such bubble of vapor will always be forced along the line until it enters the carb bowl and then vents to the atmosphere.

In order for a fuel system to be vapor locked there has to be a pump and the pump must have to lift or pull the fuel past some obstacle that it wouldn't flow past by gravity alone. A water choked fuel solenoid check valve at the lowest part of a system might well provide the necessary obstruction, but you still need a pump to get a vapor lock.

I can think of only three situations that might be properly called a vapor lock. The first is so simple that it never applies and that is simply a siphon tube that has filled with so much vapor that the siphon no longer flows. The second occurs when an impeller cavitates (boils) a liquid and can no longer provide enough vacuum to lift the liquid. The third occurs when a diaphragm pump encounters a bubble of vapor anywhere on it's suction side that's big enough to expand and contract preventing the vacuum from being transmitted to the liquid further down the tube to the larger volume of liquid, the tank.

I absolutely do agree with each of you that the best system flows freely with no requirement that gravity force the fuel through any uphill sections of tubing.

Bill

Great dialogue guys! Another successful episode of "Myth Busters". This is what makes this forum the best.
And then there's the issue of getting the fuel-line off the fuel-valve barbed outlet ! I've heard lots of complaints and justifiably so. It can be tricky for the uninitiated.
I'm lucky in that Iv'e got long fingers so getting both my index fingers in under the tank to wriggle the line off hasn't been that bad but; get a drop of fuel on the line and it gets too slippery to pinch and push. I came up with this: Another home-made tool that works perfectly for this task. By placing the fork on one side of the clamp or the other (In my fuel-line routing case the clamp at the inlet side of the fuel-filter), I'm able to push the line off or pull the line on. Pulling the fuel-line back onto the barb only requires that I align the end of the line with the barbed end of the pet.-cock. Once aligned I can easily pull the fuel-line back on.