fuel line to carbs

[graybird78]

the fuel inlet to feed the carbs. should it be pointing up to the tank , or should it be pointing down to the engine. mine were pointing down. I pointed them up.engine seems to run better. was having pinging problem. with the inlets pointed up and 45 miles later not pinging, and bike seems to have more power. I had a couple of kaws that the inlets always pointed up. If inlets pointed down fuel lines very close to engine. could it be that fuel getting hot and causing some fuel delivery problems. plug color has changed to very light tan from previous white. seems likely that this would be somewhat of a problem.

[TopCatGr58]

Hey there Graybird,

Sounds like you're onto something regarding your lean condition. Folks have stated that there shouldn't be a large loop of fuel line that dips too far below the carb bowls, or it might impede the flow of fuel. The fuel is gravity fed, and if it has to climb back up the tube/fuel line before it can get into the carbs, then it might not flow as quickly or thoroughly. I have mine pointed up, and try to keep the fuel lines as short as possible so they don't loop.

Your tan color is what you want, pristine white is too lean and too hot!!! Congrats, and enjoy!!
T.C.

[graybird78]

fuel lines

Thanks for the words of encouragement topcat.just been thinking about this long and hard and I came up with same conclusions.so spent better part of last night rerouting lines.just seemed to me that they should point up.they hung so low that they were almost touching the engine.

[graybird78]

lean condition?

Did forget to add that I'm using 91 octane gas and installed 1 heat range colder plugs.cleaned and lubed vac ad unit.replaced vac ad hose.did run compression check hot.results #1 145 #2 140 #3 135 #4 145 .

[Steve Linderman]

Fuel Lines...

Hey guys...
we've been goin over the same subject on another page...
please consider this...the tank sits above the carbs...the "inlet" is above the bowl chamber...the needle & float (s) regulate fuel flow at speed...the fuel flow is "vacum assisted" and therefore "acts" kinda like a "fuel pump".
The fuel system is only "gravity fed" when you turn the petcoks to PRI (if everthing is "right")
Some may expierence "problems" of a similiar nature if they have a vacum leak (lean burn or "pinging")
There are several reasons why (the factory) routed the fuel lines in the way they did...consider just these few...

1. You (or someone else) will someday need to remove and turn the tank around, and re-attach the fuel lines (for service) try doing that with real short lines

2. Chapter 4, PG 4-5 (Yamaha Factory service Manual)
E. ADJUSTMENTS
(1) Float level adjustment
(skip the 1st two paragraphs)
"If the float level is to low, a rich air/fuel mixture will be caused by the high fuel level.
If the float level is to high, the low fuel level will result in a lean mixture"

3. "shortening" or modifying the fuel lines will not "change the float level"

4. you may be adding "XSive pressure" to the needles and should one leak you can fill your airbox or crankcase in a BIG hurry

5. The Factory plumbs them that way for a reason...and 99% of all XS's (that I've seen) were plumbed "down through the middle air horns...and out through the outer airhorns...and the "inlets" were pointed DOWN...HUH? DENNY

6. Liquid "seeks its" own level...so one little bend (in the basement) ain't gonna hold back NO gas (pray for good needles)
HUH Rob ??

A vacum "leak" anywhere will cause a "lean" condition (unmetered air flow)
when it comes to fuel flow...believe me you can empty the tank in mere MINUTES...with both petcocks flowing...accidently yank off a feul line that you forgot to turn off and you'll see what I mean.
modifying the fuel lines may cause you more headaches than it's worth.
besides you can re-plumb the bike for a few dollars with clear fuel lines (unless you buy 25ft HUH? DENNY )
And that way ALL your troubles will end...'cause you can See the fuel flowing...even at Night
try that with your 'ol run-of-the-mill basic black fuel lines
Plus it'll impress the neighbors HUH? Gary

Good Luck...and keep postin'
Steve.

"experientia docet stultos" (L)
"Experience teaches (even) fools"
"FUNK & WAGNALLS Desk Standard Dictionary"
"cir-1936 Pg.889"