carburettors from the grave...

Great information. Kopcicle, carburetors were once my enemy, now they are one of my escapes from this crazy world that no longer makes sense. I have found that the best tools to use while working on carburetors are patience and a strong determination to NOT fail. A "parts replacer" will tell you it couldn't be fixed, a mechanic will tell you it was a challenge.
 
This set is twice as much fun, 2005 YZF600R only 11,000 miles but sitting for years, the gas cap drain got plugged, water got in the fuel system.

20180920_151649.jpg 20180920_151851.jpg
 
All to often the novice will attempt to make up for other causes of flooding by bending the tab down onto the needle valve so far that no fuel will leak but also no fuel will flow . A general rule of thumb is if when upside down and the float adjustment tab is just resting on the needle valve adjust so that the float arm is parallel with the float bowl to carb body parting line . This only works if the floats have not been previously mangled .
Soaked , heavy or soggy floats .
even Nitrile floats have their service limits and susceptibility to modern fuels and alcohol content . If a float is suspect place it in a jar with fuel and compare it with the other three or a known good float . The difference will be obvious .
Worn needle valve . Seems obvious , replace .
The damage from constant contact with a needle seat will show as a definite ring around the Nitrile rubber tip . This just won't work . However in most cases the best cleaning agent for even the most green and ugly needle valve is simply your fingers and a bit of mineral spirits . The problem with this repair is its only half of the sealing element .
Dirty , worn or damaged needle valve seat . Simple enough ,replace .
Simple yes but not always the cause . A needle valve seat can be brought back to life with a little ingenuity . Remove the needle valve and leave the seat in the carb body for now . Find a drill bit whose shank , not drill , just fits in the seat . Cut the shank off the drill and chuck it up in a drill motor . Go over to a grinding wheel and attempt to reproduce the angle of the needle valve Viton/Nitrile tip on the exposed end . Finish this pointed down onto the side of the wheel . The reason for this is we are building a make shift valve seat cutter and using the grind marks as cutting teeth . Turn the shank around and do the same to the other end only this time the angle should be around 15 to 20 degrees . Those of you that have ground valve seats get busy as I explain the rest . Take a q-Tip and a bit of scotchbrite and either by hand or in a well controlled cordless drill and clean the valve seat . By hand take a few turns with the 15 degree end of the shank in the seat and observe the results . If you can see a definite bright ring all the way around the seat you're done . If more work is needed it may help to stick a bit of fuel line over the shank and use that to turn the shank . If that doesn't work by all means get out the fine valve grinding compound and use the drill motor . The seat was wasted anyway all you can do now is waste time . Do the same with the other end of the shank and attempt to establish the seat . This takes very little pressure and happens usually very quickly . Problem is after all this you may still have the problem and the needle and seat despite initial observations were not the cause .
The often over looked needle valve seat O-ring . Ignore this if your needle valve seat screws into the carburetor body . Oh this one still gets me on occasion even though I have the McMasters part # written on the toolbox (this for most BS34's )
Viton® Fluoroelastomer Shore A: 75 -40° to +400°F 9263K565 4.26 per Pack of 25
When you can undo the needle valve seat retaining screw and plate and the seat falls out it's pretty obvious that the fuel isn't getting past your needle and seat . It's going around the seat . Replace the O-rings and be happy . Don't cut them on installation , use a bit of grease and they should press in firmly . Verify that this is your dimension and install away .
Testing your repair .
After a carb clean of any kind I place an auxiliary fuel source at least three feet over the carbs and tip , bump , vibrate , shake and last but not least reproduce their on the side stand angle for several hours under that fuel to verify that there are no further leaks or overflow . As little room as we get to install these things I know I don't want to do it twice .
If a clean idle can't be established with the idle mixture screws less than 3 3/4 turns out from seat go up a pilot size . Put another way , you should see lean misfire anywhere from 3/4 to 1 1/4 turns from seat and rich misfire no further out than 4 turns . The sweet spot ideally is between 1 3/4 to 2 3/4 turns . Once again for those of you under the influence of cleaning solvent vapors , midnight microwave mystery meat burritos , exhaust fumes and or liquid libation , please , PLEASE , adjust the valves first . All will be right with the world if you do and if you don't gawd almighty will kill a kitten .

~kop

I was sitting in a parking lot waiting for my sister to come out of an appointment and had nothing else better to do . I'll be more than happy to edit in response to any reasonable input .
Hi, I guess you are talking about removing mixing screws and problems associated with that procedure. I have 1982 xs650 heritage so I will probaby have to this as well. Can this be done without taking carburettors out??
Leo
 
Also what are those hollow posts on both sides of carburettors just over float bowls? Are there screws in there?
Leo
I'm thinking you have quite a bit of reading to do . Yes , the idle mixture screws are in those vertical round casting / casings on the engine side of the carbs. I have removed the mixture screws while the carbs are still on the bike but for very specific reasons. Removing the carbs is a 15 minute deal with the bike on a lift, sufficient tools, pliable boots and manifolds and correct practice. I can't imagine carb service while still on the bike. (that's just me) .
What the novice doesn't appreciate when they plunge head long into these carbs is that an idle mixture problem can be float height, needle valve and seat leakage, crud in the carb body, crud in the idle jet and finally an issue with the idle adjustment screw.

Any and all issues with these bikes are a system problem. Any issue can bring the whole to a stop. I start with a valve adjust, followed by a static timing of the ignition (to be followed by a dynamic adjustment of timing and dwell later) before even attempting carb adjustment and synchronization.

The original post was written over ten years ago and posted here near five years ago and I still answer. I'm really not that hard to find. If you really don't get it PM and I'll walk you through it .
 
Boy...you really confuse me. There are mixing screws and now other screws on side of carbs just over floats? The other ones are in front of carbs over butterfly valves?
I have been told that I may have a diaphragm crack. Do you think this could be the case?
Leo
 
Ok. Thanks , that horizontal tube has nothing. What about this nipple tube beside intake on both sides. One has a 4 in long rubber tube attached to it sealed off with a screw in it and the other on the other side is rubber capped off with tube clamp.
Do you know what they are for?
Leo
 
I think your talking about the carb boot vacuum tubes.......These are usually connected to the petcocks on 78-83 tanks because the petcocks are vacuum operated........If the Petcocks have been changed to manual ones then those tubes will be blocked off..........If the petcocks haven't been changed then blocking off those tubes will make the bike near impossible to start or ride
 
Back
Top