VM fuel screw has no effect, runs rich with screw seated??

[Guest]

I'm stumped how they are supplying fuel with the screws seated. Out of 4 sets of carbs, I barely was able to build a rack that didn't have any of the fuel screw tips snapped off. So I installed this known "good" set because I was having this issue with the last set that were "professionally" rebuilt.. From a previous post it was suggested to baseline the carbs to 3/4 turn out on fuel and 1 1/2 on air screws. So those were the settings i started with, two of the carbs I had to richen with the air screws and are currently at 3/4 turns out and the plugs look good. The other two carbs are sooty and seem to have no adjustability, also if I remove the sync plug the RPMs shoot up. I got it idling as best as it will, then I synced them. Riding the bike is really not bad at all, better than the last set of carbs, but I don't want to run a half assed bike. I searched the forum and it seems that most people think that if you get the fuel needle tips out that the carb bodies can be reused. I was thinking maybe the hole in the bodies are deformed from previous repair, or that the choke circuit is somehow supplying fuel. So any ideas? This is for the GS1000.

[btbarb]

I have one carb body that I boogered a bit getting the fuel screw out, the opening is a bit bigger than it should and causes the fuel screw to seat a bit lower than it should, that carb does require me to set differently than the others but it's fine.

Float levels too high, choke linkage not closing all the way, bad orings, leaky petcock into #3 vacuum hose could be sources of unwanted fuel. If you're acquired carb set was jetted for pods and pipe and you're running stock, maybe the pilot jet is not stock (too big).

Higher RPM is normal if you temporarily remove the sync screw.

You're going to need to know the specifics of your "known good set", jets, oring condition, cleaned proper, etc..

[OldVet66]

The first thing I would need to know is what has been done with this set of carburetors. Have they been stripped down, dipped for 24 hours, floats adjusted, and new O-Rings installed? Have the valves been adjusted and the carburetors bench synced before you tried them on your bike? I got royally screwed by a so called professional carburetor re-builder early on, and have since consigned the carburetor bodies he sent me to the scrap bin because of the condition of the Pilot fuel screw seats (very bad condition). Having said that, I was able to re-build them myself, with help from this site, installing a stage three jet kit for my pipes and pods and eventually at it's best, get 44 MPG out of them. The problem was the tuning never seemed to hang in there and I was constantly having to re-adjust them. It seemed every weather change required an adjustment. I finally gave up and scrapped that set of carburetors, rebuilt a good set with no pilot fuel needle seat damage and found them very easy to adjust, learning a lot along the way. I might not be all that far from you depending on where you live in Maryland .

[Big T]

Your probably correct in that the fuel needle seats are distorted and too large now

Try those screws at 1/4 turn out and see how they perform

[chuck hahn]

I am going with bottom pikot screw tips are boogered up.

[althomas101]

Btbarb,
Float levels too high, (Actually i think they are too low as it almost dies when comming to a stop)
choke linkage not closing all the way, (they won't push down any further)
bad orings, leaky petcock into #3 (this was wrong with the bike when I got it, fixed with a new petcock)
Old Vet
Have they been stripped down, (Yes)
dipped for 24 hours, (no just blasted with air and spray cleaner, though cleaner sprays well through the pilot hole into the venturi, i do plan to soak in berrymans before I give another go at them)
floats adjusted (like I said i think they are low, they are consistently set at 25mm)
new O-Rings installed (yes, intake o-rings as well, ether doesn't show any air leaks)
Have the valves been adjusted (not yet, yes I know it can affect idle quality)
the carburetors bench synced (just vacuume synced)

All, I think I'll just swap the one good carb from the last set, order new fuel screws from Z1, soak the carbs in chem, give them a quick boil, blast with air and give them another go. That should only leave me with possibly #1 carb having a boogered fuel pilot hole, and I have 4 more of those carbs so I'll do the same on them and just swap carbs till I get one that works.

[chuck hahn]

SLOW THE HELLL DOWN and loose the word "QUICK" from your vocabulary when dealing with these bikes!!

I will be blunt as a sledge hammer here...You either dip them for a FULL 24 hrs, intall new orings , and get the valves and everything else done or stop posting questions as to why its all fvvcked up.

We go thru this a million times a month here and STIL STIL STILL nonne reads the turtorials, listens to the advice that given, and think they know the "short cuts".

[althomas101]

LOL! Chuck life's too short. Since I'm a direct person, I appreciate that quality in others. Basically I made this thread because I couldn't find one that verified whether a carb body is shot if someone boogers a fuel screw. I'm an active member of a Honda forum, and every spring it is the same thing "what's wrong with my bike" the answer is almost always the carbs are dirty, so I get where you are coming from. However dirty carbs are ALWAYS lean, air doesn't crystalize, so if there is a plug in a carb body it is in a fuel circuit. I'm having RICH running conditions, and can't get them lean out. Totally different issues in my mind, if I’m wrong please enlighten me. I did read the VM tutorial and found it helpful. So to address your immediate issues with me:
1. Didn’t soak the bodies = I plan to, but I don't think that it will make any difference since I'm obviously getting fuel.
2. Didn’t do a valve job yet = I fail to see how valve lash will affect a carburetor’s ability to meter fuel. I know it will affect sync, which has a minor effect on mixture, but not a total failure of the carbs mixture capabilities.
3. New O-rings = yep bought and installed the full Monty from cycleorings per the VM tutorial.

I appreciate that you have taken the time to read my post, and validate that the carb bodies can get damaged beyond repair, but using this as an opportunity to rant is not helpful nor does it inspire a sense of community and camaraderie.

[chuck hahn]

Here is hiow valves adjustments effect a carbs ability to meter fuel..


Fuel can only come out of the carb from suction ( provided by the cylinder).
The venturi creates a LOW pressure symptom directly above the air jet..thus the atmospheric pressure down the vent tubes pushes the fuel UP the needle jet and pilot jets so the fuel can be sipped in to the cylinders. Granted loose valves will be fully seated and sealed against the valve seats UNLESS the edges of a valve are chipped or the seat itself is burnt and pitted.

Now, IF the valves are leaking ( from being too tight and held open ever so slightly) then the carb cant function right.

Richness is caused by float hts being too LOW most of the times. The fuel has to be jut at that optimal ht as per the specs in the manual and heres why.

If the float ht is too LOW it allows the fuel to rise too HIGH in the bowls before ( and even if ) the float needles shut it off. If the float needles dont shut off or meter the flow properly guess what? Yup....excess raw fuel is dircelty dumped thru the carbs into the cylinders.

Conversely, a float tht thats too high will make a lean situation.

Now for the screws. if they are broken or have been resharpened and are too short, they cant slow down the fuel flow from the pilot cicuit right. pictire a faucet thats worn out in the sink..it shuts off all the way at the knob but not at the inner workings and it drips.

So whats going on in your carbs is most likely one of these 2 things or a perfect storm of a combination of the two.

[btbarb]

Richness is caused by float hts being too LOW most of the times. The fuel has to be jut at that optimal ht as per the specs in the manual and heres why.

If the float ht is too LOW it allows the fuel to rise too HIGH in the bowls before ( and even if ) the float needles shut it off. If the float needles dont shut off or meter the flow properly guess what? Yup....excess raw fuel is dircelty dumped thru the carbs into the cylinders.

Conversely, a float tht thats too high will make a lean situation.

Hey Chuck, you talking about the carbs right-side up on the bike or upside down on the bench?

[chuck hahn]

Neither...with the bowls off and tilted just so the floats rest against the spring pins on the float needlse..this is the place to measure ft hts from.


EDIT..off the bike and as I described.. tilt them and then rest them on a rolled up rag or something so you can have hands free to adjust the tang. Be sure to do both floats in each carb to the same levels.

[chuck hahn]

Guess i should also mention to see that then pins spring is actually working!!! Thats an important piece of the puzzle as well.

[althomas101]

Thanks Chuck, you convinced me to check the valves prior to further diagnosis of the carbs, as in my experience valves tighten over time from wear in the seats. Also I get what you are talking about with the floats, I think we have the same understanding, but you are talking about the float height with the carbs upside down on the bench vs. me talking about the fuel level while installed. I put them at the high end of the range (24mm +/- 1mm, I'm at 25mm), as I didn't want issues with overflow. This also should have a leaning affect.
I'm definately dropping the $20 for a full set of fuel needles as well.

[OldVet66]

The pilot fuel circuit is very small and can easily be totally clogged up and the bike still run if they are not all clogged. That's why it is so important to soak in dip for 24 hours or more, the small passages are the hardest to melt the varnish and crud out of. I don't think the pilot fuel circuit works exactly as pictured by most people. In my last rebuild I noticed that it's adjustment seems to move the air adjustment range around. Since Pilot fuel needle adjustments require air adjustments for highest idle it starts to make sense after playing around with them a bit. My initial adjustment left a stumble in the 1,500-2,000 RPM range (cruising around town in traffic), very annoying seeming to indicate too rich. Turning the Pilot fuel needles in did not cure it. At those settings my air adjust settings were turned in quite far for highest idle. I opened the pilot fuel needles a bit (close to 1/16 turn) it moved the corresponding air adjustments for highest idle closer to 2 turns out and gave enough latitude to tune out the stumble. I think if you adjust the pilot fuel needles so the air is closer to two turns for highest idle the VM carburetors are happiest. What makes it a PITA is the fuel screws with damaged seats take minute adjustments when they are close to being right and if you are not careful you can skip over that point and not even know it. The carb bodies with damaged pilot fuel needle seats are also the ones that do not seem to have any response to air adjustment.

[chuck hahn]

If you do the wet check with a fuel level guage along side the bowls, do it with the bike at adle. If they fall within the manuals specs you good to go.

If they read high or low wet, youll know which ones specifrically you need to tweek when you take them of..and the beauty of the wet method is that the guage will show you how much of a tweek youll need. If the guage is ..say 1/2MM low on bowl 2..then you move the float ht 1/2 mm lower on that carb.

In other words..carb 2 is at 25MM now.

You start the bike and hold up the tube next to the bowl and it reads 1/2 MM low.

So the NEW HT for carb 2 will now be 24 1/2 MM...follow the math here??

By dropping the float ht to 24 1/2 MM your allowing the fuel level in the bowl to RAISE 1/2 mm and it will now read within specs on the guage tube.