Carb masters: 3rd gen still will not idle on pilot circuit with butterflys closed. Flooding into cyl

The fuel line should be parallel to the yellow line but down to just below the lip by the mixture screw--looks like about an inch (25 mm) lower.

At the level you measured--that is causing the flooding and oil contamination, and the float needle valve is not shutting off the fuel.

Now why are the needles not shutting off the fuel flow?

On the bench i will blow lightly into a clean piece of tubing on the fuel tee and raise the float by hand until it seats to verify that the needles will seal the inlet shut at the right angle.

 

word. I will getr. enjoy these lovely last days. much obliged

 

WUT! That low. holyschitte. ok....

 

More like this perhaps...

 

"Now why are the needles not shutting off the fuel flow?"

Perhaps during my early noob meanderings of bending tang, I have lightly mutilated the smooth factory surface they once had, allowing the inlet needle wire hangars to hang-up or ever so slightly get caught somehow. I did try to 0000 steel wool them smooth but who knows. Might that be an semi- 'educated' guess?

"On the bench i will blow lightly into a clean piece of tubing on the fuel tee and raise the float by hand until it seats to verify that the needles will seal the inlet shut at the right angle."

Great suggestion. Will try for sure.

In my many attempts setting floats, there have been certain angles that I have questioned pertaining to successful fuel shut off as you say. The needle appeared shut but it needed a teeny touch to get it to seat fully. When I have set the floats high, say 13mm vs 9mm to try to lean the bitch out, the tang was at such a sharp angle it would push the needle spring button more diagonal than down, and make a improper shut off more likely at a tweeked angle. Seemed to me the spring button would probably bind on its housing more than slide down freely. Make sense? Rewind back to the Honda peeps claiming it would work, but these angles never looked right to me, so back down they went and the gas flood.

When I bought the VT600 inlet needles, the corresponding seats were included. Both old and new seats are stamped 2.4.

 

Yes if you can get it to shut off and hold the fuel down to there you will be very pleased--able to actually adjust the mixture and idle speed, start using choke when cold.

When you get in, hold the carbs up in that same view from the side and look at how your enrichment tube protrudes down into the bowl region. i don't have a 3rd gen set on the bench right now, but the 1st and 4th are close enough. Basically you want the maximum fuel level to just cover the bottom of the enrichment tube/jet so that it can pull fuel up when you open the enrichment circuit (choke lever). On the 4th gen that extends down into the bowl well below the plane of the bowl/body gasket mating surface. On the 1st gen it looks to be right at or just slightly above the mating plane. Your 3rd gen is closer to the 4th in construction so i would expect your level to be lower than the last picture--the yellow line would intersect the bowl toward the mixture screw either right at the mating surface or a little down into the bowl--depending upon what you see of the enrichment tube.

 

The 4th gen seats are 2.6 and i think that refers to the flow rate in cc/min, or it is the orifice diameter in mm. Mikuni does it one way and Keihin the other, i don't remember right now which, but 2.4 should be okay.

Those shorter inlet needles are not going to be working in your favor re: bending the tab angles, but hopefully they can be made to work everytime with confidence...

 

Doode. Just the paragraph about where the fuel should be in the bowl is the money revelation. Some time ago I put out a post fishing for just that very simple thing. Boosh! And here it is. Thanks. I will send you a pic of the outward side of one of my carbs and all the cluster of pencil marks striping the side trying to dial this level. I think I just graduated from VFR750 high school to college

 

The previous fuel level is the pencil mark below the plug. That was 9mm with the VT600 needles. Fuel level in the tube is the same needles at 13mm.

 

Feels like fuel level is right below pilot

 

any higher than this and the needle & tab start to bind. this is 13mm with VT600 needles.

 

Only by luck are those needles going to seat...

On the 1st gen with the needle seated in the jet, the end of the needle plunger extends up above the centerline of the pivot pin axis (drawing a line perpendicular to the needle axis and the pivot towers). The needle length from plunger to tip is 15.3 mm.

On the 4th gen the end of the plunger is right at the centerline of the pivot axis.

In both cases there is at least 0.5mm of needle barrel showing between the spring groove in the needle and the face of the jet.

In two of your pictures it appears that the spring is very close to touching the face of the jet which could be preventing the needle from seating. In addition the plunger is way below the pivot axis centerline, hence the extreme angular bend in the float tab.

You might be able to double or triple up on the jet crush washers to get the plunger up to the pivot centerline, or maybe the other set of ( VFR ?) jets are not as deep as the VT jets, but the spring bottoming out on the jet face before the needle tip seats in the jet would still be a big problem.

The 3rd gen float tab looks similar to the 1st gen--the 4th is plastic and not adjustable.

The 1st gen pilot jet extends to within 1 mm of the end of the choke jet. The 4th looks like yours with a longer exposure on the choke and the pilot is the shortest player.

 

What kind of motorcycle?
Don't tell me generation. Just tell me the brand, model, and cc's.
Tell me how many miles are on it.
Tell me if the intake is stock and tell me what kind of exhaust.
How far above seal level?

From zero 1/4 throttle the engine works on pilot jet and pilot air screw. Thats it.
#40 pilot jet and factory setting on pilot air screw with stock exhausts and intake.
THATS it.

 

Squirrelman did HOURS of amateur and informal inquiry into this fuel level issue with carbs on and off the bike, both level and set at installed angle while trying to establish how to accurately determine the correct clear tube level measured against some reference point, not easy to locate, and even the slightest inclination of the bike left-to-right will result in some inaccuracy. Never did establish an exact, repeatable reference point agaqinst the carbs or bike frame.




On most I-4 engines the right fuel level is usually just below the line between the carb body and the float bowl, but sometimes as much as 2mm below, never above.


Here are some photos taken with carbs resting on a test stand, all fluid heights are equal when carb set is level in both axes across the air box, while rears are about 6-8 mm higher than front at the normal angle installed in the bike.

For measurements to be repeatable and useful, the fuel pump would need to be working to keep levels topped up with 3psi pressurized system to help find float needle leakage. Might be useful to be able to compare actual line pressure where first fuel bypasses with new or used needles/seats. Under the "it can't hoit" file: i polish the brass seat with a bit of metal polish on a Q-Tip just to help remove any invisible scratches, and usually a brighter polished line does appear. External tubes confirm your float setting accuracy.

I never tried measuring cc volume on a full float bowl, but i have measured the time it takes to drain from full, about 25- 28 seconds it seems.

 

Why get involved with all of this???

Just set the floats like the workshop manual says and be done.
Oh BTW if you just buy NEW float needles you won't have to adjust the floats EVER!!

Just buy new float needles and check the float height -DONE.

You will love this....There was a Datsun B210 that had a clear glass on one side of the float bowl so you could SEE THE FLOAT LEVEL.
So when the float level was wrong it was time for a new float needle.

 

Well still flooding. Swapped float valves & seats with new(from a VT600 and no funds for OEM). Doubled up crush washers to shim up the assy. Still flooding... I even set one carb at 4mm and the other at 13 just to see the difference. NO difference in fuel level. WTF. Kennybobby- the top of the plunger is now at the centerline of the pivot pin...

 

Your killing me!!!! I will sell you my old float needles with the crush-washers and the seats! Hows that? My new install is good, I notice less of a stank when I turn the bike off in our garage. Before the re-furbish, there was a stink of petrol. Now its less.

Anyway let me know...btw I did a get new R/R from Ricks and am thoroughly impressed!!!!! Big fins = Gud Heat Diperssion :smile:

 

Hey! Thanks for the offer. What shape are they in? Kinda silly to buy old if they are just like mine, I mean my old ones. But if they are goot, I am interested! Yeah I have a Ricks R/R also...sweet

 

I forget what my cost was for the new ones. Maybe $27.00 per carb? I mean my bike is a high mileage unit thats been used consistently. When the carburetors were taken apart they were very very clean :smile: If you look at the float needles under magnification, they looked good. I never had issues with gas getting into my engine oil mind you.

If you want them, I will sell em to yah for $40.00 and I will be generous and pay shipping :smile: Its a gamble I guess, Your call.

 

Possible cause?

On one of the forums another member was having this same problem and it turned out that a tube that goes from the bottom of the float bowl upwards (spillover) had a hairline split in the tube. It had gotten water in it during the winter and when it froze it expanded and split the tube length wise. Check yours with a magnifying glass.