Gasoline in intake boot vacuum nipples?

I’ll try to make this short:
1977 Kz650 with VM24ss carbs.
Recent work performed on the carbs (as in within the last 6 weeks;) thorough disassembly and ultrasonic cleaning, reassembled with all stock brass and all new o-rings. (Increased main jet size from OE stock to account for 4>1 exhaust, left pilot jet at stock)
Float height checked/set to OE manual spec with a dial caliper. The floats were checked for leaking and found okay.

Other work performed includes checking valve clearances and found to be in spec, adjusting ignition points gap and setting base timing with a timing light, replacing spark plugs, and then vacuum syncing the carbs.

While syncing carbs with an old motion-pro mercury carb stick, I noticed between runs that small amounts of gasoline siphoned back into the plastic tubing “gauges.” That really bugged me. A lot. I’d never performed this procedure before, so I just let it bug me.

A week or so later I saw one of the sync nipple caps looked like it wasn’t pushed on all the way, so of course I decided to pull it all the way off. This was after a long cold soak, probably at least 24 hours. Gasoline dribbled from the brass nipple and I dumped several drops of gasoline from the cap. I checked the other carbs and they all exhibited the same symptom.

This bike takes a special touch to get started when cold; it “seems” to flood almost instantly. Once running, it is amazingly smooth with good power all the way from idle to redline. Hot and warm starts are instantaneous.

If I leave the petcock on “prime,” the carbs eventually (hours later) overflow from the overflow tubes. So I don’t do that. How is it that these carbs are dumping gas into the vacuum sync nipples, and possibly into the cylinders, while parked, and not through the overflow tubes?

I plan to subject myself to the drudgery of the “clear tube” method of checking float heights, as the carbs are currently off the bike.

If I NEED to purchase FOUR float valves, where should I get them and how much should I spend?

I welcome any input. It would be nice to put this thing back together one more time and just ride it.

Entirely normal to have fuel in the vac cap. When you turn off, the fuel vapour in the inlet tract condenses on the inlet walls and runs down into the vac cap.

Larger main jets would make it run too rich. Go back to stock. Larger primary jets will help with the cold starting. With this adjusting one thing at a time will yield the best results. Start from scratch and do the clear tube test, adjust then move on. 

SWest wrote:

Larger main jets would make it run too rich. Go back to stock. Larger primary jets will help with the cold starting. With this adjusting one thing at a time will yield the best results. Start from scratch and do the clear tube test, adjust then move on. 

Yeah SWest I did shoot from the hip when I increased the main jet size while reassembling the carbs, but that was based on what I understand to be common knowledge when exhaust is 4>1. That decision seems to have served me well because I don’t think the thing is running rich except when at closed-throttle-idle of (smooth) 1,000 RPMs. And I left the idle/pilot jet stock, which I expected would leave things a tad lean if anything.

The carbs are off because I wanted to replace the camshaft half-moon plugs and put a helicoil in one of the bolt holes that wouldn’t quite torque up to spec when I was reassembling after checking valve clearances.

I'll get some clear vinyl tubing and check the float heights the “correct” way while I’m waiting on parts.

Maybe I got spoiled from years of fuel-injected cars and I just don’t know how to start the darned thing, which would boggle my mind because this ain’t my first rodeo.


 

Warren3200gt wrote:

Entirely normal to have fuel in the vac cap. When you turn off, the fuel vapour in the inlet tract condenses on the inlet walls and runs down into the vac cap.

Wow, thanks for chiming in and putting my mind at ease, Warren. I tried talking myself into thinking something like that but just couldn’t quite get there until you explained it.

OK I will ask which set of carbs you are working with. Do they have only and air screw or only a pilot/fuel screw or yet some have both? How large of increase did your try for the main?

gd4now wrote:

OK I will ask which set of carbs you are working with. Do they have only and air screw or only a pilot/fuel screw or yet some have both? How large of increase did your try for the main?

Sorry! Should have specified pilot screw type (accessible from underneath in front of float bowls.) I went with #105 for the main.
 

You might get away with openi the fuel screws 1/2 turn. 

reversion is a hell of a drug.

gas and air doesn't just go in one direction into the engine..
it heads back out the front of the carb to the air filter.

here's a video of a cloud of fuel hanging above the intake trumpets.
you may want to turn down the volume initially.

Your float valves are leaking. That's what's putting fuel into the vacuum nipples and making cold starts a flooding exercise.

The vacuum sync ports sit in the intake tract downstream of the slide. When a float valve fails to seat, fuel level in the bowl rises past the design point and can be drawn or siphoned into those ports, especially after a long soak with the petcock open. The fact that it happens across all four carbs and that leaving the petcock on prime eventually causes overflow from the overflow tubes confirms this is a float valve sealing issue, not a freak one-off.

Per the factory manual, the two culprits are dirt between the needle and seat preventing closure, or wear on the needle and seat themselves. Given you've already done an ultrasonic clean and reassembly, wear is the more likely suspect at this point, though a tiny particle of debris finding its way back in during reassembly can't be ruled out.

The manual's procedure for addressing this:

- Remove the carburetor, take off the float bowl and float, and wash the bowl and float parts in a high flash-point solvent. Use carburetor cleaner if necessary on the float bowl and metal parts only.
- Blow out the fuel overflow pipe with compressed air.
- Examine the float, and replace if damaged. If the needle is worn, replace the needle and seat as a set.

On fuel level: the factory manual specifies a design fuel level of 30 ± 1 mm and a service fuel level of 3.5 ± 1 mm. Your plan to use the clear tube method to check actual fuel level is exactly right with the carbs already off the bike. If the level is off after you've confirmed the valves are seating properly, the correction is to bend the tang on the float a very slight amount. Bending it down closes the valve sooner and lowers the fuel level; bending it up raises the level. After any adjustment, measure the service fuel level again and readjust if necessary.

If the needles show any groove or ridge where the viton tip meets the seat, don't try to save them. Replace needle and seat as a set on whichever carbs show wear. Getting all four sealing cleanly is what's going to fix the flooding, the vacuum port fuel, and the petcock-on-prime overflow in one shot.

Sendhendrix wrote:

... I plan to subject myself to the drudgery of the “clear tube” method of checking float heights, as the carbs are currently off the bike.


 

Needn't be drudgery.  Member hardrockminer illustrates how to check float level 2 carbs at a time with the rack off the bike on Page 2 in the link below.
www.kzrider.com/forum/3-carburetor/61368...n-setting-fuel-level

Good Ridin'
slmjim & Z1BEBE