Carb venturi fuel drip

[68ragtop]

Trying to find the source of my hard starting 97 XP. Classic case of starting hard when its warmed up & sitting for 10 minutes. I have had the carbs apart twice & have gone through them thoroughly. They have all oem parts & while I haven't replaced any internal parts, they have passed tests.

What I have found to be a possible culprit is after the engine has been running & I shut it off, both carbs drip fuel from the high speed fuel transfer ports. I have tested the needle/seats. they will hold 10+ PSI with no leaks. no leaks in the fuel system, no pressure in the fuel tank. I also tried bumping up the popoff pressure with no change.

So, is it normal that some fuel can drip out of the port, or should it stop without one single drip the second the engine stops pulling vacuum. Somehow fuel is transferring out of the fuel chamber & into the engine. maybe a small amount is normal & this is not the cause of this skis hard starts, but I am looking at everything very closely right now.

I would think the if the needle & seat do not leak, then the fuel chamber should be sealed & nothing would drip.
If it can drip, it would have to have a leak somewhere? I was thinking maybe the regulator diaphragms, but neither of them drip fuel out of the atmosphere vent holes.

If nothing else, I can pull apart my GSX & see if it drips anything at all. That machine restarts perfectly when its hot.

 

[Sportster-2001-951C-Stock]

Did you also confirm the mylar metering plate high speed check valve is sealing?

I'm pretty sure you have, but thought I'd mention it just in case.

If your idle mixture is off a bit it could have a negative effect such as excess fuel in the crankcase vaporizes and displaces air. What's the easiest way to get it started, open throttle to get air or what?

Don't know how hard yours is to restart but opening the throttle to get air might be your best restart procedure if the idle mixture isn't too rich.

 

[Sportster-2001-951C-Stock]

You might consider a plug change as well, a new plug has a much better chance of igniting a mixture that's not optimum.

And, along those lines, you might consider trimming the plug wires. Especially if it also breaks up at WOT.

Starting and WOT are probably two instances that challenge the ignition system most, if the plugs are questionable?

I've been known as a quick test, to pull the wire back up off the insulator about 1/8 inch just to make an air gap which makes the voltage a bit higher and can coax a slightly fouled plug to begin firing.

 

[68ragtop]

The check valves are good, but I believe they are only their to prevent the low speed circuit from pulling air from the high speed side instead of fuel. they wouldn't stop fuel from flowing into either jet so I don't think they could cause a nozzle drip? I am fairly baffled & I understand these carbs fairly well.

When I restart it I just let it crank, & when it fires it stumbles for a while. If I crack the throttle the acc pump gives it more fuel, so that doesn't seem to help much. I am not sure if its stumbling because there is still too much fuel, or if the fuel chambers are empty.

Honestly I would like to just replace the needle & seats, because it has all those symptoms. But they don't leak a bit. I am not a fan of just throwing parts at it, but am getting close.......

Plugs have been changed & I also tried leaning out the low speed. But as that got lean, it would start to starve for fuel after long idles. So, I turned the slow speed screws out until it would not get lean. there at 1-3/8 turns out right now.

 

[Strizzo]

Just hold it at 1/4 throttle when cranking, the little squirt from the accel pump will not make much difference when the motor is already flooded. Check if the needles hold pressure just under the pop off pressure, as that will be what it sees when you shut it off after running.

 

[Bills86e]

tuning

I agree with Strizzo post #5 as culpret in the venturi dripping fuel. If your ski motor gets water thru the bottom end, chances are the Rotory Valve Cover is worn and cause of additional hard starting, especially when hot, and also results in tuning difficulty.

Bills86e

 

[68ragtop]

Right now the pop off is set at 38. I will run it to 30+ & see what happens. I don't think its a worn R-valve as the first start from cold is nearly instant & so are the restarts if its only been sitting for a minute. I suppose I could pull the RV cover, but its a virgin low hour machine, so I'll feel like I'm violating it a bit
The ski is running great right now otherwise. Runs strong, idles well & no hesitations.


What pressure should the fuel tank vent check valve release at? it starts to release at 5 psi. While that seems a little high to me, I wasn't concerned as I didn't feel 5lbs a fuel pressure would do anything when I have tested the carbs at over twice that.

I wish I lived on a lake, its such a pain to solve issues like this without time on the water to test.

 

[68ragtop]

maybe I'm too spoiled with my 95 720 XP. I went through it last winter & that thing runs so well I think the starter will now last forever. It literally starts right after I hear the solenoid & stater engagement. Almost never hear it crank for more than a second.

 

[68ragtop]

well, I feel like I've come full circle for today. I watched post engine shut off a little closer. There are a few drips that fall from the venturi's immediately after I shut it off, & then it ends, so I may have over reacted As I have never actually stuck a borescope down a carb & watched that closely. I guess I never had a reason too. I also pressurized the fuel lines & carbs to 30 PSI & no drips.

I think next time out I will pump the accelerator pump before starting it & see if it gets better or worse & go from there.

 

[Sportster-2001-951C-Stock]

"check valves are good, but I believe they are only their to prevent the low speed circuit from pulling air from the high speed side instead of fuel."

You're quite right about that, however, my idea was if the check valve isn't sealing it may allow some fuel to dribble from the fuel chamber while the engine is shut down.

Anyway, are you sure it's not too lean? A worn metering needle can stick in it's seat if the tip is torn or grooved, pop-off test will usually reveal a problem in this case.

My carb observations from this weekend:

So, as I was looking through the manual again for the procedure to set up the throttle cable sensor, I noticed the suggested idle mixture is 1.5 turns out instead of 1.25, so I opened them another 1/4 since I haven't gotten around to retuning them yet anyway and richer can't hurt when it comes to 2-strokes. Well, I noticed my heat-soak start after sitting for long periods improved considerably, my observation is she fires much easier now.

I made several changes to my carbs all at once this year and lowering pop-off a few PSI was one of them. The original issue was resolved and I don't attribute lowering the pop-off to the solution so I'll be returning to the original pop-off next time the carbs come back off.

Edit: I should admit, I don't as a habit start my boat with the throttle in the idle position, I usually crack the throttle open and to be completely honest have not worked on a "best" starting procedure yet.

So in short, it has been starting well enough to satisfy but opening the idle mix screws another 1/4 seems to have made a noticeable improvement.

 

[manolocross]

The needle might be holdin pressure but the diaphragm might be holding it open when cover is on... Check the needle lever and make sure it's flush with carb body!