Bike won't start after warmed up (Part 2)

I was thinking the vacuum tube was letting fuel into one carb due to a bad sealing petcock.
Steve

I don't think the vacuum tube has been compromised. I do know that the tank has a slight drip every few minutes if it's off the bike. I didn't think that would hurt anything so I haven't taken it apart yet. Awhile back I had issues with fuel overflowing out the main jet emulsion tube. I replaced the float needles in hopes it would fix it. My tests will conclude if it is indeed a fuel issue. Just have to wait till I get back in town later this week.

ThatFiveOhTho wrote: Thanks for the input. I'll be going through the carbs again to make sure all is well. In the mean time I've thought of a test for fuel. I'm going to use starting fluid to see if it is indeed a lean start condition where fuel in the bowls isn't high enough. If that doesn't work, ill give the bike another ride and before parking it I'll drain the fuel out of the bowls to see if it prevents a rich start 20 to 30 minutes later. If it does, I'll know that excess fuel is making its way into the cylinders while parked.

Am thinking the carbs at hand have overflow circuits that should prevent excess fuel from making its way into the cylinders while parked. Might want to assure that the drain hoses are unobstructed and allowing excess fuel to escape and exit underneath the bike.

When fuel has risen high enough to enter the overflow tube, the fuel level has already exceeded spec height, and thereby promoting an excessively rich mixture.

An unwanted fuel level rise above spec could be caused by a leaking float valve, hanging float, etc.

When parked, a properly functioning vacuum operated petcock in either non-PRI position should halt fuel flow to the carb, which doesn't remedy a leaking float valve or hanging float, but prevents additional fuel from reaching the float valve.

Let us know whether or not starting fluid produces instant running in the warm start scenerio.

Good Fortune!

Thanks for taking the time to sort this out. Unfortunately I've been in new Mexico with my wife so nothing will be tested till late Tuesday. However, a more accurate description of the issue can be had after some thought.

1. I have narrowed this down to a fuel issue, and I'm leaning toward rich vs lean. Parking the bike after a ride and leaving it longer then 20 minutes results in a seven second delay, followed by the bike firing slowly then picking up slowly only after snapping the throttle a bit. Not snapping the throttle results in a slow climb from 0 to about 1000rpm. There is no studdering or popping at all once it's running. Driving the bike will raise the idle to normal in a matter of minutes. Anything between freshly killing it to the full 20 minutes results in a proportional difficulty starting.

2. A long time ago, I was adjusting the idle screws and let the bike idle a LOT longer then I should. (Probably 20-30 min). After killing the bike to adjust sync afterwards it took all but 10 seconds of sitting to replicate the same problem that happen right now. I then let the bike sit since it had gotten too hot to tune.

3. I have the pilot screws out 2.75 turns on all. The bike still had the original caps and the screws measured 2.75, 2.3, 2.5 and 2.4 roughly. I feel like this is rich but with anything less then 2.75 I notice stumbling.

4. I have a sticky resin in the intake that was formed by some uncured silicone permatex from the boots (new boots, just was overcautious about leaks, please flame me.) getting sucked in and mixing with gas. It's sticky to the touch and smells pretty bad. I intended to clean it later in the week but wasn't sure if this was causing my no starts or not. I had the problem before hand.

5. When pulling off the carbs while the bike is hot, I notice wet fuel around the carb boots that I can wipe between my fingers. There isn't a puddle of fuel but I have a strange suspicion it's just too much fuel vapor rapidly condensing with cooler air.

6. When starting hot I can sometimes hear a very breif look ignition like the cylinders fired maybe once with the remaining charge before encountering the problem mixture, it lasts maybe a fraction of a second, then it takes 7 seconds to start again.

Hopefully this helps point this in the right direction in the mean time. Thanks.

Maybe the petcock is dirty inside whereby the diaphragm-spring-o'ring mechanism isn't fully shutting off fuel flow when the engine isn't running (i.e., improperly allowing some flow in non-PRI position when the engine isn't running), and which condition is allowing the unwanted fuel flow to pass down the vacuum hose, through the vac nipple, and into the intake port, thereby causing an excessively rich condition (in at least the one cylinder) upon attempted starting 20-30 minutes after a run.



The likely remedy would be disassembly and cleaning the petcock, and if needed, also installing a petcock kit that includes the necessary internal petcock parts.

Good Fortune!

Alright. After assembling the bike I've found that the air filter stenches of fuel. I don't think this is normal. Also, the air filter lid is completely cracked down the ring, providing a substantial air leak with the carbs, and potentially causing the pilot screws to have to be at 2 3/4 turns out. I've ordered a replacement. I also cleaned the intake valves, removed most of the gunk. Will be running some fuel cleaner to get the remains out. I've also discovered that my carbs do not have any overflow mechanisms. No brass tube going up out the bowl. The petcock is fine. Took it apart and found no evidence of any fowl play.

Heading to work on the bike, drivability was great. Idle was steady and reliable. Wide open throttle the same. Didn't have time to test if the main issue is still there, but I will check when I get home, and perform my tests after 30 minutes of the bike being off.

ThatFiveOhTho wrote: . . . cleaned the intake valves, removed most of the gunk. Will be running some fuel cleaner to get the remains out. I've also discovered that my carbs do not have any overflow mechanisms. No brass tube going up out the bowl. The petcock is fine. Took it apart and found no evidence of any fowl play. . . .

As known, when carbs don't have overflow circuits. it's more critical than ever to assure perfectly functioning float valves.

Good Fortune!

I actually have a spare set of bowls with the tubes. Is there any draw back to using those off of the spare set of carbs?

If they will fit I'd use them. Wish my 33's had them.
Steve

I will put them on this weekend when I get the chance to tinker again.

A bit of a smaller detail that I noticed: when dead cold, I can start without choke for about 15 seconds before It requires the choke to be on. To boot, I cannot start the bike cold with full choke, and using full choke Durning the process of starting caused the idle to drop to a stall. I'm getting close. Very very close to solving this problem.

Full choke just dumps fuel in the engine. Try partial choke. Being able to start with no choke at first suggests a rich condition.
Steve