Petcock or Vacuum... You be da judge

[Michael March]

Got my bike back from the shop Friday after the carbs were cleaned and synced. All was well, it runs GREAT. Never better in fact.
Parked it for two days of cold rain. Yesterday, it fired up immediately, and then just as quickly (about a second) it went out and would not start again. After monkeying for a long time, it finally flamed on when I switched both petcocks to reserve. Funny, the fuel light never came on and it wasn't that low on gas. So I filled up and switched back to "on" and rode about 30 miles yesterday, stopping several times. No problems. This afternoon after lunch, I went to start it again, same thing. Instant flame on then off then would NOT start. Now after much fiddling with the petcocks, it finally ran and is running fine now, started it on "res" but have been running it with the petcock on "on". I know that there is a vacuum that sucks the fuel in, do you think a vacuum hose is misplaced? What are some other possible causes? I don't think it's gunk related, as it runs fine once the initial start gets over. I'm planning on talking to the mechanic, a good one who I trust, but he is a Suzuki tech after all, so I thought I'd "ask the experts." Otherwise, I think I'm down to cosmetics for this bike and then look out.... ROAD TRIP!

Mike

[beechfront]

could be a number of things. my guess is a fuel line routing problem.

[ratbyk]

Fuel Line routing as Corey suggested.
Another possibility is that there is a lot of crap in the tank and the filter/stand pipes that rise in the tank above the petcocks are plugged/restricted over their lower section.
Or as you originally suggested, the vacuum hose/hoses are leaking/split/not hooked up to the intake manifold.
Ken/Sooke

[Hobbit]

starting

My son's 650 Maxim soes the same thing. I think that after it sits a while, the fuel in the float bowls evaporates enough ao that the fuel is not coming out of the main jet. At cranking speed there is not enough vacuum to open the valve to put the fuel back in the bowl.
I've gone through the lines, filters and petcocks and can't find anything else wrong.

[TopCatGr58]

Hey Michael,

There is NO VACUUM that sucks the fuel into the bowls, they are gravity fed. What the vacuum does is pulls the valve/octopus open to allow it to gravity flow into the bowls. Aside from possibly having the hoses connected to the wrong petcock spigots, the octopus may not be opening very well. It doesn't open well during starting, and that's why they have a PRIME position on the petcocks, which allows you to bypass the Octopus and feed the bowls directly. SO... perhaps they are evaporating to a low level?? Try using PRIME instead of RESERVE, but first, pull the hoses from the petcocks, and have a cup/bucket to catch the fuel, and turn your petcocks to ON and then Prime to see which one flows in which position. The front one should be the one that flows on Prime. Then connect the hoses that go to a "T" and then directly to the carbs to the front prime/nipple.

Then you can be sure you're using the PRIME function to refill the bowls before attempting to start it!
T.C.

[Michael March]

Here's the latest:

It still wouldn't start this morning, so I switched the petcocks to prime and waited about thirty seconds. Then it started fine. Once it starts, I can switch it over to run for the whole day and all is well. Still don't know what's wrong, does that sound like the fuel lines are hooked up wrong? If so, I've got a shop manual and a Clymer's and I can see if there's a diagram in there.

[Dragonrider]

Mine was the same way. The gas in the carb bowls is getting lost enough over-night until it doesn't have enough to start. That's exactly what prime is for.

If you aren't leaking gas out the bowl drains or gaskets, I wouldn't sweat it.

It it doesn't start on the first try, switch to prime for a moment.

[Materi]

Yeah...I don't think I would jack with it if it starts on "prime". Believe me man, after fighting the common XS "fuel in the air cleaner and everywhere else it isn't supposed to be" problem, yours is a nice problem to have.

[Michael March]

Well, they're hooked up right. Still the same problem. Won't start if it sits for a couple of hours. Funny thing is that never was true before, so clearly SOMETHING is different, but I can't figure out what. I guess I'll take everyone's advice and live with it. I'll just have to put it on prime to start it. Maybe that's good, now I can leave the key in it and no one will be able to take it without knowing the secret starting sequence...

[Michael March]

The bike had a very difficult time starting this morning. I'm going to try running on "prime" all the time and see if that helps. Question: will this effect the fuel light coming on or the ability to still have some reserve miles in the tank to switch to? With the teeny gas tank on the Midnight this makes a difference!

[xswilly]

I have to agree on the fuel in the bowls emptying out over night
and the engine won't flow enough fuel until it starts
but my question and concern, is where is the fuel from the bowl going?

i hope it is not going into the motor

[red bandit]

if you run it on prime, you have no reserve.

[Michael March]

I don't think it's that the bowls empty out. The reason is that it always fires right up and then immediately gets starved for fuel. I think the bowls are full, the bike lights up, and then the fuel won't flow. Since I have no reserve on prime, I'm going to continue to run on "run" because it runs fine on "run" once it's running. Does it matter which carb boot the vacuum line runs to? Right now its on the second from the left.

[John]

Michael, have you checked the jet for the choke circuit? It is a part of the float bowl. The slender, brass tube that protrudes into the bowl area sits in the small well that is part of the bowl. Check to see if it is clogged. That could explain the hard starting when the engine is cold, and after sitting overnight.

[Michael March]

John, would that mean that if I didn't choke it at all, it MIGHT start easier?