Drained my carburetor...

babblefish · Post by **babblefish** » Wed Sep 16, 2015 3:49 am

Has anyone ever put such a heavy load on their scooter as to drain the carburetor dry? I did today. Riding up a long, very steep hill at full throttle. Engine started bucking then just shut off as if someone turned the key off. At first I thought I over stressed the engine causing a mechanical heart attack. Pulled off the side of the road and waited a few seconds then tried restarting the engine. Guess the carb refilled by then because it restarted fine and I made it up the rest of the hill (at a slower speed) and rode the rest of the day with no issues.

I guess the old saying is true; some people can break a crowbar in a sandbox, lol.

PeteH · Post by **PeteH** » Wed Sep 16, 2015 1:09 pm

Interesting - I hadn't heard of fuel-starving the PGO scoots. You hear about this on the classic Vespas with big kits/carbs, which is why SIP and others sell a fast-flow fuel tap. I wonder if your fuel filter is the culprit, or if the petcock on the tank is a bit compromised. I guess you could bypass the filter pretty easily with a bit of replacement fuel line or connectors, then go try the same hill. The tank petcock, assuming the Blur has one, is a trickier proposition to test.

I haven't looked for a Blur service manual, but perhaps there's some documentation in there about expected fuel flow per unit time from the tank.

k1dude · Post by **k1dude** » Wed Sep 16, 2015 5:31 pm

I'm not sure that was your carburator running dry. I live around big hills and have occasionally had that problem in the past. It used to come and go and I could never figure it out. Drilling the gas cap helped, but it still occasionally happens. It's always on a really hot day going up a steep hill at full throttle.

I suspect it has to do with 2 unrelated events. I think it has to do with the gas overflow tube being clogged or a clogging particle in the jet. It occured with less frequency once I drilled my gas cap. But now, I think if I fill the gas too high and then ride up a steep hill, the sloshing fills the overflow tube and my cap vent simultaneously causing vapor lock. Or, a little chunk of something clogs the jet. It always seems to be right after a fill-up when I hit the big hills.

The reason I suspect those two culprits is because a couple times it cleared itself after puttering to a stop with an occasional backfire - then attempting a restart. Both times, I would coast to a stop, let it sit for about 20 seconds, then restart. Both times, it would try to catch, but would die after sputtering and farting. Even after I hit the kill switch and turned the ignition off, it would continue to diesel for a few seconds. Then, it would backfire. After the dieseling backfire, it would start right up and run like a champ - as if nothing had ever happened. I think the violence of the dieseling/backfire either cleared the clogged tube or jet or both.

It hasn't happened for about a year now (fingers crossed).

charlie55 · Post by **charlie55** » Wed Sep 16, 2015 10:08 pm

May be a stretch, but if I'm interpreting the Blur carb diagram correctly, the float is hinged towards the front of the scoot. So, if you're going up a steep incline, it's possible that all of the fuel has moved to the rear of the bowl and is forcing the float up. If it's being consumed at a high rate because of the climb, then there might be enough fuel pushed back to maintain the upward pressure on the float (thus forcing the inlet closed), but not enough left under the main jet. Also, IIRC, the carb is fed from secondary fuel tank, and that's filled from the main tank via the vacuum pump. The secondary tank has a return line to the main, so it's never pressurized and feeds the carbs strictly by gravity. So, it may not exert enough force against the inlet/float in a steep angle climb.

babblefish · Post by **babblefish** » Wed Sep 16, 2015 10:55 pm

You may be correct that it is a float issue. I opened up the carb to check and it is a little low, so I made an adjustment to raise it. We shall see in a few days if that cures the problem since I ride that hill often. Ah, the joys of living in a hilly city.

babblefish · Post by **babblefish** » Thu Sep 17, 2015 2:18 am

So, it appears that a low float level was the culprit. Rode the same hill (and a couple of others, just for good measure) after raising the float level and she's fine.