How to check fuel to cylinder?

Bike: 1977 Piaggio/Vespa Bravo? Complete original w/ 2,100 mi.

Prelims: Fresh gas, clean petcock, good flow to carb, great bright blue spark, good compression w & wo CR.

Problem: Bought it yesterday after a few good test rides and damn if it doesn't die on the wife halfway home. Restarted once but only got another 100ft. Crap! At home, no start and only a pop/backfire or two after numerous attempts.

Pulled plug but don't know enough aboutt these micro engines to know the difference between wet and too wet. OK, it was a bit damp and shiney and not bone dry at least. Freewheeled engine to clear it. Reinstalled plug after a good shot of starting fluid... and still nothing.

Pulled plug again and freewheeled engine with the tip of my finger in the sparkplug hole to see if it was drawing/delivering gas. Finger wasn't exactly wet or smelling of gas but then again, not bone dry either.

How can I determine if my no start is due to flooding or starvation?

Any tips on clearing a flooded engine?

Any tips on using starting fluid?

Thanks guys!

Mr Bentwrench

Louisville, Ky


Re: How to check fuel to cylinder?

Probably Fred /

Search freds guide in wiki

Re: How to check fuel to cylinder?

Back fire = timing is off

Re: How to check fuel to cylinder?

Bob Hitchcock /

Thanks for the wiki link. They are so handy. Have a link to a service manual now as well.

Just pulled and throughly cleaned the carb assembly. Was quite optimistic I had cleared a possible main jet obstruction but was very disappointed with the same old no start. Rechecked spark just to be sure and its strong, bright and consistant.

Of note though is the PO had just replaced the complete head to fix the original broken CR spring. I am assuming that the CR can not be an issue as I can not keep my finger in the hole while cranking with CR open or closed. Also, shouldn't my finger be wet even a bit?

Will have to look at a timing issue now as I can only assume I'm drawing gas without combustion and even a good shot of starting fluid didn't even make a pop. It kinda suddenly died while running so something may have slipped on the breaker plate.

Any tips on using starting fluid? Pull the plug, shoot and replace or through the carb throat? Any other possible ideas other than timing?

Re: How to check fuel to cylinder?

Michael Thomas /

You can do it either way, in the plug hole or carb intake. You may also try to drop the exhaust and see if it starts, it may be plugged.

You can also check and see if you are getting fuel to the cylinder by installing a DRY plug and then trying to start it for a couple of minutes. Pull the plug and see if it is wet at all.

Re: How to check fuel to cylinder?

Downhill Harvey (OFMC) /

Did you clean the banjo screen on the carb?

There's a screen behind that.

Re: How to check fuel to cylinder?

Take the carb off and remove the float bowl. Then hook the fuel hose back up.

Gently raise the float with your finger and turn on the fuel petcock.

Release the float and you should get fuel dribbling out.

If the fuel does not come out pull the petcock and clean the screens.

Re: How to check fuel to cylinder?

Bob Hitchcock /

This appears to be the root of my problem. Its getting gas... then running out!

It eems that the bowl is filling too slow and will not keep up with the carb's draw. If it sits with the petcock open for 20-30 minutes, it will start and run fine... until it runs out of gas. Let it sit for another 20-30min and repeat.

I have cleaned the banjo filter, seat and needle and have great on and off flow operating the float up and down with the bowl off. However, when refitted (twice now to double check myself, it still seems to have a too slow feed and runs out of gas.

Is there anyway to adjust the float level on these things. My needle in correctly positioned in the slot of the float arm (not above and too high limiting flow) and there is no tab to adjust any range of operastion.

Should this go to a new thread on this now?

Re: How to check fuel to cylinder?

remove your fuel cap and see if the flow improves.

Re: How to check fuel to cylinder?

Michael Thomas /

Check the flow from the petcock also

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