Some months ago I was at a friend's place, trying to start an old Vespa which had not been used for some time. I and the owner disinstalled and disassembled the carburator, suspecting that it was clogged. There was spark but the engine neither started with the kick starter, nor by pushing the bike. Then another friend joined us afterwards and he said that a good way to make sure that the carb really was the problem was to inject some premix into the combustion chamber and then use the kick starter, so he did that with a syringe via the spark plug hole, reinstalled the plug and its cap and kick started it without even reinstalling the carburetor! Without the carburetor installed, the air was free to flow inside the engine in large quantity: it was a little bit like having the throttle full open and so the engine started loudly and revved high until it ran out of gas. Then, after having cleaned the carburetor, we reinstalled it and used the same trick to pull some gas into the carburetor before the bike was able to run on its own. To me, that trick looked quite inventive and it was the first time I saw it. I would be afraid to use it on my bikes, though, especially in a two stroke like that Vespa: I wouldn't know whether the condition is lean or rich at the injection time, plus you don't know how high it will rev and revving a cold engine high is harmful. So, have you ever used that trick or seen it being used? Do you agree with me about its dangers?
Why would you do it without the carb ? Yes every man and his dog has tipped some gas down the plug hole or straight in the air intake to start something up that doesnt want to start
In that case, when our friend proposed to do the trick, the carb had already been disassembled and it would have taken some time to put it back together. Wow, I split the cases of my YZ250, did the top end of the 610 and I found out about that trick after more than 10 years since I started wrenching with engines! I get that one would do it on a lawn mower, but would you do it, with the carb installed, on a more expensive motorcycle?
Great way to determine carb or ignition problem, running for 5 sec won't be a problem. And you know the ignition is good, so clean the carb 5 more times!! Just use premix. Chris
I do it all the time on old lawnmowers that I get, and often use it on old motorcycles that I get. Good way to verify "proof of life" before going farther.
I'm not the first and you won't be the last!! I think I remember surpize had a friend that does it in the southern hemisphere! Chris