79 vespa grande runs for limitted time (severely limitted)

Ok i hardwired it. That part works.

I took the air box appart and cleaned it up (screen too)

I took the petcock out and soaked itin carb cleaner.

I replaced the fuel line.

I removed the carb and disassembled it. Cleaned it, and reassembled it.

In the process i broke the elbow for the throttle cable. It has been repaired. Qlthough may need adjusting.

Now itll start up and drive for a quarter mile then bog and stall. Then it wont start until it sitsfor a long time.

I checked the fuel line. It flows.

Any ideas?

Re: 79 vespa grande runs for limitted time (severely limitted)

running a fuel filter? whats your spark plug look like when this happens? or maybe a bad condenser?

Re: 79 vespa grande runs for limitted time (severely limitted)

The closest thing to a fuel filter would be a little screen in the carb.Spark plug is gapped at .027. The manual says .02 but the old one i took out was at .03. And a lotnof online sources vary so i split the fifference.

What do you mean by "whats [it] look like?"

Re: 79 vespa grande runs for limitted time (severely limitted)


JD B has it right.

You buy a filter and install it in the fuel line.

Treats sells them. Any speck of rust will clog the tiny hole on a jet.

I also think you might have a bad condenser.

They can be a pain to change on the Grande.

What he means by" Look Like" i think.

1)Take the spark plug wrench with you on the ride.

2) When the bike boggs and quits remove the spark plug and reconnect it to the wire.

3) Crank the bike while holding the plug base (metal base part) against the metal of the cylinder and crank the engine. Its helpful to use an old bike moped tire tube of bungycord to hold the plug to the engine.

4) Observe the quality of the spark.

You want to see a brilliant blue or white spark.

if you see dim red or yellow or no spark then the condenser is bad.

As the condenser heats up it is failing and making the spark happen at the points not the plug.

5)Try this and post back.

Re: 79 vespa grande runs for limitted time (severely limitted)

So i looked at the points. They look clean. I dont have a feeler gauge so i didnt touch them. But they arent corroded.

I cleaned the carb again. And did a little looking online. My petcock has good flow. The fuel line has good flow and i do in fact have a screen filtering the fuel as it enters the carb. Is this sifficiant?

I tried to take it for a run down the street and could get it started at all. I then decided 'what the hell' and took the plug off and thumb checked the compression. I dont know how much it is supposed to push but it does a little. What does the 8:1 in my owners manual mean? I have no idea they should label this lol.

So yeah the face of the piston is brown with shit. Im gurssing it needs to be clean. How do i replace the condenser? Im figuring i will need to clean the piston and block etc which involves taking the clutch? Or whatever it is above the flywheel off anyway so i might as well just go big or stay home right?

Which cylinder kit would be good for me. Like hell. It'll be in pieces anyway lets make a shopping list on a new post.

Re: 79 vespa grande runs for limitted time (severely limitted)

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