Vespa Si runs only with new plug (every 100 km)

Eran Kaufman /

Hi There folks,

My friend vespa Si is acting very strange.

it was mine before and i restored and modified it

it has a DR kit,new 13.13 carb (dont remember what jet) malossyi multivar,new crank bearings and seals...in general very nice.

btw it's an electronic ignition model

when i was mine i wasn't riding it very often,but it always started and ran without problems.

since my friend bought it from me, he rode it more and started to have problem. the problems are always the same - the moped doesn't start, he changed the plug on my advice and it worked,about 80 miles later it happened again, he changed to a new plug and it worked again, then the same thing happened for the 3rd time !!

Yesterday we changed the plug again and it started on the first kick.

what could this be?

when i took out the "old" (80 miles) plug it wasn't black or sooty, actually it looked quit well,kind of brownish - maybe a bit dark.

could it be an electrical issue after all?,can the spark be to week to ignite on a plug that is not brand new?

how can i check it?

thanks

Eran

Re: Vespa Si runs only with new plug (every 100 km)

barney gierer /

make sure you have a clean hi flowair filter. then if it keeps fowling plugs consider down jetting. maybe double check his fuel ratio. if the plug is dark and a new one fixes it then its a carb/jet/fuel issue in my opinion

Re: Vespa Si runs only with new plug (every 100 km)

60 to 80 miles sounds like a tank of gas, communicate with the new owner what's different.

oil ratio, dumping the oil into the tank first (bad!)rather then premixing and switching to reserve (contaminated tank) come to mind.

plug heat range is important to a clean plug, side electrode burn is a basic indicator, 1/2 the distance is ideal.

even riding style can contribute to fouling, short trips, lugging on hills, other things.

all this is an alternative to basic motor health and tune.

Re: Vespa Si runs only with new plug (every 100 km)

On a bike with crankcase oil,you can foul often because of a leaky oil-side seal.Does Vespa have this? I'm thinking not.So it's probably what they said about oil mix being too great. don-ohio

Re: Vespa Si runs only with new plug (every 100 km)

Eran Kaufman /

I told him to premix 2%, i hope he does it.

i think i'll have to check what jet is in there, i remember trying few jets so it's not the stock one for sure.

the moped does have a polini hi flow air filter,we even drilled few extra holes cause it was too rich running in my opinion. maybe it is still too rich

Re: Vespa Si runs only with new plug (every 100 km)

barney gierer /

Whar kind of pipe?

Re: Vespa Si runs only with new plug (every 100 km)

Eran Kaufman /

It's a Proma Circuit

Re: Vespa Si runs only with new plug (every 100 km)

barney gierer /

Cool. That setup should run great. Might be that you need to rejet. I had to do the same this summer to a bike (simalar build) thay ran fine last fall. I fowled a plug as well.if your worried about running to lean then get a temp sensor

Re: Vespa Si runs only with new plug (every 100 km)

barney gierer /

I think I have a 70 in there now. Still a tiny bit rich.but thats ok

Re: Vespa Si runs only with new plug (every 100 km)

Eran Kaufman /

So running rich will causes this? it's not a weak spark?

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