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vespa VBB oily spark plug

Discussion in 'Bling and Appearance' at netrider.net.au started by sydneycraig, Jul 2, 2009.

  1. hey all

    have a vespa VBB but with a new (2000kms) lmi engine.

    recently failed to start after not using for a week or so.....looked at spark plug and was very oily, black, wet.....wiped it down and tried again...it started for a fraction of second then cut out.....

    put in a new spark plug and it starts but will only run a second or 2, again with some oily deposits on the plug....

    so im thinking the fuel is too rich...too much oil?!!

    help appreciated


  2. I'd be thinking its rich from the information you have told me also.

    Check the choke too as that may help as it modify's the air/fuel ratios for cold starts and if left on can probably plug up the spark. (not an expert)

    But try lean it a little and see if it makes a difference, but little bit at a time, dont get lean happy and blow an engine.
  3. the choke only stays on when you hold it out and pulls back itself so dont think its that....ill try adding a little extra petrol to make less rich....that is right?!?!
  4. Whoa, hold on there Craig! You've got two different things confused.

    You are talking about the amount of oil in the petrol. This ratio will be in your owner's manual if you have it. If not, ask your mechanic. A quick google suggests 2% oil but I couldn't find any information for an 'lmi' engine.

    When people talk about rich/lean mixture, they are referring to the air:fuel ratio. This is controlled by the carburettor, and adjusted by a screw. Again, refer to your owner's manual or mechanic.

    Now to your oily spark plug. If you are putting more oil in than the manual specifies then it could be the problem. If you are putting in the correct amount of oil, keep doing that and find the real problem...

    Were there any problems before it failed to start?

    Is your spark plug sparking? If you feel confident, take it out, reconnect the spark plug lead, rest it on the engine (so that only the outside of the spark plug touches the metal, not the electrode at the end) and crank the starter briefly. You should see a nice fat spark. If you don't, then you have some sort of electrical problem.

    If you do see a spark...
    Is your choke sticking?
    Is your air filter blocked? When was it last cleaned/changed?

    There are more things to check, and someone who knows your engine will be able to offer more specific advice, but that lot should give you somewhere to start.

    Let us know how you get on,

    PS: Nice scoot!
  5. hey

    thanks for the info there....

    there is still a 1/4 tank petrol and was working ok before (if a little blue smoke) so gues the fuel/oil mix is pretty much correct.

    so i checked the spark plug and there is a spark...

    have just taken the air filter out and it 'looks' clean....blue mesh type....should i soak in petrol(right!?!) anyhow

    starts for a second or 2 still but then dies and the spark plug is covered again..

    have fiddles with the air/fuel mix screw but no settings seem to help much either way....lost where it should be now too!!!! :( currently at full tight then 1 1/2 turns left..

    thanks for your help

  6. Keep in mind I am pretty inexperienced so if anyone has any better ideas jump right in.

    Ok so you have spark, this is a good thing.

    For now lets assume you have compression, as I don't know of any problem that would cause you to loose compression just from sitting around for two weeks...

    So fuel is suspect number one - that is to say there is too much of it. The workshop manual for my bike suggests a worn or stuck float valve as a possible cause. This sounds plausible to me - after sitting for two weeks the fuel got a bit gummy and has stuck the float valve.

    So your carburettor probably needs a clean, but you might get away with giving it a sharp tap with the handle of a screwdriver to unstick the valve (use your judgement as to how much force to use - it's your carb after all!).

    There are a number of threads here about air filter cleaning - refer to them as I haven't a clue!

    Also, search the 'net for carb settings, I'm sure you will find some 'starting point' settings if you google your carburettor model number. Or it will be in the workshop manual.

    Good luck
  7. some bikes are a biach to start if left for a while. try spraying some start ya bastard from stupid crap auto, in the airbox or wd-40. could be a case of fuel not in the carby cuz no suction. and you tryin to start it could be flooding the engine causing the black sparks
  8. Willzah, I don't follow. How does 'no fuel in the carburettor' lead to 'too much fuel in the combustion chamber'?
  9. update - so i have been starting (trying) every day or 2 and it has become easier to start and running for longer each time i do so.....have just started it up now and it started first time, no choke and ran for about 5 secs then just quietly died....restarted fine and ran slightly less time.......starts ok pretty much each time but just will not keep going....sounds like its running normally from what i remember

    i have been adjusting the air/fuel screw each time slightly but the best spot i can find for it still no good!! also cleaning sparkplug which still gets some black wet residue, but not as much as before...

    any ideas appreciated
  10. ok, so after going away for a few weeks its now starting every time but only for about 5-10 secs......restarts less each time unless left for a few mins...

    so assuming it has some sort of reserve of fuel that is burning off but not getting replaced??!

    still lost here!!
  11. You could be right. I don't know what fuel tap arrangement you have on your Vespa, but it sounds like it is off or blocked. Fuel may be trickling through and pooling in the float bowl so that there is enough to start it, but not flowing enough to keep up with the engine.

    Try disconnecting the fuel line after the tap, and seeing if fuel is flowing out at a reasonable rate when the tap is turned to ON and RESERVE (have a rag to catch the drips and direct the line into a clean glass jar or something to avoid a mess).
  12. yep, tried that....the fuel is coming thru OK, the fuel filter in the carb is clean, have checked the fuel jets are not blocked, ....there was quite a lot of sedement/crap in the fuel tank which i have cleaned out but as there seems to be pretty constant flow from the tank i dont think its blocked....

    think it might be time to hand over to the mechanic!!