Coughing and Spluttering 2

[beaver]

Hi all, 1st post so howdy.

I have a T5 Classic which coughs and splutters at high revs for the first 5 miles and then runs fine. I've had a search for the problem I have seen a similar post but the problem there was spluttering AFTER 5 miles. Any ideas what's going on? I changed the gear oil and sparkplug and cleaned the filter last month. The change in tick over when taking the filter off seems to have made it a little worse

Regards
Stu

[paddedjohn]

Hi Stu welcome to the site. Have you checked the choke isnt sticking on a little? I could be wide of the mark but if it happened on a car thats what i would suspect.

[Rudi]

welcome

mmm regarding your question...im not so sure
but i would guess its not choke, otherwise it would work good while engine cold, and then start fouling when hot

fuel dripping in crank? but then it would'nt take 5 miles to start running fine, but much less

weird...i cant think of anything

do you remember the color of the old spark plug?

[beaver]

Hi Guys and thanks for the replies so far. I remember thinking the old plug looked health. It may have been dry and brown and not much oil on it

I did try pulling the choke on while riding to see if it made a difference but it only made me nearly crash. I'm still not sure if it's fuel starvation or too much fuel. Keeping the throttle on fuel say in 4th, when it gets over 55mph it starts to lurch and will take about 3 to 5 big gulps nothingness then back to normal running without moving the throttle. After 5 miles everything is tickertyboo.

[Rudi]

you didnt say how you start it cold, with choke? starts easy?

if it runs a bit too rich , engine wouldn't stop (is that what you mean by "nothingness"?), but just smoke a lot

fuel starvation is more likely
and lean mixture will probably have more effect while running cold

could be the float level
or fuel line inside vespa improperly

again, an educated guess...
i think you should inspect plug, thats the best way to at least rule out rich mixture
which would show on the plug as black or wet residue

[beaver]

Hi Rudi

Never starts 1st kick but always on the second with the choke. It only smokes when it's been stood for a couple of weeks but the smoke clears quickly.

ISTR that this started over a year ago but wasn't very prevalent. It seems to have gotten worse now to the point it does it all the time. ISTR it was alway worse in winter

Stu

[Rudi]

55 is almost top speed
maybe the engine is too cold

anyway....cant think of sth else...

[beaver]

It's actually good for nearer 70. I think I may try to increase the fuel flow. Anyone care to tell me how to do this. I do have the Haynes book but it's always much easier to ask someone who knows

[beaver]

I've changed the HT lead and cap today but no difference. I did notice that when it spluttering that the needle on the fuel gauge was dropping from full to nearly half then back to full when the spluttering stopped. Could it be the ignition coil?

Stu

[joey]

"Coughing and spluttering" doesn't actually give us much, and when you say "high revs" are you talking 3/4 or full throttle?
To me it sounds as though your rings could be due a change, but then if it's running sweet after 5 or so miles then there might be nothing wrong at all.
Your motor needs to be fully warmed up before you can use it to it's full potential so that both piston and barrel have expanded to their full extent, it's only then that you can tell how it's running.
Do a few plug chops at various throttle openings and then you'll know if it's running ok.