:help: Hey all

A while ago my moped broke down due to crud in the spark plug gap, I had to replace the spark plug and cap. Since then (about 2-3 weeks ago) it's been running fine until the past couple of days, now it has started slowing down going uphill and acceleration has become more sluggish - just like it was before it broke down!
The new spark plug has turned black around the gap, and my guess is the air/fuel mixture may not be quite right. This morning I altered this slightly to make the mixture leaner (though I'm not sure if turning the screw anti-clockwise DOES make the mixture leaner!) and it seems to be accelerating a bit better but I'm not sure if this is the best thing to be doing...

Does anyone have any experience of this kind of thing, have any advice for me etc? I'm not too clued up on this aspect of looking after an engine - however, I'd much rather learn to do it myself than take it to a garage, pay £60 then take it back 2 weeks later because the problem reoccurs! :help:

your spark plug should be the colour of milk chocolate,try turning down the fuel mixture and check the plug gap,may be better with a new plug so that you can define the colour as the old one will be burnt black

Is it a two-stroke engine, rather than a four-stroke?
What make/model/cubic capacity is your beast?
What is it's mileage?

your spark plug should be the colour of milk chocolate,try turning down the fuel mixture and check the plug gap,may be better with a new plug so that you can define the colour as the old one will be burnt black

Milk chocolate... hmmm just made me hungry! :P I'll need to buy a stick thing to measure the plug gap then (not sure what it's called). Fortunately I have a spare plug at home, thanks.


It is a 2 stroke engine, 50cc (beast!? :hihi: ). The mileage is 2600 Km - about 1615 miles, and the 'ped is 5 years old... I've had it for the past 3-4 months and done 870 miles on it (just worked that out and can't believe it's that much already!! :o ).

Thanks for the help guys...

have you checked the air filter ? if its old/dirty may need replacing or cleaning depending on what type of filter it is , this can cause a rich mixture black plug , is the plug sooty or is it black and oily , sooty is a rich mixture , oily could be more serious .depends on is it a 2 stroke or 4 stroke engine ?

It is a 2 stroke engine, 50cc (beast!? :hihi: ). The mileage is 2600 Km - about 1615 miles, and the 'ped is 5 years old... I've had it for the past 3-4 months and done 870 miles on it (just worked that out and can't believe it's that much already!! :o ).

Thanks for the help guys...

Are you using really cheap two-stroke oil? If you are this is a false economy.
Have you cleaned/replaced the air-filter?
It is unlikely that you should have to be messing about with any of the air screws, and recommend that you put it back to where it was. If you are running too lean you are at risk of burning a hole in your piston.
Is it restricted? If it is, and you tell us what make/model it is, we will see about unleashing its' full potential.

have you checked the air filter ? if its old/dirty may need replacing or cleaning depending on what type of filter it is , this can cause a rich mixture black plug , is the plug sooty or is it black and oily , sooty is a rich mixture , oily could be more serious .depends on is it a 2 stroke or 4 stroke engine ?

Air filter has been checked and is clean as the day it was born, the plug is black sooty - definitely not oily and the engine is a 2 stroke. The bike is an Aprilia Habana.
Thanks for the help tinker. :thumbsup:


Could I do any damage to the engine by changing the mixture to see if that makes a difference? And how can I tell once the mixture is at its most ideal?

Are you using really cheap two-stroke oil? If you are this is a false economy.
Have you cleaned/replaced the air-filter?
It is unlikely that you should have to be messing about with any of the air screws, and recommend that you put it back to where it was. If you are running too lean you are at risk of burning a hole in your piston.
Is it restricted? If it is, and you tell us what make/model it is, we will see about unleashing its' full potential.

I can see I'm not typing quick enough at the mo! lol

I am using Castrol 'Scoota' 2 stroke oil, it's the most expensive I've seen around. For the air filter see my previous post and I was told the bike is restricted when I bought it, though it seems faster than it should be ;) .
I certainly don't want to spend money 'unleashing its full potential', thanks for the offer though SHarper. :thumbsup:

The Habana is restricted by four seperate methods:-

A small washer in the variator.
A jet restrictor in the carb.
Two restrictors on the exhaust system, an inner flange restricting flow, and a resonator tube that impedes scavenging.

Removing these restrictions allows your engine to work as it was designed, and will cost you nothing..

as sharper says dont use a cheap 2 stroke oil , make sure you have the correct grade of plug and the correct gap , when you fit the plug that is clean and correctly gapped you will see after using the bike after say 10 miles or so when you take the plug out wether the mixture is right as depoix rightly says it should be a chocolate/coffee coloured if it is white you have a lean mixture sooty a rich mixture if you alter the mixture screw on the carb take note of the original setting , i am not sure at the moment if it is clockwise or anticlockwise to weaken the mixture , but if you need to know i can check .i would not think by making a small adjustment you will damage the engine i never have with my bikes in the past , just keep an eye on the plug that will tell you if its ok good luck .

The Habana is restricted by four seperate methods:-

A small washer in the variator.
A jet restrictor in the carb.
Two restrictors on the exhaust system, an inner flange restricting flow, and a resonator tube that impedes scavenging.

Removing these restrictions allows your engine to work as it was designed, and will cost you nothing..

I appreciate why you say all this, however removing these restrictions will cost me a minimum of training, instructors and passing my CBT - something which I can't afford at the moment. Otherwise I'll just be breaking the law and invalidating any insurance cover I have.

i am not sure at the moment if it is clockwise or anticlockwise to weaken the mixture , but if you need to know i can check .i would not think by making a small adjustment you will damage the engine i never have with my bikes in the past , just keep an eye on the plug that will tell you if its ok good luck .

Thanks again, I have marked the original position of the screw so I can always put things back to the way they were. If you could let me know which way to turn the screw to make the mixture lean that would be really helpful!! :thumbsup:

This thread is sooooooooooo riveting.

This thread is sooooooooooo riveting.

Riveting!? :confused:




I haven't mentioned rivets once!! :P

Thanks again, I have marked the original position of the screw so I can always put things back to the way they were. If you could let me know which way to turn the screw to make the mixture lean that would be really helpful!! :thumbsup: i think that should be anticlockwise to weaken the mixture , it is trial and error , ps dont touch any ( rivets ) ha ha .

i think that should be anticlockwise to weaken the mixture , it is trial and error , ps dont touch any ( rivets ) ha ha .

No prob's, I'll leave them well alone! lol, thanks for that...

Have you tried putting Shell Optimax petrol in rather than the normal stuff? I use this in my bike and you really can tell the difference. Ok it's a bit more expensive than the standard grade, but you shouldnt notice it that much as you should be getting good mpg's out of the scooter.

As for the rivets, these should be a silver colour, not milk chocolate. If the rivets do become discoloured you can easily replace them by drilling them out and fitting new ones - but it should be noted that this will have absolutely no effect on the performance of the bike.

[QUOTE=Marky543]Have you tried putting Shell Optimax petrol in rather than the normal stuff? I use this in my bike and you really can tell the difference. Ok it's a bit more expensive than the standard grade, but you shouldnt notice it that much as you should be getting good mpg's out of the scooter.
QUOTE]

I would if I could, however I don't have a Shell garage anywhere near me, the nearest one used to be on Chesterfield rd but closed down months ago.
Would using something like BP's super unleaded make much difference? I generally just use supermarket petrol.

Since I changed the mixture the bike was running better, but sounding a lot louder, like an angry wasp!
I've checked the plug again shortly after switching the engine off after doing about 20miles and it's now a dark brown colour, it also had a little oil on it. This morning it was sluggish again and nearly gave up a couple of times, then it seemed to warm up and suddenly it was very, very quick.

What would you do next, make the mixture slightly less lean? Possibly put it the other way entirely and make the mixture slightly richer than it was originally and see what happens?

Any help much appreciated!! :help:

Hi Briano,
I noticed that you mentioned earlier that you said you had a spare spark plug at home!
When I was a lad and had a smaller 2 stoke bike I always kept at least one spare plug, a plug wrench and a rag stowed on the bike somewhere. 2 strokes always were funny with their plugs and I often had to change one in a hurry to get it going. You don't want to be stranded away from home.

Always keep a spare plug on your bike under the seat with the tools, I don't know if your bike has a tool roll?.

Hi Briano,
I noticed that you mentioned earlier that you said you had a spare spark plug at home!
When I was a lad and had a smaller 2 stoke bike I always kept at least one spare plug, a plug wrench and a rag stowed on the bike somewhere. 2 strokes always were funny with their plugs and I often had to change one in a hurry to get it going. You don't want to be stranded away from home.

Always keep a spare plug on your bike under the seat with the tools, I don't know if your bike has a tool roll?.

Hi, yeah it has the original toolkit with that included. I keep meaning to put that spare plug on the bike, damn I just know I'll be needing it before I remember! :rolleyes:

Hi, yeah it has the original toolkit with that included. I keep meaning to put that spare plug on the bike, damn I just know I'll be needing it before I remember! :rolleyes: you have made an adjustment to the mixture , you have weakened the mixture , the plug is now a dk brown colour that is an improvement from the black sooty plug i would not turn the mixture screw back it will make it run too rich again i would make it just a little weaker still but only slightly it sounds almost correct , and as muddycoffee rightly says make sure you carry a spare plug with you at all times as i have always done in the past , if you continue to have problems it could be the choke needs checking and also the petrol/oil mixture ratio setting asuming this is autolube engine . if you have a manual look it up .

you have made an adjustment to the mixture , you have weakened the mixture , the plug is now a dk brown colour that is an improvement from the black sooty plug i would not turn the mixture screw back it will make it run too rich again i would make it just a little weaker still but only slightly it sounds almost correct , and as muddycoffee rightly says make sure you carry a spare plug with you at all times as i have always done in the past , if you continue to have problems it could be the choke needs checking and also the petrol/oil mixture ratio setting asuming this is autolube engine . if you have a manual look it up .

Cool, thanks very much for the help. :thumbsup:

I shall be making the engine a little more leaner tonight then and making sure the spare spark plug is safely stored on the scooter!

hello mate are you leting to bike warm up for about 5min or 10mins befor you set off it probs doing that thing you said because no letting in warm up

:help: Hey all

A while ago my moped broke down due to crud in the spark plug gap, I had to replace the spark plug and cap. Since then (about 2-3 weeks ago) it's been running fine until the past couple of days, now it has started slowing down going uphill and acceleration has become more sluggish - just like it was before it broke down!
The new spark plug has turned black around the gap, and my guess is the air/fuel mixture may not be quite right. This morning I altered this slightly to make the mixture leaner (though I'm not sure if turning the screw anti-clockwise DOES make the mixture leaner!) and it seems to be accelerating a bit better but I'm not sure if this is the best thing to be doing...

Does anyone have any experience of this kind of thing, have any advice for me etc? I'm not too clued up on this aspect of looking after an engine - however, I'd much rather learn to do it myself than take it to a garage, pay £60 then take it back 2 weeks later because the problem reoccurs! :help:

If this is a 2 stroke ,my money is on you have had a minor seizure,and now its possible the rings are stuck in the grooves or worse.I would be having the head and barrels off to have a look.
If that is the case then you have 2 problems,the damage,and whats caused it.A weak mixture,insuficient 2 stroke oil,or letting it get too hot.

How does the Engine sound?

I personally would find out the factory setting for the mixture and put it to that,cos if you get it too weak ,if you havnt already got bigger problems ,you soon will have.