rich, lean - how do you check it?

[oldgreyandslow]

Odd question perhaps, but back in the olden days when I was working on my cars setting the misture usually involved some weird contraption in place of the spark plug that you could use to see the colour of the combustion and hence get the mixture right, colourtune or some such thing I think.

I'm about to strip down the carbs and using the guide Cam posted (got the PDF version) will jet acording to that, but its running a standard pipe now and I will be changing that shortly, so wonder if its worth changing the jets now, and also how do I know if its currently too rich or too lean

By the way current fuel consumption is bloody awful, about 25 mpg ffs!

[porndoguk]

With a probe and a specilist tester, usually at dyno centres.

but old school mechanics can just smell it,

[hardnutdvd]

they still sell them spark plug contraptions. they are called colourtune

[porndoguk]

they still sell them spark plug contraptions. they are called colourtune

Morgan Carbtunes Sell them i believe,

[skinnydog0_0]

crude method but it's okay is to get one of teh plugs out and check it, you want it biscuit brown, if it is oily dark colour it's rich if it's pale brown/white-ish with blisters it's too lean.
But as porndog says best to get it on a dyno and get it set properly once you have the pipe on.

[porndoguk]

crude method but it's okay is to get one of teh plugs out and check it, you want it biscuit brown, if it is oily dark colour it's rich if it's pale brown/white-ish with blisters it's too lean.
But as porndog says best to get it on a dyno and get it set properly once you have the pipe on.

i was told that you cannot accurately tell if a bike is rich or lean at idle as its running of the pilot screw and pilot jet settings which arnt used ones the bikes on the mains, so i would just get a probe stuck down the exhaust, but again that will tell you overall A/F mixture but it wouldnt be able to tell if one cylinder was lean and the other was rich unless they had independant lambda sensors on each pipe outlet.

[skinnydog0_0]

crude method but it's okay is to get one of teh plugs out and check it, you want it biscuit brown, if it is oily dark colour it's rich if it's pale brown/white-ish with blisters it's too lean.
But as porndog says best to get it on a dyno and get it set properly once you have the pipe on.

i was told that you cannot accurately tell if a bike is rich or lean at idle as its running of the pilot screw and pilot jet settings which arnt used ones the bikes on the mains, so i would just get a probe stuck down the exhaust, but again that will tell you overall A/F mixture but it wouldnt be able to tell if one cylinder was lean and the other was rich unless they had independant lambda sensors on each pipe outlet.

Yes true, but the bike has been running at normal speeds so the plugs should be a fairly good- if crude pointer, and as the carbs are going to be off the bike the plugs shouldn't be too hard to get at and check.

[lizard821000]

as already said, best bets a dyno place mate, they will show you graphs of the A/F reading over the rev range, but also as said, hard to tell if one cylinder isnt lean or rich. plug checking is pretty crude on 4t but still a good indicator of those symptoms. 4t are alot more forgiving when it comes to this, a 2t would blow in a minute with the same problem. a good idea would be to check your jetting on the carbs too.

if your lean on your pilot and chop the throttle at WOT , the pilot circet will cut in.....so deffo worth checking the settings on the airscrew.

[Cammo]

By the way current fuel consumption is bloody awful, about 25 mpg ffs!

Sounds like blocked jets or other carb parts. Follow the guide, clean the carbs, jet accordingly and go from there!

If you want confirmation of the jetting take it to a dyno afterwards.

[Cru Jones]

Unless you're checking the MJ, there's no easy way of doing it. With my RS125, you work your way backwards from the MJ. So, put in a new plug, warm it up to temp then do a plug-chop at WOT in at least 3rd gear (hard to find places to do that). Assuming MJ is good then do the needle (need to be done on a track for that), then air screw, etc. On a diesel, ahem, 4T, the easier quickest and most effective way is to bring it to a tuner and have them dyno the bike.