Colourtune Diagnostics - or not


Active Member

OK, so cylinder #1 shows a splashy, quite erratic and non steady flashing. Cylinder #4 (of 4) is quite steady without the erratic flashing and irregularity in brightness, in terms if the color and flash pattern.

A can't get it to idle unless it's rich (HS8), but I don't think that is particularly noteworthy. At best it's a bit rough but I think you have to be a genius to pull it off without a bit of lump. Any suggestions about whether this obvious difference in combustion view is indicative of anything untoward and if so what might I do to smooth things out?



Well-Known Member
Sounds like the front carb is maybe running lean? HS8's at idle on our engines are barely sucking enough air through to mix fuel and air (hence why they nearly always idle a little rough). I would check your valve clearances and ignition timing, points gap to confirm they are within spec as they can throw off your chances of tuning the carbs too.

To be honest I've never been a fan of the colourtune system. In theory its a great idea, in practice I've seen issues. You might want to have a slightly faster idle to hep you with identifying the correct mixture for both carbs. With the higher revs (say around 1200-1500RPM) you'll get a better chance of sufficient airflow to mix air and fuel.

If you feel that's not really working out for you I would try the factory manual method of lifting the air pistons about 1 - 1.5mm and listening to the engine speed. I've normally found that a lot more reliable a gauge.

Hope that helps,



Staff member
I don't know about 4 pots, but with the colourtune I use it to get close then play with the mixture till it idles right afterwards.