I have just purchased a series C Comet and having issues tuning it to run correctly. It came with a 930/71 Mk1 concentric carb, which was worn, so I replaced it with a new premium one from Burlen services. I used the same settings as the one that I took off but it ran very rich. Wet sooty plug and white smoke from exhaust. I've reduced the main jet from the 270 that was fitted to the previous one and gone down to a 250. I've replaced the throttle valve to one with a higher cutaway and moved the clip on the needle up to the top notch. None of this seems to have made a difference. The bike runs ok for short runs but the plug and clouds of white clearly indicate it's far from right. Anyone using the same carb and can let me know their settings or suggest other changes I can try. Many thanks.
Super rich Comet
- Thread starter paulthom1199
- Start date
White smoke usually means burning oil. So does a shiny wet oily looking spark plug.
Black smoke means too rich. Usually with a rich mixture the plug is black and sooty, but not oily in appearance.
Simon
Black smoke means too rich. Usually with a rich mixture the plug is black and sooty, but not oily in appearance.
Simon
Remote diagnosis is fraught with pit falls but if I said 'clouds of white' I would be looking a few inches past a new Burlens carb in the direction of the engine.
Sorry I cant help you with the settings concentrics are not on my favored list but plenty of people here can, and if you find that thir settings and yours (originally or now) are in the right ball park its time for the spanners
Sorry I cant help you with the settings concentrics are not on my favored list but plenty of people here can, and if you find that thir settings and yours (originally or now) are in the right ball park its time for the spanners
I did wonder about the engine being an oil burner, rather than rich running, but the compression is really good which makes me think too rich. The plug smells of petrol rather than oil. I could just be kidding myself but would like to eliminate the carb before digging deeper.
Seems your needle jet is far too rich as setting the needle to its lowest position does not cure the richness. Look at a diagram at AMAL pages downloads that shows what component in a carb does what at different slide positions.
Vic
link:
Amal tuning
Vic
link:
Amal tuning
Thanks Vic. I note that the original Comet carb, 229F/1DV, had a 200 main jet. I think I'll try that. Confused as to why the previous owner was running a 270 but must be worth a try.
OOPS. My bad. Didn't think about the needle jet. I believe standard size is 106 and they supply as low as 104. Will try that as well. I will check to see what size was fitted to the worn carb I replaced. Thanks.
I don't think you want lower than 106.
I have found the slide needs to be weaker than 3.1/2, I have hand cut mine.
Float level could be too high, But if it's new, I would not think so.
About 200 for a main jet, But as Vic says, That should be only at high speed.
Did you tell Burlen's it was for a 4 stroke.
If you look at the burlen site it shows all the different jets, And ID of them.
Cheers Bill.