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[Micah]

Hey guys, just wondering what carb jetting I should start with on a 2004 500cc bullet sixty5. I have put a Bellmouth air intake with gauze and an Indian made exhaust with shorter and freer flowing silencer. At the moment I have a 27.5 pilot jet, the pilot airscrew is optimal at 2 turns out. My needle is as high as it goes and the main jet is a 117.5. The spark plug is mostly black with a little white on the tip. It hesitates a bit around second gear mostly ok otherwise, overall the throttle isn’t overly responsive but this might just be the fact that it’s a Royal Enfield. I did have a 125 main jet in but it felt sluggish at full throttle so I changed it to the 117.5 because it was my understanding that for every one size you go up on the pilot jet, you should go up 3 sizes on the main jet, please advise if this is incorrect. Now full throttle feels better but the hesitation around second gear wasn’t there until I changed the main jet. I was thinking of trying moving up the needle one notch.
Any comments would be appreciated, it’s nearly midnight here in Australia so I most likely wont respond with my gratitude until tomorrow.

[Edward]

Micah, I have a 2005 500 classic with the short exhaust and an american Ace air cannister free flowing air filter. My Micarb carb settings are 2 1/2 slide,P2 needle jet and 125 main jet. The needle is in the original position. The mixture is spot on and the carburation perfect. I hope this helps, Edward.

[Nettshubby]

I would also suggest the richer needle jet. I have a 125 main, 27.5 pilot, 2.5 slide, and needle in second notch from bottom. This is with a cone filter and shorter silencer, on my 2003 Sixty5.

[Nettshubby]

Forgot to say, I also have a 1 tooth bigger gearbox sprocket, easy cruising at 60 ish. (Usual wavy speedo needle!)

[Micah]

cheers guys, I went back to the 125 main jet and its actualy pretty good, I must have been tripping last time i road it. Since you both use the 2.5 slide i might give that a go. Im pretty sure I got a needle jet that is one size richer. I tried moving the jet needle one up from the bottom and it started sneezing so i put it back to the richest position and that seems to work for me.

[Micah]

Just an update on my progress, Iv gone up to a 130 main jet, a 2.5 slide, a P2 needle jet, and moved the needle to second richest setting. this has vastly improved the top end, however I'm still struggling to get the low end nice. Compared to other bikes the return to idle is slow, iv changed between 27.5 and a 30 pilot jet without noticing any change. in both cases it is optimal to have the air screw 2 turns out however I can take the screw completely out without killing the engine... is that normal?

thanks

[papasmurf]

The return to idle being slow could just be the throttle cable being a bit "sticky" or the lever/spring the carb end sticking.
(I prefer to check the simple before engaging in major spanner work.)

[Presto]

I agree with papasmurf. But a common cause of an engine failing to return to idle when the throttle is shut off is a weak mixture in the pilot circuit. It is a mistake to think that ‘2 turns out’ (or the famous ‘one and a half turns out’) on the pilot air screw are ‘normal’. There is no ‘normal’. That setting, like every other setting on the carburettor, needs to be adjusted for the engine in question. Our hosts give very clear help in the technical notes section on this site on setting the tickover correctly for both Mikcarb and Amal carbs. Once the pilot air screw is turned out a certain amount any further outward adjustment will have no effect, as the pilot air passage will now be fully open. Seems to me this carb needs fine tuning on the pilot circuit, jets and air screw.

[Micah]

Papasmurf cable is brand new and the Spring is strong, I can see that the slide responding as it should. I think iv got it now, the 30 pilot jet had the most power so I stuck with that as well as moving the needle back to the richest position, and BAM! Even more power! However it was making a slurping sound at idle so I checked the float height and it was at 22mm so I changed it to 24 and now it doesn't slurp snd feels spot on.

Thanks presto I had a suspicion that it might be a symptom of a lean condition and you were right. I'll take it for a burn through the hills this weekend just to make sure.