Hitchcocks Forum

Hi everyone,
I took my Classic 500 Bullet (2000) bike for a long spin after it passed the MOT on Saturday morning. After buying it back recently I fitted an Indian made short silencer from H's and it also has an Amal 900 series carb' fitted running through a tea caddy filter. I noted that it pulls a lot more cleanly from the lights and races up to 50 mph. It never did that before. When I owned it a few years ago I had the Mikcarb fitted and the long long silencer.
I am very happy with the performance gain. It is also a bit louder but not offensively so in my opinion. I am not a thrasher but having the extra mid-range zip is a real bonus for me. My only gripe is a little bit of "rough running" when in top gear at just a little past half throttle. The spark plug is a little sooty. Is it worth dropping the needle a notch? The roughness is not bad and not that much of a problem but I'd like to get it running as sweet as possible.
regards,
Alan

Hi rado. Lowering the needle one notch WILLl make a difference with the “lumpy” mid range, however, the sooty plug might be indicating the main jet is too big. You say you don’t often thrash the bike but it would be better to get the main jet right first before changing the needle. Getting the main jet right will give several benefits. Optimum power, lower carbon build up, lower fuel consumption. The other benefit is that it is far easier to change the main change than the needle clip position. Although you loose some petrol when you remove the main jet cover (collect in a cup and re-use) replacing the main jets is very easy, compared to a lot of fiddly work changing the needle clip. When you have that right the current needle position might well be correct. I know it’s a bit of mucking about doing the full bore plug chop but it will pay off in the long run. BTW…make sure the air filter is clean/new before starting on the adjustments. As said in the beginning here, the main jet MIGHT be too big but it might be OK, but it is best to find out. If the flat out run shows a nice brown mixture strength on the plug, then all you need then is to lower the needle, perhaps even 2 notches..

Correction: Hi rado. Lowering the needle one notch WILL make a difference with the “lumpy” mid range; however, the sooty plug might be indicating the main jet is too big. You say you don’t often thrash the bike but it would be better to get the main jet right first before changing the needle. Getting the main jet right will give several benefits. Optimum power, lower carbon build up, lower fuel consumption. The other benefit is that it is far easier to change the main jet than change than the needle clip position.

Hi Les,
Thanks for the message. At the moment the main jet is a 180. It did have a 200 fitted. Air filter is brand new so no worries there. I'll give it a blast this afternoon and let you know.
Thanks

I've got a similar problem, I've dropped the needle one notch; the plug is still sooty though with an encouraging bit of chocolate brown around the tip. Am I right in thinking you can get the main jet out through the bottom of the float bowl on a Mk1 Concentric?
Also, it's idling so well I am loath to interfere, but is good idling a sure sign of a correct idling mixture?

Hello Les and John R,
I just took it out for a 70mph run for a mile. The plug is still a little sooty but like John R's the electrode and tip are showing signs of that bicuit/chocolate brown colour. I am tempted to leave it as it is! However I need to work out MPG as I am a tight soul.
I think you can remove the jet from below but I prefer to whip the whole carb' off.
regards,
Alan

Just a couple of friendly words – the main jet has no noticeable function until the throttle needle is lifted clear of the needle jet, around ¾ throttle. It’s also worth mentioning that with ethanol (and other additives) it’s no longer possible to ‘read’ plug colours as we used to. This also applies to iridium plugs. It is possibly a better approach to adjust settings by the way the engine performs in use. Cheers!

Yes, I did wonder about the main jet. But soot is soot; I want to try to lean it up, and I was wondering about a smaller needle jet. On the other hand, It's running really well at the moment.

Hi guys----and RICHARD R }--- Yes, I totally concur with you. Adjusting settings base on how the engine is actually performing on the road has to be the ultimate test-bed. It's no good being Technically Perfect if the "patient" dies --(ie, seizes, goes BANG ! etc.)---is it ??.... As mentioned in another thread, riding technique also comes into play as well. At the end of the day ours is a real "Hands-On" situation.

Good on yer, RICHARDR - good to hear a voice of common sense out there...........