Hitchcocks Forum

Hi all, first post here but I can see plenty of experienced posts already on here. I bought a 2003 bullet 500 4 speed electric start last year. After having lots of trouble with the original carb, I decided to fit the Amal mk1 30mm carburettor and air filter kit from here,which I love. I think it comes standard as: 3 Cutaway Slide Hard Anodised,200 Main Jet,106 Needle jet,Premier Pilot Jet. Since fitting the bike starts from cold kick start after 5 or 6 kicks. Starts from warm first kick every time. Idles nice, but when I am facing wind or even taking a slight hill in 4th gear 60mph the bike drops speed making me have to drop to 3rd to about 45mph and if I don't ease off the acceleration when in 4thit starts chugging (I guess flooding) and I need to drop to third,low acceleration until it runs smoothly and I can build my speed up to 60mph. I have moved the needle from the middle groove to the top groove, ( thinking it was to rich with full acceleration, this has stopped the chugging in top gear but I still have no power if I have any resistance on the bike. I have noticed that my fuel screw on the carb is only three quarters of a turn out from closed but this is where it runs smooth. Would you recommend changing to a smaller jet size?? My bike also back fires when de accelerating, it has always done this since I got it, I see on another thread here that it might be a bad fitting on the exhaust, so I'll try that tomorrow. Thanks

Hello DrewH, Have you checked your spark plug's colour, that can give you an indication about the carburation. Have a look too at the ignition advance by the same time, it's too a good source of engine's power loss. Hope it will help you.

Thanks Wdco42, I actually haven't changed the spark plug since changing the carb so I will do that tomorrow and check for colour. It has an electronic starter that doesn't have points to adjust as far as I know?

Drew, what WDCO is suggesting is that you use the spark plug as a guide to how the engine is performing. You need to conduct a "plug chop" which is where you ride in top gear until the "chugging" appears, kill the ignition and coast to a stop. Do this in a safe place! Then take out the plug and check the colour. Black and sooty means running too rich, now you can start adjusting the carb to address the problem. The important thing to understand is that the plug is being used to diagnose the problem, (obviously the plug needs to be working properly!) but is not the problem itself. On another track, as you are not the first owner, do you know what has been done to the bike? I'm wondering if the gearbox sprocket has been changed for a larger one to make cruising in top easier? The standard sprocket for your bike is 17T but it should pull an 18 but if the PO has gone larger, say 19T, the motor may be struggling in top gear. We've seen this from posters here before, so worth checking!

REgards, Mark

What was the original carb? and what was wrong with it?

Hi Mark M, ah ok I understand now about the spark plug, I will try this out tonight if I get a chance. Unfortunately I don't know if there was a gear change, if I remove the inner gear box cover would it be marked? I plan on removing this cover to inspect the kick start and regresse. I know when the old carb was running smoothly, I never had any problems in top gear even against really strong head wind there was always more power than I needed,( I stick to 60 mph) the problem has only started since fitting the new carb.

Hi Beezabryan, I am not sure what the model was called. It had the hand adjustable air screw, and the fuel over flow pipe and connected into the original air boxes and filter. I was having problems on almost every trip. It would idle perfect, then after a run to stop at traffic lights it would sometimes just idle so low and cut out or other times it would idle so high you would think the engine would blow. I could never get it running smooth even after cleaning. Sometimes it would kick first go from warm other times it might take me 15 minutes to get it going. Which was a disaster it it happened to stall at lights or a roundabout

Ok Drew, if it pulled ok in top gear before, that helps us to eliminate the gearing as a problem!

REgards, Mark

Hi Drew, has the carb got a choke slide and if so, is it fully raised [open] when you are riding? It should be. Regards, Paul.

Hi all, I put in a new spark plug and went for about a two Mile ride, when it was slugging,I put it in neutral and switched the engine off and pulled in at the hard shoulder. When I removed the spark plug it was a light to medium brown.I put the plug back in and drove it home with more slugging top end. I removed the spark plug again and it's gone a darker brown.
Hi Paul, it has got a choke lever and I have just removed the air filter to check if the slide is the full way open and it it. When I took off the air filter I noticed a light brown petrol liquid collected on the rim of the carb and air filter, would this suggests rich carb? Thanks again everybody

Are you sure the light brown liquid is petrol based.