Hitchcocks Forum

Good Afternoon (timezone depending),

My 2001 Bullet 500cc has recently been in the garage, during this time spent in Enfield A&E, I got the guys to replace the standard filter with a pancake performance filter, and also some jets to suit this. I have an aftermarket exhaust fitted by the previous owner, so went with the following jets: **MAIN JET, 117.5 ** **PILOT JET, 27.5** **NEEDLE JET, P0 (RICHER 500cc)**. The bike starts and ticks over beautifully, however when driving away from the garage, I noticed some stuttering in second gear. Upon going into third, the engine refuses to pull and loses lots of revs. From previous experience, I'd say this could be a jets problem with the new filter, but they match as close as can be to those recommended in any guides I read. Any advice? Many thanks.

Try running it without the filter. Not all filters actually flow more air than the standard set up and it's possible that the engine is being choked by not being able to draw enough air. This supposes that all the jets and other fixings on the carb are properly installed and not loose or blocked, of course! REgards, Mark

Has the tappet/valve clearances and a compression check been done on this bike?

Will do both of these this evening! Will report tomorrow, thanks!

Hi BOLOGNE --------------Those jet sizes are only a RECOMMENDED starting point... Here is the current set-up on my 2005 Classic 500 ]----Carb Type = Mikcarb VM28, Float Height = 24mm, MAIN JET = 120, NEEDLE JET = P2, PILOT = 30, SLIDE = No3, NEEDLE CLIP POSITION = No3, AIR FILTER = Tea Caddy, PLUG = Irridium, GEARBOX SPROCKET = 19t, EXHAUST = modified standard to free flow.....Also }--- Standard 4-speed gearbox and final drive sprocket....It has an alloy barrel and our hosts 8.5 : 1 piston... I use alternate premium and super grades of fuel.. it's tractable around town but will ACCELERATE in 4th gear. !!............... Note the size of the MAIN JET... I still think it could be a tad larger !! You need to re-jet a bit more, especially for mid and top range....What carb. is fitted and what slide is in use ?? PS, New Year's Day ride over the Peak District---some mud-plugging plus a spirited run to home on my local dual carriageway (indicated 65mph cruising)..

Hi Bologne, I have the same jet sizes as you, however i'm still running the standard air filter with straight through exhaust and i find it will still stutter on occasion when opening the throttle wider in say second gear from a junction.

I have the clip in the lowest groove on the needle, so you could perhaps try this first and see if there's any improvment, but i think you could well end up with 125/130 main jet as minimum, P2 needle jet, maybe 30 pilot jet and 2.5 slide.

Replace the main jet first and carry out plug chops to check results.

One thing at a time and not to radical, easy to get confused and start chasing your tail if you try to change too many things and not check progress. cheers gwilly.

----------- just a useful tip here}-the slide No's change by removing a 1/16" off the bottom of the slide, thus reducing the cut-away and increasing the vac. at initial lift ( remembering to shim under the needle clip by 1/16" to restore original setting in relation to the slide itself ). If you have a few spare VM28 slides kicking around it's cheaper than spending some £15 each time.

I'd say if you've replaced the jets that this is the most likely cause of the problem. My suggestion would be check the colour of the plug. If it is black then try dropping the needle if not the reverse. This will hopefully tell you if you need to down size your jets or not. Air filters really shouldn't have that dramatic an effect as if it is are then it is far too restrictive and should be discarded or replaced.

Update so far:

Pushrod adjustments made, and the engine sounds healthier.

Tried without filter, and it changed the symptoms but didn't solve them. This leads me to believe that it's just a misconfiguration of the jets, as some of you stated. It's back down the garage right now. Thanks all! Will keep you posted.

I ordered a larger main jet this morning for my 30mm Mark 1 concentric - 225 - and a stainless bellmouth with gauze cover. The main jet should help fuelling at the top end and the bellmouth might remove any breathing restrictions caused by the conical air filter (the carb was making the occasional gasping noise) on opening throttle at lower speeds. I am not worried about dust - our climate is hardly dry.