Hitchcocks Forum

Hi everyone. Thanks again.
So, I'm inspecting this because my 350cc bullet starts without use of the choke when cold and splutters on the road sometimes when you open the throttle quickly.
Normal running, tick over and ridding are really good but when you want to suddenly gun it and open the throttle quickly she splutters and you have to let off a bit, know what I mean? I've experienced in other bikes in my life and imagine it's just a carb set up problem or something else simple?

I've inspected the spark plug looking for a nice dry biscuit colour but I'm not sure. Here are some photos's of the plug ----- http://img.photobucket.com/albums/v292/ ... 270001.jpg ----- http://img.photobucket.com/albums/v292/ ... 270004.jpg ----- The second picture is a bit of a better representation of the real life colour the first one was with a low level flash, so although a sharper image is less "real." What do you think? Any advice on where I should be looking to resolve this unimportant but sometimes frustrating little problem?
Thanks again.

Hi Matt. It's hard to tell from your photographs exactly what the colour of your plug is, but as a guess I'd say it looks a bit on the weak side. HOWEVER we'd need to know what throttle opening was being used at the time. Here are a few tips. The Pilot Jet controls tickover only and has an adjuster on the carb body (sounds as if yours is set ok from your description). The Slide Cutaway controls the smooth transition from tick over to the Needle Jet (in effect throttle openings just off tick over). The Needle Jet takes care of most of 'normal running' up to around 50ish mph. And finally the Main Jet looks after 50ish to whatever you can get out of your bike. In general I'd say that if you're giving your bike some throttle at anything less than 50, and it's hesitating then you may need to alter the needle position within the carb itself. It's an easy enough job and is covered by our host's Technical Notes found on the left of these pages. If need be a bigger jet can be bought if adjustment fails. A bit more info would help though about what speed your bike hesitates. Hope this helps. Tony.

Thanks Riggers. So we think the problem is the mixture is to lean? This would make sense because when I sprayed WD40 on the carb manifold with the engine running I got exhaust smoke a few seconds later so there was an air leak (creating a weak mixture?) To remedy this I replaced the stiff and worn rubber O ring and that improved the throttle hesitation problem quiet a lot but it's not solved it altogether. The problem happens at low speeds in second and third gear (and from tick over.) So do I understand correctly that I need to make the mixture richer by moving the clip to a lower groove one notch at a time until I feel that it runs nicely? I have fitted a smaller silencer than the original giant cannon of an exhaust, the new one is from a 500cc. Would this explain having to make the mixture richer perhaps? Thanks again. As always I am learning so much!

Hi again Matt. Yes you've got the right idea regarding the needle - lift the needle to enrichen the mixture. Also, as you have fitted a freer flowing silencer this will also require a richer mixture. Here's a tip - if you want to check the plug colour after altering the needle position you must cut the engine within the Needle Jet rev range, coast to a stop and then check to plug. Using the jargon this is called a 'plug chop'. You're looking for a nice milky coffee colour to the plug - too white and the mixture is too weak; black or sooty and it's too rich. Move the needle one notch and then road test the bike - it's a pain in the a*@e but the only real way of getting things right. Good luck! Let us know how you get on.

Ah great Riggers. Thanks so much. I look forward to doing this tomorrow. Do I actually have to ride? Can I not just hold the throttle open in neutral for twenty seconds? It is the standard 500 exhaust, it's just smaller so probably only marginally freer flowing. I should get away with a clip needle height adjustment and not neet a new needle. I'm really enjoying this. The mysteries that are engines become clearer with every step. I find it's always something simple. It's not as complicated as I used to and a lot of people imagine. (I hope I'm not speaking to soon! Ha, but I do have faith.) Cheers buddy.

Hey Matt. Ahhh if only it was THAT easy (putting bike on stand I mean)! No mate you can't because the engine will have no work to do and that will muck everything up. Actually factually once you get the knack it's very easy to take the carb off, uncrew the top and take out the slide etc, alter the needle and put it back together again. Once you've done it about 50 times it'll be second nature (only joking)!. Well off to pub now - no more answers tonight mate!

Just one more comment - Enfield Bullets are great bikes for learning the mysteries of the internal combustion engine, especially the classic models (i.e. before they started to 'improve' them). Nearly all 4 stroke engines work the same it's just most have more cylinders, carbs, injectors, pistons etc. Your Bullet has just one of everything - nice and simple to understand! Cheers mate.

Hi MATT------- can I just add my full support to RIGGER's postings ?? To expand on that "Plug Chop" procedure.... The reason for this is to enable you to almost "view" in your mind's eye just what is going on inside the combustion chamber at the very hottest or worst time as far as the components (Exhaust valve) are concerned. This occurs when the engine is at full running temperature, is at max. rpm and on as full a load as is possible....Govmt. BIKE HEALTH WARNING !!!... THIS IS AN EXTREME TEST !!...Approach with a cool and calm frame of mind!! So,try this}---- clean, gap & fit a correct plug, plus another couple for the tool kit.(include the plug spanner and some clean cloth.)....assuming all else is OK with the bike then go on a run for say 5 to 10 miles of open roads (ie NOT crawling around town.) and within which is a good, long uphill stretch...Now, going UPHILL, in 3rd (on a 4-speed box) with your hand hovering on the clutch lever-- keep the engine at FULL throttle AND MAX.RPM--- but only for a count of say 10 seconds. Now, as QUICK as you like---pull the clutch in and HOLD IT IN ----- switch the ignition off (NOT the De-compressor--that allows cool air in and spoils the results)---and coast to a stop...Remove the plug and view it. Using the other plugs repeat this a couple of more times and get an average "reading" from your results. I must add that if you feel the engine start to tighten-up or become sluggish during that 10 second period then immediately abandon this test. Don't worry---just take your time and get the hang of doing it, away from crowds is best. I'm off now to see if I can con RIGGERS into buying me a pint as well-- LoL !!!

Matt,you haven't told us if this is a problem that's only recently come about.No use adjusting needle settings
if it was fine before.
If it's starting ok cold without choke that indicates it's rich (enough) if anything.
Plug gap looks a little small but i couldn't be sure because of the picture angle(couldn't get second pic up).
It's also customary to fit a new plug before making major adjustments.Is points gap .015"?
I only use a projected tip plug,(535)
After all the problem may be just an old duff plug.
Also check the fuel flow and cap to make sure it's venting.
Jack

Hi Jack. Thanks for the input. This is a bike that I just bought for £250. It was sitting for a few months outdoors and was last in service in Spain. I've owned it for a few days and it's had this problem to varying degrees since I first started it. Fuel flow is good. Points are set correctly and the spark is a good blue one. The plug however is the old one. I have two spare new ones so I might just fit one in the morning and see before I do anything drastic. Alan, thanks again for the input mate. I might do that test one of these days but for now I'm happy to guess-temate the set up to a good degree. All the best chaps.