Forum

[TimG]

OK, I am now formally brassed off with my carb problem which has been ongoing for some weeks and gradually getting worse. Bike is a 2006 Classic 500, with MikCarb fitted with S+B cone filter. Carb has been upjetted (three years ago) to suit sports exhaust and filter, otherwise standard. Bike has been running absolutely perfectly until a few weeks ago. At low revs, coming up to, or idling at, junctions or other stopping points, the bike's idle becomes lumpy and then it spits back and stalls. Violence of spitback varies from slight cough to an explosion which can blow the carb off the bike.

What do I know about the problem? (A) If it's going to happen at all, it always happens after low speed work (e.g. in traffic), coming down to idle, or at idle itself. (B) It never occurs on a positive throttle (i.e. pulling away from idle). (C) It is nearly always preceded by a "lumpy" or uneven idle, almost as if it is starting to eight-stroke. (D) It gets worse as the bike and/or weather gets warmer.

What have I done so far? (A) Given the air filter a thorough clean. (B) Removed the carb and cleaned the pilot, needle and main jets, slide, etc. and reassembled. No difference one way or the other.

What I have NOT done: fiddled about with the mixture. That way madness lies, unless you know exactly what you are doing, and I don't.

The inlet stub is a bit aged and seems not to hold the carb very well, even with the clamps done up as tight as I can do them. I may replace this. I really hope someone can come up with something relatively simple, otherwise I am going to have to start exploring really weird scenarios like sticking valves and bent pushrods...

Cheers

TimG

[Alan R]

Hi Matey--------OK,I'll start this one off then. We had a similar thread on this very subject a few months ago---can't remember just what the outcome was though. Here are a few "foundation" questions for starters }---- mileage ?? How long have you been riding it ?? Has it done this before ?? Has the carb. ever been Ultrasonically cleaned ?? Were ALL THE JETS & other associated items changed to the figures as per our hosts guide ?? An easy way to start off this diagnostic would be to substitute A.N.Other Micarb from a working bike that's set-up to the same spec. Is that a possibility ?? Can you dismantle the carb again and let us know exactly all the jet and slide Nos. that are fitted ?? Points gap / plug type ?? "Ah well" said ZEBEDEE, "time for bed !".........

[m1ks]

I suspect the one we had a while ago was the same one? I may be wrong but i'm sure i've read and possibly commented on a post of Tims before?

I'd agree with Alan, if possible take a good carb and fasten it to yours and try it to see if it still occurs, if so, I'd start looking at a compression check to see you're getting good sealing, tappets, ignition timing and points, (battery condition and quality of spark at low revs?)
I'm assuming from your comments it pulls cleanly and accelerates well in the higher rev range?
Which leads me to think carb needing a good clean in the pilot jet dept, I note you say the joints isn't so good, (undoubtedly in part to previous spittings off but this could have worsened the problem allowing air to leak and leaning off idle further?
When was the head last decoked also? just another random thought of the possibility of spots of carb intermittently stopping the valves fully closing?
Hope some of that helps

Mike

[TimG]

Hi Alan R and Mike...yes, it probably was my post, but at that point I was on probably the wrong track, faffing about with points (after changing which all this started to happen). I have thoroughly cleaned the jets and carb internals. I can't seem to get the bike to idle at a reasonable speed either, the idle seems to slow more and more as I ride. I will be rechecking the points and changing the plug too, as the existing plug has been in for ages and is probably knackered. I am still baffled as to how to set the points gap at the correct point on the cam, but have some ideas. If none of this has any effect, I will try the WD40 test on the manifold to see if we have any leaks. Sadly there are no Enfields within reach to swap carbs...

Cheers
TimG

[Bullet Whisperer]

Hi Tim,
You say in your last post that all this started to happen after you were 'faffing around with the points' - I think there may be an answer in that. Perhaps the ignition timing is a little out and needs correcting. I would certainly be looking at that first, given that info. Paul.

[Phil (PJ) Berks]

Hi Tim, I have had exactly the same problem with my 2003 Sixty5. When you changed the points were they pitted and or burnt, if so this points (pun intended) to a weak capacitor so I would change that as a matter of coarse....If the engine was pulling OK before I would not attempt to alter the ignition timing unless you have a dial gauge and depth pin to put in the plug hole, trying to mark off 0.8mm BTD and adjust the back plate is a pain especially if you’re on your knees..........I had already refurbished the innards’ of the carb with our hosts Jap made kit due to water contamination which had caused corrosion so took hours of cleaning......Also check the rubber manifold connection which is prone to micro cracks.......If the PAV system has been ditched check the blanking on the inlet stub is not leaking – tapped mine M5x0.8 and sealed with an M5 screw and RTV down the hole.........Check the inlet stub gasket to inlet port....Mine was made up of 2 glued together paper gaskets and a metal sandwich heat resistant gasket which was dimpled on both sides which gave a path for air to be drawn in, this I have changed for a single gasket using Blue non setting sealer....I now have it ticking over OK but when I put the Colour Tune on it all the spitting back returned so its new points and capacitor tomorrow.......I had checked the coil and primary and secondary resistances were fine..............Good Luck......

Phil (PJ)

[simon]

Sounds like ignition to me, I'd check that the bob weights arent stuck and the return springs haven't become disconnected. Also check for a white deposit on the points which would suggest a dying condenser. the sudden on set of this issue means that something has suddenly changed which means there should be a simple cause that can be tracked down. If it is carburation it is a sign of leanness so in that case I'd look for an air leak between the carb and the head. Good luck. S:)

[John J]

Hi, There are a couple of things to check, if only to rule them out. First is to ensure that the carb. top O ring is airtight and that the cable entry cover is sound. Second is to check that the enricher slide O ring is sound also the top rubber cover. I use a little gasket sealent to ensure an airtight joint on the carb. top and cold start cover.

[Dennis C]

Hi TimG. ---- Have you checked the timing yet?. Your previous query stated the fault started after replacing points, this has to give a clue to your starting point for this problem!.

[Les H]

Hi Tim, I'm not sure if your engine used to have the emmission control hardware attached? If so, I guess it has been removed? The control system was operated by a small air tube on the inlet manifold. This has to be blocked off when the the piping is ditched, so depending on what method of blocking the valve, ( different methods are used) I was just wondering if the sealing of this small pipe has failed/failing and letting in air. I had this happen to me once and the bike became unrideable untill I spotted the problem and put it right...just a guess, thought I'd mention it.