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Backfire problem

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Backfire problem
Started at 11:38am on the 10th May, 2018 by Geraintosaurus
Geraintosaurus Subject: Backfire problem
Hi all, I've had a backfire problem with my 2000 Bullet 500 for a while that I'm getting increasingly anxious about. It only happens in the low revs range, mostly as/just after I downshift. In addition, recently I noticed the bike feeling like it's about to stall when going up a gentle incline at low revs. I also think I can hear a sort of light clanking sound coming from the engine - possibly the piston is hitting the cylinder head due to poor ignition timing? - but I haven't had the bike long enough to know if it's normal. It's not too loud, but audible over the engine noise. I've changed the spark plug but I haven't adjusted the gap as it's the resistor version and my manual only has gap recommendations for the non-resistor version. I don't think it's a spark plug problem though, but what do I know? Anyone know a way of diagnosing this? Assuming it's timing, any idea which way I need to rotate the timing plate (or whatever it's called), or how I might find out? Or might I need to fiddle with the carb? I have a mikcarb - will I need to get new jets and if so how do I know which ones? Thanks in advance - it's hard to enjoy the ride when I'm thinking about the damage to my precious exhaust or any damage it's doing to the cylinder! Geraint
Posted: 11:38am 10th May, 2018
Geraintosaurus Subject: Backfire problem
Oh - one other thing - I've been trying to understand setting ignition timing and have read about setting it in the 'fully advanced' position, and apparently this is where the bike 'spends most of its time'. It seems like to access this setting I have to take off the timing plate thing using a special tool on the cam? Basically I have no idea what this means, can anyone help or direct me to a good video/manual?
Posted: 11:57am 10th May, 2018
Geraintosaurus Subject: Backfire problem
Oh and I have a conical air filter which might affect carb tuning. But the bike came with this and didn't have issues then so I don't think it's the direct cause.
Posted: 11:59am 10th May, 2018
Geraintosaurus Subject: Backfire problem
Final PS: I'm not sure if backfiring is the right word - sputtering maybe? Don't know if those two things are the same, but it's usually not too loud and sounds more...well more sputtery. And I have a sports exhaust, so I'm told, just not sure which...
Posted: 12:10pm 10th May, 2018
papasmurf Subject: Backfire problem
A bit of popping and crackling in the exhaust is par for the course on big singles of British, (Indian) Origin. But "pinking" in the combustion chamber when under load is serious in the long term:-
Also called spark knock, preignition or detonation. If left uncorrected it can ruin the motor. Caused by either a lean fuel condition, carbon deposits in the combustion chamber, over advanced ignition timing, wrong spark plugs, or overheating.
Posted: 12:26pm 10th May, 2018
Adrian Subject: Backfire problem
Question re the backfiring? Is that popping and banging in the exhaust, or is it actually spitting back through the carburettor?

A "light clanking sound" suggests mechanical rather than pre-ignition, it could be a slack primary chain, these make a bit of racket as the chain adjuster clatters against the alloy chaincase. If it's constant you could have a big end failing, though a loose alternator rotor can make some expensive sounding noises.

As long as it stays in one piece the piston will not hit the head, however badly your ignition timing is out, once it reaches the top of its stroke it goes back down again. Running with the ignition too far out will damage the piston, though.

Your incline problem might be caused by "lugging" the engine at low revs in too high a gear, use the gearbox and appropriate revs. The big single engine might have plenty of torque but don't abuse it in this way any more than you would by over-revving it.

I get the impression that your Bullet has come as something of a culture shock. You might want to gen up a bit by reading some classic literature on the subject of old motorcycles from the practical point of view. May I suggest a copy of the 1950's classic "Motorcycles and How to Manage Them"? As your Bullet is essentially a 1950's motorcycle it might be very helpful. There are several copies on ebay at the moment. If you haven't already got them, an owner's manual and a workshop manual would be a good idea too.

A.
Posted: 12:39pm 10th May, 2018
Geraintosaurus Subject: Backfire problem
Thanks papasmurf - looking at my manual, it says too far advanced ignition timing may also cause kick back when starting. I get this occasionally - should I be getting it at all? And it kicks back quietly, as in it doesn't sound like it's 'ignited' per se but maybe I wouldn't hear it anyway?
Posted: 12:41pm 10th May, 2018
Geraintosaurus Subject: Backfire problem
Hi Adrian - this book sounds like a brilliant idea - thanks!

I had a feeling it might be a rider problem with the engine lugging - I guess it just sounds 'healthier' to me in the low revs so I try to keep it there but that's probably a mistake.

I think the sound is coming from the cylinder, but I will just go turn it on to make sure.
Posted: 12:44pm 10th May, 2018
Geraintosaurus Subject: Backfire problem
I've read Zen and the Art of Motorcycle Maintenance but that turned out to be more zen than motorcycle maintenance...
Posted: 12:47pm 10th May, 2018
Geraintosaurus Subject: Backfire problem
Oh, sorry, I missed your question about the backfiring. I only get smoke through the carburettor when trying to kickstart, occasionally. Otherwise it's a sort of low rumble from the exhaust.

Having just put my head next to the cylinder, the noise is coming from there I think but now I'm wondering if perhaps it's just the ignition itself... hard to say but it sounds vaguely more like a pop now than a metallic clang. I just noticed it suddenly one day and so assumed it was a problem but I might be over-reacting.
Posted: 01:05pm 10th May, 2018
Geraintosaurus Subject: Backfire problem
Oh, sorry, I missed your question about the backfiring. I only get smoke through the carburettor when trying to kickstart, occasionally. Otherwise it's a sort of low rumble from the exhaust.

Having just put my head next to the cylinder, the noise is coming from there I think but now I'm wondering if perhaps it's just the ignition itself... hard to say but it sounds vaguely more like a pop now than a metallic clang. I just noticed it suddenly one day and so assumed it was a problem but I might be over-reacting.
Posted: 01:05pm 10th May, 2018
Adrian Subject: Backfire problem
No, not really applicable. This is more in the line of Whitworth spanners, Brylcreemâ„¢ and black and white public information films (come on Alan R, you know you want to!).

As you seem to have been struggling with this quite a bit, is there a friendly vintage or classic club that meets anywhere near you, local branches of the Royal Enfield Owners' Club included? I think you will find most are helpful and will realise that not all of us started mucking about with old bikes in our teens over 40 years ago.

A.
Posted: 01:20pm 10th May, 2018
Adrian Subject: Backfire problem
Our replies crossed.

The odd backfire through the carb when starting isn't unknown, if it has developed in the exhaust on over-run it's most likely an air leak, you can remove the silencer and exhaust pipe, clean all the carbon off the exhaust port in the cylinder head and on the pipe/silencer inlet, and carefully reassemble the lot with a good smear of nothing more special than ordinary bathroom silicone RTV paste. Wipe off the excess, leave it to set and that should hold it.

It sounds like your Bullet could actually use a proper service if you have someone nearby who is competent with old bikes.

A.
Posted: 01:40pm 10th May, 2018
Lord-Toady Subject: Backfire problem
I need to check the timing, the tappets and clean the carb on mine, mine is a bu**er for spitting back through the carb when trying to start it. I found it started better if I gave it a bit of gas while kick starting but I found it would spit back through the carb and the kickstart would vibrate violently with the kickback. I have now started trying to kick it over and give it a tiny bit of gas just after I have finished the kick while the flywheel still have a bit of momentum left in it and then it normally starts but if I give it gas while kicking it spits and kicks back. :)
Posted: 03:02pm 10th May, 2018
Leon Novello Subject: Backfire problem
Fix the kick-back problem first; too many kick-backs will strip the teeth in the oil pump spindle, thereby wrecking the engine.
Posted: 12:42am 11th May, 2018
p Subject: Backfire problem
Two things come to mind; one: check for air leak between carb and cylinder head - easily done with can of aerosol.... look through forum to find out about it. Two: engine runs, so timing somewhere near right - remove points cover and mark backplate to rim of casing with a thin pencil line or scratch, (now you know you can always go back to that), now slacken the two "long nuts" slightly and experiment moving backplate a tiny bit either way by trial and error to try and eradicate problem (you can leave the cover off for now and go and play on a nice quiet bit of road until you have found a position where all runs smoothly - a tiny clockwise movement may retard ignition enough to solve your problem.
Posted: 08:55am 11th May, 2018
Mark B Subject: Backfire problem
I found Pete Snidal's Bullet manual to be a very useful book, explaining things in a simple way, giving practical advice even on the basics such as how to ride a bike, and talking about maintenance, repairs and upgrades in language that lay people like me can understand.
Posted: 12:46pm 11th May, 2018
Geraintosaurus Subject: Backfire problem
Thanks guys, this advice is great! About to try all this out. One more question: if my timing backplate won't move any further clockwise, is there something I can do about that?
Posted: 05:04pm 11th May, 2018
Geraintosaurus Subject: Backfire problem
I've bought some silicone sealant and as I understand it I need to seal the part indicated in the picture below:

IMG_20180511_171443_Copy

I sprayed WD40 onto the bit between the carb and the cylinder and the revs did increase, so clearly I need to reseal something there - I just replaced the rubber bit so I don't think it's that. So question is can I use the silicone sealant to seal the manifold to the cylinder (see picture below)?

IMG_20180511_181701_Copy
Posted: 06:30pm 11th May, 2018
Adrian Subject: Backfire problem
Yes regarding the silicone RTV and the exhaust port, you will also need some around the other end of the exhaust pipe where it fits into the silencer. If the exhaust pipe is a very loose fit in the head a strip of alloy cut from a beer can and wrapped around the end of the pipe will take up much of the slack, but it will still need the RTV.

On the inlet side you have now successfully identified a leaking inlet gasket which needs replacing. The answer here is to remove the carb and unbolt the alloy stub, carefully clean off any remains of the old gasket or sealant from the joint face on the cylinder head inlet port and on the alloy stub so that they are both spotless, and check the stub's joint face with a straight edge to make sure it isn't distorted. You will then need a new gasket from out hosts:

http://accessories.hitchcocksmotorcycles.com/2368?qty=1&continue_url=http%3A%2F%2Fwww.hitchcocksmotorcycles.com%2Fpartsbooks%2Fpages%2F1868

Rather than RTV I would use a dedicated automotive gasket jointing compound on this such as Wellseal, not loads but a good thin even film all round.

A.
Posted: 10:22pm 11th May, 2018

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