I have always wondered, but forget to ask. It happened again yesterday. It was pretty cold. I tried to crank the engine, but it wont turn over. Then suddenly a big bang :2guns:. And nothing. Tried to again start, but wont. The battery was weak, and dying, I told my friend to push start. Again, when I cranked the engine as he was pushing me, big bang... then the bike starts. Keep of getting these bangs once or twice a month, usually when its cold.
What causes these bangs? Is it mis-adjusted valves? Did valve adjustment today, one of the exhaust was little tight (I could still rotate the bucket, so have just dropped in a lower one).
If it helps, one of the sprak plug was quite white. The other was normal black.
when you turn the engine over fuel/air mix is drawn into the engine and normally the spark plugs ignite it and the engine starts. but if you have a weak battery it might have enough juice to turn the engine over (and ingest fuel and air) but not enough power to ignite it. so all that unburnt fuel is put in the exhaust untill you get one spark, then BAM! back fire. also when its cold the chances for lean misfire increase which also puts un burnt gasses in the exhaust.
Yea pretty much collection of gas and air in the exhaust and then a little sparkie ...
You dont want lean misfire ... cos its just 1 step away from detonation which really at speed in 1 cyl you will hardly hear it before it eats a piston. I saw a guy who in the 18 months since I told him to fix his jetting in his honda CM400 managed to blow it and rebuild it and is very smartly still running the same damn jetting.
OK that was the short version, the long and freaking hilarious version is this.
18 months ago I was broke and unemployed. So I Craigslisted a "will work on your bike for food" ad.
This Genius showed up with a CM400 honda with 1700 miles on it and a cored exhaust and the thing was popping at idle and he wanted to change a tar. I said OK I'll pull it and get it swapped and you owe me 25 for remove and refit, and 25 for the shop guy to do it ... we're cool, we do it, he pays me and I mention to him that his carbs need cleaning, rejetting or something to make it run right.
The dude took offence, said this perfect looking (and it did look nearly so) bike and you say its got crappy carbs. You must be a scam artist. I say OK bye bye. Oh yea, I love it when Peckerheads pay $1500 for a 82 bike and think they got a steal and complain when you want $200 to do carbs, vlave adjustment etc. Its like standing in the starbucks line to get your 12 oz cappuccino for $5 and complain gas has hit 4 a gal. Perspective dude ... perspective. Old crap needs to be checked before you can turn it loose on the road.
Then last week he calls me. He blew up the thing on a ride to wilmington. Then he rebuilt it. He rebuilt the carbs like I had said ... I said WTF, I never asked you to rebuild nothing. I said clean and rejet. He says ... no no no, I sent it to this guy in SC and he rebuilt it to new specs. I said, yea it was set up sheitety when new. That's why it blew.
I told him to come by ... yea its still popping, and well, I suggested he take a ride back towards wilmington exactly like he did before and see if it blows up at that same location as before ...
Anyway he said he'd bring it to have me fix it ... I say, sorry I dont work on other people's bikes any more ... he says why ? I said, too many idiots think I am scamming them. :mad:
Cool.
Buddha.
so improper valve adjustment has nothing to do with it?
OK a bad valve will first want to stall right after a cold start.
If you continue to ignore it well past that, it will act up and misfire.
So yes I would look at all causes of leanness, cos a tight valve causes loss of mix which = lean.
Cool.
Buddha.