Hello I seem to have a ever so slight stumble just off idle at very small throttle inputs. My bike is a 2005 B1200S with stock everything and I haven't pulled the plugs off the carbs at least untill either the warranty period is up or my first 1000kms service. I don't have the manual yet
but I know just from the specs that the compression is low enough that I don't need high octane gas. I've been filling up with med grade (89) as a pre-caution untill I get some sort of verification from the manual that regular gas is ok. What I'd like to know is:
1. Could the slight stumble be caused by the octane being higher than a recomended 87? If the gas is slightly less "burnable" very slight throttle inputs would exagerate the problem. Personally, I don't think this is the problem but I like to explore all the angles. Is regular gas ok? I may try a tankfull and see if it helps.
2. Jetting, I understand that these bikes leave the factory slightly lean to try and slip by the facists at the EPA. When the stumble comes on at the specified throttle input, it works fine for about 2 secs then slightly stumbles then works again for another 2 secs. What I'm thinking is that when you first put the throttle so that it will stumble the carbs are already primed and ready to go from normal throttle inputs as you demand slightly more gas at low rpm(<1500rpm) there isn't enough vacuum to draw that teeny tiny little bit of exta gas through the pilots to get you over the hump. It seems that only one cylinder is not getting enough juice to get over this hump so normally you could experiment by backing off 1/8th of a turn on each cylinder to see if it helps once you find which cylinder is slightly lean you just give it that little teeny bit of extra gas it needs and you're good to go. Or if you want to play it safe just turn all the pilots out an 1/8th of a turn and it usually cleans up any carburation issues and may give you better throttle response. But due to the EPA wanting to be our mommies
we can't do this very minor and nessesary adjustment without voiding warranties and such. Once over the "hump"(>1500rpm) vacuum takes over and there is no stumble at all. So I feel this is a very minor problem. It also has been cold and sh!tty so who knows maybe in the summer it's perfect.
3. Carb Sync, this is the easiest explaination. One cylinder is synced slightly less than the other and is not pulling it weight. This slight mal-adjustment would be exaggerated at low rpm and low vacuum. This would be fixed at the 1000km service. When I received my bike is was super crappy outside and the dealer told me that the mechanic took it only for a very short ride so this mal-adjustment might have gone unoticed because unless you were specifically looking for it you would never notice it at all.
As I said it's extremly minor and I only noticed it in the last little while. If you put someone on the bike who's never ridden it before I'd wager he wouldn't even notice it. If it is a jetting issue it's so slight I can wait untill the warranty period is up and by then I'll be probably looking at slip on's and jet kits anyway. Thanks for any input.
