Hi All,
I have a 2004 Heritage with carby.
When i start the bike it runs fine and i let it warm up for about 2 minutes before riding. Once i take off the bike starts to surge and backfire repeatedly for about the first 1 to 2 kilometers but only under load. If i stop it seems to idle fine. After that it just comes good and stays good for the rest of the night. If i stop for a couple of hours and start the bike it is all fine.

It only seems to do it after the bike is started from cold. Oddly enough if i only let the bike warm up for 30 seconds or so then it rides ok at first and then the surging starts after about a minute of riding. I have also noticed that even when it is running ok it still does not have quite as much power as usual.

There are 2 relevant events around the time it started doing this.
Firstly, the bike was serviced about 200 kilometers prior to this starting during which the Vacuum hoses were replaced, otherwise a normal service.

Secondly, it started happening shortly after filling up with petrol.

My immediate thought was water in the petrol and i tried adding Methylated spirit to the petrol over 3 tanks and seemed to get an improvement but the issue was not totally gone. I also tried leaving the bike for a week and disconnecting the petrol hose and pumping out about a liter of petrol while set to reserve. This made no difference.

I have been riding it like this now for a couple of thousand kilometers and still have the same problem. Unfortunately i can't afford to get it looked at for the moment and although i have tools i'm not overly mechanical.

Can anyone help with some simple suggestions i can try that might assist.

Thanks in advance
Simon.

 

Check the vacuum hoses that were replaced. One of them might have come off or a couple of them were swapped around.

 

Thanks Thundermug i'll have a look, any other ideas?....anyone????

 

There is an important vacuum line at the top of the carb for the V.O.E.S. If my brain meds are working right, check that. I would treat your fuel with Seafoam to scrub out your fuel system but I think your living across the pond judging from your use of the word "petrol" so you will not find any sea foam. you will have diesel fuel injector cleaner however & you can use that at around 3 ounces per gallon or 1 ounce per liter with good results.
Give your bike a lil choke if it runs rough & tell us if it runs better or worse when you try this!
Hatch.

 

My carb'd Dyna used to do that when it had the CV carb on it. The only way to reduce it slightly that I could find was to not fully close off the choke until about 5 miles had been covered - just left it open a tiny bit.

 

might check intake for leaks

 

That's how I am first thing in the morning!!!!
My Sporty needs lots of warm up, then its ok.

 

My carbed 2002 Lowrider does the same until warm - 2-3 miles. I rarely operate cold with less than full choke.

 

Your bike is running too lean. Check for vacuum leaks by spraying some wd-40 or carb cleaner around carb and base of carb while it's idling. If you hit a leak with the carb cleaner, the rpm's will change. Trash in the carb will also cause this. In colder weather, the bike will require a richer fuel mixture. Maybe your bike just needs to be re-jetted.

 

Have you changed the style of air-filter from the original ?