I've had my bike for two years now having driven some 16.000km on it. Since I bought it though it has exhibited some odd behavior when starting which I sort of accepted as "old carbureted bike"-behavior. Now I can only run-start it.

Before she only started on full choke (fine). Mainly I noted that the bike will die out on me if i ride it too quickly after starting i.e. giving it gas/turning handle too "soon". What happens is the starter cranks the engine (it sounds fine), it 'catches' on, starts and goes to 2000 rpm with the choke fully engaged. If going for more than a minute, it'll go to 2800rpm (cause it's warm?).
Usually, this would be an indication to me that it is warm enough to ride but what happens now is; it goes to 2000-2800rpm for 1 minute, not touching the bike, at which point it will slowly decline in RPM and die out cause it's not turning quickly enough. Looking back this was the same behavior it would exhibit if i gave it gas too early. It would run but slowly get 'strangled'.

If it happens I can't start it conventionally for the rest of the day. However, what never fails me is if I run start it (remind you, it's 270kg of bike): 2nd gear. clutch in. run. push starter/clutch release. It always works; once it catches it goes to 2800rpm and I know its good to ride. i can disengage the clutch and let it idle stable at 1100rpm. Once I get her going like this (once warm enough?) she will run for the rest of the day. I can leave her for 6 hours, start her on the choke no problem. If I leave her overnight (she gets cold?) she wont start and I have to run start her.

Any ideas??

I have had these symptoms appear sporadically since I bought it, so 1½ year ago I did the following:

• Cleaned and synched the carburetors.
• Changed the spark plugs
• Changed the battery
• Checked the fuel lines
• Took her to a mechanic who said she started fine.

A guy helping me the other day told me, based on the above behavior, that it could be the coil (Danish; "tændspole").

Any ideas??

 

Well that's one way to get cardio. Sounds like flooding under choke

Does it start if you don't use choke? What about partial choke?

The behavior on starting where the idle races then slows down is normal for mine. I usually feather the choke back to keep it under 2k, and within a minute or so I can turn off choke and ride away. I've noticed that it doesn't really like throttle-under-load until then, but mine will keep running on choke if I let it

I'd start with the easy stuff and look at the air filter, confirm that idle is set correctly, and set idle mixture screws to factory setting (take note of the number of turns for each screw just in case). Also if it's old gas you'll want to drain it and put some fresh gas in it, especially if it contains ethanol

The next step would be to confirm spark. I like using inline spark testers for this job. As you pull each plug, you should check if they are wet and smell like gas. If so, that'll be a confirmation that she's rich or flooded. If she's lost spark then you start to suspect plugs, coils, or other electrical problem upstream

Let us know what you find

 

On every carbureted bike I've ever owned, I start with full choke (when cold) and as soon as it runs, back the choke off to about 2/3, Wait another minute or two, and choke is backed off to about 1/4. A minute or so of that, and choke is then turned off completely (the trials and tribulations of living with carburetors).

Was taught that full choke is for getting the bike started only, and as soon as that is accomplished it needs to be backed off. I'd not leave an engine running on full choke for more than 3~5 seconds.

Not to say that you don't have a problem...your carbs might be in need of a thorough disassembly and cleaning, but I'd modify your starting procedure first.