Virago Techical - Engine stalls using choke
Cold Start - Choke Problems
Whenever I have to cold start the bike, if I try to give it full choke it stalls. This happens from anywhere around 50 degrees all the way down to freezing. The only position that works, and this is regardless of temperature, is about 1/4 to 1/3 open. When it is warming up, I have to let it sit and idle. If I try to give it throttle it stalls, until it has warmed significantly to the touch (usually a few minutes). It also does not race as it warms up like my other bikes have. When its ready, I totally close the choke and ride.
This is the first V-twin that I have owned, and I wasn't sure if this is a peculiarity of this engine style or bike. It does get annoying when everyone else is warmed up or if I'm in a hurry, but it is nothing more than a minor annoyance.
Probable cause and Repair method:
This condition strikes me as being a lean problem. That is to say, the choke isn't delivering enough gas. The choke has a fuel supply circuit and an air supply circuit. If the fuel supply circuit is plugged, or partially plugged, or one carb is plugged, even, then the farther you open the choke, the more air supply you'll let in without the corresponding increase in fuel. Hence the engine will stall for lack of fuel. At half choke the engine appears that is will run, probably mainly on its regular fuel supply from the pilot circuit, but it will take a while to warm up with no choke to help it, because fuel entering a cold engine will tend to bead up (form drops) on the cylinder walls, rather that atomizing properly for full combustion. Once the engine is finely warm, it then runs O.K.
The answer is not new carbs, but most probably cleaning the ones that are on there. I clean 'em by spraying carb cleaner through the circuits and alternatively blowing through with compressed air, until everything is clear. But disassembling, cleaning, and adjusting carbs is something you have to learn. Float levels need to be checked and the carbs have to adjusted and synched once they are back on the bike also. Your guy should find someone competent to do this. Unfortunately, the dealer price for this service maybe fairly high. For strangers, my price is $150 plus parts, taking into account that carbs are a hassle to take off and put on, that problems are not always easy to find, and that I'm struck with the project until the bike runs right.
I have had to pull carbs back off again on a few occasions to find stuff I missed on the first pass, although as I gain experience I know most of the pitfalls by now.
Engine Stalls Using Choke by Mac McCurdy
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Note: This Tech Article was created from the VOC site data.(Virago Owners Club)