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Hi, all.

Name's Bob and I'm an old motorcycle fanatic and former mechanic who, at age 55, has decided what he wants to do again for a short time before he grows up, is do the mobile motorcycle mechanic thing.

I've recently worked on a couple of v-stars and currently and getting ready for my second visit to a 650 I'd recently gotten running, but it was experiencing a problem I have seen very widely reported but have yet to see anything resembling a solution that works for the majority.

The problem being a great idle, but open the throttle very much, and nobody's home.

It's definitely a fuel starvation issue and I've become increasingly convinced that obstruction of the venting for the float bowl is the issue. The effective float-bowl volume on these things is quite small, especially given the engine displacement. If it's not getting refilled very quickly (fuel pump, filter, float needle valve, etc) it could drain it dry, but it'd allow at least very brief large throttle usage before that happens. This one never does.

It's like the main jet is too small or a vent restriction won't let the engine suck up any fuel because the float bowl has less than atmospheric pressure in it. I think a simple test would be very slightly loosening float bowl screws to allow some air leakage into them but not enough to allow fuel leakage (or much of it) out of them.

I was hoping to start a new thread to report on my progress in determining a most likely cause and solution for this seemingly widespread problem.

I should note that when I first met the bike, the carb internals were full of the nasty, sticky crap that results from the fuel evaporating maybe half as much as it will. Pilots were clogged. I only removed the bowls, though, and am not convinced I got the vents adequately cleared. The tank was also full of fuel that was nowhere near combustible.
 

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Nice to have you aboard, Bob. I think that you will get an answer to your problem. I seem to remember the same circumstances from another fórum member. Hang in there, you are going to love your ride when it gets done.
 

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Nice to have you aboard, Bob. I think that you will get an answer to your problem. I seem to remember the same circumstances from another fórum member. Hang in there, you are going to love your ride when it gets done.
Oh, it's not my ride. It's a customer's bike. Probably about the 50th bike I've worked on this year, but the first that I've left not running perfectly. I knew I needed to research and reflect a bit rather than waste billable hours chasing my tail.

My current theory is inadequate venting causing the float bowls to be reluctant to give up their liquid contents to the main jets. I'm going to test this by artificially venting the bowls differently. Won't even need to ride it. If I loosen the float bowl screws just a little and hit the throttle and get ANY improvement, I'll be satisfied venting is the issue and I'll take pictures and really document the cause and solution, since I have yet to see something like that presented anywhere.

I've seen venting presented as one of a number of possible causes. But the symptoms I've seen described are consistent with mine so my guess is that if its ventilation on the one I'm working on, it'll be ventilation with most of them.

My own ride is a CB550, but I won't go off-topic to say much about it here. It'll eventually get a ton of space in my blog, though, as it's easily on my top 10 list of bikes I wished I owned and am glad I do/did.

I've quite enjoyed my short test rides on this particular V-Star, though. It's an 03 650 Classic. Kinda fun to ride, though I'll never get used to forward-mounted foot controls or the disconcerting tendency to resist turning, initially, then to fall rather abruptly into the turn, wanting correction. I'm not accustomed to this much rake, and the way it seems to remove counter-steering as a correct way to do things if the turn is very sharp.

But once rolling (as "rolling" as I could get it seemingly on just the pilot jets), it's very nice and comfy.

Anyway, that's my intro. Love motorcycles at the "sickness" level, and pretty experienced at wrenching on them and hope to make some contributions to the body of knowledge contained here.
 

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Welcome to the forum from Northwest Illinois. Glad you joined us here and look forward to reading your posts and increasing my courage at tackling problems with my own bike. Post often and ride safe.
 

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Welcome to the forum from Northwest Illinois. Glad you joined us here and look forward to reading your posts and increasing my courage at tackling problems with my own bike. Post often and ride safe.
Love your tagline! Similar to my saying "It's never too late to have a happy childhood. "

No stars for me today. Just Finished a mean streak, on my way to a shadow, then end the day with a big dog mastiff. Looking forwarding to riding that one as 2 liters should be kinda fun.
 
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