Hello. I'm pretty new to working on bikes. I've only built little 1 cylinder scooter engine before. I'm probably in over my head on this one, but that's how we get better, right?
Here's my 1973 CB500 idling and me revving it. If you listen closely after a few revs, I'll really punch it, and the bike stalls. It will stall completely if I punch it hard enough. I wanted some of you more seasoned people to tell me: Is this pilot error? (Ie: Don't pull the throttle back that fast, dummy!) Or is this a real problem, like I think it is?
http://www.youtube.com/watch?v=_ECfgiOP4JY
(it won't let me post a youtube link, but just amend the youtube URL with the above)
A little history: I bought it last year, ran fine for a couple weeks, until one day on the freeway I lost more and more power, as if I was running out of gas or something. It seems to definitely be a fuel problem, and I'm guessing the jets in the carbs are clogged, because tank is pretty rusty. There are inline fuel filters on the bike, which is probably the only reason why the bike runs at all with such a rusty tank.
So I wanted to ask you guys: where should I start? What are the simple little things I can do before taking the carbs off and completely dismantling them?
When was the last routine 3000 mile check list performed?
Do that first before complaining about any sort of performance issue.
Look at the spark plug tips. They tell you what sort of combustion conditions are happening inside.
Check the air screw adjustment position. Report.
State what condition the air filter/induction status is. Are there crappy pods on the bike?
Lesson on these carbs:
They are mechanical slide carbs. Meaning they are directly coupled to the throttle grip.
At idle, vacuum is what is pulling fuel through the jets. When the slides are suddenly opened, the vacuum is suddenly lost and the jets stop flowing fuel in any volume, which take the mixture outside of combustion range. (There are no accelerator pumps, fuel injection, or computer mixture control on this bike. And nothing to prevent someone doing a dumb thing to the throttle.)
These carbs are set to runs rich at idle so the throttle opening results in some acceleration.
Normally, with a stock bike in stock configuration, you can whack the throttle to one half of total throttle travel (mark your throttle grip) and get smooth acceleration in any gear under load conditions. Twist it more than that the the engine will stumble as physics demands.
Assumptions:
Air screws set correctly.
Tune up check list completed.
Carbs operating correctly.
All head pipes equally warm.
Stock air filter arrangement.
