OK, so what causes this behavior?

[robertbarr]

I see this all the time -- situations where an otherwise good running engine will fall on its face when the throttle is opened. On any carbureted car engine I ever worked on, this would be a problem with the accelerator pump. On CV's, though, I'm just not sure. There's no obvious equivalent to dealing with a drop in vacuum.

I sold a set of O-rings to this guy, and here's the email I got:

I received the o-rings yesterday, ( Thank You ) I replaced all o-rings, put carbs back together, put on bike, i don't have a gas leak any more, ( Thank You !! ). The leak was coming from the gas tube that has 4 o-rings on it between number one and two carb. But I still have a problem i can't find. The bike starts great, Idles great, very smooth. I give it a little gas and it runs great, a little more gas , runs great, a little more, runs great, then just a little more gas and it flutters to a stop unless i throttle all the way back down to an idle. I've check everything i know to check, just can't seem to find what might be wrong. Anyway enough of my problems. Just wanted to thank you for the o-rings at a great price. Have a great weekend, i hope your riding, because I'm not :-( . Thanks again, Don Hall

Has anyone solved this particular problem?

RB

[SqDancerLynn1]

One problem I have seen over & over Is they expect it to be like a car and run without the air filter/airbox while they are working on their bike. Which as you know doesn't work

[rustybronco]

If the air box is on, its sounds like a fuel delivery problem, rust, crap in tank, water. ect.
need a little history, send them over here.

[duaneage]

Maybe a problem with the slides, he might not have assembled them properly. Float level could be all wrong too and when the main picks up it leans out. Fuel delivery is a prime candidate, petcock vacuum switch could be leaking and when he opens the throttle the weak diaphram closes and no longer lets gas in.

have him run it on prime and see if this fixes it. A petcock can easily be tested this way, I don't know why more people don't do this test before buying coils, gas treatment, iginition modules, batteries, spark plugs, etc.

My guess is petcock or a clogged screen in the petcock. Definately not a O-ring at fault.

Bob, you need to get a GS, enough Honda 650's, get a 650G!

[denydog]

Has anyone solved this particular problem?

Do we know if this is happening at rest in neutral, or while riding in gear? When you said "will fall on its face when the throttle is opened", it made me think of my test ride after my first attempt at cleaning my carbs. It idled smoothly, and revved in neutral mostly ok, but when I accelerated in gear, it would pull to about 2000 - 2500 rpm then bog to the point were it seemed like it was barely running. I could let up on the throttle (to below 2500 rpm) and it smoothed right out.

Turned out the main jets were still 50% plugged up, so I think when it tried to transition to the main jets, there wasn't much there. Just thinking.