Sudden loss of power - gas related?!!

yeh - there's an issue!! The red connector is melted, and I have the wires in independently - with some plastic pieces between them - and the red wire also began melting them a bit. That's an interesting connection between the mis-firing and the alt going out! I've cleaned the connections on that piece, but need to check out the wires coming from the R/R. Thanks for the reminder.

It's all in the process of elimination. Check the three yellow wire connection as well while your there. Also have a look at the wires, you said you have rewired and connected them independently, at that time did you make sure that you spliced into clean wire? ( I made that mistake and had to redo mine.) Pack the connections with dielectric grease. Make sure your new connections are clean and tight.
You probably know this already, but hey....
Hope you find the source of your trouble.

OuttaTown said:

Well, well...during my 'break' (I work from home) - went out to just check the bike out. It started well with 'choke' - and after warmed up some, it responded a bit to the throttle, but was doing some serious back-firing. Checked all vacuum connections that I could and they appeared fine.

I had removed the air filter last night as well as its bottom frame so I could see inside - so as it was idling, I thought of holding my hand over the dual hose small 'housing' or cover (for the small foam filter at the front of the filter housing), and RPMs went up slightly. I slowly moved the accelerator and the motor powered up smoothly and without missing - as per a normal running bike!! Interesting!!

I'll put everything back in place this evening and see how it responds. The foam piece there appears very "well used" so will try to find a replacement!

Click to expand...

I think you may have found the problem. If holding your hand over the sub filter housing allows better running, you may have one or more torn diaphragms in the carbs, causing a vacuum loss. A disintegrated sub air filter could cause the damage to the diaphragms. I'll qualify that by saying I've never had need to open my ST's carbs, so I'm just putting forth an idea gleaned from this forum.

OK...there's a new twist on things!! Not a happy thought!!
Will try to do a search on that one!

Thanks for all the advice, guys.
First off - the neutral switch light is back on again - wire connector had fallen off somehow...so all is good there and between the kick stand switch.

BUT - the back-firing continues - tho the throttle cutting out the motor is no longer an issue.
Back-firing seems to come from right hand side, seemingly from #1 cyl, tho when pulling plug wires while idling, #3 doesn't change RPM at all (strange. Tried several different plugs).
It runs great at faster speeds, that is, revs up to 6k no problem and has plenty of pickup and power when throttling on the road.
Back firing occurs a-plenty when cold and just warming up - with minimum 'choke' and picking up RPMs by throttle. Symptoms have not been at all consistent...one time won't pop at all, next a lot. Once, even, the throttle cutting out the motor did happen, but disappeared the next time and hasn't reoccured...and I don't know what I did to make it do it again, or what stopped it!

Here's what I've done so far in addition to the tests and checks from post #18.
-- Read several other posts where similar-to-exact symptoms occured - most were mostly resolved by a series of trial and error w/o any "ah-ha, THAT solved it" answers...and such I'm finding is the case for me. Isn't cut-n-dried by any means.
-- Mentioned earlier - by-passed the fuel shut off (and plugged #3 vacuum line)
-- visually checked and verified all connections at all vacuum hoses and connections that I could see and reach (haven't pulled carbs); sprayed carb cleaner, while idling, on accessible vacuum hose connections w/o any real noticeable change in revs.
-- sealed #1 cyl (front right from riding position) vacuum line - no change (haven't done so to #'s 2 & 4 yet. Guess that would be important in the process of elimination).
-- regarding RPM unchanged when pulling the #3 plug wire : Tried plug/coil wire #3 on #1 plug, and all is fine there - idle pulls way down when #3 wire removed from #1 plug, so it isn't coil or wire.
-- gas cap: blow on vent hose, and it is clear; suck on cap hose nipple and it is clear...yet - when I open the cap, there is pressure in tank. Why might that be? Is it same on yours?

I believe that about covers it. Still sticks in my head as a vacuum related issue...but short of pulling the carbs, I think I've covered most of what has been mentioned. I'll keep chipping away at it as I have time, and if I make a solid "discovery" i'll be sure to post it. And, if anyone else has some experience with this, or more ideas - I'm open!

What a great forum this is - but it's only that way because of the great people who participate and serve each other! Thanks again,
Peace to you this week,
Gord

Pressure in the fuel tank is normal. When it gets to a certain level, like when the engine heats the fuel up causing expansion, you will hear the fumes venting through the cap like farting sounds.

Problem resolved: Carb piston diaphragm had a small tear in it. Put in another used, but good one! Back to purring well...
Bush, in thread #23 hit it on the head in his first comment about the torn diaphragm. Whether or not that's caused by the sub air filter...no way to tell. Thanks, Bush!!
Maybe this can help someone else with an older bike that's having the same issues.
Thanks, all, for your ideas.
Cheers,
Gord

Thanks for the update.

+1 on the followup. Always appreciated.