running on 3

[XS1100_OEM4ME]

Ok, so I got my bike 99% done. Now it runs great, Lotttts of power Starts right up 10 sec on choke then off too the races Twice, when I got stuck at a light for a while, idle droped 100 rpm and acted like it was running on 3 cyls. Sputtered at take off, then smothed right and ran great again Carbs are "VERY" clean, in sync and adjusted, plugs and wire caps are new with the 1/4" trim done, oil & filter are new, tank has been cleaned (no rust ever) two new inline filters at carbs Once I get it going, it runs fine, idles fine, till I get stuck idleing for several min. any thoughts

[SFerinTEXAS]

First thing I'd do is to give the battery a good look. Age, water level,etc. At idle it supplies the needed juice to keep coils and tci running until you increase the rpm,s and the positive charge rate kicks in.

[XS1100_OEM4ME]

Batt

The battery is new, put in in two months ago, it is a wet cell, but I charged it at 3/4 amp till full voltage.

First thing I'd do is to give the battery a good look. Age, water level,etc. At idle it supplies the needed juice to keep coils and tci running until you increase the rpm,s and the positive charge rate kicks in.

[SFerinTEXAS]

The reason the battery comes to mind is I had an Idle stumble, the battery was only 2 months old so I didnt even think of it. Pulled the carbs and to my surprise the pilot jets (1st guess) were spot clean. Pulled the "new battery" out and found the water had dropped below the plates in 2 cells.I try to pull it at least every 2 months to check the water now.

[XS1100_OEM4ME]

Good point

Good point, I havent checked it sence I installed it, I know they sometimes settle and could need toped off. It works strong and cranks like it is fine, but easy check, will do, thanks

The reason the battery comes to mind is I had an Idle stumble, the battery was only 2 months old so I didnt even think of it. Pulled the carbs and to my surprise the pilot jets (1st guess) were spot clean. Pulled the "new battery" out and found the water had dropped below the plates in 2 cells.I try to pull it at least every 2 months to check the water now.

[TopCatGr58]

Hey Oem,

Next time you take it out for a little ride, either take your voltmeter with you, or come back home with it warmed up, let it idle and check the voltage after several minutes of idling, and you may find it dropping below 12 volts. The OEM ALT doesn't generate an effective charging voltage at idle, it's best voltage kicks in at 2500+, it's been known for folks to drain a battery working on it while just idling!

It's enough voltage to keep the TCI working, but drops voltage to the spark plug coils, especially if they are running on the ballast resistor circuit. Folks have found that due to the dual plug configuration for a coil, that it can run low on voltage to the point that it will have enough power to fire the main plug that gets lit when the high voltage first comes from the coil to the first plug, but then there's not enough Kv left to travel thru the engine, and then back up thru the second plug.

Another thing could be IF you have the Octy, that under idle there's not enough vacuum to keep the octy valve fully open, and a loss of fuel flow could occur, the bowl could run low and result in stumble/miss? JAT!

T.C.

[XS1100_OEM4ME]

Tc

Thanks TC, I also install a new headlight bulb, it was rated 60/55 instead of the 55/60w in the manual dont know if it has a higher pull at idle Dont think it is the octy, could be, but it is my undrestanding that intake manafold vacuum is at its higest when at idle, butterflys shut almost closed and pistons sucking in air, seems like it would be at max like on a car when idleing.

Hey Oem,

Next time you take it out for a little ride, either take your voltmeter with you, or come back home with it warmed up, let it idle and check the voltage after several minutes of idling, and you may find it dropping below 12 volts. The OEM ALT doesn't generate an effective charging voltage at idle, it's best voltage kicks in at 2500+, it's been known for folks to drain a battery working on it while just idling!

It's enough voltage to keep the TCI working, but drops voltage to the spark plug coils, especially if they are running on the ballast resistor circuit. Folks have found that due to the dual plug configuration for a coil, that it can run low on voltage to the point that it will have enough power to fire the main plug that gets lit when the high voltage first comes from the coil to the first plug, but then there's not enough Kv left to travel thru the engine, and then back up thru the second plug.

Another thing could be IF you have the Octy, that under idle there's not enough vacuum to keep the octy valve fully open, and a loss of fuel flow could occur, the bowl could run low and result in stumble/miss? JAT!

T.C.

[TopCatGr58]

My understanding is that intake manifold isn't necessarily highest at idle, but it's high when the carb butterfly valves are almost closed. When under strong throttle the butterflies are more open, less vacuum being directed to the vac. adv. port, so less advance of the vacuum advance mechanism which actually retards the advance timing to the more powerful range of 30 or so degrees btdc.

But when running at let's say 5k rpm, but cruising...the butterflies are closer to being closed which directs more vacuum to the advance pot increasing the advance more towards the max of 52 degrees it can reach. But that's because the engine is generating more vacuum running at 5k rpm than at idle. Otherwise at idle, the vacuum advance to pull to full throw and cause the engine to race just from the idle vacuum level...so that's why I don't think it's generating max vacuum at idle, therefore less vacuum pulling on the OCTY to keep it open flowing vs. when running at 4K or such.

T.C.

[XS1100_OEM4ME]

Thanks, Like I said, just trying to figure out what is causing this miss after idle, I am thinking it might be a plug fowling after idleing, I am a little rich on the mix screws (by the book, that is) Going to pull the plugs and look, clean and adj any that look rich, thanks

My understanding is that intake manifold isn't necessarily highest at idle, but it's high when the carb butterfly valves are almost closed. When under strong throttle the butterflies are more open, less vacuum being directed to the vac. adv. port, so less advance of the vacuum advance mechanism which actually retards the advance timing to the more powerful range of 30 or so degrees btdc.

But when running at let's say 5k rpm, but cruising...the butterflies are closer to being closed which directs more vacuum to the advance pot increasing the advance more towards the max of 52 degrees it can reach. But that's because the engine is generating more vacuum running at 5k rpm than at idle. Otherwise at idle, the vacuum advance to pull to full throw and cause the engine to race just from the idle vacuum level...so that's why I don't think it's generating max vacuum at idle, therefore less vacuum pulling on the OCTY to keep it open flowing vs. when running at 4K or such.

T.C.

[bikerphil]

When she starts misfiring, take a wet rag and touch each one of the headers, maybe find out which cylinder is cool. I had a similar problem recently and it turned out to be a bad spark plug. JAT

[XS1100_OEM4ME]

Good thought, that is what i am thinking, one is weak and fowling at idle, and thanks Phill for all your help with sooo many other problems, you have helped keep this old bike one the road Hope you had a great Thanksgiving and wishing you and yours a Merry Christmas God Bless

When she starts misfiring, take a wet rag and touch each one of the headers, maybe find out which cylinder is cool. I had a similar problem recently and it turned out to be a bad spark plug. JAT

[motoman]

All an interesting read but betting the issue is #3 carb...................

[Ken Talbot]

... idle droped 100 rpm and acted like it was running on 3 cyls. Sputtered at take off, then smothed right and ran great again...

Pick-up coil wire(s). Bet it was running on two...

[motoman]

Bet your right Ken..........I'll see that two and raise ya one pick-up wire.

[Barnfresh]

Picked this up at Harbor Freight today... Trying to find a place in the fairing to make a 1.5" hole. I think it would be very useful to keep track of electric system before she starts missing or won't start. Good information for $7.