Idle problems, help please!

[KevRG]

After I've been riding my bike for a while, and it's totally warmed up, it idles at 2500-3000 RPMs, but if i set the main idle screw (that adjusts the butterfly valves) any lower, it idles so low when it's cold that I can't even get it to start.

Also, sometimes it will take a while to fire, and sometimes lets out a loud back fire when it does. Could this be related to the idle issue? Any ideas?

[jjz28]

You may have an air leak causing the idle high and you need to clean the carbs. The bottom of the bowl has a tunnel that you clean it out, it helps with the cold starting. I had both those problems. Will the idle go down with the adjustment?

[BA80]

Have you cleaned and synced the carbs Kev? If they aren't clean and properly synced they will be hard starting and the Idle will be all over the place.

These carbureted engines are cold blooded. I ride 16 miles to and from work every day and my engine doesn't get completely warmed up and idle right until about 8 miles.

[KevRG]

I cleaned the hell outta them when i rebuilt them over a month ago, and i know i have them close as far as synching. i think i need to take them somewhere and have that done properly. I don't have a vaccuum guage and i tried the whole synching by ear thing, couldn't get it to work. And yes, when i turn the screw out the idle does go down, but that only works when it's hot. Then when it's cold again it wont start so i have to turn it in again.

[motoman]

I cleaned the hell outta them when i rebuilt them over a month ago, and i know i have them close as far as synching. i think i need to take them somewhere and have that done properly. I don't have a vaccuum guage and i tried the whole synching by ear thing, couldn't get it to work. And yes, when i turn the screw out the idle does go down, but that only works when it's hot. Then when it's cold again it wont start so i have to turn it in again.

Use the 2-position enricher(choke) when starting cold........thirty seconds from cold start-up, pop it in one click.........couple more minutes riding, pop it all the way in. The other thing, your not even close on the sync unless U use correctly do it with merc. stixs or vacuum gauge(s).

[BA80]

I don't have a vaccuum guage and i tried the whole synching by ear thing, couldn't get it to work. And yes, when i turn the screw out the idle does go down, but that only works when it's hot.

Are you turning the screws on the top front of the carbs or the screws in between the carbs?

[motoman]

Are you turning the screws on the top front of the carbs or the screws in between the carbs?

Same question-mark I had............wasn't too clear there..........

[KevRG]

used the idle mixture screws, that originally had the caps on them, to sync so to speak. They are turned out between 1 and a quarter turns and 1 and a half, which is what the dealer told me to do in order to get it close. i know they're not synched all perfect or whatever i just wanted to get it running to where it runs enough for me to ride it (which it does) without paying the yamaha dealer 6 million dollars to do it for me. The screw I'm talking about that I use to control the butterfly valves and adjust the idle after the machine is running is the big master screw on the back of the carbs. I'm just trying to work the kinks out of everything.

[BA80]

Kev, these screws IN BETWEEN the carbs are for syncronizing the carbs.




What you have been adjusting are the idle mixture screws. Vacuum guages of some sort are needed to syncronize the carbs. The gauges ar a good part of the idle mixture adjustment too but NECESSARY for the sync.

T99Ford is in Bozeman, he is the closest I can think of that could give you a hand with this. There may be someone closer though.

[jjz28]

Wasnt the newer carbs supposed to be more turns out than the earlier 78-79 carbs? I know mine is start at like 1-1/2 but i thought the newer type was 2 1/2 but i am very new to these bikes, just a thought on that as it looks like your carbs are the newer ones. NEVER MIND, i see you have a 79. I thought those were your carbs in the pic. I would delete this if i could. Sorry.

[BA80]

The carbs in the pic are off of a 79 special.

[KevRG]

Kev, these screws IN BETWEEN the carbs are for syncronizing the carbs.




What you have been adjusting are the idle mixture screws. Vacuum guages of some sort are needed to syncronize the carbs. The gauges ar a good part of the idle mixture adjustment too but NECESSARY for the sync.

T99Ford is in Bozeman, he is the closest I can think of that could give you a hand with this. There may be someone closer though.

Ahhh, thank you man, gonna try an do a little more tweaking. Been away for a week. Just now got back to my computer.

[BA80]

Away for a week! What did you do, go to the grocery store?

Kalispell IS kinda in the Boonies.

[KevRG]

ahaha, nahh, went to helena for apprenticeship classes

[tom clisham]

cable screwing up?

My SG was doing that recently.Stop at a light & it would run 2 grand & couldn't kick it down.
Found out the little tab that locks the cable into the handlebar control ( the one that's part of the cable, not the one held by the screw) had come loose from the cable, & allowed about 3/8 of an inch motion at the control. Had to throw it away. Well, i kept it in case i decide to solder it or something.
Anyway, that cured my runaway idle. Replacing the cable, that is.