Fouling plugs because of warming up without choke?

[t3rmin]

So I've been trying to set a new record and ride the bike to work every day this week but this morning the bike wouldn't cooperate.

Don't ask me why, but instead of letting it warm up with the choke on as usual, I turned the choke off and turned the idle screw in until it was "idling" at 2k rpms. I went inside for a few minutes and came back out and adjusted it back down to 2k when it had gotten a bit warmer and walked up to 3k. Then I went back inside but a few minutes later noticed I couldn't hear the bike any more.

It had died and pretty much refused to get and stay running again. When I did manage to coax it to life it was running really rough (not on all cyls) and wouldn't idle. My impression is that plugs are fouled, although I had to get to work so I haven't had a chance to examine them.

The plugs are new as of yesterday evening and have less than 10 miles on them. Could idling the bike without choke while cold cause the mixture to be off enough to foul plugs or am I barking up the wrong tree?

[DimitriT]

Don't ask me why, but instead of letting it warm up with the choke on as usual, I turned the choke off and turned the idle screw in until it was "idling" at 2k rpms.

So why not take the plugs out and check them. I bet you are running lean rather than rich and plugs are clean. It sounds like you leaned out the bike and it won't run now when it's cold.

I would just start over with the mixture screws. Get the bike warmed up. Turn them all the way in (gently). Back them out 1.5 turns. Then while you are idling the bike adjust the screws till you find that spot where the RPMs drop when you move from that spot. You will need a "IV bottle" fuel tank or some way to supply fuel while you do this. Once you get them there, don't mess with them.

Use the choke when starting and warming up the bike.

[t3rmin]

Well I will pull the plugs when I get home but I was impatient for some answers! ;-)

I adjusted the mixture screws just yesterday using the highest-idle method when the bike was nice and hot and am fairly confident they're set pretty much right-on. I've also vacuum-synced the carbs just this weekend. Regardless of this morning's apparrent "insta-foul" I have been fouling a lot of plugs overall, so I'm wondering if maybe my float levels are too high?

[louisciccoli]

It doesn't make any sense to me why it would foul the plugs by just idling it at a higher RPM. Is it more likely that you backed the idle screw back out too far to the point of it not being open enough to get the engine to start? Just my thoughts.

[t3rmin]

Nope. It died on its own when the idle screw was tight enough to give 2k rpms and wouldn't start again whilst on the same setting. Besides, I tried twisting the throttle a bit while starting.

[t3rmin]

Well although I can't account for why the bike died by itself while set to "idle" at 2k, it started right up when I tried it after work. Must have been pretty badly flooded after cranking it so much in the morning. I haven't even changed the plugs and it's been running great ever since. Must have been a fluke.

[KEITH KRAUSE]

In the future, I suggest letting the choke do its job warming up the bike. Just learn how much choke is needed for outside conditions. Don't adjust the idle adjuster. Your idle adjuster should be set at 1,000/1,100 rpm's when fully warmed up.
Also, don't open the throttle at all (if you are) while on choke as this just by-passes the choke circuit.
If the bike is in otherwise decent tune, it will warm up as it should following the above.

[t3rmin]

Yeah, those are basically the conclusions I'd come to. ;-)

Is it normal for it to pop/miss a bit while on choke? Runs great when warmed up so I assume that's ok.

[KEITH KRAUSE]

If the bike's in good tune it shouldn't pop or miss. A little pop here and there isn't a big deal. I mean, the bike is 25 years old.
If it pops only when warming up and the choke on the correct amount, it may mean you're a bit rich on one or more cylinders. If your plug(s) are on the dark side to begin with and you add choke, that's hinders good spark. If it goes away as soon as you release the choke, that suggest a rich condition.
But it can also be a weak spark. Did you ever take some plug reads? Don't read them right after warming up/choking. Ride the bike so it's completely warmed up/hot and then take reads on all of the plugs.

[t3rmin]

Well I'm in the midst of adjusting the valves for the first time and then I'll do another vacuum sync so that may shore things up. Other than that the only variables will really be the float levels and the mixture screws since the carbs are clean as a whistle, I have a brand new Dyna S ignition, new plug boots, 12+v to the coils and good primary and secondary coil resistance. The floats are within factory specs but we'll see if they need to be tweaked...

[Road_Clam]

So I've been trying to set a new record and ride the bike to work every day this week but this morning the bike wouldn't cooperate.

Don't ask me why, but instead of letting it warm up with the choke on as usual, I turned the choke off and turned the idle screw in until it was "idling" at 2k rpms. I went inside for a few minutes and came back out and adjusted it back down to 2k when it had gotten a bit warmer and walked up to 3k. Then I went back inside but a few minutes later noticed I couldn't hear the bike any more.

It had died and pretty much refused to get and stay running again. When I did manage to coax it to life it was running really rough (not on all cyls) and wouldn't idle. My impression is that plugs are fouled, although I had to get to work so I haven't had a chance to examine them.

The plugs are new as of yesterday evening and have less than 10 miles on them. Could idling the bike without choke while cold cause the mixture to be off enough to foul plugs or am I barking up the wrong tree?

I am going to ask the same question I ask the other 345,678 riders who's bike wont idle, and coughs. Did you have your carbs DIPPED in professional carb solvent? Sounds like you have the always popular "plugged pilot jet(s)"

[t3rmin]

Yup. Carbs have been completely disassembled, dipped in carb cleaner bucket, reamed out with matchstick-wire "tool", sprayed in every orifice with carb cleaner, blown out thoroughly with a compressor, and rebuilt with a Robert Barr o-ring kit. They're quite clean. Any hiccups I've got now are probably due to out-of-adjustment valves, poor sync, and/or float levels that need tweaking (although they are within spec).