Bonneville America Forums Forums Technical Forums General Tech Maddening intermitent dying at idle!!!

Okay, I'm out of ideas so I need some outside of the box thinking...

I got my bike back from 12,000 mile service - oil change, new plugs, air filter, carb balance and valve job. Bike ran better than every at high RPM, but after warming up to operating tempurature "sometimes" (often but not always) it will die when I pull up to a stoplight. No stumbling, just cuts out but then is always able to fire right back up.

I tried raising my idle speed. Same symptoms.

I checked my airbox for leaks and all electrical connections. All electical connections were good and I tightened the hose clamps between the airbox and carbs and carbs and the engine. Same symptoms.

I pulled the tank and looked for vaccuum leaks. I have a CA bike so I disconnected all the emissions stuff and put balancing hoses between the carbs and intake manifolds. Same symptoms.

I bought a D-tool from Brent and adjusted my air/fuel mixture to 4 turns out and then synched my carbs. Same Symptoms.

So I don't get it. It never dies at speed and if I hold the throttle over 2000rpm when I stop, it doesn't die. If it were an electical problem I would expect it to not matter if I was stopping or going.

So I'm out of ideas and I don't want to give up and take it back to the stealership where they will not be able to reproduce the problem and just waste my time (and probably try and charge me for it too).

Oh yeah, a couple more questions:

What does the throttle positions sensor do on our bikes and what is an air control valve? The manual says that is the type of fuel system we have.

What should our idle be set at?

I had the same thing happening all the time, and when I finally installed a tach, I discovered that my idle was way to low. I run just over 1000, and it has not happened again.

Yeah, I have a tach and I have raised my idle to 1600 rpm (!) and the symptoms still persist.

I just got back from an experiment though. I disconnected my throttle position sensor and went for a ride. Throttle response wasn't as smooth as before but guess what... the bike didn't die. I rode around - stop and go - for almost an hour and it did not die once.

As I understand it, the TPS controls ignition timing - something about resistance. How does it work? Would a faulty TPS be able to explain my symptoms? I have my doubts because when I got home, before turning the bike off I started fiddling with the sensor, turning it and stuff, and it made my idle jump around a bit but didn't kill the bike.

I also read in another post that one of the wires connected to the bottom of the carbs is related to the TPS somehow - can someone verify or explain this?

Jonathan, that has to be an incredibly maddening problem. Let us know how it is finally resolved.

Sounds to me like either more playing with the idle mixture screws or a jet change for the pilot jet.

I ditched the TPS last year.
Haven't missed it.
Book says if it goes bad you have to "renew the carburetors".
LMFAO!!!
The wires to the underside of the carbs are carb heat.
(I ditched that too).

I would not run the mix screws at 4 turns.
It is getting to the point of the spring pressure being to
little and they could vibrate out.
I would keep them at 3 turns.

just my opinion.

the only thing I think of about the idle problem is
if one of the idle jets has some junk caught in it.
could be restricting fuel flow at idle.

Checked the fuel filter at the carbs?

Haven't checked the fuel filter, but in my experience with other bikes, when this gets blocked, the symptoms show themselves in the form of fuel starvation at prolonged high RPM operation as the float bowls drain. But what the hey, I'll check it out.

And Snekeptp, I think you're right about the mixture, she now seems to be running a little rich anyway so I'll turn her back to 3 1/2. Eventually I'll tune her properly, I just wanted to rule out a lean condition for the time being.

Just got back from another test ride with the TPS disconnected and sure enough, this time it started dying at stoplights... AGAIN. The difference between yesterday's ride where it didn't die and today's ride where it did was that today I spent long stretches on the freeway and it would die when I stopped at the offramp, wherease yesterday all of my riding was around town stop and go. I just don't get it but keep the ideas coming!

A few more things to now check off the list:

Fuses checked - all good, tight connections.
Fuel filter - totally clear.
Spark plugs - torqued and gapped correctly. ( I was really holding out hope for this one, but no...)

There is one electical connector by the carbs coming down from the frame that doesn't connect to anything. It is female, 2 prong with one purple and one black wire. I believe it is for a 12v accessory outlet though - can anyone confirm this for me?

Quote:

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I believe it is for a 12v accessory outlet

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That is correct.

Here's stab in the dark....when you throttle off and come to a stop, something is completely shutting off your fuel supply...could there be a blockage in your carb/carbs? I did this once to a mower engine, and it worked....try lightly tapping your carb body with a small hammer. The carb float was stuck, and the tapping loosened it. Maybe try this... Empty most of your fuel from your tank, then add some fuel treatment like STP, or some carb clean-out. Start up and rev the stuff through the carbs.

Went to the stealer and scheduled a return service - they actually didn't hassle me too much so that was good... They said I would have to restore the bike to stock before they would look at it though.

So I turned the fuel screws back in half a turn and re-synched the carbs (leaner than before, but rich enough to eliminate the popping) and reattached the smog stuff. Since I was messing with vaccuum line connections anyway I started testing stuff with my vaccuum gauge and pulling off vac lines to see what would happen and I found that when I pulled one of the vac lines, held the throttle open, and then closes it rapidly, the engine would die just like it had been. hmm... Okay, hooked up the stock stuff as tight as I could, including a new squirrel condom and went for a test ride. Died. Okay, that didn't work. So I pulled the smog stuff off the rest of the carbs and intakes and replaced them all with new squirrel condoms. Fired her up and her idle was way smoother than it had EVER been. hmm... Took her for a ride and she ran great and didn't feel like she was going to die as the rpms dropped, and most importantly didn't die at all. Went on the freeway, fully expecting it to die when I pulled off again but no, she kept running. Back onto the freeway again and off again and she still kept running. I got her home after an hour and a half and no problems at all. <knock on wood>

Here's my current theory: The root cause was a vaccuum leak at the one squirrel condom that was in place and another at one of the smog line hookups (they were both a little loose). When I pulled the smog stuff and jumpered the carbs and intakes with vac line I used some old, low quality line I had laying around that itself was cracking a little bit and didn't form a tight seal so I still had a vaccuum leak even though I was blocking the vac ports differently - my new seals still weren't good enough. The problem was made worse as the bike warmed up and the rubber expanded faster than the metal fittings makign the connections looser still.

The leaks weren't severe enough to really show up under constant throttle but when I was experimenting with the vaccuum gauge I found that when getting off the throttle, the vaccuum drops way down before coming back up and steadying out so when I was pulling up to a stop and closing the throttle, the vaccuum dropped and the minor vac leak was enough to drop the vaccuum just enough more to kill the engine. Ah, all I needed was a little science.

So we'll see - I'll keep testing it this week and if it's fixed, great, and if not, well at least I've got a service appointment this Saturday. I'll keep my fingers crossed that this is it. Wish me luck.

Excellent....sounds like you found the problem. Vacuum leaks are hard to find, yet they can cause so many symtoms that a person can waste a lot of time and money trying to find the problem source elsewhere. First thing I did when I got my new bike was to get 4 small ss hose clamps and seal those condoms down. Eliminates leaks, and holds the condoms tight so they won't pop off.

you can put a rubber band around your condoms to keep them from coming off.

Well day 2 of experimentation was a complete success. Again took her out on a long ride - stop and go - on the freeway, lots of stop and go - no dying. I don't want to get too excited but I am cautiously optomistic that I have indeed resolved the problem.

Those are really good ideas about securing the block-off caps with clamps or rubber bands. Cheap insurance.

And now that the smog stuff is all unhooked I think i'm going to stip it off completely and have a much cleaner look. You know, this whole thing was a good experience because it gave me a chance to really open her up and realize that she's not all that complex of a machine - something beautiful about the simplicity... and I love working on a bike with no f'ing fairings.

keep a close eye on your condoms. having one come off or finding out you have a hole in one can mess up a great ride.

Just wanted to post a quick follow up. Been riding for 4 days now and still running strong. Definately vaccuum leaks.

Adding to mental tool kit: When diagnosing intermitents always check and recheck the following first:
1) Vaccuum leaks
2) Loose ground wire

I got small packet of condoms a guy who works with Holly(?) carbies. They fit ok and take up no room in my jacket pocket. Plenty of spare ones now.

You're the man!

Gerry

Ok guys, I need some english here for a sec.
"squirrel condoms"?? Huh?
Maybe I don't have an issue, maybe I do but I have to keep the choke pulled out so the RPM's are 1100 or I get the same thing; dying when stopping. It'll idle at 800 with the choke fully in but if I leave it there, she'll die the next time I stop.

Is this an idle adjustment? Should I seek out Trojan man for squirrel condoms? Sorry for not understanding, but I'm rather new to the the wrench turning sect.

there are 4 vacume ports on the bike .
1 on each carb , on the front of the carb pointing up and
just behind the rubber carb to intake boot.
the other 2 ( 1 on each intake )
are just infront of the boot and again pointing up.
each has a rubber cap ( squirle condom ) sealing it.
if any of the caps are loose you will have a vacume leak.
if any of the ports have something other than a cap
some of the emmisions crud is still connected.

Nick, the funny term refers to the vacuum caps on the intake manifold and carbs' ports (four total). You can see two in this photo:





Try increasing your idle. The enricher is doing that for you. Use the turn knob not the choke. The bottom left knob in this pic:

Yeah 800 rpm is a pretty low, especially if you're not synched up. I would first raise your idle. Not sure what others would suggest but I like to set her so she idles at 1400 rpm when she is warm (1200 when cold).

I keep mine right around 1000 to 1100.

Ok, it's starting to make sense now. Thought for a minute I'd have to go back to biology class!
I'll raise the idle and check the caps. Thanks for the clarification.

Thanks to everyone who contributed to this thread.

Just fixed a problem related to those pesky vacuum caps - no idle at normal idle speed, left carb popping, and backfiring from left exhaust. The cap closest to the engine on the left side was gone except for a dry rotted ring of rubber.

Replaced the cap, no popping, idle normal, spares in my saddle bag. Ready to ride to Indy for the Moto GP. Life is good.