stumbling, stalling, backfiring

[Rikugun]

I was off Monday and went for a ride. I stopped for gas and was about 50 miles into the the new tank when I noticed some sluggish response at lower revs. At a light the throttle response had deteriorated further and at the next light the bike stalled. Hard to start and had to keep revving it to stay running.

No stops for a spell but below 4k definitely not right. Above that seems fine. Down a long grade, off throttle it backfired loudly 4 or 5 times. At some point I turned the petcock to Prime and it seemed to improve. Back to On and it seemed to get worse again. I'm not really sure about this, tried several times and not always repeatable.  After about 40 miles of this nonsense it cleared up, and ran fine the rest of the way home (petcock in ON position). The temp & volt gage were normal the entire ride.

The first symptoms were similar to a carb overflow incident I had on my first test ride but when I pulled over this time no fuel was evident at the overflows. By the time I thought of trying the enrichener for diagnostic purposes, the problem had cleared up.

After accumulating 1500+ miles I was just beginning to have confidence in Matilda and now this. Any thoughts?

[QBS]

Are you running an inline fuel filter?

[h2olawyer]

Mine will act up in a very similar fashion when the carbs get heat soaked.  If you are not going fast enough to get some good air movement around the carbs, you get a bit of vapor lock.

I normally experience the problem in group riding (typically slowish) or when the ambient temp is over 95F.  It is worst after a long (45 - 60 minute) slowish (35 - 40MPH) ride, a short stop of 5 to 10 minutes, then hard to start, doesn't like to run below 5K.  Clears up some after a couple miles - still some rough low RPM issues for a while longer.

H₂O

[YellowJacket!]

Just a thought.

Hot tank + new cold gas = condensation?

David

[Rikugun]

Yes to the fuel filter and it does not seem to have any debris visible in it. I didn't consider the condensation theory and I suppose anything is possible. So far, of the suggestions provided, I'm leaning towards the heat buildup theory.

I have read of other members experiencing driveability issues during slow, hot rides and I've noticed some of these myself. This was pretty severe relative to what I've encountered thusfar and had me a bit concerned as I was riding alone and not close to home.

It may be that I just have to learn the limitations of this model and adjust my riding accordingly. I can't commute with it due to the type of work I do and mostly pleasure ride avoiding highways like the plague. This usually means running a tank of gas on backroads with average speeds in the range h2olawyer mentioned. Ironically, I may have to ride my air cooled bike when the weather is hot. :-\

There's a company in my area called Melcor that makes thermoelectric cooling modules. It's the technology used to make those 12v "ice chest" sized coolers you plug into your car's power outlet/cigarette lighter socket. Maybe I need to epoxy a couple of those elements to the carbs! I guess I could get some thin aluminum plate and cut a bunch of fins to glue to the bowls as well. What kind of glue transmits heat the best?  :)

[Hartless]

do you have any liner in your tank , such as kreem. i had/have it peeling in my tank and it clogs the petcock , causing the same symptoms

[h2olawyer]

Hmmmmm - a Peltier cooler for the carbs.  Interesting idea!  There are a few astrophotographers using DSLRs that make insulated boxes with a Peltier cooler to keep the camera cold.  This prevents amp glow on long exposure shots.  I might ee about doing this for the carbs.  Hadn't thought about that one - I was just hoping my eventual swap to an 83 fuel system would be the cure.

Peltier coolers are cheap and an experimental system could be fabbed up for under 540.  Figure on cooling the carbs about 15 - 20 (F) below ambient temp.

Guess I'll start doing measurements and souring materials next week -after I get back from the dark sky weekend I'm doing in North Park, near the Wyoming border Leave Friday AM & returning home on Monday.  Hoping for good views of Stephan's Quintet, the Deer Lick Galaxy Group, and some stunning looks at the Veil Nebula and the Cocoon Nebula - plus a ton of other really cool stuff up there.  Might even spend one night trying to get a good image.  However, I'm now looking for a smaller & lighter scope for imaging.  My 8" Newt is just a bit heavy & makes for too much leverage on my small GEM mount.  I may even just go with a couple lenses for my DSLR and figure out how to attach the guide scope to that system.  For now, though, I'm stuck with the Newt.  As long as I get the balance perfect, I can get some decent images.

H₂O

[Rikugun]

Thanks h2o, I was hoping someone would latch onto the idea and run with it! Every once in a while I like to send an idea up the flag pole and see if anyone salutes. As the "idea" man here, I don't really have the time to work out the details of my own creations. In other words, insufficient smarts to implement my own ideas!  :(

I threw out another idea earlier regarding fan cooled carbs (taking the spot where the YIC lives) and it only received minimal interest. It's a shame, really. I had en"visioned" attaching a giant V-stack funnel to the fan giving the thing an S&S Harleyesque look that would have been awesome....or completely hideous, depending on your pov.....   

But I digress as usual. Anywho, I have no idea what you're talking about in your last paragraph so I'll just wish you luck with your stellar snap shots!  :laugh:

Hartless - I don't think that's it but thanks for the thought. The tank is lined with a darker colored liner and based on what I can see through the cap opening, it appears to be uncompromised.

[fret not]

Rikugun, your problem sounds like it could be your fuel pump.  The diaphragms can crack and loose their ability to function well.  I'm not saying that is your problem but it could be.  Higher revs could produce enough pumping action to pass fuel but at low revs don't pump well enough.

[Rikugun]

I considered the pump while this was going on. The problem went away but I suppose that doesn't eliminate the pump as a possibility. If it is failing, perhaps under extreme heat it's symptoms begin to show?

The more I think about it, it does seem heat related. At one point I was in traffic and spent three traffic light cycles trying to cross the main street of a particular town during noon traffic. During that time the idle slowed and the engine eventually quit. Even after getting under way the symptoms persisted and worsened. I abandoned the exploration of the areas intended and took a familiar rode towards home base that had miles of 50 mph roads with no stops for miles at a time. It took some time for the bike to "normalize" but then it was a hot day.

Or maybe I'm just trying to make the diagnosis fit the symptoms.  :-\

[GT @ oh.]

I had a similar scenario...got home adjusted the pilots and havent had it in +3000mi. since then

[Rikugun]

I would hate to think all that drama was caused by a slightly lean idle mixture !? Maybe an extra 1/4 turn out couldn't hurt though.....

[Rikugun]

I don't think this was the cause but I've been feeling guilty for not having checked the valve lash as of yet and did so last night. Five of the 8 valves were below spec - 2 EX and 3 IN. There was 6000 miles on the odometer when I got the bike and 7500 now. I don't think the valve covers had ever been off.  Miraculously, I had the shims required to bring them into spec although one is on the loose side of the tolerance.

One more item scratched off the "to-do" list.

[Walt_M.]

Always check carb synch after a valve adjust.

[jasonm.]

Mine will act up in a very similar fashion when the carbs get heat soaked.  If you are not going fast enough to get some good air movement around the carbs, you get a bit of vapor lock.

I normally experience the problem in group riding (typically slowish) or when the ambient temp is over 95F.  It is worst after a long (45 - 60 minute) slowish (35 - 40MPH) ride, a short stop of 5 to 10 minutes, then hard to start, doesn't like to run below 5K.  Clears up some after a couple miles - still some rough low RPM issues for a while longer.

H₂O

VApor lock?  these carbs have a vent right on the top with a hose. Only way a vapor lock happens is if the vent(s)is blocked.

[QBS]

A well running V will run well with a failed fuel pump...to a point.  That point is about at about 1.5 gals. into the 4.5 gal. V gas tank.

[gmac]

I may be way off here, but the last time I saw this was several years ago in a car.

I filled my tank, took off for a 90 mile trip, about 20 miles out (car got about 25mpg) I started to loose power, can't remember for sure if it was back firing, but rings a bell, and eventually didn't have enough power to pull the car faster than 30MPH. Can't remember why but for some reason I got the idea to check the fuel filter, was full of water (luckely it was mounted on the firewall and easy to get to). Dumped it out, started right up, and back on the road. About 20 more miles down the road, same deal.

Maybe water in the gas from the station? Maybe took a while to cause a problem as the water should settle to the bottom (right?) and that would be a little different in a bike tank with the tube for the main VS the reserve, and would maybe explain why the prime worked once (the prime comes off the reserve I believe) and not so much later (as the water settles more to the bottom of the tank).

Just a thought.

Gary

[Rikugun]

Took it out for a test ride after work yesterday. Slow speed maneuvers are difficult as engine seems to be surging slightly. Idles too low even when warm so I pull over and turn it up but it just runs faster but rough. Still seems to run good at higher revs though. When I get home, the engine dies when I pull in the clutch to stop. hmmm

Tried adjusting idle mixture , eliminated the pump, yics, plugged all vacuum lines -  idle is still hunting and requires fast idle or it will quit. I grabbed a can of carb cleaner and start spraying around the intake boots looking for what now seems like vacuum leaks. Despite what looks to be dry rot cracks developing in the boots, they seems ok. Guess what's NOT ok? Any spray that gets around the throttle shafts raises the engine speed. This I did not expect.

By now it's after 8, I realize I'm starving and perhaps just a wee bit depressed over what I've just learned. Lights off, shut the garage door, head for the house mumbling to myself "stupid F'ing GD throttle shafts, expletive, expletive, etc". Ok, so I was hungry, depressed, AND p.o.'d.

So thanks for all the suggestions. I did empty the bowls into a container and sumped the tank looking for water but got none. The vent lines were clear and I would have gotten to the carb sync but unfortunately it turned out to be something a little more challenging. At least it seems so as this is new territory for me.

[Re-Vision]

Idle hunting around sure sounds like you need to synch the carbs.   BDC

[QBS]

Problematic low speed running would seem to point to blocked pilot jet or jets.