Stalling Interstate

[XXTi]

My neighbor recently bought a 1999 Interstate and really liked it until last week.  It started stalling unpredictably after it is ridden for a while.  It seems to have the problem most often after he rides it, stops for a break and takes off again.  It has been running rough and stalling shortly thereafter.

My first thought was a plugged tank vent or a kinked vent line.  We blew air through the tank vent and could hear air venting in the tank. The vent line was also clear.  One interesting thing was that the tank went "whoosh" when we opened the gas cap.  It was obviously under pressure, so I guess I don't understand how the vent system works.

The next thought was a plugged tank screen or that the aftermarket fuel filter was clogged.  We took the tank off and the screen was clean.   We could not find a replacement for the aftermarket fuel filter, so we eliminated it and ran the fuel line from the petcock directly to the fuel "T" like the OEM configuration.

The bike runs great while it's in the garage and doesn't have the problem until it's been ridden a while.  I'm wondering about the ECU.  I thought about trying the one from my 2003 Std. as a test unit.  Will it work?

Has anyone had a similar problem?  Can you shed any light on the issue?

[Don07tncav]

I had the same problem and had to rebuild the petcock. Maybe time for a Pingle for him?

[eric in md]

petcock... rebuild it tor replace it. or try to ride it with the gas cap open ..

[X Ring]

petcock... rebuild it tor replace it. or try to ride it with the gas cap open ..

+1.  Also the I/S uses a different ECU than a standard.

Marty

[XXTi]

Thanks for the info guys.  We did try to start it with the gas cap open and it still stalled and ran rough.  It seemed to be running on three or four cylinders.

I wish there was a local Tulsa place to find a Pingle.

[John U.]

The whoosh sure sounds like a blocked/kinked vent line.  One the other hand running on fewer than 6 cylinders could be clogged slow jets. Get some Techron fuel system cleaner and give her a heavy dose. It may take a while for it to work, give it time.
Does it idle well? A bike that will run better wit the choke on than it will with it off is another sign of clogged slow jets.
Let us know how it works out.

[gordonv]

Since the bike sounds like it was running fine when first purchased, and unless it's been parked for a lenght of time (winter) and not run, then I would not suspect the jets, unless you found crud in the tank when you had it off.

It sounds more like to me, from what I've read, not experienced, that the carbs are being starved of fuel. Does it happen with a full tank, or only after it reaches a certain point (the IS has a fuel guage, check the level at which it happens at). My thought is that the petcock is not allowing fuel to feed through it and that it is only working when you have a full tank. Could also be the vent tube, but you've said after opening the cap it still wont run.

You did mention you have a working Valk. If you have more time than money, swap petcocks.

My understanding is that the ECU (ICM) are fully interchangable and will work on any bike, if you want to test them. But the IS ICM is different from the other 2. I wouldn't keep them that way.

[XXTi]

Thanks again guys.  I don't really think it's a jet problem.  The bike runs great when it runs.  It idles and accellerates perfectly until it starts acting up again.  The problem has occured with fuel levels of nearly empty to brim full.  The vent system is a little puzzling since we know it's clear, but pressure still builds in the tank.

He is taking the bike to a local area dealer tomorrow.  I'll let you know what they find.  We're rooting for the petcock.

I was using the wrong term for the ICM.  Thanks for the correction.

[Red Diamond]

There is one other thing that can happen and it has not been mentioned. The alternator and battery. If the battery is good and the alternator is failing or failed, the bike will run good for a while and then stall. If it sits for a while, it will start and run good until it draws all the power from the battery, and stall again. On the tank vent issue, if the tank holds pressure, the vent may be pinched in a location that you can't see. Forcing air thru the vent tube does not mean it is not kinked or pinched. Rebuild the existing petcock, it more economical and reliable.

[Mr.BubblesVRCCDS0008]

On my I/S when the alt. failed the first sign was the display went blank or started acting real funny. I'm betting still a vent issue or petcock. I converted mine to manual about four years ago because it started leaking two days before a ride to the romp in the swamp.I never have changed it back to vac since then. Yes you have to turn it off and on but thats how all manual valve work.

[Patrick]

I'm wondering if the air blown into the vent is overcoming a slight kink in the line leading you to believe the vent is clear.. The tank shouldn't become pressurized.. Also the air blown into that line from the bottom just be existing thru the ' T ' and not reaching the tank.. Its an easy thing to check..

[Cliff]

I'm wondering if the air blown into the vent is overcoming a slight kink in the line leading you to believe the vent is clear.. The tank shouldn't become pressurized.. Also the air blown into that line from the bottom just be existing thru the ' T ' and not reaching the tank.. Its an easy thing to check..

I agree vacuum can close a partial restriction while blowing into tube (pressure) can overcome the restriction.  My bet is the vent tube,,,, the whoosh is the in rush of air rather than a release of pressure.

[XXTi]

We removed the tank and blew compressed air through the metal vent connection.  We also blew through the rubber vent tube.  No apparent problems, but maybe I'm missing something.  Can anyone tell me how air gets into the tank?  Is there a vent hole in the filler cap or somewhere else?

That's an interesting idea about the alternator/battery.  The battery did die suddenly on Sunday afternoon.  Thanks for the tip.

[Cliff]

We removed the tank and blew compressed air through the metal vent connection.  We also blew through the rubber vent tube.  No apparent problems, but maybe I'm missing something.  Can anyone tell me how air gets into the tank?  Is there a vent hole in the filler cap or somewhere else?

That's an interesting idea about the alternator/battery.  The battery did die suddenly on Sunday afternoon.  Thanks for the tip.

If the vent tube is slightly pinched the pressure will likely be able to force it's way through, but while using the fuel from the tank the vacuum felt on the rubber tube could collapse and close at the point of the pinch.  Try and apply a vacuum at the top of the vent tube rather than pressure to see if it remains open.  There is only one vent on the tank and the vent tube connects to it.  I believe there is a "T" in it with a short tube connected to nothing acting as a vacuum break to prevent siphon.

[shortleg]

  If the tank went woosh when you opened it
that is a sign of a kinked vaccume line.
         Shortleg[Dave]

[gordonv]

+1

If the tank has a vent tube, this is to equalize the atmesphere in the tank to the outside presure. If in the sun and heats up, presure increases and vents out. As fuel is used, a vacuum is created, and air presure from outside comes in.

As for using compressed air on the tube, unless you set your compresser to 6 psi, you where most likely using something closer to 40 psi (or higher) and this would have over come any restriction. You should blow on it with your mouth (don't inhale) with the cap open.

[BG99IS]

I am the neighbor who has the Interstate that stalled 6 times last Saturday and finally had to be left on the highway when the battery died on Sunday after a good deal of perspiration (mine and XXTi's) during diagnostic work Saturday evening and Sunday afternoon.   It went to Honda of Tulsa on Tuesday.  The mechanic called on Wednesday and said they couldn't find anything wrong with it.  I asked if he was sitting down then told him the whole story.  He called back in a couple of hours and said that the diaphragm on the fuel petcock was leaking and that he would have another one there on Thursday.  He called Thursday and said it was fixed.  Since Thursday is gun club day, I picked it up at noon on Friday.  It made it home Friday and all over town on Saturday.  I intend to do a longer test tomorrow morning. 

As I understand it, the fuel valve automatically shuts off when the engine is shut down and the vacuum goes away.  If the diaphragm on the fuel valve leaks, it will close when the engine is running or just not open again after the engine is shut off.  The latter was the case last weekend.

Many thanks to everyone who offered advice.  I learned a lot about this bike in the last week.  I can't expain the whoosh when the cap was opened when I finally got home last Saturday except to say that the vent hose did appear to be kinked but that was obviously not the main probem.  It only whooshed once and that was after riding about 20 miles on a tank that was less than half full.

XXTi insists that gasoline with ethanol is not good for old motorcycles and I have to admit that it could have caused the diaphragm failure.  I would appreciate opinons on 10% ethanol versus "pure" gasoline.

Thanks again.