Hiccup. Fuel Delivery Problem?

[Steve K (IA)]

Took a ride to visit my Sister yesterday...80 miles away.  36 miles in, suddenly 2 or 3 cylinders dropped off like I was running out of gas.  ( it sounded like the right bank shut down) I had 2 bars on the gas gauge and 160 miles on the tank.  Reached down and switched to reserve and it immediately started firing on all cylinders.  Came to a town a few miles further.  Gassed up and took 4.7 gal.  Switched fuel selector back to run,  continued on to my sisters place and returned home with no further problems.

I can't figure out what happened.  Any idea's?  ???

[Leathel]

my bike started dropping 2 cylinders but mostly on cold start up, I figured fouled plugs but it did the same with new plugs, being 2 cylinders I figured coil so pulled the one I thought was out (plug difference) and found it had rusty earth connections so cleaned that, run a tap through the threads and replaced the bolts (also had rust)

No more issue so I repeated on all coils.... might not be your issue but I first thought mine was fuel when it first happened

[sandy]

Most of the time, your problem is the fuel petcock beginning to fail. Buy a "cover set" for your petcock and rebuild it. Don't forget to replace the vacuum line to the petcock.

[gordonv]

Reached down and switched to reserve and it immediately started firing on all cylinders.

What have you done recently, removed the tank? Possible pinched vent tube putting the tank back on.

But lets think, this has happened only once? That doesn't mean it's going to happen again, maybe wait for it too, then worry. I would wait for it to happen again before you reach reserve, and this time open the file cap listening for air to come in.

[Paladin528]

The fact you switched to reserve and it picked up says you were almost out of gas.
On My IS when it hits the last 2 bars it may run out before the second bar goes out and starts flashing.
If I am nice and steady it will start flashing about the same time it starts stuttering.  In the twisties its hit and miss.

Just the fact you filled it up and it worked fine say, to me, its normal.

[Paladin528]

Just to add 160 spirited miles will get he pretty close to reserve.

[longrider]

Rebuild the petcock as was mentioned.  Be sure and perform a test of fuel flow when the new one is installed

[Steve K (IA)]

Most of the time, your problem is the fuel petcock beginning to fail. Buy a "cover set" for your petcock and rebuild it. Don't forget to replace the vacuum line to the petcock.

I rebuilt the petcock with OEM cover set and new Redeye vac line about 3 years ago, but not many miles ridden.

The fact you switched to reserve and it picked up says you were almost out of gas.
On My IS when it hits the last 2 bars it may run out before the second bar goes out and starts flashing.
If I am nice and steady it will start flashing about the same time it starts stuttering.  In the twisties its hit and miss.

Just the fact you filled it up and it worked fine say, to me, its normal.

But just a few miles down the road I stopped and filled up and it only took 4.7 gal.  (2000 I/S)

Reached down and switched to reserve and it immediately started firing on all cylinders.

What have you done recently, removed the tank? Possible pinched vent tube putting the tank back on.

But lets think, this has happened only once? That doesn't mean it's going to happen again, maybe wait for it too, then worry. I would wait for it to happen again before you reach reserve, and this time open the file cap listening for air to come in.

The last time the tank was off was when I rebuilt the petcock and put on a new vac line 3 years ago.

Rebuild the petcock as was mentioned.  Be sure and perform a test of fuel flow when the new one is installed

After rebuilding the petcock I did check it.  It worked as it should.

Guess I will have to see if it happens again.

[SCain]

I've experienced this several times on my 99 IS, it happened a few times on my 97 Tourer and it happened yesterday to F6BANGER coming down Hwy 550, but it only happens in very hot weather.
To me it seems like a slight vapor lock, just switch to reserve and switch back to on, normally won't happen again.
I don't think it has anything to do with a petcock begining to fail IMO.

[Willow]

If you've extra length in the fuel line it can act like that.  A partial blockage (kink) in the vent line can also do that.

Switching to reserve puts just a little (1 gallon) more fuel weight above the tank drain.

[gordonv]

I've experienced this several times on my 99 IS, it happened a few times on my 97 Tourer and it happened yesterday to F6BANGER coming down Hwy 550, but it only happens in very hot weather.
To me it seems like a slight vapor lock, just switch to reserve and switch back to on, normally won't happen again.
I don't think it has anything to do with a petcock begining to fail IMO.

Steve K, is there anything not OEM in your fuel line, a fuel filter maybe? The above reminded me of another one that happened only in hot weather and was an added fuel filter.

[RWhitehouse]

I've experienced this several times on my 99 IS, it happened a few times on my 97 Tourer and it happened yesterday to F6BANGER coming down Hwy 550, but it only happens in very hot weather.
To me it seems like a slight vapor lock, just switch to reserve and switch back to on, normally won't happen again.
I don't think it has anything to do with a petcock begining to fail IMO.

I ran into this once on my Tourer. Was riding from Utah down the freeway into Vegas, about 110* ambient and I was putting the hammer down to get into the a/c sooner. On a long incline, holding it 90-95, I noticed some hiccups that felt like cylinders dropping. It was intermittent, but got worse in time, eventually leading to it feeling like it was only on 3 cylinders and had very low power.  I only had about 50 miles on the tank, but switching to reserve immediately fixed the problem. I have to assume getting a bit more head pressure (by using the bottom of the tank, rather than a couple inches up) was enough to overcome the vapor lock and push fuel through. That was the one and only time I ran into that issue. Never happened before, or since. I also have a Pingel manual valve, so no issue with a OEM petcock potentially choking off.

[The emperor has no clothes]

I've experienced this several times on my 99 IS, it happened a few times on my 97 Tourer and it happened yesterday to F6BANGER coming down Hwy 550, but it only happens in very hot weather.
To me it seems like a slight vapor lock, just switch to reserve and switch back to on, normally won't happen again.
I don't think it has anything to do with a petcock begining to fail IMO.

I ran into this once on my Tourer. Was riding from Utah down the freeway into Vegas, about 110* ambient and I was putting the hammer down to get into the a/c sooner. On a long incline, holding it 90-95, I noticed some hiccups that felt like cylinders dropping. It was intermittent, but got worse in time, eventually leading to it feeling like it was only on 3 cylinders and had very low power.  I only had about 50 miles on the tank, but switching to reserve immediately fixed the problem. I have to assume getting a bit more head pressure (by using the bottom of the tank, rather than a couple inches up) was enough to overcome the vapor lock and push fuel through. That was the one and only time I ran into that issue. Never happened before, or since. I also have a Pingel manual valve, so no issue with a OEM petcock potentially choking off.

I think there is also the possibility in really hot weather, with a good load on the engine, that the heat collapses any little turn in the fuel line.

[Cracker Jack]

Apparently some people erroneously think that pulling fuel through the reserve port provides a greater head pressure below the petcock.
That is simply not the case, the head pressure is dependent on the surface level in the tank providing the restriction thru the petcock for the two routes is not different.

[The emperor has no clothes]

Apparently some people erroneously think that pulling fuel through the reserve port provides a greater head pressure below the petcock.
That is simply not the case, the head pressure is dependent on the surface level in the tank providing the restriction thru the petcock for the two routes is not different.

The “main tank’s” inlet is 3” or so higher than the “reserve’s tank” inlet. I believe this would result in a lesser pressure for the “main tank”.

[RWhitehouse]

Apparently some people erroneously think that pulling fuel through the reserve port provides a greater head pressure below the petcock.
That is simply not the case, the head pressure is dependent on the surface level in the tank providing the restriction thru the petcock for the two routes is not different.

Take a soda bottle and fill it with water.

Poke a hole in the middle of the bottle, and poke a hole at the bottom. Which one has the water shoot out with more force?

[cookiedough]

4.7 gallons fillup seems for an I/S just about 1/2 gallon shy of needing to go on reserve.  It has been awhile having to switch to reserve while riding but normally for me is like 5.3 gallons or even more with a 6.9 gallon I/S gas tank.  Once that last LED light starts flashing I have tops 15 miles to go before needing to flip to reserve and right before running out of gas on NON reserve, my I/S has no power like it has no gas going thru it much, give it throttle and does no good.

I would not worry too much about it again until it does it again then start thinking on it.  Maybe your 4.7 gallon fill up was not totally full either you can get another near 1 gallon in the I/S gas tank filled up full to the very top filler neck when down a tad from totally full you think it is full though.  I get gas locally saving 6 cents per gallon if use CASH knowing I was close to 4 gallons needed so put 10 cash in pre-pay at pump knew it was going to be close to overfilling.  That last 1 buck I had to GENTLY squeeze the gas pump trigger to get it all to fit in where most would have stopped at 9 bucks not 10 bucks until full.

[Steve K (IA)]

I've experienced this several times on my 99 IS, it happened a few times on my 97 Tourer and it happened yesterday to F6BANGER coming down Hwy 550, but it only happens in very hot weather.
To me it seems like a slight vapor lock, just switch to reserve and switch back to on, normally won't happen again.
I don't think it has anything to do with a petcock begining to fail IMO.

Steve K, is there anything not OEM in your fuel line, a fuel filter maybe? The above reminded me of another one that happened only in hot weather and was an added fuel filter.

I have a Quick Disconnect from RedEye.  I put that in there many years ago.  And it's been a few years since I had the tank off.

[Steve K (IA)]

4.7 gallons fillup seems for an I/S just about 1/2 gallon shy of needing to go on reserve.  It has been awhile having to switch to reserve while riding but normally for me is like 5.3 gallons or even more with a 6.9 gallon I/S gas tank.  Once that last LED light starts flashing I have tops 15 miles to go before needing to flip to reserve and right before running out of gas on NON reserve, my I/S has no power like it has no gas going thru it much, give it throttle and does no good.

I would not worry too much about it again until it does it again then start thinking on it.  Maybe your 4.7 gallon fill up was not totally full either you can get another near 1 gallon in the I/S gas tank filled up full to the very top filler neck when down a tad from totally full you think it is full though.  I get gas locally saving 6 cents per gallon if use CASH knowing I was close to 4 gallons needed so put 10 cash in pre-pay at pump knew it was going to be close to overfilling.  That last 1 buck I had to GENTLY squeeze the gas pump trigger to get it all to fit in where most would have stopped at 9 bucks not 10 bucks until full.

When I fill up, it's full to the top.  Any more and it would overflow. 
In all these years I've only had to switch to reserve a few times and I had at least 180 miles on the tank with the RES flashing.

[MarkT]

Apparently some people erroneously think that pulling fuel through the reserve port provides a greater head pressure below the petcock.
That is simply not the case, the head pressure is dependent on the surface level in the tank providing the restriction thru the petcock for the two routes is not different.

This is absolutely correct and I proved it.

If the pressure is higher with the fuel pickup at the bottom of the pickup tube above the petcock, than it is at the top of the tube - that is from the reserve feed than the main tank - then taking a transparent fuel line from the petcock, turned and routed back up above the fuel level, should show the fuel level higher when fed from the reserve rather than the main port, right?  Think of that a second.

Now look at this picture.  I did exactly that with this piece of fuel line.




The fuel level line was marked for the reserve level - note the mark at the fuel level.  Switching to the main feed, the level didn't move.  AT ALL.  And it makes sense.  The column of liquid is exactly the same height in both cases.  In one case that column passes through the feeder tube.  In the other it bypasses it.  The height of the column is the same in both cases and thus, the pressure.  IOW, also think of a siphon with a transparent hose.  It matters not the route it takes - the level in the hose after it passes up and over the high point, dips down low than is turned back up again above the level of the container's contents, will be at the same height as the level in the container being siphoned no matter what route is taken. 

[RWhitehouse]

Apparently some people erroneously think that pulling fuel through the reserve port provides a greater head pressure below the petcock.
That is simply not the case, the head pressure is dependent on the surface level in the tank providing the restriction thru the petcock for the two routes is not different.

This is absolutely correct and I proved it.

If the pressure is higher with the fuel pickup at the bottom of the pickup tube above the petcock, than it is at the top of the tube - that is from the reserve feed than the main tank - then taking a transparent fuel line from the petcock, turned and routed back up above the fuel level, should show the fuel level higher when fed from the reserve rather than the main port, right? 

(deleted, I'm an idiot )

Brain fart on my part. I was thinking of relative pressure at the pickup point, rather than at the carburetor.

[Cracker Jack]

Apparently some people erroneously think that pulling fuel through the reserve port provides a greater head pressure below the petcock.
That is simply not the case, the head pressure is dependent on the surface level in the tank providing the restriction thru the petcock for the two routes is not different.

This is absolutely correct and I proved it.

If the pressure is higher with the fuel pickup at the bottom of the pickup tube above the petcock, than it is at the top of the tube - that is from the reserve feed than the main tank - then taking a transparent fuel line from the petcock, turned and routed back up above the fuel level, should show the fuel level higher when fed from the reserve rather than the main port, right?  Think of that a second.

Now look at this picture.  I did exactly that with this piece of fuel line.




The fuel level line was marked for the reserve level - note the mark at the fuel level.  Switching to the main feed, the level didn't move.  AT ALL.  And it makes sense.  The column of liquid is exactly the same height in both cases.  In one case that column passes through the feeder tube.  In the other it bypasses it.  The height of the column is the same in both cases and thus, the pressure.  IOW, also think of a siphon with a transparent hose.  It matters not the route it takes - the level in the hose after it passes up and over the high point, dips down low than is turned back up again above the level of the container's contents, will be at the same height as the level in the container being siphoned no matter what route is taken. 

Mark, thanks for describing your experiment which demonstrates what everyone who has taken a fluids/hydraulics class already knew.

RWhitehouse, what you're erroneously not considering is the head developed inside the normal pickup tube.