1998 1520 bogs and stalls after downshift

[f6 white buffalo]

Hey Folks ,  get your thinking caps on

  last fall   I have had my 1998 1520  bog down and stall without being able to restart.... once  after downshifting from 4th to 3rd in the  65  mph range and once after sitting at a light with a severe downhill lie ..

since these occurrences maintenance work completed have been

complete cleaning of carbs
syncing of carbs
inspect and or replaced all vacuum and breather lines
60 k timing belt service
rebuild petcock
clean out tank thoroughly half a dozen times
check gas cap for clogs and back pressure
replace plugs on non vacuumed carb ports

took the bike out for the second time since getting back from the dealer and on a downshift from 4th to 3rd at 45 mph  she bogged down and quit  again, as soon as I pulled in the clutch at the next light she cut off ...tried starting her but she just wouldnt start  ,  

after 5 mins I was able to get her started and goosed the throttle hard until she ran smooth again....eased her home on back roads and 2 miles from home took her up on the highway  and she ran ok...didn't downshift at high speed because towing in my area is wicked expensive

the dude I bought the bike from had told me that he was a serial downshifter and had a certain part replaced because of that

waiting on him to return a call to tell me what that part was

the dealer he uses sucks at answering questions about previous maintenance

this bike runs like Gold ...full power  , shifts great , runs out like a dream .....except for these few instances

any ideas out there before I turn her over to the dealer again

   thanks in advance

[Gavin_Sons]

Has to be a fuel issue, try opening the gas cap and try to replicate it stalling out. Maybe the vent hose is kinked.

[Bighead]

Has to be a fuel issue, try opening the gas cap and try to replicate it stalling out. Maybe the vent hose is kinked.

+1 that is where I would start.

[Crackerborn]

Try a search for the problem on the tech side. I agree with Gavan Sons that it is likely a fuel issue, but vacuum lines not properly placed can cause all sorts of issues. That is why many do a desmog. Your local stealer will not do that, so check your local board for knowledgeable mechanics.

[IamGCW]

Agree on the vent issue.  Some put a zip tie in the cap to allow air into the tank while test riding.  

Be sure you are not actually running out of gas.  As always check the easy things like battery voltage, fuel level, and look for kinked hoses.

Gil

[Hook#3287]

Sure does sound like fuel starvation.  Can't see how downshifting can cause your problem.  Am interested in what part needed replacing from downshifting.

What did you clean out of the tank?

[f6 white buffalo]

Guys ,

thanks for the replies.....dealer went through all vent and vacuum lines , I checked vent lines  before I rode , vacuum should be ok still...dealer did a cap vent test , no pressure detected ...still waiting to hear what part was replaced by a serial downshifter ...typical rust chips from tank when cleaning , not an overwhelming amount but enough to be glad I cleaned it ...the tank screen is new  so they likelihood of a clogged petcock is small but possible ...how did stomping the throttle once getting it started clear the back up ? is a question I have ...she rode beautifully after that .......I thought originally the glasspacks were breaking down and intermittently clogging airflow, but inspection ruled that out ...definitely fuel related ...can gas be getting into the cylinders somehow or when the bike lurches forward is an air bubble getting gulped into the fuel lines....that would be a temporary hiccup I would imagine but where the heck would air be coming from....going to ride her calmy and not downshift at high speeds for a bit and see if it happens again...too much of an coincidence that it happened 3 times simulating the same movement ...the bike and gasoline lurching forward in the tank ...thx guys .....appreciate your input and suggestions

[Bighead]

Don't know of any part that would need to be replaced because of downshifting,people been doing it for years with no problem. I have been doing it for years with no problem. I still don't think your problem has anything to do with down shifting.

[Jess Tolbirt]

I would check all wiring under the tank, maybe a hard downshift might be making the tank shif and short out a wire? maybe the crankshaft pickup coil bad? thats a strange problem you are having,..

[Firefighter]

When you say bog you mean it quits or the engine idles down or what. If it quits at speed the engine will turn until you stop or pull in the clutch. Makes a difference to try and diagnose.
Checked for trash in air cleaner area? Enrichment valve in correct working order? Possible ignition, loss of spark: bad ground or power wire, or ign. component.
Mine would quit at slow speed, turned out to be battery ground to frame, and the starter would still crank over fine. I ran an extra wire from the battery negative to the frame and a lot of things worked better.  Firefighter

[Hook#3287]

Don't understand the timeline.  Did you have the problem, then have the dealer go through it to fix it and you still have the problem?  If so, your dealer should own the problem and find it.

If it's fuel starvation, which it sounds like, downshifting, fast stops, riding down hill, causing the gas to slosh around or if VERY VERY low, not reaching the petcock, it would still take a mile or more to effect running.

Try shutting off your gas while riding and see how long it takes to stumble, it's a while.

If it was mine, I would remove the tank, check the petcock, the tank screen, the petcock to #6 intake line, the gas vent line and then all gas feed lines.  While there, I'd do a desmog to get rid of all the extra piping and crap you don't need, ruling out any issues they create.

You said you had a carb cleaning, did that include checking the floats and jets?

[Willow]

Check the condition of the screen above the petcock.  No amount of rust flakes is acceptable.

Does she have an inline fuel filter or quick disconnect fuel line?  If so, either of those items could be suspect.

Lastly check the vacuum line to the petcock for leaks.

[Jess Tolbirt]

I just had another thought, your petcock needs vacuum to make it open if you are downshifting hard and going wide open throttle you will lose vacuum to the petcock from the #6 cylinder. as long as you are wide open, that will close the petcock until you back off of it,,then again there should be enough gas in the carbs to over come this,,,

[f6 white buffalo]

thanks all for your responses ...I took the bike out again today and she ran fine for 10 miles in low to mid speed running in town. As soon as I went on the hiway and ran through the gears she became fuel starved and instantly lost power at the throttle and bogged down and shut down as soon as I coasted off the exit and pulled the clutch . I waited for a few minutes , popped the cap , didnt hear any pressure release at all, and eventually got her to start and laid hard on the throttle to get power back up eventually. I drove another mile and she started losing power and bogging down . not getting fuel ...I got her home eventually and again popped the cap to listen for pressure release , and no pressure. I removed the cap and covered the inlet with a cloth and replaced the chrome surround tightly and took another ride..she started out ok but repeated the loss of power and then I brought her back home bogging . Im starting to worry Im going to affect my timing riding it like this ....I believe the clogged gas cap is ruled out now , as is the exhaust ...someone on another forum here said maybe rev limiter , ignition problem , starter ground etc ..the usual suspects ...very frustrating . Am going to remove tank , check petcock for clogs again, check airbox and vacuum lines and vent hoses  ......still not convinced we dont have debris in the tank ....how does a bike go back and forth from running 100% to bogging and dying within a quarter mile , waiting , then being ok again after spanking the throttle ...the dealer went through the checklist and gave everything the ok ...vacuum was ok , timing , carb adj . syncing , inspected glasspacks , all he had left to offer was a clogged gas cap ..which I think I just ruled out ...let the hunt for a cure  begin ...and thanks again guys

[Willow]

Go back and read my post. You haven't eliminated any of those suspects.  A break in the vacuum line my be unlikely at this point although maybe not if it's only limiting flow.

A quick disconnect line is highly suspect.  Check to see if it has one.  An inline fuel filter or clogged petcock screen could be limiting flow.

It's not a big problem.  It is just a bit difficult to pin down.

 

[Jess Tolbirt]

pull the petcock out and see if its not partially clogged, make sure the vacuum diaphragm is not full of pin holes  and check the vacuum line and make sure the vacuum port on the carb is not clogged...

[trout dude]

After doing carb work did you replace fuel hose? I'm asking because if it has a dip in the line it will cause this to happen. I know this first hand it happened to me when i was rebuilding my wife's bike. It would run all day at slow speeds but not on the interstate.
  Dennis

[Grumpy]

One place I would look is the diaphragm in the petcock, if it has a pinhole it will not fully open, especially under acceleration or high speed when vacuum is low.  Simple to check, pull the vacuum line off the petcock, and use a mity vac or similar tool to pull a vacuum and see if it holds, if not the diaphragm has a hole in it.

[f6 white buffalo]

Willow, I have neither a quick disconnect or a in line fuel filter . I keep going back to the tank itself. The fact that letting her sit for a few minutes and then getting her to start and stomping on the throttle has cleared her up speaks to a clog at the petcock. Does the housing of the petcock ever need to be replaced . It appears to be a cast item and has no moving parts aside from the rebuild kit components . I assume I have it installed correctly as I ride the bike sometimes 30 miles before she instantly loses power , bogs and cuts out when I pull the clutch , which I am careful not to do until I am somewhere safe  . What does pulling the clutch have to do with shutting her off instantly , she is bogging and starving , but doesn't kill until I pull the clutch ...this is fascinating ..thanks for the help...she can be such a beautiful beast when she s running like a watch , but then such a bastid when she is choking and dying ...thanks

[f6 white buffalo]

After doing carb work did you replace fuel hose? I'm asking because if it has a dip in the line it will cause this to happen. I know this first hand it happened to me when i was rebuilding my wife's bike. It would run all day at slow speeds but not on the interstate.
  Dennis

trout dude, I absolutely did rep[lace the fuel line off the petcock and it is a longer one than the original . I tried to lengthen it a bit to make tank removal easier while being careful not to make it too much longer ...but I had this problem BEFORE I did that as well, but will look into the length of it and see if it is sagging ...but again, I experienced this problem prior to lengthening the fuel line

[f6 white buffalo]

Sure does sound like fuel starvation.  Can't see how downshifting can cause your problem.  Am interested in what part needed replacing from downshifting.

What did you clean out of the tank?

the previous owner states he had to have the yoke on the driveshaft replaced . Im now not looking to downshifting as being a cause anymore. The problem is persisting without any downshifting happening...just a coincidence it happened twice right after a downshift ...have ruled out a clogged venting fuel cap , will inspect for vacuum , and fuel line kinks or leaks ...someone suggested I hit the rev limiter but I don't high rev the bike ....someone else also suggested upgrading fuel valve and replace the OEM petcock ...what say you ...any thoughts ...

[f6 white buffalo]

When you say bog you mean it quits or the engine idles down or what. If it quits at speed the engine will turn until you stop or pull in the clutch. Makes a difference to try and diagnose.
Checked for trash in air cleaner area? Enrichment valve in correct working order? Possible ignition, loss of spark: bad ground or power wire, or ign. component.
Mine would quit at slow speed, turned out to be battery ground to frame, and the starter would still crank over fine. I ran an extra wire from the battery negative to the frame and a lot of things worked better.  Firefighter

I will be cruising along sometimes after going under full power and smoothly for 30 miles , then all of a sudden the bike appears to start starving for fuel or air....it slowly loses more and more power until it s barely running and I am careful not to pull the clutch as that makes it shut off instantly into a dead stall... the ground wire scenario will be the first thing I check tomm as well as your other suggestions ..thank you ...

[f6 white buffalo]

Check the condition of the screen above the petcock.  No amount of rust flakes is acceptable.

Does she have an inline fuel filter or quick disconnect fuel line?  If so, either of those items could be suspect.

Lastly check the vacuum line to the petcock for leaks.

wouldn't that tank screen have to be completely choked off all the way up its length to disrupt flow enough to bog down and then stall ....would miniscule debris starve her enough to cause this ?

[sandy]

Mine had some of those symptoms and I replaced the whole petcock with a new OEM. That was in '07 or '08. No more issues. Next time it starts to stumble, go to reserve and see if it keeps running, After a mile, go back to "on" and see if it stays running. If so, replace petcock.

[Mr Whiskey]

One place I would look is the diaphragm in the petcock, if it has a pinhole it will not fully open, especially under acceleration or high speed when vacuum is low.  Simple to check, pull the vacuum line off the petcock, and use a mity vac or similar tool to pull a vacuum and see if it holds, if not the diaphragm has a hole in it.

Got a buck an a quarter says it wont hold vacuum,
My .02

[f6 white buffalo]

Mine had some of those symptoms and I replaced the whole petcock with a new OEM. That was in '07 or '08. No more issues. Next time it starts to stumble, go to reserve and see if it keeps running, After a mile, go back to "on" and see if it stays running. If so, replace petcock.

hi   want to understand the why of that maneuver  ...how does going to reserve bypass a faulty or clogged petcock ..doesn't the fuel pass thru the same place ...thx

[Jess Tolbirt]

start the bike and let it idle,, pull the vacuum line off of the petcock and and stick your tongue over the end of it,, does it have lots of vacuum? if not replace the line to the carb,,if it does rebuild the petcock..you have lots of vacuum at idle and very little under power if the petcock has a pinhole in it as soon as you gas it,,the pet rooster closes and no gas gets to the carbs,, i am guessing that the carbs are never filling up and running right at just about empty and when you gas it you are running out of gas,,and change the filter,,

[Bighead]

After doing carb work did you replace fuel hose? I'm asking because if it has a dip in the line it will cause this to happen. I know this first hand it happened to me when i was rebuilding my wife's bike. It would run all day at slow speeds but not on the interstate.
  Dennis

trout dude, I absolutely did rep[lace the fuel line off the petcock and it is a longer one than the original . I tried to lengthen it a bit to make tank removal easier while being careful not to make it too much longer ...but I had this problem BEFORE I did that as well, but will look into the length of it and see if it is sagging ...but again, I experienced this problem prior to lengthening the fuel line

Here is your answer and solution. Put the fuel line back to original length.

[Willow]

trout dude, I absolutely did rep[lace the fuel line off the petcock and it is a longer one than the original . ...

Oops!  What Bighead said is correct.

The carbs holds about two miles worth of fuel, give or take, in the bowls.  Depending upon you running demand for fuel, the actual symptom will drag a bit behind when the bubble in the fuel line actually cuts off fuel to the carbs.

Fix the fuel line.

[signart]

Exactly what I implied over a week ago on the tech board. We shall see.