Bike sputtered and eventually died while climbing a long steep grade

[popnlock]

So this weekend i took my bike for a long ride through the Adirondack mountains in NY. Getting to my destination there a a few long grades and my bike seemed like the fuel was cutting out as i was driving up the incline and i eventually pulled over for a bit let the bike cool down for about 10 min then started again and it was fine for a while but then started sputtering again while driving up a long grade. The same thing happened on my way home however when it was sputtering and i got to the top of the climb i pulled in the clutch to downshift for the down hill and the bike just died. I was able to coast to the side of the road and let the bike sit for only a few (less than 5 min) and it started right up and i was able to make it home no problem.

Long story short. After the bike warms up and i ride up long grades the bike sputters. Could this be a petcock issue or something else. I recently cleaned out the fuel petcock fyi.

Anyone with suggestions I'm all ears. Thanks.

[DoktoroKiu]

Did it seem to be running hot?  I wouldn't think a grade would be any trouble for a bike, though.

Where was your fuel level when this was happening?  If it was anywhere less than half I'd suggest trying to run with a full tank to replicate the issue (or switch to reserve when it happens and see if that helps).  I don't know why pulling over would help a fuel supply issue like this, though.

[ace50]

What RPM's were you running when going up the inclines? Above 4K or lower?
Next question is do you know your valve clearances? Temperature differences, running, then setting to cool, could effect valves clearances, if they are tight and you loose lower RPM power. Affects compression somewhat. Higher RPM it would seem to run OK.
Just a thought as mine did this with tight clearances. No power below 4K.

[HPP8140]

elevation? thin air?

All my gs500s did this in the mountains.

[popnlock]

Tight valve clearances were my second guess. I am unsure of what they are i bought the bike last year and i have not checked them. Probably due for that maintenance. My fuel level was well above half and yes i did try to switch to reserve but that didn't make any difference. My RPMs were above 4k probably around 5k-6k i was traveling about 60mph.

[ace50]

I'd check your valves seeing as you don't know were they are. Then go from there.

[The Buddha]

Valve clearances being tight will act up right at start up. I dont know how many times to post this.
A valve that is a shade tightish, will result in a bike that start up great, 5 seconds after it starts up it will want to stall unless you rev it to 5k. Then after, 3-4 mins of that and it will hold idle and run like the dickens till you have to shut it off and ti gets cold again.

Valves that are even more tight will never get to that second stage - the after 3-4 mins stage. Or when its even worse, will not run in that cylinder at all.

Valves that are loose - make a lot of noise.

Only those 2 options.

So no sense thinking why on your way to grandma's house, after 36.31 miles of driving and filling up @ the GASS CORRNER exactly 2.315 gal last week and riding through 12 seconds of fog tuesday the 13th why your bike sputtered.
If it did that, its not the valves.

You may have cavitation issues in the gas, you may have air filter that is clogged slightly but works ok in dense air but doesn't in thinner air ...

Likely carburetion, specifically the air intake section of it.

In high and dry areas - the high desert specifically, they sell 85 octane. And wonder of wonders, the cars and surprisingly bikes too, run just fine in that environment.

So my first suggestion - clean everything - especially where there is metered air flow. Then clean the gas flow section (or say screw it and clean it all when you have it apart) starting with the air filter. Oh heck clean the fuel cap too, clogged vent can do this. And dont slap tank bag on it.

Then before you get back to that location, make sure you have a fill tank of gas.

If it sputters - then get a plug reading (you may be too rich of all things especially if you run fine @ sea level)

Cool.
Srinath.

[gsJack]

I spent hours on end screaming thru the Adirondack and Smoky mountains at 7-9k rpm on my 97 and 02 GSs back 10-15 years ago.  The only time I've opened up a GS was in the Adirondacks on my 97 back in 2002 when it hit 110mph on a bit of level straight road in the mountains NW of Lake George.  The GSs are happy at high rpm's but don't like to be lugged at low rpm's.  There were a couple of upgrades on I-77 on the way to the Smoky Mtns  that required a downshift at Interstate speeds to keep the GS happy.  I've never run at less than 4k rpm on the 97 or less than 3k rpm on the 02 even just putting around locally.  Are you keeping your revs up in the mtns?

If you have cold compression and can't hear the tappets when it's hot the valves are not your problem.  A tight valve will cause it to run rough at start up but it will smooth out and run smoothly in a minute or two as the engine warms and the valve clearances increase unless it's an extremely tight valve.  If you are keeping your revs up look for a fuel problem although I've had a plug with 7-8k miles on it misfire at high rpm's.  I've changed them at 6k mile intervals since, plugs are cheap.  I've never had a fuel or carb problem in all my 180k GS miles because I don't mess with my carbs.

[DoktoroKiu]

Even with my very tight valves the bike never died while I was giving her gas.  It would die when I was coming to a stop with the clutch pulled (RPMs would dip too low), and it always idled very unpredictably.  It took VERY long to warm up to where I could idle without choke.  If your bike starts up and runs (without choke) after about 20-30 seconds of warming up with the choke then your valves are probably OK.  But depending on the year and the mileage it could be time for a clearance check.  Mine had almost 10k miles on it with no valve clearance maintenance and all four of my valves were too tight to measure.

[bombsquad83]

Oh heck clean the fuel cap too, clogged vent can do this. And dont slap tank bag on it.

This was going to be my first suggestion.  -> http://gstwins.com/gsboard/index.php?topic=41061.msg461586#msg461586

If that doesn't work, try running on prime instead of main or reserve.  Prime eliminates the need for vacuum to allow fuel flow, and runs off the reserve line.  If running on prime cures the problem, then it's a bad petcock.

[popnlock]

I cleaned out the fuel cap the end of last year, the bike is due to have the valve clearances checked so i will do that first then go from there. The problem is most of my riding occurs around town with sub 40 mile rides typically so the issue never arises on a day to day basis but i may be taking another long trip to the Adirondacks in a few weeks and i will follow up after that.

[popnlock]

So i am finally getting around to fixing my bike after not riding for a long time due to a flat tire and lack of funds to properly replace it but now i have the new tire and am ready to roll and fix my initial problem. So i opened up the top of the engine to check the valve clearances and it looks like both of my intake valves have clearances that are larger than what they should be.

The left intake i can fit a .1mm feeler gauge and the right intake i can fit a .12mm feeler gauge. The exhausts are very tight with a .1mm gauge so i am assuming those are ok. I have not taken the shims out yet because i don't have the valve shim tool.

I spoke with a local shop and the guy there said that although it is uncommon to have the clearance be larger that what it should be it is not unheard of and that this could be causing backfire with deceleration which is another issue i have had with my bike.

Questions for the forum:
1) Dose anyone think this could also have been the cause to my sputtering issue?
2) Is there another way to remove the valve shims without the valve shim tool?

[The Buddha]

My valves on my 89 between 30-48K always was needing thicker and thicker shims.
Not that uncommon. Also shims wear a wee bit as well, they sure as heck cant get thicker.

Dont worry about the clearances unless the yare like 3-4X the upper end of the spec or are under the lower end. And dont bother swapping in those crappy Chinese shims, they break.

Cool.
Buddha.

[bombsquad83]

I don't think the problem is your valve clearances.  Did you ever try running on prime to see if that solves the issue.  I think you have a fuel flow issue that shows up at higher speed and distance.  It's pretty common on this bike.  You might need to repair/replace your petcock or replace the vacuum line.  We will know if going to prime fixes the problem.

[popnlock]

So i guess i will leave my shims as is, easy for me and backed up by the forum  . As far as the petcock and running on prime i will try to go for a longer ride this weekend and check to see. I will report back results after this weekend, thanks.

[popnlock]

If it turns out to be a petcock issue what is the best replacement for one and where to get it?

[bombsquad83]

By the way on the valve check, make sure you measuring in mm and not inches.  If the 0.1 mm feeler didn't fit on the exhausts, you should be checking which feeler below that size will fit (if any).  The factory spec clearance is 0.03 mm - 0.08 mm, but many here run up to 0.13 mm on the exhaust valves to allow the valve to cool and therefore wear better.  Tight valves will cause worse issues (burnt valves or worse) than just slightly loose valves.  Very loose (maybe 0.15mm and above?) I would be a little scared at that point of throwing the shim at high rpm.

You can buy a new OEM petcock from any online dealer for around $50, or you can get a 07 Honda CRF250X for about $30 (also can be found from an online dealer) and retrofit it to remove the need for vacuum.  Just do a search on CRF250X petcock and you will find all you need for that.  Before you get a new petcock, I would think about replacing the vacuum line.  Another member was having issues with his petcock, and it was solved with a new vacuum line.

[ned from PA]

Hasn't this topic been covered in previous threads?  When going up a long, steady grade, your engine vacuum drops (since throttle is open) while fuel consumption is high.  Sometimes the vacuum is insufficient to keep the fuel petcock diaphragm from fully opening the petcock, so bike sputters.  This condition can happen even when the fuel tank is relatively full.  At the top of the hill, you usually close the throttle, causing the vacuum to increase and let more gas back into the carburetors (or else switch to "prime" on-the-fly to clear the fault).

Leaving fuel petcock on prime all the time is not a good idea, though, because a leaky float valve can cause fuel to overflow from the carburetors when bike is parked.