Engine stalling on idle when stopping - why?

[Sparker]

Hi!

I have had this situation very many times: I am approaching a stop, I close throttle, pull in the clutch, apply brakes, engine dies by the time I'm stopped or before that. Even if engine is hot.
After that it takes some cranking with open throttle to restart the engine.

Even though (I think) I understand how carburetor works, I don't understand what's going on there when this happens, or why this happens. Like, why did it stall in first place, if it idles fine, and why does it take so much cranking to start it up, did bowl become empty or did engine get flooded? Could someone explain this please?

Oh also, I've just finished cleaning my carbs myself first time, bike runs but I am still not done tweaking the idle. And this happened with bike once already, but again the motor was pretty cold and idle wasn't set up well at that point - hope it gets cured after more tweaking.

[Bluesmudge]

I'm going to guess that the bike has between 12,000 and 22,000 miles on it and that the valve clearances have never been checked. The Suzuki maintenance interval is every 4,000 miles for valve clearance checks. Most GS500s will make it to 20,000 miles without a shim change before the clearance actually gets to zero and starts doing damage.

Most likely your valves are very tight. Usually exhaust valves. When this happens the bike starts up great when cold but will dies easily when the RPMs drop once the bike has warmed up a bit, like coming to a stop sign or stop light.

The other possibility is a carb issue, but its always best to set valves to spec before playing with the carbs anyways.

[Sparker]

Hi, thanks,
that's interesting because a mechanic checked valves this summer, and he replaced two shims there, I don't remember which though. But also it's been around 5-6k km since it was done.

I was thinking of replacing the cylinder head gasket soon, since it leaks a bit. So I might as well check clearance when replacing it.

Oh, btw bike is at 50k km now. Sorry I didn't mention it before.

[Bluesmudge]

The other possibility is that the bike is tuned too rich at idle. You should double check the valve clearences before messing with the carb too much.
Usually when the carb is rich then rpms will drop past the idle set point when you let off the throttle and then slowly climb back up to your idle speed. The opposite for lean, they will hang for a bit before settling down. If your idle is set a little low, or bike isn't fully warmed up, or the bike isn't running perfectly, then that drop of rpms will cause the bike to die before they can rise back to your set idle point.

You could try closing the mixture screws a bit, maybe 1 full turn, to lean out the idle mixture. Do you know how many turns out your mixture screws are set? From the factory they are hiding behind a brass plug that you have to drill out on the bottom of the carb.

[HPP8140]

what year is the bike and is it stock?

[Sparker]

So, I've just done first big ride since I cleaned the carburetors, 250 km. Indeed it still stalls whenever I pull in clutch after engine has been revving high, even when hot and has been running for a long time. At least it still works and starts up easier, so my carb cleaning attempt was not in vain. 

Bluesmudge, thanks for your advice, I have bought feeler gauges and I will check valve clearance ASAP.

Do you know how many turns out your mixture screws are set? From the factory they are hiding behind a brass plug that you have to drill out on the bottom of the carb.

I don't know, but that's how it looked on both carbs. Is it the idle mixture screw on the photo? I've read that they are blocked only on US models. My bike is not from US.

what year is the bike and is it stock?

Hi, it's 2001 model imported from Italy, everything is stock.

Also, guys, what do you think about this boot where carburetor mounts? I've tried to spray it with carb cleaner and propane while bike is idling, to see if it's leaking, and found no difference in bike RPM.

[Armandorf]

in the carb photo, yes , that is the mixture screw, the other welch bronze plug is a mistery to me.

i have the same symptoms, and a leaky gasket also.

i have two theories:

1 gasket leaks compression more when its hot so some cycles are lost, sometimes i can hear some erratic misfires when the engine is getting hotter, this can stall the bike at idle

2 valve cleareance

i will correct the valve clearance and report it, i hope to be able to do it next week.
i changed sparkplugs with no effects.

remember to soak the oil (with a rag, clothe, something that absorbs it) in the tappet to remove the shim easily, took me hours to figure it out, is the key for an easy removal of the shim.
Also, if the clearence is too tight a thinner shim could still give you less clearance than expected, best to measure the gap again with a thinner shim, if you are lucky you have from other valves to try

Also, guys, what do you think about this boot where carburetor mounts? I've tried to spray it with carb cleaner and propane while bike is idling, to see if it's leaking, and found no difference in bike RPM.

the oring behind the boot will lose the seal over time, best to rplace it, it gets really hot because its in contact with the valve head

intake boots(carb engine side to cylinder head) orings flatten out, change them. they cook, use Viton.
i used a impact tool to remove the bolts and it came out in 1 minute. or use your creativity.
used a wood screw to remove the cooked oring.pinch it and a few twists,then pulled , it came off easily
Changed the screw to allens

[HPP8140]

adjust carb idle screw and re-test
no point moving further into carbs unless you have verified exhaust valves are not tight

[Sparker]

You guys were right, both exhaust valves are so tight I can't rotate the buckets. One intake valve is <0.02mm too, but I can rotate that. Tomorrow I'll take the shims out and measure them.

Ugh, already made mistakes doing the job. I don't have the tool so I was using the ziptie-under-valve method. I removed one shim and removed the ziptie from under valve. Then I rotated the camshaft once over the bucket without shim  ... silly. Cam shaft lobe has slight marks at edges now. Fortunately the lobe edge didn't chip off. I spotted a few specks of metal on the bucket and cleared it out with a wipe. Then I realized, how do I press back the bucket if I don't have the tool ... double silly. I managed to push it back by using some 90-deg hex keys, and put back the shim.

[Bluesmudge]

I'll just take a quick bow for calling the valve clearance issue first. Good on you for already getting into that engine and checking the clearances.

Now...Buy the motion pro suzuki valve shim tool!!!! It's like $15. Its worth waiting a few days to have the right tool for the job in my opinion.

Since your clearance is too small to fit the .02 feeler in there, you will have to blindly order shims. Once you get yours out and measure it, I would order a few shims (you will probably use them all eventually if you keep the GS500 for awhile). So if you pull out a 2.70, I would buy a 2.65, a 2.60, and a 2.55 and maybe even a 250. Most likely you will end up using the 2.60 but its nice to not have to order shims twice and you will use them eventually.

[Armandorf]

If you are cheap or don't have availability of the tool you can use a  rear shock adjuster(for 125/150cc) as valve tool. you rest it on the edge of the bucket, you can rotate the engine if you hold it there while the cams rotate. Luckily I had one and fits almost perfect, I still would like to acquire the tool..
Beware you will leave little scuffs in the cam if the edges of the shock adjuster are sharp, maybe you can sand them or live with it. It is not on the lobes so it doesn't matter really.
Essentially you could use any metal piece that thickens and is somewhat stable/square where it seats so it doesn't fly off .
You can drag it to push the bucket by rotating the cams, this way the pushing piece is being"eat" while rolling on the cam.

Second way not recommended is to uninstall the cams, please don't because you have to use a torque wrench to re tighten it and taking off and putting the cams is dangerous and you can ruin the seat ,or lose the timing or scratch the cam machined section that rests and spins with the valve head.
There was a time that I did it that way out of frustration, and without a torque wrench.(I realized it when I was reassembling it afterwards...)
My valve clearance changed afterward so I changed the tension on the bolts.. bad.

For other users,
 How easy is to "burn" a valve if you use it with little clearance?
 (0.02 mm feeler gauge barely fits with great effort.)

I understand some of the physics involved behind:
Valve needs contact to the head seat to dissipate the heat absorbed by the flowing combustion, so I believe the only ones you can burn are the exhaust ones.
With a greater valve clearance the valve spends a little more time in metal to metal contact so it's colder.
With no clearance no contact, bad compression.
A greater clearance is also safer because you have more room for changes over time or expansion with a hotter engine.

[Sparker]

I have put new shims and it runs so much better. It started only after 30s of choke in +6c cold, typically I'd have to warm it up for a few minutes. I accelerate and pull in clutch, RPM doesn't dip below its normal value. So nice! Thanks again for the tips!

If you don't mind I have a few questions:

1 Left exhaust clearance now is somewhere between 0.1 and 0.15mm, I guess I can leave it like this? I have only 0.1 and 0.15mm shims in the set, so it's as precise as I can measure it now. I've read somewhere that it's fine for exhaust clearance to be above 0.08 specification. Even if it's 0.15 in worst case, I hope nothing bad will happen?

2 For right exhaust I had to put a 230 shim instead of previous 250 (good you've persuaded me to order more shim sizes  ), now clearance is 0.08-0.09mm - so it means the valve was not closing for ~0.1mm before?! I guess it is the problematic valve which was messing up engine work so much? I hope I haven't destroyed the valve, I've been riding like this for maybe 1000-2000 km.

3 Left exhaust bucket barely rotates, unlike others. I could rotate it a bit by pushing the notch hard with my whole palm via a screw driver. It neither goes up/down by hand as well. What do you think is going on there?

4 How bad do you think is the cam lobe now? This is how it looks after one rotation without shim in place. I can't really feel the roughness by finger, but then it's cold outside and my sensitivity is low. I assume in worst case it might wear the shim below and eventually get polished again?
If anyone ever finds this message via search, never rotate cam shaft without shim!

If you are cheap or don't have availability of the tool you can use a  rear shock adjuster(for 125/150cc) as valve tool

It feels that being cheap doesn't go well with owning that motorcycle Thanks for advice though, I might buy that one. By the way, I wrote to a local Suzuki dealership here just for fun, they offered the tool for 120 euro  ... and all other options were weeks away from me, so I reverted back to zip ties.

[Armandorf]

1 Left exhaust: measure it again.
I reccomend to aqcuire a metric set of gauges, that has many between 0.02 and 0.15, you can stack them to make up for the missing sizes

no problem going loose, you will shorten the interval only, and it will make more noise.
remember it being 0.03 to 0.08 on intake and 0.05 to 0.015.exhaust

2 Right exhaust
Logic says that you gained 0.20 in clearance with the thinner shim and now you have 0.08 gap , so (0.20-0.08) and you couldnt fit a thinner gauge than 0.12, yes it wasnt closing entirely.
However i would say that you have to take into account the oil between the bucket and the shim, so maybe it is a bit less, around real 0.10. i think that when you force the feeler gauge it can squish down a bit for the shim "floating" on oil in the tappet. Putting numers on this is impossible actually but for me there is a tiny gap.

Hope you didnt burned the valve, i think that if you didnt redline it or made large trips at sustained 6-7k + rpm for long periods and over a hot engine you could be fine.

3 Left exhaust again, no measure.
why do you think you have 0.1?   what feeler gauges fit and how free or forced?
Pleas remember 0,1 is 0.10,  not 0.01( only one one in both cases, easy to misread)

 If it  rotates freely at least when cold the valve should be closing. 
Or barely closing also if you are forcing too much to rotate the valve .
You have oil and the tappet rotates so i think that it will rotate with great effort even with the valve not seating in the valve head.

You dont have the correct shim size?
What do you mean by: "It neither goes up/down by hand as well."?

4 It could be worse, at least the nicks are dispersed in an oval shaped pattern and in the center where it pushes it is not so bad.
I wouldnt re use that shim on other valves. it could get scratched and you end up scratching others lobes with that shim. At least flip it upside down if you put it on other tappet in the future.

It feels that being cheap doesn't go well with owning that motorcycle Thanks for advice though, I might buy that one. By the way, I wrote to a local Suzuki dealership here just for fun, they offered the tool for 120 euro  ... and all other options were weeks away from me, so I reverted back to zip ties.

Same boat, i have to order through ebay and with shipping it ends up costing hundreds.
I hope to remember for my next valve adjustmente to take pictures of my "tool".
I ordered carb jets from ebay two months ago and havent received them yet, they have more time been sitting in a deposit in the customs than flying. Have not got the mail notice to pick them up yet.

[Sparker]

What do you mean by: "It neither goes up/down by hand as well."?

So let me explain, the shim bucket is normally seated so free that it rotates freely and, if there is enough gap, it can be moved up too. For instance it happened a few times that I was trying to remove shim with screw driver, but it didn't go and instead it just pulled whole bucket up.

But the left exhaust bucket is seated so tight that it takes a lot of effort to rotate it with or without shim, and also I wasn't able to pull it up with tweezers. It sits really tight.

I have also read that the bucket is supposed to freely rotate during normal operation, and it should result in circular (bowl-like circular) wear pattern of shim. That shim does not have circular pattern, it has a 270-degree grove on its shim top side (see photo) and a straight line (I assume from cam lobe). So yeah, looks like the thing didn't rotate much or at all.

About the size and clearance, previous shim was 2.74mm (marked 272, although caliper says it's 2.74), new one is 2.60mm, so math states I should have gained 0.14mm. Closest gauges I have are 0.1 and 0.15, 0.15 didn't fit, 0.1 fits, I don't remember how free though.

In fact I also have 2.65 shim lying around, and it would bring the clearance to specification, but decided to keep it a bit higher.

I recommend to acquire a metric set of gauges, that has many between 0.02 and 0.15, you can stack them to make up for the missing sizes

Oh that's a good idea to stack them up, now I am ashamed I didn't think of it. I have 0.02-0.09 gauges with 0.01mm step in my set, but starting with 0.1 it goes with higher interval.


So Armandorf, what about your measurements? You only measured one clearance at 0.02mm, and the rest were good?

[Armandorf]

" left exhaust bucket is seated so tight..."
maybe the valve was abused before, i dont know if it is really important to rotate or not.oil locking it with suction could affect the up and down movemente but it should rotate.

Anyway, the important thing is retaining compression.

After all your valve adjusting you should do a compression test, but you have a leaky gasket also.



Maybe when you change the gasket you can test compression(hoping you piston+rings are ok, or use a teaspoon of oil to take that of the question)  or even take the valve head for testing to a repair shop that hones cilinders and rectifies uneven headvalves planes, like a machinist with a lathe(not neccesary, but as an example) , to be inspected, dont know how expensive that could be where you are located.
they do an hidraulic test, applying pressure an measuring it doesnt lose pressure over time, the can also machine new seats, calibrate shims and machine a new plane if it is warped. when taking out a valve they measure it and check if it is bent.etc
i know that in alot of places this is expensive and difficult, very labor intensive and it is way easier to change the valve head for a good used one.

here both options end up being expensive so i prefer the shop.

my measurements are in a paper that has being lying around getting covered in grease and dirt for months now.
in the last post i was talking about your valves.

My valves:
i did an adjustment a few months ago and i was lucky enough to correct the gaps by switching in between the shims.
i had the two intakes with a 0.05 difference(0.06 and 0.11), and one exhaust that was really tight 0.02 had a thicker shim than the admission so i switched them. intake afterwards was over 0.05 and below 0.08. exhaust was around 0.08 with the "new"shim. the other valve is 0.03 or so. im not using the bike much at all , but its mandatory to correct it


Yes, to switch them, i had to rotate the motor and i was like, oh wait, if i rotate without shim this will be disastrous(thank god i paused for an instant), luckily i have a few shims that were from another dead valve head but they are crap,scratched and suspiciously worned of random sizes that arent useful, but at least they are good for a hand turn to interchange shims.

Ialso have "supplements" they are like a very thin washers that you put under the shim, not the best but it works out. i didnt used them,dont like them , but they are a resort to "recover" tickness of a shim...or make up for a size you dont have between two shims.
It is rare to happen because the seats tend up to wear and the valve gap closes, if the valve started to wear it would also make the shaft of the valve to protude more pushing the bucket up and closing the gap.
i really dont see a scenario where the valve gap would increase over time.

i stil need one thinner shim for the other exhaust that was very tight. Or take the shim to the machining shop to remove material ... i think that is what i will do, easier, cheaper and faster.
i would love to have various shim sizes and the correct tool.

but starting with 0.1 it goes with higher interval.

1mm= shim  number 100
2mm = shim number 200
2,72 mm= shim number  272

0.1mm= 0.10mm
0.05mm= the half of 0.1
0.5mm= 0,50mm, half a milimeter

if your set  starts with 0.1 it is useless , doesnt have enough small sizes, if you mean 0.01 its ok.

[Sparker]

After all your valve adjusting you should do a compression test, but you have a leaky gasket also.

Thanks, I will try to check compression somehow.

Oh I see, I wrote in prev. message "I was thinking of replacing the cylinder head gasket soon, since it leaks a bit", what I really meant is the head cover gasket, the one with four half-circles next to cam shaft ends. I don't think it can affect compression? The motor is not sealed anyway, it has those breather holes at the top of head cover.

[HPP8140]

3. I have purchased a couple GS500s where the previous owner neglected the valve adjustments. When this happens, the left exhaust valve suffers the most. For example, when I purchased my 2002 GS500 with 14k miles...I had to drop down three shim sizes to gain clearance (left exhaust bucket does not spin by hand on cold engine and that valve will lose clearance much faster than the others), so good idea to run the clearance loose over .1mm.

The good news is that you should still be able to get good life out of the engine. My bike now has 96k mi and that left exhaust has lost clearance much more than the others. I got brave and started ordering custom shims from precision shims in Australia shipped to the USA...I now have a 1.80 shim in the left exhaust, but I am scared to go any lower, but the goal was to reach 100k and I have the clearance to do so with that shim change at 90k.

[Bluesmudge]

HPP8140, if you want to keep that engine running forever you can have a local machine shop recut the valves/seats and set then set the clearance back to factory spec so you are back to using a ~2.70 shim. Have them do new valve seals and guides while they are at it. The top end of the GS500 is the longevity weakness, but if you do that plus new piston rings and top end gaskets it should be good for another 50,000 miles or more.

Sparkler, I had a GS500 top end where none of the buckets could easily rotate. I might have mixed up the buckets when I put them in after a top end rebuild since I don't remember labeling them that time. They really should go back in the same exact valve. I rode it 20,000 miles that way. It's a GS500 so if it happens to be running ok I would just ride it as is. Don't let perfect be the enemy of good.

Also to double up on what Armandorf said, you can stack feeler gauges to get the measurement between 0.1 and 0.15. Like .08 and .06 gets you a .14 feeler gauge. I've said it before that I would run .15 as the absolute max, but if I had the right shim I would prefer to be closer to .08. So if it was .14 I would drop a shim size and run .09. If it was .13 I would drop a shim size and run .08. If it was .12 I would leave it. Just personal opinion. When in doubt go with the factory spec. I have a theory that wider clearances accelerates wear at the valve/seat because the valve has more time to accelerate when closing. So in exchange for less frequent shim changes you w might be accelerating engine wear. When in doubt follow the Suzuki spec of .03 - .08 but only if you will actually check clearances every 4,000 miles. Wider specs are suggested on this forum because people don't like doing valve adjustments and it buys you more time between shim changes.

I'm sad to hear it costs so much to ship the motion pro Suzuki valve tool to where some of you live. The tool itself is relatively inexpensive and makes the job 100x easier. Imagine doing one of the 8 valve GS motors without the right tool.

[HPP8140]

HPP8140, if you want to keep that engine running forever you can have a local machine shop recut the valves/seats and set then set the clearance back to factory spec so you are back to using a ~2.70 shim. Have them do new valve seals and guides while they are at it. The top end of the GS500 is the longevity weakness, but if you do that plus new piston rings and top end gaskets it should be good for another 50,000 miles or more.

Thanks for the info. I do my own maintenance, but that looks like it will involve re-installing the head and I'm not sure the rest of the engine is worth it at this high mileage. I've had 4 GS500s at this point, I usually find another lower mileage bike, make one good bike and sell the other cheap to someone looking to learn, but it's been difficult to find another GS500 lately...also only looking for 2001-2002.

It's looking like I may need to move on from the GS500...manufacturers are bringing back sub 400-500 cc bikes, like Kawasaki, so maybe Suzuki may be tempted to bring back the GS500 to compete in the market segment . I have a two bike lineup, the GS500 could be found cheap, was such a reliable and versatile workhorse machine to put the miles on (easy to maintain learned valve adjustments) and saving my newer bike for occasional nice days...hope I can find another one.

[Bluesmudge]

I understand it doesn't make sense to most people to put $500+ into the engine of a cheap bike with that high mileage. But if you are like me, you have the GS500 set up just the way you like it, enjoy the bike, and $500 is less than the cost to move to a new bike and less total work than moving/re-doing all your personal bike mods on a new bike. Once you do the work, you basically have a new engine because the bottom end of the GS500 is known to be indestructible. The top end can be removed with the engine in the frame if you want, so it's just a few weekends of work if you outsource the machine and valve work.

Definitely not the solution for everyone, but there is something cool about keeping a high mileage bike running. My GS500 is not even to 60,000 miles yet. I have a personal goal of getting this bike to 120,000 miles some day in the far away future. Maybe by 2040.