Odd running/fueling on 2000 GS500E. Bogging at low RPM, popping when cruising.

[Oscar_Muffin]

I'm in the UK and went out and bought myself a GS for a fairly good price (Knowing that it has this issue). So, it's a 2000 model (17 liter tank) with just under 30k on the clocks. Now, I'm not sure what any of the previous owners have done to the bike but I can tell you that it has a stainless exhaust on it that seems to be almost identical to the standard exhaust (Except made from stainless).

Here are the symptoms

Bike idles fine at around 1500 rpm
Strong smell of fuel from the exhaust
Occasional popping from the exhaust when riding at a consistent RPM (5-6k)
Quite literally no power below 4k RPM You have to really rev the bike and slip the clutch to get the bike moving, when it hits 4k rpm it takes off like a rocket though.
No fuel leaking from anywhere.

Normally these symptoms would tell me that an (or both) idle circuits/jets are blocked but the fact that the bike idles fine makes me doubt this.
Is it possible for a really bad jet change to cause this issue. (I haven't started looking into the bike yet) but can anyone provide the standard jet sizes? Far too much fuel would cause this sort of bogging and the strong exhaust smell correlates with that.

I'm going to check for vacuum leaks, adjust the mixture and balance the carbs tomorrow. If that doesn't help I'm gonna take a look inside of them.

[Bluesmudge]

Total guess here, but I'm thinking when they put the aftermarket exhaust on the previous owner re-jetted waaay too rich and/or set the mixture screw to be too rich. The main jet must be more-properly sized and once you are using only the main jet the bike runs ok.

Does the bike have the original airbox and paper filter? How do the spark plugs look?

You will have to open the carbs up and see what jets you have in there.

[Oscar_Muffin]

I'll take a look at that stuff for you later buddy. As I said, I picked it up yesterday and rode 200 miles home in the rain. I've got a few days set aside with this bad weather to sit in my garage and tinker. One thing I can say though is that... Am I supposed to be able to see the filter element with the seat off or should there be a lid on the airbox?

Oh and yea, the bike seems to run fine on the main jet (4k rpm upwards) but although the exhaust is quiet I can hear popping, not when I'm decelerating but random pops as I'm riding along.

[Oscar_Muffin]

Total guess here, but I'm thinking when they put the aftermarket exhaust on the previous owner re-jetted waaay too rich and/or set the mixture screw to be too rich. The main jet must be more-properly sized and once you are using only the main jet the bike runs ok.

Does the bike have the original airbox and paper filter? How do the spark plugs look?

You will have to open the carbs up and see what jets you have in there.

Well, I found the issue and it was a fairly simple one, makes me wonder how somebody messed it up. Upon removing the tank and doing a quick inspection of the top of the carbs. I was greeted by this horrible sight in the right carb....




How somebody managed to put force the needle into the wrong hole is beyond me, and then they were probably unable to get the spring in because of it. Obviously the slide was stuck open and the needle wasn't even in the fuel jet. Explains the strong fuel smell and exhaust popping. Luckily nothing was broken or bent and I was able to put it back together correctly and it runs fine now. It's odd because the rest of the bike seems to have been taken decent care of. Only problem now is the valves need adjusting (Tappets I assume) and I think the CCT is shagged. Apparently a 1st gen Hayabusa manual tensioner fits.

[mr72]

If you think the valves are tight then don't delay checking them. They are bucket under shim. No tappets. This isn't a pushrod car engine. It's easy btw to get that needle in the wrong spot.

[Oscar_Muffin]

I reckon the valves are loose and quite noisy, just confirmed operation of the automatic CCT. So the cam chain shouldn't be a problem unless it's at the wear limit which I doubt.

Tomorrows checklist is:

Confirm correct valve timing
Measure valve clearances
Balance carbs

The valves are possibly the one thing I don't like about this engine. Suzuki made a simple engine then decided to put dual cams and buckets in it. (I confused tappets with shims). I would have much preferred a single cam with adjustable rocket arms but hey, you can't have everything.

Balancing carbs because ever since I got it running correctly it's doing an odd thing on idle where the revs suddenly drop 500 rpm and there's a loud clunk. Sounds like the gearbox, haven't tested if it does it off clutch but that's the reason I'm checking the timing and clearances. I'm fairly sure it's not the cams skipping a tooth as it's done it enough times that the engine would have smashed itself to bits.

[mr72]

Noisy top end is a happy top end. You want more clearance, not less. Your running problem might be clogged pilot jets. You'd know immediately if the cam timing was off. Engine would either barely run or bend valves and then not run at all.

[Kookas]

Noisy top end is a happy top end. You want more clearance, not less.

Only to an extent though right? There's an upper limit to the valve clearance so still important presumably.

The valves are possibly the one thing I don't like about this engine. Suzuki made a simple engine then decided to put dual cams and buckets in it. (I confused tappets with shims). I would have much preferred a single cam with adjustable rocket arms but hey, you can't have everything.

I think those are all for performance reasons, to be fair. Especially in a bike like this where you want every last bit of what little power it has.

[Oscar_Muffin]

I know it's probably for performance but it's just a bit awkward on an engine where the valves go out of spec fairly quickly. People tend to neglect the valves because the cams gotta come out to do it.

[Oscar_Muffin]

As it turns out somebody didn't neglect the valves, at least the clearance. But they did neglect to properly time the exhaust camshaft. First picture is the intake cam, lined up as it should be. Second picture is the exhaust cam, it's set about 1 tooth late I think. So that knocking is the pistons making sweet love to my exhaust valves every so often.

[mr72]

I have never checked that myself on my GS, but off one tooth might be enough for the pistons to kiss the valves. If so, the valves may likely wind up bent. I'd do a compression check once you get the valve timing sorted, maybe even before you put the cam cover back on, in case you will wind up having to pull the head.

[Oscar_Muffin]

I've already sorted the timing, I think it may have been a couple of teeth off. But, I had a look into both cylinders with a bore scope and there is a slight mark on each piston where the valve has been hitting. It doesn't hit that hard because if it does it on idle, the engine drops about 500 rpm then recovers. It also doesn't do it until the engine is hot, and even then it only did it rarely. So the clearance was enough to miss when cold but just enough to kiss the piston when everything starts to expand.

Turning the engine over by hand and on the starter, there is plenty of resistance on compression and the buckets under the cams move freely. So, I picked the bike up cheap enough that it's not really worth taking the head off and doing a full inspection. Everything is free and the valves seem to seal. Missed a blown engine by a hair there I reckon.

Just need to order a new cam-cover gasket as whoever did the valves last stuck it back on with sealant.... so it came off in several pieces. Overall I've spent about £40 (49$) getting a half price bike back into good running condition.

[mr72]

compression check is cheap insurance. might help head off a wild goose chase later.

good work getting the valve timing sorted. now before you tinker too much with the carbs, see my blog post, which is oh so popular these days:

https://joshkarnes.blogspot.com/2017/09/fixing-common-gs500-carburetor-issues.html

[Oscar_Muffin]

Just had a quick scan through your post and most of it seems like fairly common stuff. I haven't had the carbs off yet but I've checked for vacuum leaks and obviously I've had the tops off and checked the diaphragms. What prompted me the check the valve timing was the extremely low vacuum readings (75mm/hg) when trying to balance them. Checked for any leaks using starter fluid and there didn't seem to be any. But, as I do with every bike I buy. I'm going to run some in-tank injector cleaner through it and if all seems good I'm just going to leave them. If it ain't broke, don't fix it

[Oscar_Muffin]

Guess I have a job to do while I'm waiting for spare parts. Some plonk (Presumably the same one that messed up the carbs and timing) has filled the hole where the tachometer drive shaft exits the head with the metal JBweld stuff in an "Attempt" to seal it. As you can guess it isn't sealed. I now have to remove all that gunk and manufacture a new seal. Anyone have a picture of the hole so I know how deep it should be?

[Oscar_Muffin]

As it turns out that part is supposed to be easily removable, but mine is basically glued in. I'm attempting to soak the JBweld in white vinegar to soften it up. If that doesn't work I'm going to remove the exhaust cam and knock it out from the inside. The sleeve probably wants replacing but I think the gear will be fine, however. What I currently have is an assembly where the sleeve is separate from the threaded part that attaches to the cable. However, I can only find the type where the sleeve is attached to outer part that bolts to the engine, Like this.



Would a one piece sleeve fit my bike or would I have to find a two piece one?

[mr72]

I wouldn't put vinegar on an aluminum part but it's your bike. Acetone might do a better job at getting JB weld to cut loose, but the king of all would be to use a heat gun to soften it.

I have no idea about what the correct fix for your problem is. Gonna be a long list, sounds like.

[Oscar_Muffin]

The JBweld wasn't budging. Since I had the head off I removed the exhaust cam.. yea, the one I just re-timed. And (carefully) bashed the thing out from the inside with a screwdriver and copper hammer (just in case I missed the screwdriver). I did test the hardness of the two to check that the sleeve wasn't going to damage the head as it mushroomed from the impacts, it didn't.



Whoever glued that in, I hate strongly dislike you.

I've also been informed that the one piece sleeve should fit as long as I also get the correct drive gear. https://www.cmsnl.com/products/gear-tachometer-driven_2643145002/#.XT9qwfJKiUk