GS650 idles but dies with throttle

[powderhound]

I'm starting to get back into working on my '83 GS650 that's been sitting for 3 years. Before I put it away, I put on freshly rebuilt carbs (I believe it was with stock jets), but never really ran it with the new carbs. After pulling it out from storage, I took the carbs apart, and did a full clean and set the idle mix screws at 2.25 turns. I had some issues with the carbs flooding initially while on prime, but a quick knock on the side with a wrench seems to have unstuck the floats, and they're sealing up well now. I adjusted the float level as best I could, 3 are right around 5mm (measured with a clear tube), but the fourth is more like 3mm. The bike starts up fairly easily, and once it's warm starts almost instantly, and idles at about 1100 rpm.

The problem I'm having now, is that as soon as I give the engine more than ~1/8 throttle, it completely loses power and dies. If it were running, just not that well with partially open throttle, then I wouldn't be as confused, but the engine just seems to completely give up when the throttles are open. I'm kind of stumped, but here's my plan of attack:

1. Valve adjustment. I haven't done this yet, and it's definitely over-due. I'm going to try to get this done over the weekend, if all goes well & I can find parts
2. Try to replace the original airbox, and see what difference it makes
3. Beat my head against a wall

The bike currently has:

• Stock exhaust (rusted on the bottom of the 2-3 cross pipe)
• Stock jets
• Custom single, large, cone air filter

The plugs are currently flaky black, but I'm not sure if that's from the original problem of the carbs overflowing or from it running rich now. I need to pick up additional plugs this weekend. What other information would be helpful?

My goal is to get her back on the road, but I want to do as little work as possible to get her running right before I put a ton of time and money into other areas.

Does it make sense that the engine would completely die with any throttle at all just from the airbox? That's my current suspicion, but I would love some help! I'll see if I can get a video recorded this afternoon.

Thank you!

 

[BigD_83]

You are out .75 turns too much on your idle A/F mix for stock jetting, but with that filter, you might need the extra juice. I suspect it is still too much.

I'd first go back to the stock setting of 1.5 turns, which admittedly is a little lean.

http://members.dslextreme.com/users/bikecliff/images/carbspec_float_height.html

Then hit the valve adjustment. Struggling to start cold is a bad sign.

Once you have that sorted, do a highest idle adjustment of the carbs, then a carb synch.


When you are totally frustrated, sell that black beauty to me , unless it is a GL, then kerrfunk might be interested.

 

[Steve]

Mostly good advice from BigD, but I would refine it a bit and change the order. :-k

If you have not adjusted the valves, do that first.

You have the stock airbox installed now? Yes, I saw that you have a different filter, but just verifying that the airbox is actually installed, not sitting on the bench, pending getting the bike running right. Without the airbox, and stock jetting, it WILL falter with throttle input.

The carbs have been "freshly rebuilt". By you or someone else? Drop the bowls, make sure the rubber plugs are installed over the pilot jets.

I have never had a bike run decently with the mixture screws at 1.5 turns. When installing a fresh set of carbs, I start with them at 3 full turns out, then adjust from there. Yes, 3 turns is a bit rich, but so is applying the "choke". It helps the bike start easier and run better until it warms up, then you can start leaning down the mixture to find where the idle speed starts dropping. Most of my bikes have ended up around 2.5 turns, but each bike is different. In fact, each CARB is different. On my son's 650, one of the mixture screws has to be out about 4 turns for that cylinder to fire correctly. Might have a too-small pilot jet in that carb, I have never investigated.

Once you have the mixture screws set for a preliminary setting, do the carb sync before the mixture tuning. If one of the carbs is closed a bit too far (out of sync), it won't matter how much you turn the mixture screw, you won't notice any change in engine speed. Do the sync first, make sure each carb is contributing to the total power output, THEN tweak the mixtures.

.

 

[powderhound]

Ah, must have missed that with all the guides being written for 750's and 850's. I'll lean it out a bit and see what happens. I definitely wouldn't say it's tough to start cold, just takes ~15 seconds with the choke on. Would a bad valve adjustment cause it to be that drastically different under 1/4 throttle vs idle? I was under the impression that the engine simply wouldn't run well with poorly adjusted valves, but that it would be fairly uniform across the throttle range.

 

[powderhound]

@Steve, the current filter is a completely custom job. I wouldn't be surprised if it flows even more than pods. I did try covering it and limiting the air flow to just a couple of small holes as a possible analog to the stock airbox, but you never know with that. I'll be running to the parts store tonight to see if I can find an air filter for the old stock airbox.

The carbs were originally rebuilt by terrylee, and he did a fantastic job. I then got overwhelmed with work, and let the bike sit for a couple of years, with gas in the bowls. I pulled the carbs and did a pretty thorough clean (no dip, but scrubbed with a toothbrush as much as possible). They still seemed to be in pretty good shape despite the gas sitting in them. The plugs are definitely installed over the pilot jets.

 

[BigD_83]

I definitely wouldn't say it's tough to start cold, just takes ~15 seconds with the choke on.

That would be my definition of hard(er) starting.

My 650 starts at the touch of the button when cold. It didn't before a valve adjustment and a thorough cleaning of the carbs. If they sat that long with gas in the carburetor, you're probably due for a full strip and dip.

With the stock airbox, my A/F mix screws vary from 2 to 2.75 turns out using the idle drop method.

Steve, thanks for reordering the steps...

 

[Steve]

~15 seconds to start??? I get worried when it takes more than 1.5 seconds. Usually it only takes setting the "choke", turning the key ON, then giving the starter button a stern look to get it running.

Valve adjustment is critical. The valves always get tighter, which makes it harder to start the bike.

Also, if it has been sitting that long with gas in the carbs, you are due for another cleaning. If the gas had Sta-Bil or some other additive, you might get by with blowing some carb cleaner through the passages to make sure they are clear, but no amount of scrubbing with a toothbrush is going to clean the passages that need to be cleaned. In fact, it doesn't even matter if the outside of the carb is clean or not. You can have the grungiest-looking carbs EVER. As long as the passages inside are clean, it will run beautifully.

Thanks for the clarification on the intake. I somehow got the impression that you had a single filter inside the stock airbox, which would not change jetting requirements much, if any. If you have a single "pod-style" filter, you might also need to change jetting, but that would not show up as the problem you are reporting right now.

I would start with a valve adjustment and a carb clean, that might 'fix' it enough to do some jetting checks to see what else needs to be changed.

.

 

[tom203]

"...You can have the grungiest-looking carbs EVER. As long as the passages inside are clean, it will run beautifully."

sounds like my carbs!

 

[roeme]

(...)I then got overwhelmed with work, and let the bike sit for a couple of years, with gas in the bowls. (...)

Dude, how could you knowingly?! It doesn't take much to drain the bowls, and methinks after some time it should've been obvious that the bike's gonna sit for a while...

But yeah, I know, Life is what happens while you're busy. I'm mainly complaining because I just cleaned carbs which have been sitting approx. 20 years with gas in them. Oh the horrors...

 

[powderhound]

Haha I know! I'm repeatedly kicking myself for letting it happen. But I guess that's how life is sometimes.

As a quick test while I wait for the proper air filter to arrive, I replaced the stock airbox and put some filter foam from a Briggs and Stratton in the box. It seemed to run quite a bit better like that, but still would die above about 1/4 throttle. I have hope that getting back to a stock air filter will help.

Carbs are clean, and I verified that all passages were clear and that nothing was clogged (followed this guide with the "special tool").

Next step: valve adjustments

 

[powderhound]

Also @Steve, my wording wasn't great. It generally starts in just a couple of seconds, and then I've held the choke for ~15 seconds to get her warmed up. Hasn't been hard to get her running.

 

[Steve]

Holding the "choke" for only 15 seconds is a LOT better than most. Some complain that they have to warm up their bike for about 5 minutes before they can even think of getting on. Cranking for a couple of seconds isn't bad, either. However, a proper valve adjustment and carb sync (in that order) will reduce that cranking time even more. :encouragement:

.

 

[powderhound]

Just finished running through and measuring valve clearances. Current numbers are:

[TABLE="class: grid, width: 800"]
[TR]
[TD][/TD]
[TD]Cylinder 1[/TD]
[TD]Cylinder 2[/TD]
[TD]Cylinder 3[/TD]
[TD]Cylinder 4[/TD]
[/TR]
[TR]
[TD]Exhaust Clearance[/TD]
[TD]<0.038mm[/TD]
[TD]<0.038mm[/TD]
[TD]0.038 - 0.051mm[/TD]
[TD]<0.038mm[/TD]
[/TR]
[TR]
[TD]Exhaust Shim[/TD]
[TD]2.60mm[/TD]
[TD]2.70mm[/TD]
[TD]2.65mm[/TD]
[TD]2.65mm[/TD]
[/TR]
[TR]
[TD]Intake Clearance[/TD]
[TD]<0.038mm[/TD]
[TD]0.038 - 0.051mm[/TD]
[TD]0.051 - 0.063mm[/TD]
[TD]<0.038mm[/TD]
[/TR]
[TR]
[TD]Intake Shim[/TD]
[TD]2.65mm[/TD]
[TD]2.65mm[/TD]
[TD]2.65mm[/TD]
[TD]2.70mm[/TD]
[/TR]
[/TABLE]

It looks like no one had done any adjustments to the bike since it was first bought. The valve cover gasket was in really rough shape, and cracked the moment the valve cover separated from the head. No time like the present to get new ones. Do the silicon gaskets from realgaskets.com fail to work with the GS650GL's tach sensor? Looks like they might lift the sensor a bit too much to engage properly.

 

[Steve]

First, it is apparent that you have INCH feelers, so do yourself a favor and use the INCH numbers. (It's also easier on the spreadsheet I just sent you.)

Next. You have no "X" shims at all? I usually see at least one, if they are, indeed, straight from the factory. You are apparently going to need some 2.60 shims and at least one 2.55. Since the 2.60 in EX1 is your thinnest shim, remove it, put a quarter in its place. Put the 2.60 in EX2, measure the clearance. If it's now too large, move one of your 2.65s there and call it good. Move your2.60 to IN4, do the same check. Now move it to your 2.65 positions to see if a 2.60 will work there or if you need to get some 2.55s. You might want to order a 2.50 for EX1, just in case a 2.55 isn't quite enough.

Finally. You are correct in suspecting the Real Gasket. Please do not order one for your bike. Look at Z1 Enterprises to see if they have a gasket. Not sure about your bike, but the ones for my 850s are about $12, instead of the $30 or so for OEM.

.

 

[Guest]

First, it is apparent that you have INCH feelers, so do yourself a favor and use the INCH numbers. (It's also easier on the spreadsheet I just sent you.)

Next. You have no "X" shims at all? I usually see at least one, if they are, indeed, straight from the factory. You are apparently going to need some 2.60 shims and at least one 2.55. Since the 2.60 in EX1 is your thinnest shim, remove it, put a quarter in its place. Put the 2.60 in EX2, measure the clearance. If it's now too large, move one of your 2.65s there and call it good. Move your2.60 to IN4, do the same check. Now move it to your 2.65 positions to see if a 2.60 will work there or if you need to get some 2.55s. You might want to order a 2.50 for EX1, just in case a 2.55 isn't quite enough.

Finally. You are correct in suspecting the Real Gasket. Please do not order one for your bike. Look at Z1 Enterprises to see if they have a gasket. Not sure about your bike, but the ones for my 850s are about $12, instead of the $30 or so for OEM.

.

Hi, I have a Real Gasket. For the valve cover. It is hard to get it in just the right spot because its squishy and slippery. The bolts have to be played with for tightness, too loose it leaks, too tight the gasket can slip out from between the head and the cover or be kind of deformed causing leaks. I feel I need to use it cuz its 30 bucks. I have made my own gasket, it shows you how somewhere on the site, that worked fine, but I would go with stock.

 

[Steve]

Hi, I have a Real Gasket. ... I feel I need to use it cuz its 30 bucks. ...

You feel that you have to use it because it set you back a bit? :-k

On your 1000, it's not so bad, but on powderhound's 650, it's a definite No-No. On the 650, the tach drive is in the valve cover, not the head, so the thick gasket prevents the driven gear from meshing properly with the drive gear.

.

 

[powderhound]

Alright, just got through doing the first round of the valve shim shuffle. Looks like I must have been simply mistaken when I was taking measurements before. After running through them, again, I had a 2.65x shim where I had thought it was a 2.70. It looks like I was able to get pretty close to within spec (not including shooting to be on the looser side of the range). As soon as I hit submit I'm going to be placing an order with Z1.

[TABLE="class: grid, width: 750"]
[TR]
[TD][/TD]
[TD]Cylinder 1[/TD]
[TD]Cylinder 2[/TD]
[TD]Cylinder 3[/TD]
[TD]Cylinder 4[/TD]
[/TR]
[TR]
[TD]Orig. exhaust shim[/TD]
[TD]2.65[/TD]
[TD]2.70[/TD]
[TD]2.65[/TD]
[TD]2.65[/TD]
[/TR]
[TR]
[TD]New exhaust shim[/TD]
[TD]2.60[/TD]
[TD]2.65x[/TD]
[TD](no change)[/TD]
[TD](no change)[/TD]
[/TR]
[TR]
[TD]Final clearance[/TD]
[TD].063mm[/TD]
[TD].063mm[/TD]
[TD].038mm[/TD]
[TD].038mm[/TD]
[/TR]
[TR]
[TD]Orig. intake shim[/TD]
[TD]2.60[/TD]
[TD]2.65[/TD]
[TD]2.65[/TD]
[TD]2.65x[/TD]
[/TR]
[TR]
[TD]New intake shim[/TD]
[TD]2.70 (temp)[/TD]
[TD](no change)[/TD]
[TD](no change)[/TD]
[TD]2.65[/TD]
[/TR]
[TR]
[TD]Final clearance[/TD]
[TD]<.038mm[/TD]
[TD].051mm[/TD]
[TD].038mm[/TD]
[TD].051mm[/TD]
[/TR]
[/TABLE]

As per your suggestion @Steve, I'll get both a 2.55 and a 2.50 to make sure I've got options for intake 1. I'll also pick up a few 2.60 shims just in case / for the next time since it looks like the valves will be getting out of spec sooner rather than later.

Also, I'm stubbornly going to stick with the metric system. Feels wrong to work on a Japanese bike using imperial units.

CD

 

[Steve]

Also, I'm stubbornly going to stick with the metric system. Feels wrong to work on a Japanese bike using imperial units.

CD

Well, then, why not get UNstubborn enough to get some real metric feelers? :-k

Those numbers you are posting are the metric APPROXIMATIONS on the INCH feelers you are using. :-\\\

No matter, the spreadsheet will handle both systems. :encouragement:

And don't forget to get your new torque wrench that shows newton-meters.

And your tire pressure meter that displays in kilopascals.

.

 

[powderhound]

Well played, sir!

 

[powderhound]

Alright, I just finished up my valve adjustment, and they should all be in spec. Intake #1 is slightly loose, but it's significantly better than it was before. However, I'm still having similar issues as before. When I give it ~1/8th throttle, it revs fine, I've taken it up to ~4k rpm and it's about as good as I can tell without it on the road. However, if I give it more throttle than that (e.g. ~1/2 throttle), then the engine falls flat on it's face and dies. I took a quick video to hopefully show what I mean:

I'm still running with a piece of foam for a Briggs and Stratton inside the stock airbox, since my air filter doesn't come in until Friday. I'm seeing a small amount of bluish smoke from the right side exhaust, and it does smell a bit rich.

Things I've done:

• Valve adjustment
• Cleaned carbs
• Adjust fuel mixture screw to ~2.25 turns
• Re-installed stock airbox (but with temporary foam filter)

Next steps:

• Install stock air filter (Friday)
• Vacuum sync carbs
• ???

Anyone have any suggestions for other next steps or things I can test?

Thank you all again for working through this with me!

Carson