Intermittant engine miss problem

[Guest]

Hi all
About 2 years ago I dug my 1982 GS650GLZ out of a 10 year storage and put it back on the road. I bought the bike back in 1987, and we've been through a lot together...

It's running quite well with one exception that I'd like to address. About 95% of the time the engine runs perfectly - the carbs have been rebuilt and are dead-on, it sounds smooth, etc. But every now and then it feels like one (or more!) cylinders is cutting out. After a few minutes it heals itself and goes back to running extremely well.

I haven't been able to isolate what conditions (if any) cause this problem to occur, but it has happened a few times after a 5-10 minute run at 65mph. It doesn't seem to happen while tooling around town, but I wouldn't rule anything out.

It can only be air, fuel, or spark. I have a shiny, new fuel filter, it's see through, and looks clean. The carbs were recently rebuilt, as the fuel tank got kind of rusty over the years and all the crud did a number on the carbs. But I'm thinking that it it were a problem with a deteriorated or clogged carb it wouldn't heal itself.

Shouldn't be air related- stock air filter, clean, and again the problem comes and goes. It shouldn't heal itself if it's an air problem.

That leaves spark. I changed the plugs and the problem still persists. Not sure what kind of ignition the GS has, or if it is prone to partial failures like this. I have a basic engine knowledge of bigger car engines, but know very little about the design of the GS engine. Something to check? Do these symptoms sound familiar? Is more information required?

I'd appreciate any help... thanks all!

[roeme]

Well first thing I wanted to point out is carb/air, but from what you describe, it doesn't seem to be the case here.

I'm not familiar with the 650GLZ ignition in detail, but I would begin the search at the spark plug caps/and or the coils. Measure resistance of each cap (if you have resistor-type caps, these should not test higher than 5kΩ), and then resistance of both primary and secondary winding of each coil (I can't recall the values for those from the top of my head, but they're noted in the service manual).

Do note that you shouldn't combine both resistor caps and spark plugs with an integrated resistor.

[Brendan W]

Is that filter cleared for gravity fuel feed. Many of the modern filters are supposed to go into pumped systems and will not flow enough for a gravity system.

[tom203]

"but it has happened a few times after a 5-10 minute run at 65mph. It doesn't seem to happen while tooling around town"

I would suspect one of your carb bowls is not refilling properly after these higher speed runs.- fuel levei drops and engine misfires. The ignitor on this model is very robust.

[hikermikem]

Those 650L's seem to have very little room to run the fuel line from the petcock to the fuel tee without it running uphill. Add on a fuel filter and there's even less room...

I would lose the fuel filter and make sure the fuel line is not kinked, or contains any loops or uphill runs... See if that eliminates your high speed cut outs.

[davebgs850l]

Have you cheaked the float levels my bike would cut out at hi rpms chased the problem for a long time even moded an older petcock to fit my bike then finally cheaked the float levels if it is a fuel flow issue the bike will die out when ran under high acceleration and won't start without being primed

[CharlesMcCall]

Is that filter cleared for gravity fuel feed. Many of the modern filters are supposed to go into pumped systems and will not flow enough for a gravity system.

Interesting - never thought of that. I think I just grabbed an off-the-shelf filter. I certainly don't know what the original application or flow rates are. I'll look into it - thanks!

[CharlesMcCall]

Makes sense - thanks for the hint

[Redman]

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That leaves spark. I changed the plugs and the problem still persists. Not sure what kind of ignition the GS has, or if it is prone to partial failures like this. .
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Yes... and that is the spark plug caps. As someone else has already said.
Over time and usage and heat, they can degrade and go to a higher resistence .. And can go higher and higher somewhat intermittently and cause various symptoms that seem hard to describe... untill fail open and stay that way.
You can take the cap off of the wire, just twist and pull, and check the cap with ohm meter. SHould be about 5k ohm (5000 ohm) each. Or can leave the caps on the wires/coil and check from cap 1 to cap 4 thru the coil, and check 2 to 3, should be about 20K (5 for the cap, 10 for coil, and 5 for the other cap).

They are 4 or 5 bucks each, and if they are 20-25-30 years old..........
THe two inside are one part number, the 2 outside are another part number. Are fairly generic, not Suzuki parts, can get at about any mo'cykle parts supplier. (I can get part numbers later.)
So, yah, a spark plug cap can cause a cyclinder to drop out intermittently, more so when it is hot.

I said this about the spark plug caps, because, it is probably different than your automotive expereince.
ANd is something to check into at some point.

But your statement about the problem happening mostly after running high speed for a time, does sound more like a fuel problem.

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[Redman]

Two of these for the inside

https://www.denniskirk.com/ngk/xb05f-spark-plug-cap-xb05f.p20305.prd/20305.sku

and two of these for the outside

https://www.denniskirk.com/ngk/yb05f-spark-plug-cap-yb05f.p20307.prd/20307.sku

I think, from memory, which is fairly suspect these days.

[CharlesMcCall]

Again, I appreciate the help. I'll check my receipts and see if the plug caps are vintage 1982 or not :-)

Even if it isn't the root cause today, if they are original it probably isn't a completely crazy idea to change them. While I wait for them to arrive I'll look at the fuel filter configuration to see if I see anything suspicious. Maybe even remove the filter and go for a run to see what happens.

[Redman]

Looking at my records here at home:
XB05F
&
VB05F (not YB05F, I dont know what/if any difference)

on the 850 I had and & the 1100G
and I would think same on 650 (but then again, the 650s is the one that has some things different than others).

I suppose as long as it is 5K ohm, and is for the right size plug, it will be okay. Weither it is long or short or what angle, is just for how it physicaly fits in the area and how the wire can be run. I have seen some bikes with all 4 were the long or all four were the short.


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