Ignition System Cutting Out Between Idle and 3000RPM.Trike Teaser Pic Added.

Suzuki GS

My bike keeps missing and stumbling from idle to 3000rpm.I checked my electrical system (both hot and cold) and everything checks out with the spec's I have in my service manual.I did change the coils and got a little improvement but barely noticeable.What would you suspect next,crank triggers/pick ups or CDI unit?My ignition system is all stock.Oh yeah,I checked and cleaned all my electrical connections.

Re: Ignition System Randomly Cutting Out Between Idle and 3000RPM.

What sort of GS Ben? If it's an 80 - 82 450 then the ignitor is susceptible to dying...


I've got a Dynatek on mine at the moment and even though it's not officially supported as a replacement it works...

Re: Ignition System Randomly Cutting Out Between Idle and 3000RPM.

Ben has a GS500. Or five.......i can't keep track.

I'm at a little bit of a loss on this Ben. Could it be a weak connection around the spark plug boot or something?

Re: Ignition System Randomly Cutting Out Between Idle and 3000RPM.

Big Rich said:

Ben has a GS500. Or five.......i can't keep track.

I'm at a little bit of a loss on this Ben. Could it be a weak connection around the spark plug boot or something?

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AAaah yes I remember now.... d'oh! There goes that idea...


Good call Rich, my plug caps were toast which gave crappy spark in addition to my buggered ignitor...

Re: Ignition System Randomly Cutting Out Between Idle and 3000RPM.

Crazy idea but do you have a timing light (car type strobe light)? Clamp it around a plug lead and rev the bike up and down and see if the strobe misses beats or if it's steady when the motor coughs.

What I'm trying to come up with is a cheap way to prove that it's electrical.

If it does miss beats, then the next question is it a partial break in a wire or a short between a wire and the chassis somewhere - or maybe it's a broken plate in the battery. Try a different battery and see if it makes a difference.

Re: Ignition System Randomly Cutting Out Between Idle and 3000RPM.

Yep,GS500.I got four total but if I find the right deal,I'll have more.

teazer said:

Crazy idea but do you have a timing light (car type strobe light)? Clamp it around a plug lead and rev the bike up and down and see if the strobe misses beats or if it's steady when the motor coughs.

What I'm trying to come up with is a cheap way to prove that it's electrical.

If it does miss beats, then the next question is it a partial break in a wire or a short between a wire and the chassis somewhere - or maybe it's a broken plate in the battery. Try a different battery and see if it makes a difference.

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I don't have a timing light any more.I did change the coils and it got better but not completely.It doesn't do it when free rev'ing.It only does it under load.Hot or cold engine temps doesn't seem to make much of a difference.I added my 5 degree ignition advancer and the miss went down in the rpm range.Now it misses between idle and 2000 rpm.I checked the plate that the ignition pick ups are on.There's no loose connection and the GS has no adjustment in there.However,I did notice that one pick up is almost touching the rotor and the other has about a 1.5mm gap.I don't know how this could be unless the case cover was cast or machined slightly off center.Could the air gap be wrong and causing my issue.It seems to be random and on both cylinders.

On the battery comment.I have a new (well three months old now) Scorpion AGM battery.I really don't thing it's the problem.The plates don't float in an acid bath.Excuse me,electrolyte solution.LOL! I was told recently that I need to be more PC. ROFLMAO!

Here's what I did do.
Changed the coils to a set that was known to be in good running condition.
Replaced the spark plugs with a new set gapped to .028.Service manual says .028-.031.
Checked and cleaned all connections.Not just the connections at the coils.

What should the minimum voltage at the coils be with the ignition on and engine off?I read 11.7v for a waste spark system.Is this correct?I feel more comfy if mine was above 12v.I haven't check this yet,because my manual doesn't give any specs.The coil and pick ups check fine with a multi meter.Maybe I should check them again since the weather has cooled off.My manual says that the readings for the pick ups should be taken at a temp around 68 degrees.I took the readings with an air temp of around 88 degrees.I'm sure the bike was cooler setting inside my building out of the sun,but still not close to 68 degrees.


Just had to (brag) add this.I know it's not gonna cure my ignition problem.My bike does feel like it's geared a little to high so I ordered a JTS steel 15t output shaft sprocket.That's down from a stock 16t.Scooped that baby up for $14.95 shipped.Cheapest I have ever found it online.New seller to me,on Amazon, so I'll wait until my sprocket arrives before making any recommendations.

Re: Ignition System Randomly Cutting Out Between Idle and 3000RPM.

GS500 has the same sort of ignition as a 450 with electronic advance and the rotor is a large diameter rod with a disk on the end with a single protrusion to trigger the pickups. Yes? The air gap on those and the earlier ones should be similar on both sides. Try loosening the pickup plate and move it slightly to even the gap up.

The advancer was presumably the same part but with the tab cut in a slightly different place. I like to see 12v at the coils with it not running and 12.5 with the engine running. If you have much less than that, you could fit a relay into the system to reduce voltage drop.

That doesn't explain why the misfire is so rev specific though. What do the plugs look like when it does that? wet and sooty? It almost sounds like a carb problem rather than ignition, but let's eliminate the obvious things first.

Re: Ignition System Randomly Cutting Out Between Idle and 3000RPM.

teazer said:

GS500 has the same sort of ignition as a 450 with electronic advance and the rotor is a large diameter rod with a disk on the end with a single protrusion to trigger the pickups. Yes? The air gap on those and the earlier ones should be similar on both sides. Try loosening the pickup plate and move it slightly to even the gap up.

The advancer was presumably the same part but with the tab cut in a slightly different place. I like to see 12v at the coils with it not running and 12.5 with the engine running. If you have much less than that, you could fit a relay into the system to reduce voltage drop.

That doesn't explain why the misfire is so rev specific though. What do the plugs look like when it does that? wet and sooty? It almost sounds like a carb problem rather than ignition, but let's eliminate the obvious things first.

Click to expand...

I was just about to say it sounds more like carb than ignition after reading those symptoms...

Re: Ignition System Randomly Cutting Out Between Idle and 3000RPM.

teazer said:

GS500 has the same sort of ignition as a 450 with electronic advance and the rotor is a large diameter rod with a disk on the end with a single protrusion to trigger the pickups. Yes? The air gap on those and the earlier ones should be similar on both sides. Try loosening the pickup plate and move it slightly to even the gap up.

The advancer was presumably the same part but with the tab cut in a slightly different place. I like to see 12v at the coils with it not running and 12.5 with the engine running. If you have much less than that, you could fit a relay into the system to reduce voltage drop.

That doesn't explain why the misfire is so rev specific though. What do the plugs look like when it does that? wet and sooty? It almost sounds like a carb problem rather than ignition, but let's eliminate the obvious things first.

Click to expand...

Dual pick ups and a rotor as you described.Please ignore the red writing.I used this pic of my wrecked bike.Surprisingly it ran when I got it.Not sure if it does now, after it has set for 4 years under my car port.plugs are a dark tanish color when I checked them.I do need to pull them since I put the ignition advancer back on.The pick up plate has zero wiggle room and the pick ups have zero wiggle room on the backing plate.


I just went through my carbs three times a little over a month ago to clear out some bad fuel.Cleaned and rejetted to the proper jetting.Sync'd and/or balanced,which ever term you prefer.It was a little on the lean side and had a slow return to idle.Idle is now spot on with no dip on a blip of the throttle, and smoothly returns back to idle.Float levels are spot on.I really don't think it's a carb issue but maybe.


Random thought that just came to me during my computer stooper. I adjusted my valves about 1700 miles ago.They were in the middle of the specs.Could running the bike a little lean for a few hundred miles have caused the valves to sink into the head and cause the valve clearances to tighten up?Could that be my issue,tight valves?

Re: Ignition System Randomly Cutting Out Between Idle and 3000RPM.

Definitely do a plug chop at whatever throttle opening causes the issue, that will tell you what the fueling's doing at that point...

Re: Ignition System Randomly Cutting Out Between Idle and 3000RPM.

peteGS said:

Definitely do a plug chop at whatever throttle opening causes the issue, that will tell you what the fueling's doing at that point...

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Def will do when I take'er round de block this week.

Re: Ignition System Randomly Cutting Out Between Idle and 3000RPM.

Took'er round the block this morn after a wash down.The miss wasn't there.Ran perfect.Then,sitting in traffic this afternoon,it started missing again.When I went to pick up my son,I got a little pffft (back fire) through the right carb.Now the miss is worse again but it's still random between cylinders.Not just one cylinder.I didn't get a chance to do a plug chop.I got started late. :-[

Re: Ignition System Randomly Cutting Out Between Idle and 3000RPM.

Ok.The miss is back and it's just as random as ever.Plug chop was a little dark but not rich.I did go through,clean up the wiring connections,and refreshed the dielectric grease.I did see an improvement in performance but the miss didn't go way.Now I am thinking that it is in the coils.Maybe I need to check them after the bike and coils are hot.Maybe it's the spark plug wires themselves breaking down under load.I'm closing in on my 3000 mile valve clearance check so that will be ruled out.I think I'll work on it this weekend, if nothing happens.Lately everything has happened.

Re: Ignition System Randomly Cutting Out Between Idle and 3000RPM.

This has me stumped as ever Ben. But the coils would normally break up at higher rpm's and shut down when hot. You said it fired out the carbs and the plug were not rich? Might be just the mixture screw, slide cut away, bottom edge of the needle jet, etc.

Re: Ignition System Randomly Cutting Out Between Idle and 3000RPM.

Big Rich said:

This has me stumped as ever Ben. But the coils would normally break up at higher rpm's and shut down when hot. You said it fired out the carbs and the plug were not rich? Might be just the mixture screw, slide cut away, bottom edge of the needle jet, etc.

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All that stuff was replaced.It could be the mix screws need to come out a little.In southern country terms,it's like the bike has a random stutter and cutting out from idle(1250rpm) to 2500ish rpm.It only happens when the bike is under load like pulling a hill or starting from a stop.I'll be ripping into it tomorrow.I'll check the float levels and the mix screws.I have a hard time believing this is a carb issue.I went through them three times recently and everything keeps come up spot on.I've replaced everything that can be replaced in the carbs.Grrrrrr!I will be glad when the new edition of microsquirt comes out.It's the only thing keeping me from going FI,and I can eliminate these shitty GS carbs.I have never met a GS500 that didn't have carb issues at some point in it's life.


On the list for tomorrow is....
recheck carbs-this includes a balance/sync
recheck coils-hot and cold resistance check
check valve clearances

Re: Ignition System Randomly Cutting Out Between Idle and 3000RPM.

Make no mistake, I'm just guessing here.......

Have you advanced your ignition points yet? I know it's a common mod on the 500. Maybe try a grade of gas higher.

Re: Ignition System Randomly Cutting Out Between Idle and 3000RPM.

Big Rich said:

Make no mistake, I'm just guessing here.......

Have you advanced your ignition points yet? I know it's a common mod on the 500. Maybe try a grade of gas higher.

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No points.It's all electronic,but yes.I have a five degree advanced ignition rotor.It did nothing but move the issue down in the rpm range.I have tried every grade of fuel at every station around me.So far mid or premium grade from BP Amoco runs the best.I even tried draining the carb bowls to check for water and dirt.Everything was clean.

Re: Ignition System Randomly Cutting Out Between Idle and 3000RPM.

Sorry- thats what I meant.

Everything I can think of points to carbs/fuel. Unless maybe the charging system isn't providing proper spark at lower rpm's? I dunno Ben, I'm stumped.

Re: Ignition System Randomly Cutting Out Between Idle and 3000RPM.

What about spark plug caps? Are they in good order? I know my bike's somewhat older (15 to 20 years older is my guess ) but the spark plug caps were knackered and the right one was just about falling off. Generic NGK caps are cheap as chips if that's your issue...

Re: Ignition System Randomly Cutting Out Between Idle and 3000RPM.

peteGS said:

What about spark plug caps? Are they in good order? I know my bike's somewhat older (15 to 20 years older is my guess ) but the spark plug caps were knackered and the right one was just about falling off. Generic NGK caps are cheap as chips if that's your issue...

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The caps are in great condition and the coils check out when tested with a meter.I don't think they're the problem.

Big Rich said:

Sorry- thats what I meant.

Everything I can think of points to carbs/fuel. Unless maybe the charging system isn't providing proper spark at lower rpm's? I dunno Ben, I'm stumped.

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That's cool.


I'll give the charging system a good check but I don't think there's an issue.I've been riding and haven't had any issues with lighting or starting.