Intermittent Misfire on All Cylinders

[oldfaithful]

I know it's been some time since I've posted, but the ole girl has been running well for several years now...until now.

 

I just returned from a long motorcycle road trip (5k mi) and knew she needed a sync, which I did. No biggy. The real problem is that she's developed an intermittent misfire at idle. It's not bad, the idle just sounds uneven, and with the timing light you can see the spark skip every couple seconds when idling...and all 4 cylinders have the miss. If it was just 1 cylinder, that might be easier to diagnose. With all 4 cylinders sporadically missing, I'm at a loss.

 

The bike has plenty of power, and runs like it should...except at idle. No backfires, no trouble starting, typical gas mileage.

 

Has anyone ever noticed an intermittent miss like this, and might anyone have any guess as to the cause? Thank you for any suggestions you might have!

[BlueSky]

Check for corrosion at the spark plug wire caps and the caps.

[luvmy40]

My '83 has an intermittent stumble at idle. I've got her dialed down a bit low, about 950rpm+/- and I don't know if it's one specific cylinder or not.

[cowpuc]

:sign yeah that:

 

I would also pull the plugs if it hasnt been done in a while and drop in a set of stock spec, nothing fancy NGK's and gap em at 32 thou so they got room to grow.. Being the smaller plugs, I have always found them to be more sensitive to blackening from a little over chocking which a good habit of getting it off choke at start-up may help prolong life of the plugs..

On another note,,, I just went this with Tweeksis,,,,, idle and just off idle running eratic = missing under a low R load... Any chance your volt meter may be acting slightly sluggish and not as responsive to throttle (jumping right up to 14 volts at 1500/2 grand?? That stammering and slight bucking and sluggishness at low R's cleared right up when I replaced the Regulator... At first I thought I was seeing/feeling a weak stator but, at least at the time,, it appears that it was all in the Regulator... Just something to check if nothing else!!!

Puc

[oldfaithful]

Check for corrosion at the spark plug wire caps and the caps.

 

Thanks for the suggestion. I pulled 1 and checked the plug as well as the boot and resistor. All was well there...?

[oldfaithful]

:sign yeah that:

 

I would also pull the plugs if it hasnt been done in a while and drop in a set of stock spec, nothing fancy NGK's and gap em at 32 thou so they got room to grow.. Being the smaller plugs, I have always found them to be more sensitive to blackening from a little over chocking which a good habit of getting it off choke at start-up may help prolong life of the plugs..

On another note,,, I just went this with Tweeksis,,,,, idle and just off idle running eratic = missing under a low R load... Any chance your volt meter may be acting slightly sluggish and not as responsive to throttle (jumping right up to 14 volts at 1500/2 grand?? That stammering and slight bucking and sluggishness at low R's cleared right up when I replaced the Regulator... At first I thought I was seeing/feeling a weak stator but, at least at the time,, it appears that it was all in the Regulator... Just something to check if nothing else!!!

Puc

 

That's a good idea. I replaced the R&R with an FJR unit a couple years ago. Could it be causing a misfire across all 4 cylinders?

[oldfaithful]

My '83 has an intermittent stumble at idle. I've got her dialed down a bit low, about 950rpm+/- and I don't know if it's one specific cylinder or not.

 

Have you ever put a timing light on it to see what it's doing?

[Marcarl]

If you haven't done so already, it's time to get the TCI out for a look-see and to clean the connections.

[cowpuc]

That's a good idea. I replaced the R&R with an FJR unit a couple years ago. Could it be causing a misfire across all 4 cylinders?

 

Not sure on how the FJR unit transfer Faithful... I suppose as long as its showing proper response to throttle input (touch the throttle and volt meter needle should pop right up there,,, no creepish movement stuff... Also,, turn on a blinker at idle and pull the front brake in to activate the brake light = watch the meter and rev it a little,,, that meter should bounce right to life with the crack of the throttle. My guess is that if its sluggish,,, your issue may be related to a failing Regulator or,,, possibly a weak stator... Any idea if your scoot has the updated oil splash/crank bolt with orvice?

[cowpuc]

If you haven't done so already, it's time to get the TCI out for a look-see and to clean the connections.

 

Especially if your tach is actin wacky IMHO...

[BlueSky]

Thanks for the suggestion. I pulled 1 and checked the plug as well as the boot and resistor. All was well there...?

 

Did you unscrew the plug cap and look at the end of the copper core spark plug wire? The copper core wire tends to corrode at the cap end and clipping off a half inch or more usually cleans it up. Happened to mine. The OE caps have about 9k ohms resistance.

[luvmy40]

oldfaithful,

No I haven't dug into it at all yet.

 

Cowpuc,

I just posted up in another thread that I saw a sluggish rise to 14V for the first time since I have had The Beast. It only happened once but it took about 30 sends to get from 12 to 14V from a stop at idle when I took off. Then it was all good again.

[oldfaithful]

If you haven't done so already, it's time to get the TCI out for a look-see and to clean the connections.

 

That I will have to do. Thanks

[oldfaithful]

As a point of reference, the tech operates normally. I've never seen it drop or jump.

 

The in-dash voltage meter sits in the middle at idle and quickly climbs to 14v when you give it throttle.

[oldfaithful]

Well today I pulled the kickstand switch and checked it.

0.7 & 0.7 ohms when closed

~30M & ~30M ohms when open

I cleaned the switch, sprayed with contact/switch cleaner and rechecked.

0.7 & 0.7 ohms when closed

~30M & infinite ohms when open

I don't think that's the source of the problem, besides there is the stand relay between the switch and the TCI. I doubt that there would be enough current drain at 30M ohms to cycle the relay. I could be wrong though.

Any thoughts on the stand switch???

 

So I also pulled the TCI unit. Removed the cover and it looked clean inside, but I haven't yet de-soldered the spade connectors from the board so that I can look at the component side. I'm going to wait to do that until I've exhausted every other option. I couldn't locate a replacement in the event that I damage something, so I've put it back for now.

 

Is anyone still buying the Ignitech units for these bikes. I found several old threads about group buys, but nothing recent. If I've got to get a replacement, that sounds like a good option to me. I sent Ignitech an email and we'll see what they say tomorrow.

 

Btw, every connector I've pulled has been clean and in good shape. Nonetheless, they've been brushed & cleaned.

 

Any other suggestions? Thanks!

[cowpuc]

Sure... Gather up 4 little clear glass baby food jars or something similar and drain each carb off into its own jar. Let them set for a few hours and then look closely for sediment/water/debris gathered in each jar.. Worth a peek IMHO..

[Patch]

 

The real problem is that she's developed an intermittent misfire at idle. Not likely just at idle

It's not bad, the idle just sounds uneven, So whit intermittent spark we also uneven vacuum pressures wait there a reason

and with the timing light you can see the spark skip every couple seconds when idling...and all 4 cylinders have the miss >

How is your timing light hooked to the HT lead? Directly to the plug or pickup clip

With all 4 cylinders sporadically missing, I'm at a loss. Are you using the timing light to check each cylinder say shing the light on a dark flat surface?

 

The bike has plenty of power, and runs like it should...except at idle. hmm

No backfires, and here's the reason why

 

So seems like we are looking for a common firing issue, such as pickup coil, let us know

 

Patch

[BlueSky]

When were the valves adjusted last time? Do a compression test. If the compression is low, adjust the valves.

[oldfaithful]

Sure... Gather up 4 little clear glass baby food jars or something similar and drain each carb off into its own jar. Let them set for a few hours and then look closely for sediment/water/debris gathered in each jar.. Worth a peek IMHO..

 

Good suggestion for most rough idle issues, but would that cause the spark to miss when watching with a timing light? on all 4 cylinders? I suppose anything's possible, thanks.

[oldfaithful]

 

The real problem is that she's developed an intermittent misfire at idle. Not likely just at idle

It's not bad, the idle just sounds uneven, So whit intermittent spark we also uneven vacuum pressures wait there a reason

and with the timing light you can see the spark skip every couple seconds when idling...and all 4 cylinders have the miss >

How is your timing light hooked to the HT lead? Directly to the plug or pickup clip

With all 4 cylinders sporadically missing, I'm at a loss. Are you using the timing light to check each cylinder say shing the light on a dark flat surface?

 

The bike has plenty of power, and runs like it should...except at idle. hmm

No backfires, and here's the reason why

 

So seems like we are looking for a common firing issue, such as pickup coil, let us know

 

Patch

 

Thanks Steve,

 

You're right, the miss may be throughout the rpm range but there is no hesitation or backfire...nor do I see a substantial change in the spark when increasing the rpm. But the flash is so fast I don't think I could distinguish a missed spark every couple seconds. Maybe my eyes are just old.

 

I used an induction timing light and moved the clamp from plug wire to plug wire, shining the light on various surfaces to make sure I'm not fooled by a reflection.

 

A common firing component was my first guess too. I haven't examined the pickup coil yet, but I just rechecked the manual & schematic and found there are 4 separate pickup coils with a common ground. I'll try to find the connectors and examine the ground. Thanks for making me research that common ground!!!

[oldfaithful]

Well today I pulled the kickstand switch and checked it.

Is anyone still buying the Ignitech units for these bikes. I found several old threads about group buys, but nothing recent. If I've got to get a replacement, that sounds like a good option to me. I sent Ignitech an email and we'll see what they say tomorrow.

 

So has anyone purchased the Ignitech units lately? I'm going to buy one today because I haven't found a replacement TCI.

 

dingy do you have an ignition program that is any better than the program that will be provided by Ignitech?

 

Thanks!

[Marcarl]

An easy test would be to look in the dark at the plug wires to see if there is any leakage, and if you don't see anything, spray the wires with some water. If there is a change with the water treatment it may be a good idea to replace the wires before you go much further.

[oldfaithful]

An easy test would be to look in the dark at the plug wires to see if there is any leakage, and if you don't see anything, spray the wires with some water. If there is a change with the water treatment it may be a good idea to replace the wires before you go much further.

 

Thanks, I'll give it a test.

[bongobobny]

So has anyone purchased the Ignitech units lately? I'm going to buy one today because I haven't found a replacement TCI.

 

dingy do you have an ignition program that is any better than the program that will be provided by Ignitech?

 

Thanks!

Dingy doesn't live here anymore. You could try the VMax forums and see if he is still active there...

 

Have you checked your timing coils yet? There is a connector about halfway up the rear of the frame that has been known to cause problems. Also, the coils have been known to cause issues, especially when they warm up.

 

When you had your TCI out did you bake it in the oven at 200 to 250 degrees to bake out any moisture?? Also, you need to relocate your TCI to the top of the airbox, there is enough play in the wiring harness to do this. This has two advantages, first it is drier up there, and second, in case of failure, it is right where you can get to it easily.

 

I seem to remember a while back somebody found a manufacturer that made replacement TCI boxes that even had the same shape...

[oldfaithful]

 

So seems like we are looking for a common firing issue, such as pickup coil, let us know

 

Patch

 

I found the connector to the pickup coils and it looked fine. It got cleaned & resistance checked anyway.

 

Pickup Coil resistance:

117 ohm

117 ohm

117 ohm

120 ohm

Pickup Coil Spec (from manual): 110 +/- 17 ohms

 

I'll keep looking...