I am stumped

[dbeardslee]

I'll check it but what I have is a clear miss that is felt at the muffler, seen on the tach and on the timing light.

Here's the thing - if it was electrical you'd expect 2 and 3 to be in the same condition. It looks like #2 might not be firing at all, but number 3 looks like it is firing. The only electrical thing I can think of that would only affect one plug is if you had a bad plug wire or cap - but I assume when you changed the coils you changed them wires and all.

Or you're not getting enough gas to #2. That could be because the carb needs attention, or because the valves aren't allowing enough draw to suck it out of the carb.

Seems like you mentioned doing a compression test that showed okay across the board, so that kind of leaves the carbs.

A colortune plug comes in handy for this kind of stuff. You can see pretty quick if you've got spark and no gas, or just a real lean condition. Do you have one?

[79XS11F]

It's in place. I checked it while I was confirming the timing earlier. This is the problem I am having. I have checked EVERYTHING that is typically at fault for this issue with no luck :-( the only thing that changed between when it was running like a top and this issue coming to light was storage with fuel in the carbs and changing out the cam tensioner for the auto type. the carbs have been triple cleaned and Mack did not find any issue with them ether. Valve timing is just a tiny bit off due to chain stretch but I even have a new cam chain here to install cause I figure the auto tensioner is best applied to a new chain.
Rob

[dbeardslee]

It's in place. I checked it while I was confirming the timing earlier. This is the problem I am having. I have checked EVERYTHING that is typically at fault for this issue with no luck :-( the only thing that changed between when it was running like a top and this issue coming to light was storage with fuel in the carbs and changing out the cam tensioner for the auto type. the carbs have been triple cleaned and Mack did not find any issue with them ether. Valve timing is just a tiny bit off due to chain stretch but I even have a new cam chain here to install cause I figure the auto tensioner is best applied to a new chain.
Rob

I don't think a tensioner would cause the problem unless the bike had already jumped a tooth. Which keeps pointing to the carbs. I used five cans of carb cleaner on Betsy, and a compressor that pumps up to 150 psi, but the only way I was able to get the pilot circuit clear on one carb was by using a wired pipe cleaner through the air jet hole. But again, you can check it by removing the air jet and the pilot jet and spraying carb cleaner via the red straw inserted an inch or two into the air jet hole. You should get a strong stream out of the pilot tower, and you should see carb cleaner kind of oozing out of those three holes under the butterfly.

Never hurts to double check to make sure the orifice in the bowl is clear while you've got it off, too.

[79XS11F]

When I lay all the plugs across the head they all spark equally. I do have color tune plugs. 4 of them in fact but I typically use them for fine tuning after sorting out a major issue like this one.
I know I will be pull the carbs to give them the once over and bench test the fuel levels in the bowls followed by the color tune check.

Rob

[dbeardslee]

One other thing while I'm thinking about it. You mentioned putting plastic floats back in the carbs. When I first put the plastic floats in Betsy I had to bend the heck out of the tab to get them to the right level with the stock fuel valves. That's largely why I changed them to the XV920 fuel valves. The viton tipped needles are a little longer and the tab didn't require anywhere near as much bend. I didn't like that angle in the tab as it didn't look like it would move as freely that way. And I swear those plastic floats are tighter on the pins than the brass ones. So for me it's brass floats with stock fuel valves, and XV920 valves with plastic floats.

But I'm still betting the problem is in your pilot circuit. You know you're getting spark on all the plugs, which leaves fuel as the problem. It's missing at idle, and at idle the slides are down and you're running on the pilots. And the fact that you've got one really lean plug tends to point to the carbs. If the timing was boogered up I think all the plugs would have issues - not just one.

[79XS11F]

One other thing while I'm thinking about it. You mentioned putting plastic floats back in the carbs. When I first put the plastic floats in Betsy I had to bend the heck out of the tab to get them to the right level with the stock fuel valves. That's largely why I changed them to the XV920 fuel valves. The viton tipped needles are a little longer and the tab didn't require anywhere near as much bend. I didn't like that angle in the tab as it didn't look like it would move as freely that way. And I swear those plastic floats are tighter on the pins than the brass ones. So for me it's brass floats with stock fuel valves, and XV920 valves with plastic floats.

But I'm still betting the problem is in your pilot circuit. You know you're getting spark on all the plugs, which leaves fuel as the problem. It's missing at idle, and at idle the slides are down and you're running on the pilots. And the fact that you've got one really lean plug tends to point to the carbs. If the timing was boogered up I think all the plugs would have issues - not just one.

It's missing through the entire throttle range and does not matter if the RPM is being held in a study position or altered. The carbs on this bike are currently a set of loaners from Mack and they have brass floats in them. I always set up my carbs on the bench for fuel level in the bowls regardless of the float type involved.
Myself, I don't think it's electoral for many reasons including:
- Switching out the pick up coils didn’t help.
- Re-cutting the coil wires didn’t help
- Switching out the coils didn’t help.
- Putting in new plugs didn’t help.
- Switching out the plug caps didn’t help.
- I see spark across the board when the plugs are laid on the head.
- Switching out the CDI ignition box didn’t help.
- There’s no “beastie” damage to the harness.
- All the connections appear to be clean and still fit together firmly.
I am convinced that the issue is carbs but time will tell. Unfortunately time is also slipping away … I hardly have time to enjoy using it much less work on it for long stretches.

[79XS11F]

OH, here's something odd that I noticed when I was checking the pick up coil gap and timing. Everything that is metal (steel) under the timing cover is magnetized?
I noticed when I would go to slip the feeler gage into position it would bend and stick to the pick up coil. Not strongly by any means but the attraction was there.
Now perhaps the gage itself has become magnetized or perhaps the pick up coils are magnetized I still need to confirm which. If it is the coils, their mounting plates or other steel parts they mount to is this normal? and if not, could it be a contributing part of the problem?
I do not recall having this effect in the past.
Rob

[dbeardslee]

OH, here's something odd that I noticed when I was checking the pick up coil gap and timing. Everything that is metal (steel) under the timing cover is magnetized?
I noticed when I would go to slip the feeler gage into position it would bend and stick to the pick up coil. Not strongly by any means but the attraction was there.
Now perhaps the gage itself has become magnetized or perhaps the pick up coils are magnetized I still need to confirm which. If it is the coils, their mounting plates or other steel parts they mount to is this normal? and if not, could it be a contributing part of the problem?
I do not recall having this effect in the past.
Rob

I thought the pickups were magnets. I've got a couple in a box, so I double checked. Definitely magnetic.

[3Phase]

Rob,

Yes, the pick-up coils have a magnet in them. If they didn't have a natural magnetic field in them, the TCI would have to give them some power to create an electromagnetic field.

The TCI uses the steel reluctor and the reluctance in the pick-up coils to tell it when it's time to fire one of the ignition coils.


I just read this thread again from the 1st page and I didn't see anything that mentioned the system and ignition voltage, just changing ignition coils and adding/removing the Ballast Resistor.

You've said that the engine still misses when you swap the secondary wires but are you 'positive' that it's the same cylinder that's misfiring?

It's important because you may have Mikuni Spark Plugs aka "Your carburetors are having electrical problems," which is completely different from and should never be confused with NGK Carburetors aka "Your spark plugs are having fuel problems."


You can drop voltage across the Ignition Switch, the Fuse Block, the Stop/Run Switch and every connector in between the battery and the alternator.

Check the voltage from the battery to ground with the engine running over 2,000 RPM.

Check the voltage again at the 10A Ignition fuse to ground.

The two readings should be the same within 1/2V.

Check again at the small Red/White wire on the Start Solenoid, it should be almost identical to the reading at the 10A Ignition Fuse.


If the system/ignition voltage is low, one spark plug can fire consistently but the other plug will be 'weak' and inconsistent. If the wires are long enough, swapping the secondary wires will change the polarity of the individual spark plugs.

The wasted spark setup on these bikes makes one spark plug fire positive, electrode-to-ground, and the other plug fires negative, ground-to-electrode. If you've ever read one of the old repair manuals they always mention checking the spark polarity with a graphite pencil because it takes more energy to fire a spark plug with reversed polarity.

The spark plugs may spark just fine in the open air on top of the cylinder head all day long but that doesn't mean that they'll be able to spark when they're inside the head and under load.

.

[79XS11F]

Thanks Scott
I changed out the plug leads by putting #1 on #4 and #4 on #1 and the miss remained at #1. I can see it in my timing light. #3 and #4 are running fine. They never miss a beat. based on what I see in my timing light I would hazard to guess that at idle #1 misses about 1 in 4 - 6 expected firings be it a wasted fire or not. I suppose I could count it out at idle but how often really doesn't help in figuring this out.
So #1 and #4 are shared on the same pick up coil and ignition coil but the issue is not affecting #4 even when the plug leads are switched between the 2 cylinders.
It would therefore appear to be a carb issue / bug-a-boo and the only thing that changed was storage with fuel in the carbs (bad move to be lazy).
I'm going to give the carbs the once over but fear I will not find any issue there as these carbs are already rebuilt units from Mack and they came off a running bike that had no issues.
Given the color of the plugs I was thinking that perhaps if #1 carb has an issue the plug may simply be missing due to becoming fowled.
Yesterday I had the covers off the carbs and adjusted the needles on #2 and #3 to the spec middle notch as they were set 1 notch rich. I also had the bowls off and re-set the floats to 1" from the gasket surface with the gasket removed as per my factory manual. 1" is about the middle of the acceptable float height range.
Everything inside the bowls appeared clean and good to go. I blew them out while they were off the bike and got air / fuel mist at all opening accept at the air pilot on #2. It took a few try's to get air through that one so it is suspect but #2 is not the cylinder that is missing. Not according to the timing light anyway.
I'll carry out these tests you have suggested if the carb work does not correct the issue. How is the graphite pencil test carried out?

Rob

[3Phase]

[...] I'll carry out these tests you have suggested if the carb work does not correct the issue. How is the graphite pencil test carried out?

Rob

Well, so much for that idea!

You check the polarity very carefully. Graphite is a great conductor and it runs the full length of the pencil.

Unscrew the spark plug boot and remove it from the wire.

Hold the pencil and the wire with something insulated -- don't use your hands. And don't get too close and stare at the metal end cap with the eraser or you'll zap yourself someplace that you really don't want zapped.

Crank the engine and put the tip of the pencil between the end of the wire and the spark plug, then watch the spark 'flares' and their direction.

From the Physics Forums:-

www.physicsforums.com: Forums > Engineering > Electrical Engineering >
Ignition voltage in a waste spark system.
Page 1 of 2


After everything that you've done it's such a totally improbable coincidence that the same cylinders are misfiring this year with completely different carburetors from last year. I find it difficult to believe it's a fuel problem but if the system and ignition voltage is good and the engine is still misfiring I'm out of ideas except for repainting it.

Everyone knows that shiny paint makes motorcycles go faster!

.

[79XS11F]

Well, so much for that idea!

You check the polarity very carefully. Graphite is a great conductor and it runs the full length of the pencil.

Unscrew the spark plug boot and remove it from the wire.

Hold the pencil and the wire with something insulated -- don't use your hands. And don't get too close and stare at the metal end cap with the eraser or you'll zap yourself someplace that you really don't want zapped.

Crank the engine and put the tip of the pencil between the end of the wire and the spark plug, then watch the spark 'flares' and their direction.

From the Physics Forums:-

www.physicsforums.com: Forums > Engineering > Electrical Engineering >
Ignition voltage in a waste spark system.
Page 1 of 2


After everything that you've done it's such a totally improbable coincidence that the same cylinders are misfiring this year with completely different carburetors from last year. I find it difficult to believe it's a fuel problem but if the system and ignition voltage is good and the engine is still misfiring I'm out of ideas except for repainting it.

Everyone knows that shiny paint makes motorcycles go faster!

.

I guess I'm just having trouble buying into it being electrical because what could happen to the electrical system as a result of the bike not being used for 2 seasons on a new harness. I was "hoping" carbs because it did have fuel in the carbs over this past winter again but with stabilizer and I fired the bike up a few times. I am hoping that maybe something got partly blocked up over last winter and then then there is this thing with the issue not moving to #4 when I switched out the plug wires between 1 and 4. If it was ignition electrical would the issue not have moved to #4 with the plug lead? I will carry out the recommended tests before I tackle the carbs because those tests are easier then a carb job.
Rob

[dbeardslee]

I was "hoping" carbs because it did have fuel in the carbs over this past winter again but with stabilizer and I fired the bike up a few times.

I'm not sure fuel so much goes bad but that it evaporates out in some areas and leaves the stuff that won't evaporate behind. I noticed it on Betsy. When I parked her she had a fuel tank that was about 3/4 full, and there was only about a half gallon left in the tank. And the air jet provides an "evaporation route" that leads right to the pilot circuit.

But what I"m wondering is this - were both sets of carbs left with fuel in them, or only the one that was on the bike?

[79XS11F]

I'm not sure fuel so much goes bad but that it evaporates out in some areas and leaves the stuff that won't evaporate behind. I noticed it on Betsy. When I parked her she had a fuel tank that was about 3/4 full, and there was only about a half gallon left in the tank. And the air jet provides an "evaporation route" that leads right to the pilot circuit.

But what I"m wondering is this - were both sets of carbs left with fuel in them, or only the one that was on the bike?

Mack has the carbs that were stored with fuel in them without stabilizer or the engine being run. I cleaned them several times but they needed a "fresh" set of eyes and I have such little time these days for working on the bikes. Mack will refurb them for me. The carbs on the bike now were stored with fuel in them but with stabilizer and the engine was run a few times over the winter.

[TopCatGr58]

Hey Rob,

Those plugs are telling a bit....the worse ones are not paired fuel or electrically! But I think Scott is still onto something with the weak supply voltages to the coils...despite that they are the Accel ones. Like Scott said, there is a Positive plug and a negative plug in the paired plugs of a coil pair, and IF the harness voltage TO the coils is weak, it can still cause a weaker total spark energy...and so may have enough to fire the primary plug but not the secondary reverse polarity plug. Corrosion doesn't care about the harness being NEW....storage, humidity, etc. and you can get corrosion.

T.C.