Possible ignition problem/question

I'm having an issue with cylinders 2 and 3. When I take the bike out for a ride, it's down on power a bit. Near as I can tell the carbs are perfect, as they've been cleaned, double-checked, triple-checked, and I had a staring contest with them that lasted several hours. I blinked first.

Anyway, plugs 1 + 4 are showing a nice tan color, I have a little more playing around to do with them as they're not perfect, but 2 + 3 are way off. Plug 2 is extremely sooty after just a few minutes of running, either driving or just idling. Plug # 3 is wet. All the time. Also, cylinder #2 is backfiring toward the carb and keeps popping the vacuum cap on the intake manifold off!

I checked the vacuum line coming from the petcock and it is dry. I've rechecked the fuel float levels and they are spot on, so I don't think it's off, and it seems odd that 2 and 3 are both having issues, as they're on the same coil.

So, does it seem reasonable to think that perhaps the spark is very weak on those two plugs, which is resulting in a not fully burned charge on #2 (thus looking rich) and intermittent or no combustion on #3 (leaving the plug wet)? I think the backfire on #2 is because it's rich and since it's a wasted spark system and fires more often, it's igniting the leftover charge.

Am I way off base here? The primary and secondary coil resistances seemed within spec when I looked at them a few days ago, but the caps' resistances were off, so I've got replacement caps on the way from Len. I'll recheck the coil resistances today, but as the coils are original I guess I wouldn't be surprised if that's my problem.

I may also try swapping coils/wires/caps between 1&4 / 2&3 and see if the problem moves.

If anyone thinks I'm barking up the wrong tree chasing after spark, please let me know!

Thanks,
Aaron

 

it doesnt sound too far off. you can get your spark tested to see if that shows anything. you will see if the spark is delayed/weak at those plugs.
if it isnt weak, I would look at the pickup located on the crank.

 

I would also make sure that all the connections at the TCI are clean and free of corrosion, especially the crimps where the wires enter the gang plugs.

 

hey stereo, that little bit of corrosion isnt a bad thing, is it?
:lol:

 

Corrosion is awesome! Yummy, non-conductive, oxidized metal goodness!




I like to put it on a sandwich.

 

It could be that your coils are going or gone. Another possibility is that just the spark plug wires are at fault.

If the caps don't solve your problem and neither does cleaning the contacts, first try cutting a little bit off of the end of the 2 and 3 plug wires and putting the cap back on.

If that still does not improve the situation, splice in new wires or do coil surgery to get new wires in there.

 

Primary and secondary resistances of the suspect coil are still fine, I rechecked them and they seem fine. Caps should be here today or Monday, so those will go on and I'll see if it helps.

If the wires were bad, wouldn't the secondary resistance be much higher than spec? It seems like if the coil is bad, either primary or secondary resistance would be open, shorted, or out of spec. Can a coil pass all those tests and still be bad?

I checked the connectors at the coil and they weren't bad at all, but I cleaned them up anyway. Will do the same at the TCI.

Thanks,
Aaron

 

So I have found that if I fit a new plug to cylinder 3 it seems to fire and run great. However, after extended periods of riding, it seems like it stops firing, and that exhaust pipe is relatively cool compared to the others.

My thoughts are that it actually stops firing, or that cylinder is way too rich, thus running cool. No black smoke out the exhaust, though.

I will say that mileage is only about 20-25 MPG, which would make sense if one cylinder wasn't firing, and the other (#2) had a weak spark...

I'll post back with some more observations. Went for a long ride yesterday and gotta go pull the plugs and see what I can find out.

 

OK, so here's the latest...

Cylinder 3 runs cool and very rich. The spark plug is sooty and black.

Cylinder 2 is running rich, but the exhaust pipes are the same temperature as 1 & 4, which are a good color.

On a cold start, revving a little shows black smoke out the exhaust. Once warmed, the black smoke goes away. However, the idle that used to be rock solid at ~1000 RPM now creeps up to 3K and sits there. Isn't that indicative of an air leak? I still never need to use the choke to start, but it's been pretty warm here, mid 70s since I rebuilt the carbs. Dunno if that's normal or not...

Power is not what it could be, but is much better than when #3 plug was wet.

I checked the resistance of the pickup coils, and they were within spec - 630 ohms. I swapped in a used coil I picked up that tested good, although the wires were in poor condition, and that SEEMED to help a little, but it could be wishful thinking. Though outside the motor, all plugs are sparking consistently now.

So, should I take the carbs back off and check the float levels again? Plugs indicate that #2 and #3 are running rich, but I don't know if that's because of a poor/late spark, or because they're actually getting too much fuel.

 

Did you check and adjust the valves before you began messing with the carbs?

When you had the carbs off, checking float levels, did you bench sync them before they went back on?

Were the float levels checked assembled, using fluid, or statically?

Have the carbs been vacuum-sync'ed after you got them back on?

WITHOUT the answers to the above, it sounds to me like you have one or two cylinders that are WAY rich, possibly even "dumping" fuel due to high float levels or being way out of adjustment. You could also have a tight valve or two. It really doesn't sound like an ignition problem unless maybe your battery is weak.

 

Valves have been adjusted.

The carbs were bench synched.

Float levels were set using the dry measurement method, then checked with fluid with the rack level.

Carbs have been vacuum synced as well as I could with a two bottle sync tool, but I used plastic bottles accidentally.

Battery was new at the beginning of the summer.

I'm rechecking float levels right now...

 

Has anyone mentioned a compression check. Used a colortune yet to get an idea about what is going on in there. The carbs have been gone through well over thuroughly, the coils switched, start from basics and work your way up.
Electrical: Battery, connections, plugs, coils (good), wires (good), connections.
Mechanical: compression test, color tune, sticking throttle shaft, sticking valve.

 

OK, I've gone through all the ignition connections to the pickup coils (which ohm out fine), the TCI, and the coils. I've cleaned both battery terminals and the negative grounds (on the frame and crankcase).

I readjusted the float levels pretty meticulously to get them even closer to that 3mm mark, and 2/3 seem to be better, but not great. They're still a dark sooty color.

I finally did a compression check, and they are 135 PSI across the board. A funny thing I noticed is that if you use an adaptor, the measured pressure changes - you can thread the braided line on my tester directly into the spark plug holes, or you can use the 'long reach' adaptor. I get 120 PSI across the board if I use the adapter, and 135 evenly if I don't. I guess it adds some volume, so the relative pressure decreases. You learn something new every day!

My idle is still high after the bike warms up. With new airbox boots and intake manifolds, I don't think air is coming in there. I also have new throttle shaft seals. I read in another thread that it could be the butterflies not closing properly on just one or two carbs. Idle is about 2-3K, depending on outside temperature, it seems.

Gas mileage is very poor still, only about 20 MPG.

What's my next step?

 

first, turn your idle screw down to get it to idle at 1050 or so. do it once it is warmed up. mine did the same thing
once you do that, ride home and plug chop at 4k. coast in and let it cool. see what they look like then. if they are off, hook up the sync tool and check your sync.
I assume you are using the oem UNI filter and airbox?

 

OK, I seemed to think the idle screw was backed out most of the way already, but I'll double check that tonight.

Yeah, OE style filter and airbox. Stock exhaust too.

But that wouldn't make the middle two cylinders run rich, right?

 

if your carbs arent set right (sync, pilots, floats, AND idle) I highly doubt it will ever tune right either.
at least that is my thought on it.

 

I forgot to mention, my "kinda" sync status before can be updated to "perfectly" synced. The reason why I had so many issues before was because cylinder 3 was firing intermittently, so syncing to number three was almost impossible. Now that it's at least firing consistently, syncing was a relative piece of cake!

Thanks for the advice, and I'll check the idle and report back tomorrow.

Cheers,
Aaron

 

OK, so the idle is good now. I have yet to let it cool down and start it cold, but I suspect it'll be fine. It's idling at 1000-1100 RPM steadily.

I have some more data to add, not sure what it means... Exhaust pipe temperatures, measued with a digital multimeter with a temp probe hooked to it.

Exh 1: ~240-250 F
Exh 2: ~220-230 F
Exh 3: ~175-185 F
Exh 4: ~230-240 F

I imagine that the cylinders running richer will have lower exhaust temps, while the cylinders running right or leanish will have hotter exhaust temps.

Looking at plugs 1 and 4, 4 is a little darker than 1, more brown than tan. 2 & 3 are both rich. Mixture scew is set to 2 turns out. *course screw*

I have yet to colortune them, but everywhere I've read says that usually you need to go further out on the mixture screw from the 1.5-2 turns out initial setting. If I'm running very rich, I would need to go in quite a bit, right?

 

actually, a little goes a long way on the screw.. typically the width of a dime or nickel for adjustment will make a lot of difference.

 

OK, will be colortuning this afternoon and resync after that. Will see what happens. Last ride was 35 miles averaged 55MPH but on the throttle a lot through twisties. Took 1.56 gallons to top it off is around 22.5 MPG. Not very good at all!

 

I tried colortuning, and sure enough, I wasn't able to get blue with the idle screw all the way in.

I tore the carbs off again, and examined the idle scrfews on both #2 and #3. It seemed like maybe the washer and o-ring were backwards on #2, although I did all four at the same time so it might have just flipped when I was attempting to remove the screw without draining the fuel from the float bowl. I pulled the screw, spring, o-ring and washer out and cleaned the tip of the mixture screw, which looked a little dirty. Reinstalled correctly. Then I looked at the pilot fuel and air jets. Air jets were fine, but the pilot fuel jet on #3 looked... big. So I swapped it with one from my spare set of carbs. I reassembled them, set both mixture screws at 2 turns out (coarse threads), and reinstalled them. I was able to easily get a blue flame with the colortune plug!!!

I tuned all plugs to in between yellow and blue and know I have some more tuning and tweaking to do, but I had some people waiting on me to go for a short ride. But it fires right up and doesn't stink so bad, so I know it's better. I'll check the plugs and tune them some more, but with all the great instructions available to me on this site I know I'll be able to tune it correctly.

I am glad that I'm unemployed and so haven't been able to spend money on the bike, because otherwise I would have started throwing parts at it at this point.

Thanks to everyone's advice, logic, and support.

Aaron

 

You shouldn't think that the Colortune Plug NEEDS to be Blue for the Optimum Mixture.
Sometimes that Blue is Lean.

I use the Colortune Plug to get me CLOSE to where I need the Bike to be to begin Ultra Fine Tuning.

I run the Screw Up until the ColorTune Plugs starts "Hitting"
I >> Micro-tweak the Screw up and watch it bring in the Blue.

Then, I keep adding fractions of a degree until the BLUE is at the EDGE of changing to just Slightly RICH.

Then, I begin making any adjustments to the Hole based on Plug Chops.

 

That makes sense. I guess what I meant is that I wasn't seeing any real results from playing with the idle mixture screw. Probably because one was dirty and the other carb had an enlarged pilot fuel jet, making them both run very rich. While the screw may have had some adjustment, it wasn't bringing me anywhere near "correct" as it was always way too rich. Thus I wasn't able to tune at all because no matter what I did those cylinders were always too rich.

That explains the poor mileage too. I can tell by the smell (haha!) that those cylinders aren't running so rich now.