*UPDATED* Weak spark on #2 CYLINDER

Ok I have what I hope is an easier fix! (compared to shimming valves, rebuilding carbs, syncing, etc).

Here's the story:

I have a fairly well running bike now, however, when I was colortuning I noticed a weak spark on cylinder #2. Just to give you a good picture, while the engine was running I took the plug cap off #2 and the engine didn't miss a beat (surprisingly), however, when I took the plug cap off any other cylinder it wanted to stall something fierce! (as expected) I must have synced the carbs around the problematic cylinder...

Here's what I've done so far with no results:

- Swapped plug caps
- Bought new coil
- Cleaned ground

Is there any other sources for a weak spark on only one cylinder like this? Is there something to look at before the electricity gets to the coil? Any help is MUCH appreciated!

 

Re: Weak spark on #2 CYLINDER

Before you get too far that coil feeds two cylinders, if one is weak so should the other cylinder. Pull the plug cap off and trim the wire back 1/4" and try it again. If you think you still have weak spark on that one just lay a good used plug on the head with that wire attached. Fire it up and see what the spark looks like.

 

Re: Weak spark on #2 CYLINDER

Are you sure that both cylinders would have to be a weak spark, or are you saying in general that is probably the case? I cut the spark plug wire back to make a new connection, but didn't seem to affect anything....

I feel like there has to be some sort of distributing system for the spark. How does the coil know which plug to send electricity to? Are there any points like on a distributor in a car that I can clean up?

EDIT: I should also note that I have a colortune plug so I've seen what the sparks look like on each cylinder and #2 is definitely weak.

 

Re: Weak spark on #2 CYLINDER

You have two coils. One generates spark for two plugs, the other for the other two plugs. So yes, your spark generator won't be good on one spark plug and bad on the other.

Did you try replacing spark plugs? I can't believe you haven't included that in list of things to try, that'd be my first answer. The cables themselves don't usually go bad and it sucks if they do, from what I hear, because it's unpleasant surgery to replace them.

There are no points, thankfully. This is a TCI system. No distributor. (Be happy.)

Beyond that, get a voltmeter and check the wires for resistance?

Not my area of expertise, but these seem like the logical answers to me. MN's answer above is hoping that corrosion on the end of the wire is causing enough resistance to be the problem, and trimming the corroded part off might give you full current again. Definitely worth a try, since it's free and easy.

How did you 'tune the carbs around the weak cylinder' before colortuning the system? Are you referring to the vacuum sync? Someone correct me if I'm wrong, but I don't think it would quite work like that. The bike can definitely run on 3 cylinders--two cylinders is just too much. If you haven't had the bike long enough to know what it's like when running well, you might not know the difference.

 

Re: Weak spark on #2 CYLINDER

Sorry, I'm a new at this motorcycle tuning. I've always worked on vehicles though.

You're right I don't think I know how "good" it should actually run. I think it is running fairly well because it idles good and runs pretty good throughout the range, but then again maybe it should run a lot harder.

This might be a dumb question, but I thought each cylinder took it's turn when firing, or do two cylinders fire at once?

last thing, I have a colortune plug that is brand new. I placed it in each cylinder and watched the kind of spark I got. Wouldn't this make getting a new spark plug to check spark strength un-needed?

Thanks guys for the advice!

 

Re: Weak spark on #2 CYLINDER

The ignition has what is called a "wasted spark system", each coil delivers spark to two cylinders at a time, one which will be on a compression stroke , the other on an exhaust stroke.The next full revolution, when that same coil fires again. the one that was on the exhaust stroke will now be on the compression stroke. It,s a system that saves components , most 4 cylinder bikes utilise a similiar system ,hopes that makes sense,
cheers,Murray

 

Ok, I now realize that indeed I do not have a weak spark on #2 cylinder. I thought the absence of the "glow" in my colortune plug was an absence of spark, but I now realize it was just an absence of combustion.

I was messing around with the pilot fuel mixture screw and the butterfly valves and I was able to get #2 cylinder firing but #3 and #4 both stopped firing (Pulled the spark plugs and they were soaked in gas). I then did some more adjustments and got #3 and #4 firing but #2 stopped again.

A little information on my bike... brace yourselves.... my bike is running pods + 4 into 1 exhaust. I know that will change some things people might suggest.

Also, I rented a compression testing tool so I'll have those results soon.

Can anyone shed some light on this?!?

 

Carbs...time to dive into the carbs. While you can adjust the mixture at idle with the pilot mixture screw, this only applies to fully rebuilt/clean carbs. Sticky floats, set wrong, clogged jets, missing (seen it before) jets, air leaks, anything (and likely a combination thereof) can cause the poor running situation you describe.

Checking and adjusting valve clearances is a must (and part of standard maintenance). Full carb rebuilding is basically a must if it hasn't been on the road and well maintained (most aren't until we get a hold of them 8) ).

The BEST way to tackle the intake is to rebuild and do everything intake related right, the first time, then troubleshoot from there if you have problems. That eliminates a lot of possibilities and really narrows things down.

Then you'll have to deal with the PODS. But since you'll have already gone through your carbs, you'll be used to getting in there.

 

Just read your thread from April where you detail doing the cleaning and rebuilding....

How much adjusting are you doing to the pilot mixture screw? FAT RICH to DANGEROUSLY LEAN is only about 8 degrees turn on the screw. Really fine adjustments.

After going through each cylinder with the color tune plug, and getting a good setting on each one, do another vacuum (with YICS blocked) sync. A previous sync without one cylinder firing will be way off when you get it firing again.

If you can't seem to set a pilot mixture screw to any setting where you see anything but white firing on the plug...suspect a vacuum leak. I've sworn before that something MUST be wrong with the colortune (lighting, glass dirty etc) and it HAD to be lying to me...only to find an air leak that caused that cylinder to run lean.

 

Re: Weak spark on #2 CYLINDER

They do. The coils fire 1&4 at the same time; and 2&3 at the same time. However, only one of each pair is on its compression stroke; the other one is on its exhaust stroke, so firing it is a "wasted spark."

***EDIT*** Sorry, murray, you just pointed this out. I should have read further back up the thread.

 

Thanks for the good advice!

When adjusting the pilot mixture screws I was not as careful as you recommend. I was adjusting half turns to full turns at a time. When adjusting some of the pilot mixtures I could turn 2 full turns one way (in certain spots) and it wouldn't make a difference on the colortune plug. ??? Another thing I noticed on cylinder #2 (plug is soaked in gas when I pulled it) I would turn the pilot mixture all the way shut and it wouldn't make a difference. I really don't know if this means anything though.

Well, I did a compression test and I am really frustrated by the results. (I had the engine at operating temperature with the throttle held at 2500 rpm) Every cyliinder got within 90-95 psi but if I would blip the throttle the pressure would jump a little and if I kept blipping the throttle each cylinder would top out at 120-130. What does this mean?

 

Start you pilot mixture screw at 3 turns out. Then start your fiddling a 1/8 turn at a time. Once you see a clear change, then fine tune a couple of degrees at a time. With pods you'll likely be going further out. What size pilot jets are you running? You might need to be going up in size on those too.

If all you see is whitish blue, your pilot circuit is still clogged, you have an air leak, or your pilot fuel jet is too small. If you had stock settings, you could easily eliminate the first two, but with pods, it's hard to tell WHY the fuel mixture is off.

Um...that's not how you do a compression test. It sounds like you did this on a running bike (not sure how).

How to do a compression test, make sure to have a fully charged battery:
1. Disconnect TCI - this keeps it from frying.
2. Remove spark plugs. Make sure area around them is clean before removing (blow around them using compressed air).
3. Insert compression tester on one cylinder
4. Hold open throttle, full throttle
5. Turn over engine until needle on compression gauge stops moving.
6. Record value and move on to the next cylinder.
7. Post numbers on the site.

 

Well that's not good. People's results with compression testers seem to vary--I would go use a second tester before throwing in the towel, but it might mean a top-end rebuild is in order...

Did you 'wet test'? Drop of oil in each cylinder?

Sounds like some previous owner never changed the oil...

And yes, I adjust my mixture screws in 1/8th, 1/4, and in extreme cases 1/2 turns. Two full turns is huge. It might help to put them all at 2.75 turns and use that as a starting point and just begin from scratch--it should run at 2.75, though if you haven't rebuilt the carbs it will likely be a bit lean there.

 

yea you did the compression test wrong dont worry about it do what manbot13 said

 

Ok, I'll retest the compression doing it the RIGHT way!

I'm running 116 on my main fuel jets and 41 on my pilot jets.

 

Not to be-labor the point...but was my assumption correct? Did you do it with the bike running, and that's why you mentioned the effect of blipping the throttle? I only ask in case you did harm something and we need to troubleshoot more later.

Know that because it's a wasted spark system, you can (not for certain, but it's a distinct possibility) damage your TCI with one spark plug disconnected. NEVER turn over an engine with any of the High Tension (spark plug wires) "ungrounded" (grounding the spark plug on the engine is OK). Unless the TCI or low tension coil wires are disconnected. And never pull a plug (I've seen this mentioned on other threads) while the engine is running to see a cylinder "drop out."

 

You're assumption was correct...I am guilty of pulling the plug cap off the spark plug while the engine is running on numerous occasions...

I did exactly as you suggested to do a compression test and here are the results:

#1: 70 psi
#2: 80 psi
#3: 75 psi
#4: 70 psi

NOTE: I did these tests on a cold engine and with pods on carbs holding throttle wide open.

These results look pretty low?

 

They do look really low, but really consistent, and consistent is what you are looking for.

Suspect the gauge and try another (or assume that they are tight enough and don't bother). None of the cylinders would fire if your combustion numbers were actually that low, so it's likely the gauge is reading low.

Please put your bike info in your signature (I had to search your previous postings to compare your jet sizes with stock).

You might still have jetting issues. However lets cover some basics:
Looking at your last thread, I didn't see you state that you successfully "wet" set your float heights. How did that go?

Did you remove your pilot mixture screw and flush out the passage when doing your carb clean? If the pilot circuit is clogged here, the mixture screw will have no effect.

I'm assuming, since you've stated in a previous thread that you had it running well 2-3 years ago, that you've rebuilt the carbs and have replaced a lot of rubber bits. What exactly have you done to clean and rebuild the carbs (maybe there's a step that you're still missing)?

Have you adjusted your valves?

Can you return your needle clip to it's original position (or even richer/raise the needle)? A middle position is a good starting point.

In the end, if you've been making such large adjustments to the carbs, you might need to start over with a bench sync and setting the pilot screws 3 turns out (yes, more than most suggest, due to your intake/exhaust choices. It'll probably still be lean). You should record where the settings are now, then reset them and see if small, incremental changes (along with syncing and idle adjustments in between mixture adjustments) get you to a better place in the colortune.

You should be able to get a good combustion at idle with pods, but there will be a lot jetting and shimming to come for the rest of the operating range.

 

I did not wet set my floats, I opted to dry set them because my float bowl screws are stripped. I keep looking at them wondering if it's causing me problems. What will a low/high float setting do?

I shimmed my valves first thing (this go around).

I'm almost positive my pilot circuit is clear because I can adjust the colortune plug from a yellow to a blue color. I just don't see a difference once the colortune plug is already blue. I am red-green colorblind however, and maybe I don't see the small differences in color in the blue?

Ok, with the carbs.....about 3 years ago I completely went through them and cleaned them and also soaked them in chem-dip. But since this time around I did the following.
- Broke them all down individually and completely (every jet and float and screw)
- Sprayed carb and compressed air through every passage (pilot circuit, enrichment circuit, main circuit, cleaned emulsion tube, every air jet, etc)
- Needle valve is already new as well as v-seals in throttle shaft and pilot screw o-ring is new

I have tried 3 different settings on the main needle valve clip. I started at 3rd from the top and it idled rough until you got past 1500 and would shoot up to 3-4 grand and not come down. Then I moved it to 2nd from top and it it idled pretty good, a little bit of the same problem as before. Then I moved it to the top and it wouldn't idle hardly at all I would have to blip the throttle just to keep it running. Maybe this will give you an idea of what my pilot circuit is doing. I was thinking the main circuit shouldn't have any effect on idle?