Topic: Still a miss mess.

[Lostboy Steve]

So I still have a slight miss some times at idle some times at 1/4 throttle. I've been through the carbs 3 times. I changed all my spark plug resistor caps. I checked my valve adjustments. I dont know where to go from here. Its ONLY cylinder 1. I've also noticed that when I go off part throttle (cruising) to accelerating, I can hear the the exhaust note in the right pipe (3&4) changes a few milliseconds before the left pipe (1&2). I'm doubting a coil issue. I also changed the sparkplugs just in case there was a hairline fracture in the porcelain. Any ideas? Also, its not really felt just heard and you get some unburnt fuel smell from the left pipe and a little black smoke as well. Its only at idle and slightly of idle which is why I'm leaning towards ignition and not fuel.

[DJ_AX]

What about points? Timing? Condensers? Advancer?

[Lostboy Steve]

They are all set at the stock settings and in good working order. Again, its only cylinder 1 so its got the be something from the coil on. Cylinder 4 is PERFECT. Maybe a broken wire internally?

[lucky]

You need to be more methodical about your tests.

You keep jumping all around.
Do THIS.
Get a sheet of paper and write a list.
Then perform a check on each item and check it off the list.

Sounds simple put that is how problems get solved.

[DJ_AX]

Switch wires between 1 & 4 and see if it follows.

[Lostboy Steve]

OK, heres my list:

Coil-Good
Wire-Good
Sparkplug-Good
Valveadjustment-Good

So next on my list:
Compression Check
Tear apart Carbs for the 5th time and see what the hell is going on.

Also, let me add that when I first got the bike we fiddled with it for a while and cleaned the carbs and got it to run, but poorly. The cylinder 1 misfire was there at that time. Since then I have completely rebuild the engine, soda blasted the carb bodies, then boiled them, new jets, synced, etc. Miss fire is still there and about the same.

[samIam]

I think its fuel related.  Even though your carbs are sinced, maybe back off the setting for cylinder one and see if it goes away.  Could be an internal leak in the carb that is hard to notice when you open them up.  Did you pull the emulsion tubes out when you did the carbs? 

Switching the plug wires around like DJ_AX said would be an easy way to see if its spark related. 

[TwoTired]

Are spark plug deposits the same for all?

You know you can swap coils to see if the issue follows.  I don't know if the leads you have are flexible enough or long enough.

I doubt it is an electrical problem, though.  Either carburetion, or cylinder mechanical.  (Maybe bent valve?)

Did you replace all the float needles?  Was the spring pin the same pressure as the new ones?  I don't have the facts, so I'm forced to guess.

[phil71]

i hate to say it, but it still sounds like a carb is not totally right. Sometimes soda blasting isn't enough, when they're really far gone.

[dave500]

check the plug cap resistance.

[iron_worker]

Check that carb's idle jet again. Can you see light through it? Are the air screw settings all the same? You could also check for a vacuum leak on that cylinder. Could be pulling in extra air causing a lean misfire.

I would lean away from electrical since it only happens at certain throttle positions. An electrical problem would likely be apparent at all RPM ranges or get worse under load.

IW

[DH]

Seems likely not ignition related BUT...another test to help eliminate a possibility of ignition problems is to mist the wires from a spray bottle of water and see if that aggravates the problem.
Examin the wires in a dimly lit or dark area while the engine is running and watch for arcing. Or, hook up an inductive timing light
to the suspect wire, and see if the light fails to flash while the mis fire is occcuring. Or..Ground a  test light to a good ground and run the
test light along the wire, holding the test light about 1/4" from
the insulation of the plug cable, moving along the length of the cable and see if at any point, spark jumps thru the cable's insulation and into the probe of the test light.

[matt mattison]

What does the plug look like in the missing cylinder??

[Lostboy Steve]

Saturday night I pulled the idle jet. CLEAR. I swapped the wires, problem does not follow. The resistor caps are all new. The head has been professionally rebuilt and leak checked, this blows big time. Now I'm wondering if I have a cracked ring or something. I will have to  compression test it. I didn't have my tester home on Saturday.

[Lostboy Steve]

Tonight I did a cold compression test (wake baby = receive hell). I have 120~ across the board. Cylinder 1 plug looks, well black, but dry. Rest are a dark chocolate brown. Now what? I keep tearing into these carbs is there something I'm missing here? I seem to have a good steady spark.


Btw that pic is plug one on the right vs plug four.

[phil71]

if you got strong compression and spark, you're going back into the carbs. It's so easy to miss stuff, are you getting thru all the circuits with guitar strings, do you know for sure you have ample fuel in the bowl?

[lucky]

i hate to say it, but it still sounds like a carb is not totally right. Sometimes soda blasting isn't enough, when they're really far gone.

"Too far gone" No just cannot identify the problem.

There was one forum member here that used such a powerful ultrasonic
cleaner on his carbs that the little brass balls or caps in the passageways were leaking and causing the carb to not work properly.

You said you "BOILED YOUR carbs"

He put special sealant on  the little balls and it fixed the problem completely.
I am trying to remember the name of the thread. The sealant was PILO bond.

HERE WE GO:
http://forums.sohc4.net/index.php?topic=108087.0

[Lostboy Steve]

I actually have a tube of that stuff. I guess I will go ahead and do that but again only 1 carb? And only at idle? I have plenty of fuel. #$%*.... I'm beginning to hate these carbs.

[dave500]

do a proper hot compression test,,make sure the throttle is wide open and the battery is good,,120 sounds low,youve had the carbs off five times?

[Don R]

Float level.

[Lostboy Steve]

Yes, I have literally had the carbs off 5 times. Apart 3 times. Last time I replaced all the little felt bushings and re-checked everything. Float level has been set every time.

[Lostboy Steve]

Dave I know it sounds low. It was dry and as cold as it gets. I was more checking to see if all were the same as my tester is a piece of trash and old as hell. Since all were within 5 or so psi I figured there was no reason for only 1 cylinder to have an issue if it was a compression problem. Everything is new so I wasn't banking on mechanical issues, just MAKING SURE.

[matt mattison]

I think that black plug is oil fouled and that's whats giving you a fit. I kinda have the same thing going on with my 550, but the miss isn't so bad I can't ride it. I have a leaking valve stem seal. Im temporarily masking  my issue by running 20/50 oil and mixing MS109 race fuel with high test. The race gas gives better combustion and burns the oil off. Yes, it's a bit expensive, but I just want to ride it for the season before I tear the top end down. Check your oil level and keep an eye on it. Good luck.

[Lostboy Steve]

I suppose that's a possibility however I have new seals and guides in it.

[dave500]

see if you can borrow a better compression guage,,run it hot and try it again,,sometimes a valve might not leak untill its hot,,i understand what your getting at with your cold quick test and the same result in each cylinder,have you tried another set of new plugs yet?once they foul they dont run aswell even when cleaned.