#1 Cylinder not firing anymore

Okay, this is getting really frustrating. The bike was running fine yesterday and now #1 cylinder is not firing. The #1 exhaust pipe is cold while the others are super hot. I tried to find a vacuum leak, but nothing. I get GREAT spark on that cylinder, so I do not know what else to check. The carbs are church of clean. Like I said, it was running great yesterday. Yes, I have an inline filter and the gas is brand new. Anyone have any ideas?

 

Buzz,

Compression check all cylinders.

Gary

 

Rocs, compression is good on all four. Sorry, forgot to put that down.

 

open the float bowl drain screw and see if you have fuel there. What do your plugs look like? (wet/dry black/white)

 

Just checked. Yes, I have fuel in the bowl. Plugs are dry black, but I wire brushed it til it was nice and clean and started it again, but it still has the problem.

 

change the #1 plug with #2

 

I actually just got done switching #1 with #4, and now something else just happened. I get fire on #1 and #4 now, but I am not getting any fire with #2 & #3 cylinders. I just went through this earlier this week. I did all the troubleshooting and found nothing wrong. I hooked everything back together and it all just suddenly started working again. And now, again, the middle two cylinders are not even sparking. Ugh.

 

Clean the connections & grounds to the coils, pull the connectors from the TCI & clean.

 

That makes total sense. I will do that tomorrow and let you all know.

 

Just want to be sure you understand that one coil fires 1/4, the other 2/3; so you're looking at a coil/pickup/wiring issue.

 

Mystery electrical that changes when you play with wiring is almost always bad ground or connectors.

I learned from years of working on cars professionally that when you see this kind of thing, start shaking and tugging on wiring while the motor runs...it will usually get better or get worse when you find the sweet spot where the problem is.

Also when high secondary voltages (spark) are involved, watching it run in a dark garage will often show you exactly where the spark is going to ground. In the case of a bike, you'd have to also have the tank lifted high enough to see the coils and leads entirely.

A spray bottle of water misted at the suspect components while it runs will find a bad plug wire or coil real quick too...but since you've already got the dead miss, that's not the way to go. But remember it for intermittent spark drop-out troubles.

And not a bad idea to pull connectors apart methodically, and spray the contacts of each with WD-40 or electrical contact cleaner....I've done every single one on this 750 I just got, simply to avoid this kind of gremlin-chasing later on. I don't have time for that

 

I cleaned the ground cables cause they were rusted pretty bad. I have great spark now, but those cylinders (#2 & 3) are still cold and not firing. I checked the bowls and there is plenty of gas in them. Could I have flooded my engine when I kept trying to run it without spark? If so, how do I unflood it?

 

Swap the plugs from 1-4 to 2-3, see if it'll clear em out.

If the miss follows the plugs, you know what needs to be done. Sometimes if they're just really fuel soaked, I'll leave them sit tips propped over the burner on my gas stove...flares off the fuel and dries them out.

If the misfire is still in the same holes, and you have good spark there, something else is happening...

Seems that when these intake gaskets fail, it's almost always on the bottom, and easy to miss even when you spray something around to check for it...you gotta actually shoot the spray right at the bottom arc of the boot or it will go around the leak. Fooled me twice on the old Max, no more.

If you've got a lean misfire it should pick up and start warming those pipes and firing those cyls at higher rpm though...

 

Been reading too many threads to keep them straight. Also try trimming the end off the plug wires for a better contact there...the boots on the plug ends just screw onto the wires...can get corroded in there or wire strands pushed away from the screw...

 

Ugh. Well, now #1,2,4 are not firing, but now #3 is. Now only running on #3. The others have gas wet plugs. I completely do not understand how this can happen. One day it is perfect, the next day is bad.

 

And no, I do not use prime on my petcock and the carbs have been wet set.

 

ok from what i have read you are having a random firing problem with the coils. have you check you pick up coil and made sure that you have connection down there with no wires messed up. that is all i can really thnk of when you explain what is happening. i believe there are a few lother possiblities that could cause you to have a problem. one you TCI two your pick up. both very important. or three your coils could be bad. but by sounds of it its not the coils that are haveing a problem. i hope i helped out some.

 

Yeah, i just don't understand because i checked everything on my ignition system. Everything checked perfect, no problems. I get spark when I clean off the plugs. I may try to buy another set of plugs since these have been through a lot. I only have one extra plug, which is the one I use for testing spark. There is always spark now, even on the cylinders that are not firing. Once I put the cap back on, there is no fire. It may be the plugs that are being stupid.

 

By all means fit a new set of the correct NGK plugs, properly gapped. It's not unheard-of for plugs to get saturated and quit firing not matter how much you try to clean them.

 

like Fitz said, don't make assumptions about cheap parts (plugs) that could be the whole problem.

My 650 would throw weak or no spark soon as the battery started to run down a bit from cranking...seems common in cycles. Top off the charge, throw new plugs in, see what ya get.

 

Well, I wanted to give everyone an update. I just recieved my new set of NGK plugs and the bike fired right up. It runs and is firing at all cylinders. The plug that I was moving around was bad, so I bought the good plugs. Thank you all for your help. I love this forum.

 

I just wanted to mention that the coils will fire completely un-grounded.
I tested a few sets of loose coils on my 750 once.