Exhaust 1 barely warm, other 3 nice and hot.

Hey Folks,

My bike is running on 3 cylinders from what I can tell. It has fuel and the wires/plugs are in newish condition. Battery is fine as the bike does run on 3 cylinders. I really cleaned the Carbs up real good not too long ago (couple of months ago).

My problem is that the number 1 exhaust header does not get hot at all from what I can tell. I unscrewed the drain plug for the number 1 carb and fuel came out just fine.

What is the next step of diagnosis?

 

Try switching the 1 and 4 spark cables. See if the problem travels from 1 to 4 cylinder. It probably won't, so put the cables back and switch the spark plugs for the same reason. If the problem still doesn't travel, go down to your local auto store and borrow a compression tester, test all your cylinders. If they check out ok, then go through your carbs again. Either you didn't do something right on #1 or it vibrated loose or something.

Report back on what you find.

 

Would a back air leak in one of the carb boots cause that also?

 

Depends on how bad the leak is and which boot. If its the boot between turbulent and thecarb, then you have a massive vacuum leak. Instead of drawing air and fuel thru the carb its drawing air. If its a major leak between the carb and the air box, it could cause issues but I don't think it would disable the cylinder completely. Make sure youre getting spark on that cyl, pull the plug, put the plug wire boot back on it, press it against the block and crank ot over, also check your gap.

 

I think I can answer this question. Couple of weeks ago I noticed some backfiring at around 4000 rpm, but didn't reallyl notice any lack of power. I happened to touch the #4 exhaust pipe after the engine was off and noticed it was barely warm, whereas the others were really warm. I started the bike up again and felt the pipes. 1,2 and 3 got skin burning hot within a few seconds - #4 - just warmish. This board suggested the backfiring was from a lean running cylinder, so I started looking for air leaks. I immediately found the leak at the #4 intake manifold ( rubber boot) It was so bad I could not only feel air being sucked in, but I could hear it. Took the carbs off, removed the boot to find only half of the gasket was left. I orded a new gasket from my Yamaha dealer, installed it, fired up the bike - all 4 exhausts skin burning hot in about 15 seconds.

 

Its got brand new plugs. When I removed number 1 plug wire, it ran the same as it did with the wire installed. I will try swapping the 1 and 4 and see if it changes.

Thanks for the help guys. I will report back in about an hour.

 

Sorry, meant to type "bad" airleak, not back. I think it was your post that came to mind Rickinduncan. Yeah, try spraying carb cleaner or wd-40 on your boots marshall one at a time and if you get a massive change in idle, that will be a good place to start. Don't you just love this place? lol, I know I do!

 

Good news to report. When I swapped the two wires (1 & 4), cylinder 1 started running right.

So, that tells me that either I have an issue with the physical wire for cylinder 1 (has new boots, NGK) or the coil pack is dead on that one side. I am just thrilled it is not a fuel issue. I hated tearing into the carbs. Glad I did, but glad I don't have to go back into them.

Anyone know how much a good coil pack runs? Or should I try something else first?

 

I do love this place and all other websites like it. Used to be over at SVTPerformance.com (douchebaggery ran rampant) and yzf600r.com.

Thanks for the tip macros, but turns out that there is no air leak (so far) and the wire/coil pack might be the problem.

When I first got the bike, I tested the packs with the impedance test and they seemed fine but you never know what happens. It sat outside with a cover on it for about 9 months before I just moved and am able to devote some time to it. But I never felt like it was running on all 4 and it sounded like this when I fixed up the carb rack back then too.

 

I'd be thinking it was just a bad wire. If it was the coil, wouldn't 2 plugs not be firing?

 

I have no idea. But, I will mosey around and see if I can find some answers about that and if you can simply replace the wire.

 

to my understanding the ignition works on the "wasted spark" principal...1&4 and 2&3 are 180 degrees out from one another. so while 1 is on it's compression stroke, 4 is on it's exhaust stroke. both cylinders fire at the same time, but only one is on the compression stroke, hence the "wasted spark". you have a bad wire. chase it back to the coil, replace, reboot and ride it like you stole it. as far as replacing the wire, idk. most of my bike knowledge was learned fixing and tuning my old honda SOHC-4'S, and on those, the wire is part of the coil. in that case, i would chop the wire about 3/4 from the coil, find a #10 screw, cut the head off, thread half of it into the stub hanging off the coil and thread the remaining into a new copper core spark plug wire, kill it with liquid electrical tape, cover with a piece of shrink tube and ride it like you stole it from the sheriff.

hope this helped.

 

CB is correct, 1 and 4 fire at the same time, so I'd be about 99% sure it's the wire, or the boot. Before you go chopping the wires off and replacing them, try this:

The boots on these wires screw on, so screw the boot off and cut about an inch off the end of the wire and screw the boot back on.

I had same thing happen on #3 and it was because the boot wasn't making good contact with the spark wire.

He is also correct in that the wire is part of the coil, so you either have to replace the coil, or do as CB suggested and splice the new wire in, if you have to go that route.

 

HOLD ON.

First off, if you cut an INCH of a plug wire to "freshen" its connection to the plug cap, the wire will likely then be way too short. All you need to lop off is 1/4"-3/8" max. This technique quite often works very well.

Yes, the coils fire both of their leads at the same time, hence the "wasted spark" terminology, as mentioned above. But there's no "side" to the coils, they fire both leads and that's that. The wires are molded into the coils; they CAN be replaced but it requires "coil surgery."

You also need to look inside the plug cap, where it goes onto the spark plug. The resistor "core" can come loose inside the cap. There are two screwdriver "slots" on either side of the hole where the tip of the spark plug goes; ensure that the inner core isn't loose in the cap.

 

In the idea that we should always cut with scalpel first rather than discard the limb with a hatchet, I took bigfitz's advice and only lopped off a 1/4" and re-secured the cap. Fired her up and bam, running on all 4!

Thanks for your help gentlemen. I know that at some point, I will have to replace the wires altogether and at that point, I will open them up and epoxy them closed when fresh wire has been installed.

I love this place!

 

Imagine that.

I guess having experienced it a few times does help, doesn't it.

You are more than welcome.

Check the cores inside the caps, seriously. I had one loose last season, for no apparent reason. Don't crank on them, but ensure they're tight.

 

I was amazed at the difference a $10 set of all new plug caps made. I got them because I wanted to make sure and it was cheap, I wish someone had told me to get new ones sooner.

It is a part of a basic tune up, after all.

 

I see you have your problem fixed but for other people who have a problem and it ends up not being spark related or air leak related check your pilot circut. i work at a yamaha dealership and was working on an 86 radian 600 and had the one head pipe running cooler than all the rest. The whole problem ended up being a partially plugged passage even though i had just really thoroughly cleaned the carbs. Just something else to keep in mind.