Bike loses power

[dm_gsxr]

Kind of a puzzling symptom that I'm investigating on the TransAlp.

When riding the bike, it'll occasionally drop to about half-power. I'll give it more gas or drop a gear but it's still running about half-power. Then it'll jerk as if it's getting power again (you really have to hold on to the handlebars while working this out). But it'll jerk several times, sometimes not getting the power back and others the power returns.

This past weekend, I was trying to puzzle through it and thought it might be a loose spark plug wire. Hitting a bump maybe causing the wire to get far enough away from the plug to lose one jug then my jerking the bike around to get power back causing the cable to "reconnect" again. It has backfired twice on Monday on my way home from work. I could also smell gasoline. I was again thinking spark plug(s) figuring the gasoline smell was from the plug not firing.

When I arrived home, I checked the front wire and it seemed like it was seated well. Same with the rear one. The rear cable seemed to have a lot of play while on the plug so I pulled it off and accidentally discovered the rear plug wasn't screwed all the way down. I was able to finger tighten it back down and then snug it with a socket and the bike started back up without a problem.

Well last night on my way home, I found the bike doing it again. This time though I pulled the spark plug cable off of the rear plug and power returned almost immediately. At the light I plugged it back in and it worked ok for a block or two then power went to 50% again. Again I pulled the cord, got power, and plugged it back in. It seemed to have sufficient power until I got to the driveway when the power cut again and the bike died.

After I got ungeared, I went out to check and sure enough, the plug was loose again. I unscrewed it with just my fingers (that's how loose it was) and visually checked it. While it didn't have a gasoline smell to it, the plug was black and sticky around the base on the piston size of the threads. The tip was gray and the rest from the end of the plug to the base was just black. I checked the service manual and gapped the plug (it wasn't off by much and was likely fine), then torqued it down to spec (14nm). I have the specs for replacement plugs so I'll pick them up today.

Curiously two things this morning on my way to work (it's a short, 4.7 mile ride). The bike seemed to run a tad rougher and there was one point where I felt the power drop briefly. I suspect the spark plug may be fouled (in looking at this page, it might be a tune-up issue as it doesn't look quite like the oil fouled pic). I'll snap a picture when I change out the plugs tonight (assuming NAPA has the replacement plugs available).

Just bringing it up in case folk have ideas I may have missed. I walked through the maintenance section of the service manual and don't see much else that could be done short of a valve check/adjustment. It doesn't look crazy difficult and I have the tools to perform it if necessary.

Carl

[Scratch33]

Bad Coil(s)?

[dm_gsxr]

Bad Coil(s)?

Why would that cause the power cutout and I'm really curious why I'd gain what felt like full power with only one jug working (after pulling the back cable)?

I'm not a super gearhead but I've certainly done my share of wrenching.

Carl

[nevinfs327]

Why would that cause the power cutout and I'm really curious why I'd gain what felt like full power with only one jug working (after pulling the back cable)?

I'm not a super gearhead but I've certainly done my share of wrenching.

Carl

The plug working itself loose sounds like the biggest problem.  Might need to Helicoil it.  

Maybe the perceived increase in power comes as the non-firing plug works its way loose so the cylinder that is working doesn't have to fight compression in a dead cylinder?

[Scratch33]

Why would that cause the power cutout and I'm really curious why I'd gain what felt like full power with only one jug working (after pulling the back cable)?

I'm not a super gearhead but I've certainly done my share of wrenching.

Carl

Dunno - same here; I'm just going through some things that've caused me problems on older bikes.  Is it doing all this on the same tank of gas?  When's the last time the fuel filter was replaced?

[Andrew]

Hi Carl,
  I think you are on the right road, so to speak, changing the plugs can't hurt. Make sure the threads in the cyl heads are OK, While the plugs are out check the plug wires & boots carefully, look for signs of arching (burned holes, track marks ect.) Next ohm check the wires (possible burned core) have a good look at the wires to see if there are signs of arching on them as well.
  From what you describe (sudden loss of power and sudden return of power) it does sound like a spark issue, well more like a loss of spark issue. Possible from the wires arching out or plug issues, could be coil. Does the bike in question have one or two coils? could be one is beginning to fail, but my bet is on the plug wires arching out.
If you have a light bulb test light, plug the ground wire of said test light to the frame or good electrical ground then run over the plug wires while the bike is running with the test end. Don't worry the current would rather run through the light than through you (but keep your hands off the bike just for safety sake) If the bike cuts out and you hear or see the zapping you have found the leak. And no this will not harm the test light or you. THe ign coil will only produce enough voltage to make it back to battery B- then discharge, the test light is a lot less of a load than the plug so if there is a spot that will leak the test light will find it.

  Another tip, use just a bit of dielectric grease rubbed on the inside of the plug wire boot where the boot touches the porcelain of the plug (helps stop voltage leak and will aid in removing the plug wire later )

[mugwump58]

 

[Papa Lazarou]

New plus, if there's still a prob, check the coil on that cylinder-a duff coil can cause that problem.

[dm_gsxr]

Dunno - same here; I'm just going through some things that've caused me problems on older bikes.  Is it doing all this on the same tank of gas?  When's the last time the fuel filter was replaced?

It's been going on for about a year I guess. I really only ride it a couple of times a month, maybe and one week out of four in the winter. And it only seems to do it every once in a while. I initially thought the carbs were gummed up and used some gum out but it didn't work.

Got new plugs today and will check the coil and wire tomorrow.

Oh and I haven't changed the fuel filter although I will check it tomorrow.

Carl

[dm_gsxr]

I just checked the service manual, no fuel filter. There's a fuel screen. That's what I saw when I checked it yesterday but wasn't sure so I confirmed it.

So I'll clean it tomorrow.

Carl

[dm_gsxr]

I replaced the plugs and it didn't seem to make any difference to the running of the bike. A run around the block still had it dropping to 50% power. I took off the tank and drained about 2/3'rds of it before disassembling the fuel cock. It leaked a little while I was draining it and when I removed the base, it seemed to be pretty loose. The screen was nice and clean with no odd bits on it. I reassembled it and torqued it down to spec. In doing so, I found where the fuel cock screwed into the tank was pretty loose as well so I tightened it down a little as well. After filling the tank, the bike seemed to run well enough with no drop in power. But I also note that it didn't do it every time I took the bike out for a ride. So I'll be running around a bit for the next couple of days to see if I can get it to do it again.

Carl

[Scratch33]

   Keep us posted.

[dm_gsxr]

I did some reading on troubleshooting coil issues and it seems the problem is exactly that. A failing coil. I'm going to open the bike up again tomorrow to make sure it's not just a loose wire or something and to make sure I order the correct coil. I'll likely do some testing too while I'm at it however if it's intermittent, it may not help.

Carl

[Scratch33]

I did some reading on troubleshooting coil issues and it seems the problem is exactly that. A failing coil.

 

[Papa Lazarou]

Coils can be sods to track down as a fault.

[dm_gsxr]

Well, the failing seems to be if it's cold or hot so it'll be easier to diagnose. I tracked down how to test it. Get the resistances from the service manual and test. The fun thing is I didn't realize the bike has four spark plugs. Two are out in the open but the other two are hidden. The plugs are really tucked down in the heads. I tried to remove one and couldn't because the socket got stuck.

Always something to cause issues.  

Testing tonight if possible.  Will post results.

Carl

[Justin]

Well, the failing seems to be if it's cold or hot so it'll be easier to diagnose. I tracked down how to test it. Get the resistances from the service manual and test. The fun thing is I didn't realize the bike has four spark plugs. Two are out in the open but the other two are hidden. The plugs are really tucked down in the heads. I tried to remove one and couldn't because the socket got stuck.

Always something to cause issues.  

Testing tonight if possible.  Will post results.

Carl

I think the best course of action here is to trade it in on GenII  

Although the trade in value on a Busa with 105k is probably not that good

[dm_gsxr]

I think the best course of action here is to trade it in on GenII  

Although the trade in value on a Busa with 105k is probably not that good

Oh, you misunderstand. I'm not working on the 'busa. It's fine (well, except for a headlight short). This is the TransAlp.

Either way, not likely much of a trade in on either. I do have an interested buyer for the TransAlp. Well, until now anyway.

Carl

[dm_gsxr]

As to that. I was able to get to the primary and ground on three of the coils. Per the service manual, resistance should be between .1 and .2. It's .4 on the three I can reach. Resistance on the secondary to ground with cap range is between 7500 and 10000. It's 8540 on the two I could reach. I have to disassemble the front a bit more to check the two I couldn't reach.

Can three be bad to the same resistance? The bike's had apparently good power until this started. Could two have been bad and it be ok because of two spark plugs per cylinder (redundancy) then the third bailed and caused the loss in power?

Carl

[Andrew]

Yes this is possible, but you might have noticed a bit of a rough running condition with half of the spark gone even if each cylinder had one good coil. Ever ride a BMW with bad stick coils?  Runs like crap when put under a load but not too bad at idle.

Get one of these and do a dynamic test of the coils

http://www.amazon.com/Thexton-404-Adjustable-Ignition-Tester/dp/B0002STSBM

Easy to use and cheap.