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Troubleshooting help - sudden loss of power

  • Thread starter Thread starter Roostabunny
  • Start date Start date
R

Roostabunny

Guest
Not sure what's going on or how to figure it out.

Here's the scoop, accelerated pretty hard out of my work parking lot to get across the lane of traffic. Got to the light 100yds down the road, and the bike sounded a little odd - a little more "throaty" than usual. Might have been my imagination, but I thought I smelled gas as that moment.

When the light changed, the bike seemed like it was bogging down and couldn't get full power. It was similar to the way it feels when it's running out of gas (I have no fuel guage), so I switched over to RES even though I'd filled up on the way to work. I also fiddled with the choke. No difference with either experiment - still rumbling and underpowered.

I stopped once or twice to see if I could see anything going on in the engine, but nothing jumped out at me. Rode the rest of the way home - about 25 miles overall. It idled fine at lights.

When I got home I took off my helmet, put it on the center stand, started it back up and took a walk around it. The oil window caught my eye, as I could see amber fluid about halfway up the window and a tiny bit of foam. Usually when the bike's running I don't see any oil down there. I turned the bike off, and the fluid level went up over the window fairly quickly.

The amber color didn't bother me - I just changed the oil yesterday - but the volume of it made me wonder if I had gas in the oil. The loss of power seemed fuel-related too, so that figured into my amateur assessment.

So now I'm trying to figure how it got there, what I did, and what to do to fix it. Any ideas?
 
Sounds like gas in the oil. Most likely reasons are stuck carb float or petcock is allowing fuel to flow back into the engine via the vacuum port.
 
UPDATE:

OK, let's chalk that initial post up to newbie panic at the end of a hard day. I'm no longer convinced that there's gas in my oil, and here's what I did in the last 20 minutes.

I went back out to check the oil and see if it smelled like gas. It didn't. But being a newb, all engine fluids sometimes smell alike to me, to I popped the gas cap to remind myself of the difference. When I did that, 2-3 tablespoons of fuel came out of the cap itself and spilled on top of the tank, and I thought... tank vent?

So I put the cap back, grabbed my gear, and took it back out for a test ride. Still sounded a little loud, but the power was better. By the end of the ride it seemed almost normal.

The oil level also seemed more normal on the center stand - I could see the top edge of the oil in the window.

So now I'm still not sure what happened for that 25 mile ride home. I'll update tomorrow after my ride to work.
 
Nessism said:
Sounds like gas in the oil. Most likely reasons are stuck carb float or petcock is allowing fuel to flow back into the engine via the vacuum port.
Click to expand...
Will gas in the oil cause the funky running, or is that just another symptom of the fuel problem?

How can I be sure one way or the other about the condition of the oil?
 
By the way - I should mention that the petcock's new OEM. I replaced it a month or two ago.
 
Sounds like you figured it out, gas cap vent issue.

At the risk of sounding obvious, if the volume of oil in your crankcase is the same as before, you don't have gas in there.
 
Nessism said:
Sounds like you figured it out, gas cap vent issue.

At the risk of sounding obvious, if the volume of oil in your crankcase is the same as before, you don't have gas in there.
Click to expand...
Obvious is OK - I started this panicky thread. :-D

It seemed like it went right up over the window earlier, but then when I was a little more calm I saw that it stopped shy of the window edge.
 
Also, I'll do a search on tank vents, but if anyone has any tips, feel free.
 
OK, so here's the update as of this morning's 25 mile commute.

1.) Not quite as boggy as yesterday, but still a noticable loss of power especially in the lower revs
2.) Still louder than normal, but the idle sounds fairly normal to me
3.) Despite the "normal" sounding idle, I know something's up - I can feel from the exhaust that #1 or #2 (left side, right?) is stumbling at idle
4.) This change was sudden. It seemed to occur after a brief hard acceleration.
5.) After checking again this morning, I think my oil level's stable and consistent with where I normally fill it, so I'm dropping that as a symptom.
6.) I checked the gas cap again this morning, and heard no signs of vacuum when I opened it.

So now I'm at the point where I no longer think there's gas flowing into my crankcase, but I still have a problem.

Could it still be a stuck float? Other ideas?
 
Hey fellas, just bumping this to double check on tips for troubleshooting my loss of power. Thanks!
 
have a close look at your carb boots on both sides of the carbs. you say several times it's louder, if carb boot came off it will be louder and the loss of suction through air filter will cause it to lean out and loose power / stummble.
 
Since it sounds like you're not pumping gas into the crankcase - I'd check the ignition system. See if your plugs look sooty or wet from too much gas or do they look dry and cooked.

I lost my igniter box over time and it would run for a bit and then start acting like it was starving for gas - eventually it got so bad the bike wouldn't run above idle and would spit & backfire like crazy. And verify that the charging system is working too, a weak battery or bad regulator/rectifier can cause similiar symptoms.
 
focus frenzy said:
have a close look at your carb boots on both sides of the carbs. you say several times it's louder, if carb boot came off it will be louder and the loss of suction through air filter will cause it to lean out and loose power / stummble.
Click to expand...
I took a look and they're well-seated and snug on both sides of the carbs. The airbox side has new boots (in November, I think) and the carb side has new-ish viton o-rings from Robert Barr (less than 6 months old).

I warmed it up and sprayed a little WD40 on the boots to see if it revved - no response. Don't know if that eliminates air leak as a potential problem, but it was all I knew to do to test for it. By the way, I did a complete overhaul on my airbox last month, too. Sealed it up good. Anyway, I figure a leak there would impact all 4 cylinders and not just one or two.

I also got other signs of lean running. There's a little popping and a little whitish exhaust smoke from the left-hand pipe, which I assume means that I'm running lean on either #1 or #2 or both.

I'll take a look at the plugs and check the charging voltage tonight.
 
Last edited:
Alright - got some new info after running through those steps.

Charging:
After frying the unfused circuit on my meter by reversing + and - (duh - in a rush) I got it straightened and measured 12V at the battery and 13V at around 3000 rpm. Not sure if that's optimal, but seems like enough that it's probably not the problem.

Plugs:
Definitely an issue on #1. Reading plugs is not my specialty, but even I can see that #1 is wet and grimy compared to the others. The pic is showing (from left to right) #1, #2, and #4. What are you guys reading here?

By the way, looks like the ceramic insulator might have a tiny chip out of it on #1. Is that a symptom, or might that be the actual problem?
 
The damage to the plug could very well be the problem. Scare up $1.79 and replace it. Heck, skip the latte and replace all of them. The sudden onset of the problem also points to this.

The gas cap issue still should be investigated. Lay the gas cap on your working surface upside-down, remove the two screws, and take it apart. Take notes if you need to. Clean the metal stuff with carb cleaner, the plastic and rubber stuff with Sea Foam or WD-40. It's pretty easy and only takes a few minutes, and if there's a venting problem, it might help.
 
bwringer said:
The damage to the plug could very well be the problem. Scare up $1.79 and replace it. Heck, skip the latte and replace all of them. The sudden onset of the problem also points to this.
Click to expand...

Rookie question - the gunk might be the result of a mediocre spark not igniting things well and leaving schmutz behind?

Can I pick these up an auto parts place or just cycle shops?
 
Looks like #1 plug may be damp with oil? You also say there's white smoke out of the left exhaust.
I think the spark is being compromised by burning oil. Running on "3 1/2" cylinders at best. A fresh plug will probably help, but only to help prove this. It will probably start to foul soon too.
One check you can try...
Warm up the bike fully, running as it is. Then put in a fresh plug while it's still fully warm and test immediately. If it runs much better, at least initially, that's the problem (piston ring, valve guide seal). Don't test a new plug with the motor cold. If it is oil leaking into the combustion chamber, it may immediately foul/semi-foul the fresh plug and your test will not be certain. Oil leaks are usually greater/worse before the motor heats up.
It would be great if it were just a bad plug but a bad plug won't cause white smoke to appear. Oil leaking causes white smoke. Excess fuel (rich) cause dark/black/heavy exhaust.
If you have a compression gauge, that will prove it too.
 
could be silly...but I am a silly guy to suggest it... ahem... check them rubbers on your bike to carbs and if your sitll usign the stock airbox make sure that the seal on it is good. I had mine pop off on me after a speed bump and it caused me enough grief...being I did not have the tool I needed to get it to go back on... lucky me I found someone with duct tape wrapped that around it and vwala issue patched until I got home and fixed it right =)

Good luck
 
KEITH KRAUSE said:
Looks like #1 plug may be damp with oil? You also say there's white smoke out of the left exhaust.
I think the spark is being compromised by burning oil. Running on "3 1/2" cylinders at best. A fresh plug will probably help, but only to help prove this. It will probably start to foul soon too.
One check you can try...
Warm up the bike fully, running as it is. Then put in a fresh plug while it's still fully warm and test immediately. If it runs much better, at least initially, that's the problem (piston ring, valve guide seal). Don't test a new plug with the motor cold. If it is oil leaking into the combustion chamber, it may immediately foul/semi-foul the fresh plug and your test will not be certain. Oil leaks are usually greater/worse before the motor heats up.
It would be great if it were just a bad plug but a bad plug won't cause white smoke to appear. Oil leaking causes white smoke. Excess fuel (rich) cause dark/black/heavy exhaust.
If you have a compression gauge, that will prove it too.
Click to expand...
[FONT=Verdana, sans-serif]OK, I don't love trouble, but I love the puzzle of troubleshooting. Meanwhile I'm pretty green as a mechanic and I'm trying to get my newbie head around this at a basic level. Let me see if I'm understanding this...
[/FONT]


[FONT=Verdana, sans-serif]If I'm burning oil, that means I'm leaking oil into the combustion chamber. You mentioned piston rings and valve guide seals because those are both parts that fail, thereby allowing oil into the combustion chamber? [/FONT]


[FONT=Verdana, sans-serif]Checking the plug will allow me to determine if it's the cracked insulator or oil fouling that's causing my problem. [/FONT]

  1. [FONT=Verdana, sans-serif]If it's the plug, it won't foul again, and we blame my mediocre photo. [/FONT]
  2. [FONT=Verdana, sans-serif]If it improves with the new plug, but then fouls again, I'm burning oil and there's a whole troubleshooting sequence for that.[/FONT]
[FONT=Verdana, sans-serif]Is that right?

Can you tell I'm scared of burning oil? I didn't even ask what else that fits the scenario could make the plug black.
[/FONT]
 
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