Carb air intake in the airbox
- Thread starter BumbleBerry
- Start date
John OoSTerhuis
Life Is Good!
What does your filter look like? If it’s OK that means the source isn’t coming in through the air intake opening at the rear of the filter housing. It might be oil vapor from the crankcase breather that vents into the air box through the nipple on the bottom right side.
John
John
OP
OP
Thanks John. I shall take a photo of the air filter and post it here. It looked rather normal (with small particles and dust trapped in) with an exception of a small dirty dark gray area.
Beeflips
(it's me...Greg) Returning some videotapes
+1 on the oil possibility, I've seen posts about being slightly overfilled too and coming through the breather into the carb area.
It's quite wet in there! Did you happen to lay it on it's side or overfill the oil? The engine breather is the only source of oil and there is a baffle that stops the residue getting straight on the filter.
Slydynbye
Will ride for Pie
It's normal probably caused by slightly over filled oil. It won't hurt anything.
Wipe it off, close it up, take a look at the oil level in the engine, reduce if too high and GO RIDE.
Wipe it off, close it up, take a look at the oil level in the engine, reduce if too high and GO RIDE.
OP
OP
Thank you all.
The oil level is right in the middle. But a year ago, for a while, she ran with oil level just above the top mark. Oil was changed few times since and always in the middle.
So I guess, it was because of that one time. I am waiting for new air filter too.
My concern is that BumbleBerry has lost ability to hit 160 kph and beyond. She just can't deliver. As you all know, ST's can easily hit those numbers and I intentionally watch my speed so I don't go above speed limit. But for a past 3 weeks, the power is not there at all. She barely hits 140.
She starts fine with choke, idles perfectly, but on first and second gear sort of rides with a hick-up! Until she warms up a bit more and at top gear in high way, can't go beyond 140. I have filled up with 94 octane fuel (always Chevron) and she performed a bit better. Battery is functioning perfectly, regulator/rectifier is fine (I tested both as service manual). I rode with gas tank cap removed, not change.
I don't have much hair left on my head to pull, so I keep scratching my head!
The oil level is right in the middle. But a year ago, for a while, she ran with oil level just above the top mark. Oil was changed few times since and always in the middle.
So I guess, it was because of that one time. I am waiting for new air filter too.
My concern is that BumbleBerry has lost ability to hit 160 kph and beyond. She just can't deliver. As you all know, ST's can easily hit those numbers and I intentionally watch my speed so I don't go above speed limit. But for a past 3 weeks, the power is not there at all. She barely hits 140.
She starts fine with choke, idles perfectly, but on first and second gear sort of rides with a hick-up! Until she warms up a bit more and at top gear in high way, can't go beyond 140. I have filled up with 94 octane fuel (always Chevron) and she performed a bit better. Battery is functioning perfectly, regulator/rectifier is fine (I tested both as service manual). I rode with gas tank cap removed, not change.
I don't have much hair left on my head to pull, so I keep scratching my head!
Sunday Rider
Site Supporter
Have you synched the carbs lately? How do the spark plugs look? Is the air filter clean(I know you ordered a new one)?
If this has just happened recently, and not gradually, one possibility would be your ignition coils have gotten weak.
Another possibility would be fuel delivery is adequate for lower speeds, but at higher speeds its not able to supply fuel at the necessary rate.
Since either scenario isn't a hard failure, but rather a degradation from normal, its hard to say how to troubleshoot for either condition. Ignition coils can have their resistance measured, but I'm not convinced that tells you much unless one isn't working at all. Weak ignition could show up as a fouled plug, worth taking a look.
I think there's also a flow rate test for the fuel pump, but I've never done it, perhaps someone else will chime in with their experience. I know there's been more than a few replaced fuel pumps being discussed here over the years.
Another possibility would be fuel delivery is adequate for lower speeds, but at higher speeds its not able to supply fuel at the necessary rate.
Since either scenario isn't a hard failure, but rather a degradation from normal, its hard to say how to troubleshoot for either condition. Ignition coils can have their resistance measured, but I'm not convinced that tells you much unless one isn't working at all. Weak ignition could show up as a fouled plug, worth taking a look.
I think there's also a flow rate test for the fuel pump, but I've never done it, perhaps someone else will chime in with their experience. I know there's been more than a few replaced fuel pumps being discussed here over the years.
Ditto on the plugs, and check fuel filter too, could this have started right after a fill up at the gas station. while the pugs are out check the compression to split the troubleshooting between a mechanical problem from a fuel problem. Timing can also cause this problem, 1100s have a timing belt too, might be due an inspection.
kiltman
Site Supporter
- Joined
- Apr 27, 2013
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- 2002,ST1100ABS
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- 8826
Check the routing of your throttle cable, make sure it isn’t snagged under the air filter housing
Bypass the vac. fuel valve to see if it's a fuel starvation problem. takes about 5 minutes with the plastic off. Can be back to stock in 5 min.
Vacuum Fuel Valve Bypass Method ( ST1100 ) *
Vacuum Fuel Valve Bypass Method ( ST1100 ) *
www.st-riders.net
ST1100Y
Site Supporter
I'd suspect this:
Small tare in the diaphragm of the auto fuel valve, preventing full opening of the valve core...
OP
OP
Thanks very much for all your inputs and great ideas.
I feel so dumb now, because the problem was much simpler than I thought! And the cause was a dirty air filter!! Last time, I changed the air filter back in July 2021. But I didn't look at my maintenance logbook, and it didn't seem to me that long ago. So once I got the air filter (HiFlo HF1911) opened the air box and cleaned it, and look at the air filter :
Put the new air filter in, and the oil/filter were due, so changed those, too.
She's back as normal, so we went for a 1000 km day trip!
I feel so dumb now, because the problem was much simpler than I thought! And the cause was a dirty air filter!! Last time, I changed the air filter back in July 2021. But I didn't look at my maintenance logbook, and it didn't seem to me that long ago. So once I got the air filter (HiFlo HF1911) opened the air box and cleaned it, and look at the air filter :
Put the new air filter in, and the oil/filter were due, so changed those, too.
She's back as normal, so we went for a 1000 km day trip!