ST1100 Major loss of power during roll on

[Clair]

Hey all. As some of you may have read in the ST1100 tech forum, I did my first wrenching on my '01 ST1100, doing it's 24K maint. This included Oil change (oil and filter), air filter (replaced with new K&N filter), spark plugs replaced, brake fluid replaced, final gear oil replace. All went fine. Oil changing I've done before so that was fine. Rear gear oil change was a PITA and messy, but fine. Replacing the brake fluid was easier than I expected it to be, having never done that kind of thing before. A little messy (every was covered) but it went well and the brakes feel better. Air filter was a piece of cake, other than the 10 or so screws that kept wanting to drop into the bike ...

Replaced the spark plugs too. Not anywhere near the PITA I had expected they might be. I took my time. Removed the old one at a time, gapped the new ones, and using the Plug tool inserted the new plug till it was "snug". Went pretty well and I'm thankfull I have small hands. LOL

All that was friday. I did a little ride after doing that to get dinner, so maybe 10 miles total. Everything felt fine, engine sounded good, Im a happy camper ... till today's ride.

I am now experiencing a dramitic loss of power during roll on. Normally I can cruise up parley's summit on I-80 doing 75mph in 5th and be able to roll on effortlessly to pass. Not today ... attempt to roll on and the bike experienced a dramitic loss of power. Later on as we were climbing Trappers Loop ... another road where I can climb doing 75 mph with plenty of Oomph left to spare ... I damn near had to pull over. I usually do 75+ in 5th gear going up but had to drop down to 2nd with the RPM's near 7000 to get any acceleration!!! Just a total loss of power during a roll on.

The bike cruises fine, sounds fine. If I accelerate slowly and smoothly the bike behaves fine. I did 80mph coming home on the slab stretch. No hesitations, no narly sounding exhaust, sounds normal ... untill I want to roll on to do a hard acceleration. If I try to pass ... switch lanes, roll on ... bike loses power. If I try to acclerate going up the hill doing anything other than a gental roll ... the bike loses power. ***???

Could I have F'd something up? My riding buddy who's a good wrench thinks not. Plugs were correct and gapped correct. Air filter is fine and installed fine. Bike idles fine. He rode it and said it feels fine until you need hard power. He's suspecting either hte Fuel Filter or the Fuel Pump. Any ideas???

I'm going to replace the Fuel Filter later on this week (assuming I can find one) just to be sure. It's the easiest thing to replace and probably the cheapest. We did take it off and inspect it, it looks fine. Hooking it up and flipping the Engine On switch and it filled/squirted gas as expected. Dunno but figure it's the easiest thing to do first.

I rode the bike for a 380 mile ride last Sunday doing all kinds of roads and speeds. No issues, bike had it's usual overabundance of power and smoothness. I do my maint and suddenly it has problem. Did I do something?

Any ideas or suggestions??? HELP!!!

[Trekker]

Good suggestion. Change the air cleaner back and see if that makes a difference. I couldn't use a K&N on my old GL650i.... it would dog down exactly as you are describing, and was even worse in wet weather. It's amazing how air cleaners can effect the performance.

[Darth Vader]

With a K&N air filter, your carbs may have to be rejetted.

[Clair]

Hmm, ok I'll also try to get an OEM Filter from Honda on Tuesday ... why do these things always happen on a Sunday ... a Holiday sunday no less? LOL

The K&N Filter is a two parter ... the round filter piece and a foam outer ring. I followed the instructions on the package ... "On an unmodified motorcycle, the foam ring MUST be used" ... my ST1100 is unmodified so I used it.

I don't think it can hurt to get a stock filter and try it out. That's gonna be cheaper than giving it to the dealer to find what's wrong.

Thanks.

[Clair]

Now ya see ... in hindsight that makes sense ... and I sure as hell will the next time I do this but ... since it's "only" an air filter ... I kinda tossed it and the next day was Trash day. OOPS.

[Snoweyowl]

At least you have learned, as I have, not to trash something you are replacing until you know the new works. Life is a learning experience. Good luck with your problem.

[Clair]

Wa friggin HOO!! My bike is back to being the speedy Das-Wing it always was! NO more loss of power during a roll on. YAY!

Remember the problem ... after doing my 24K maintenance and then doing a ride this past weekend I was experiencing rather nasty loss of roll on power. Basically I couldn't pass or accelerate going up a hill. Sucked really.

After posting my situation on here, the consensus was that the problem was likely the K&N Air Filter I had used to replace the OEM filter. However, most people felt this foam filter restricted the airflow too much, hence the loss of power. The suggestions were to ditch the foam filter, or better yet get the OEM filter. I opted for hte latter approach.

Yesterday I got the OEM filter from Honda/Suzi and put it on. Then went for a ride up Parley's to Kimble Junction. VALA! NO power loss!!!! I could accelerate in any gear! I went up Parley's rolling on any time I wnated!!! Doing 80mph was effortless! Need to pass? No problem! My bike is back!!! YAY ME!

So, the K&N Filter was the problem. Basically the foam filter did restrict the airflow too much. I compared the K&N against the OEM and found that the OEM had more ribs, more folds, than the K&N did. In the span of 20 folds on the OEM filter, the K&N only had 12 ... basically 5 folds on the OEM for every 3 on the K&N. This would lead me to think the K&N would let more air flow through if it did not have the foam pre-filter on. Not sure how that would affect things.

Anyway, what's important here is that my bike can accelerate again!!! YAY

[CrashTestDanny]

Congratulations!

[Byron]

Clair,

The problem the K&N was introducing was caused by more air flow. Your bike was able to suck in more air but the carbs were still feeding it the same amount of gas. This causes a lean condition you detected as a loss of power. When you put a stock filter back on it corrected the lean mixture by restricting the airflow and thus power was back. If you bump your jet size up a notch or two you can use the K&N and have more power than before. It just depends on what you want. Glad to hear it's back in the pink again. FYI, this is not as big a problem with the 1300's because the computer will automatically adjust the fuel delivery within what the injectors will supply. That is also why adding the Turbo City FPR helps with the lean spots of the 1300's. Something to keep in the back of your mind when dealing with intakes and exhausts.

[wjbertrand]

So, the K&N Filter was the problem. Basically the foam filter did restrict the airflow too much. I compared the K&N against the OEM and found that the OEM had more ribs, more folds, than the K&N did. In the span of 20 folds on the OEM filter, the K&N only had 12 ... basically 5 folds on the OEM for every 3 on the K&N. This would lead me to think the K&N would let more air flow through if it did not have the foam pre-filter on. Not sure how that would affect things.

Anyway, what's important here is that my bike can accelerate again!!! YAY

Actually more folds or pleats in the filter will allow more air than fewer pleats if the filter media is the same. If you would unfold the filter with the greater number of pleats you would see that it offers more surface area, i.e. less air has to be sucked through each square inch of filter material, therefore a filter with more pleats will breath easier than one with fewer, again assuming the same filter media is used.

The reason a K&N filter, having fewer pleats than the OEM filter will allow sufficient flow (so long as the foam ring is absent) is that the media itself is more open, i.e it has larger pores. You can do the math on the K&N's ability to actually remove fine grit with those larger pores. The foam ring, added to the K&N media however results in a total restriction that is greater than the OEM, making the mixture too rich and reducing power as you found out. This problem with the K&N filter is well documented on a number of sites with respect to the ST1100. Going back to the OEM filter is wise in this case.

[BigTom]

Hooray! Glad the problem is solved...

And glad you did it before I did. I was planning to put in a K&N next service. You saved me a lot of time and trouble...Thanks Clair

[Clair]

NP Tom. I've heard from plenty of riders who use the K&N Filter, without the foam ring, just fine and love it. I could have tried taht but opted to get the OEM filter instead. I still have the K&N Filter so I may try a run with it sometime, do a tank full, and see how the bike performs. But for now the OEM filter has the bike running great.

[saaz]

Clair, all you will notice with the K&N is a bit more intake noise, but no effect on power, economy etc. If you do notice a difference it would only be if the OEM filter was dirty.