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Discussion Starter #1
A little backstory, I bought a 97 black bird(my second one) and unknown to me that when you get up into the rpm under full throttle, acceleration starts to get a little choppy? breaking up? and that the average fuel economy is around 21 mpg and all I did was commute to work for 20 miles on the highway a few times. I thought it was the fuel pressure regulator but I looking through the manual and it doesn't seem to have one.... any thoughts?
 

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Check for the air deflectors on either side of the airbox. There's also funnel system that directs cold air off the nose ducts to the oil cooler if any of these are missing you'll get the symptoms your describing. Also do you have the stock air filter installed or an aftermarket. The carnies don't like any gauze type elements. And its picky about after market paper as well. Do thread search for the deflectors. I know Tiger has a thread with patterns for 2 of the elements.
 

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Discussion Starter #3
I have not checked either, I thought it was a more serious issue than just the air filter. Ill let you know what I find this afternoon
 

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Ordinance
No the Carby birds are a unique breed. Honda got that power plant pretty much optimized to the point that it's pretty much on the performance edge from the factory. It doesn't take much in the intake tract to piss it off. Pulling those deflectors and or moving to a gauze type element will make it act exactly as you describe.
 

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For Air Guide Plate related info click the link:

https://www.cbrxx.com/engine-airbox-exhaust-fuel-delivery/29201-template-1997-1998-cbr-1100xx-air-guide-plate.html


Other items to consider for carb related performance issues (if not already mentioned above):

1) Fuel tank vent: The fuel tank vent needs to be functional so that the fuel tank does not come under a vacuum or partial vacuum during engine operation. If the tank can not vent to allow air in as the fuel level drops the gravity flow of fuel to the carbs will be effected.

2) Engine vacuum line connection to the auto shutoff petcock: When the engine cranks/is running the engine vacuum pulls open the auto shutoff petcock to allow fuel to flow to the carbs. If the vacuum line from #2 cylinder (see the rear for the cylinder head at the #2 location...second cylinder from the left below the #2 carb) is compromised in any way the fuel flow will be restricted or nonexistent. Like wise, the the diaphragm at the petcock is not performing there will be fuel flow issues. You must also ensure that the vacuum line between the cylinder and the petcock are connected to the correct nipple at the petcock. The correct nipple/port faces across the bike at 90degrees to the ground. The nipple/port that points directly down is a not correct for the vacuum connection. It is a vent and/or a leak check port only for the diaphragm. Some related "petcock" connective info is located here:

https://www.cbrxx.com/general-cbr-xx-discussion/47299-vacuum-hose-help-please.html#post613071


3)There is no "fuel regulator" on the carb machines. When the XX went to fuel injection with a in tank electric fuel pump, the fuel regulator came into being for the fuel injection system. Model years 1999 and up are fuel injected.



4) Choke Lever (left handle bar switch block): Normal for cold first starts of the day usually require the choke lever to be pulled fully on (pull to the rear of the bike) to ensure good cold start performance. Some engine cranking may be required to allow the carb fuel bowls to fill once the auto shutoff petcock is pulled open by engine vacuum. Normally (in my experience) no twisting of the throttle is required for a stock machine to be started from cold. With the first start of the day complete the bike should start without choke (it's actually an enrichment circuit not a true choke) for the rest of the day, unless there is an extended engine off period during your ride, or you are commuting to work for an 8hr or 12hr shift day. Ambient temps will also play into this start routine. Colder temps will perhaps require the lever to be pulled on. Ensure once your up to operation temp (engine speed with slowly pick up as the engine warms with the choke in the on position) you can slowly back the choke level to the off position. It is not hard to forget the choke leveler is in the "on" position. I make a habit of pushing it forward to "off" once I rolling down the road, while scanning the dials for rpm/speed/oli pres light out, etc.


HTH,

T.
 

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Another thing to consider, especially if you have an under-tail kit (fender removal), is the ECU location.

I had a '97 that did what yours is doing, under hard acceleration it would hiccup badly, surging and then slowing very erratically. It was almost as if someone were flipping the kill switch back and forth while riding. Turns out, the ECU was bouncing around under the seat and causing this problem. Once I strapped it down with a small bungie cord the craziness ended and it rode smooth as silk like it was supposed to. Check under your seat for a loose ECU.

The under-tail kit that was on the bike when I bought it removes the little pocket that normally holds the (strapped down) ECU.
 

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Discussion Starter #8
Thanks for all the advice! So this Sunday I went out to check that nothing was missing and that the filter was the right type of material.........Well lets just say I found the problem, I've ordered a new OEM filter and ill let you guys know how she rides! 20191006_140200(1).jpg
 

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Uh ohhh
Before you go much further you need to make sure the mouse that made that nest is out. I'd also be checking your loom wiring. Hopefully they didn't go and get material for the nest from other areas.
 

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Discussion Starter #10
Did and done! I didn't think about the wiring but I could definitely see that being an issue. Ill be checking that this weekend then when I change the oil, since I have serious trust issues now about what the old owner told me.
 

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Discussion Starter #11
So went out this morning to take her to work and now she refuses to catch(the engine just turns over)? She started every time before...any ideas before I start going through vacuum hoses?
 

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Discussion Starter #15
It did right after I cleaned out the mouse home and sealed the air box back up, I then idled it for a bit and it seemed fine... I did turn the fuel valve off while working on it but that is back to the ON position. I didn't remove any vacuum or fuel lines. Maybe the idle screw is wonky? it does say to back it off 2.5 turns but is that clockwise or counterclockwise?
 

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Counter from seated. You may want to pull that vacuum line and make sure it's clear.
 

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Discussion Starter #17
Well I just feel silly now, the vacuum line just fell off while I was moving the tank around.
 

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Gotcha
At least you put it on the right port.

If your ever down Norfolk way look up my son he's riding a 03 BB.
 

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Maybe get some new hose from Honda. I just replaced all hoses and there is No Way they are coming off without some brute force. Great stuff.
 
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