DerekClouser Posted July 9, 2013 Report Share Posted July 9, 2013 (edited) Bike: 98 CBR 900rr - Fireblade Mileage - 19k miles In 5th/6th gear - At about 4.8k RPM (redlines at 12k, power band at about 5.5k) I feel like I'm getting stuttering in the engine. When I twist the throttle I get lackluster response. Once the bike hits the power band its fine and doesn't make any funny sounds if I pull in the clutch and rev the engine. I am in no ways a mechanic, but I was curious what the problem most likely is? 1-4 gears have no issues at any RPMs. Would a crappy air filter do this? Would old spark plugs do this?Sorry if this is a dumb question. Edit: It's not a terrible stutter or anything just a minor one. I do notice a lackluster in response from the engine at that RPM though. Edited July 9, 2013 by DerekClouser Quote Link to comment Share on other sites More sharing options...
Gixxus Christ! Posted July 9, 2013 Report Share Posted July 9, 2013 Carbs need cleaned. You don't notice it in the lower gears because you accelerate through them. Then when cruising steady in a high gear the problem becomes pronounced enough that you notice. The web is full of decent tech write ups on carb cleaning, all you really need is a few cans of carb and choke cleaner and an air compressor, sounds like a blocked pilot jet, possibly needle jet. 1 Quote Link to comment Share on other sites More sharing options...
DerekClouser Posted July 10, 2013 Author Report Share Posted July 10, 2013 Carbs need cleaned. You don't notice it in the lower gears because you accelerate through them. Then when cruising steady in a high gear the problem becomes pronounced enough that you notice. The web is full of decent tech write ups on carb cleaning, all you really need is a few cans of carb and choke cleaner and an air compressor, sounds like a blocked pilot jet, possibly needle jet.Excellent. Thanks for the input! I'll give it a shot. Quote Link to comment Share on other sites More sharing options...
Gixxus Christ! Posted July 10, 2013 Report Share Posted July 10, 2013 I've found that a 4x4 muffin pan is very helpful when doing carbs, helps keep all the little doo-dads organized. If you decide you can't handle it or you get lost in the middle of the job I can do it for a reasonable price. Quote Link to comment Share on other sites More sharing options...
c7fx Posted July 10, 2013 Report Share Posted July 10, 2013 Pilot jets are for idling. If it doesn't idle or when you rev it and the throttle hangs before dropping back to an idle. That would be a pilot jet. Most likely the needle is not in the right position or you have lots of crap around the needle and the main. Cleaning is a good idea also changing the plugs and filter since your pulling everything off. Watch what you clean with. Yamaha has a great water based carb cleaner that the parts soak in. Using carb cleaner can and will swell rubber parts like gaskets to 3 times their normal size. So watch what parts get cleaned with which cleaner.The muffin pans are a great idea also take notes on how many turns the screws are in. (count turns till they are lightly seated don't force them in. Also does the bike have a slip on and did it get jetted for pipe? Quote Link to comment Share on other sites More sharing options...
Gixxus Christ! Posted July 10, 2013 Report Share Posted July 10, 2013 C7, you are incorrect. The carb DIP will swell rubber. Spray is perfectly fine. If you wanna go water based, 50-50 mix of water and pinesol actually works wonders, boil for a few minutes and soak overnight. Pilot jets are involved from idle to around 1/4 throttle, which is where you usually are when cruising in high gears. I've been at this for a very very long time. 1 Quote Link to comment Share on other sites More sharing options...
Gixxus Christ! Posted July 10, 2013 Report Share Posted July 10, 2013 Also, hanging idle is usually indicative of air leak between carb and motor or a/f screws set too lean. 1 Quote Link to comment Share on other sites More sharing options...
whaler Posted July 11, 2013 Report Share Posted July 11, 2013 Bring it over...we're close, and I have a full service garage. I can help and you can learn lots. Shoot me a PM 1 Quote Link to comment Share on other sites More sharing options...
c7fx Posted July 11, 2013 Report Share Posted July 11, 2013 C7, you are incorrect. The carb DIP will swell rubber. Spray is perfectly fine. If you wanna go water based, 50-50 mix of water and pinesol actually works wonders, boil for a few minutes and soak overnight. Pilot jets are involved from idle to around 1/4 throttle, which is where you usually are when cruising in high gears. I've been at this for a very very long time.I agree carb dip will swell rubber so will some sprays thats why I said to watch out. Best thing to do is to separate all the rubber parts and clean with soap and water if need be. Some people think spraying carb cleaner down the hole will fix everything and thats what I was warning against. Not saying thats what you would do. I have had great success with carbs that have sat for decades with the Yamaha product which was just an example. I have soaked jets overnight that looked brand new in the morning. True pilot jets work mostly off idle to 1/4 throttle and overlap with the needle. I have seen many bikes that the owner adjusted the idle up to get the bike to run because the pilot was bad. They basically adjusted the pilot out of the equation and are running off the needle. Easily dx when blipping the throttle and it hovers at say 4-5k for a few seconds then drops back to an idle. What he describes sounds more of a needle adjustment issue maybe a little too rich and needs to drop the needle a position or just dirty carb/bad plug if it ran perfect last year and now this. CrazyskullCrusherI don't doubt your wrenching ability just offering a different point of view I have owned a few Honda 600's F2-F3's and 900RR's and I will say that the carbs do not play nice when they get dirty and it doesn't take much sometimes. Quote Link to comment Share on other sites More sharing options...
Gixxus Christ! Posted July 11, 2013 Report Share Posted July 11, 2013 I was assuming it used to run fine and now doesn't. Never tried the Yamaha stuff, but ill bet dollars to donuts pinesol is a fraction of the price. At any rate, a carb cleaning sounds like its in order. Derek, if you're inexperienced in this procedure, do one at a time, look at a completed one to confirm where stuff goes and NEVER remove the individual carbs from the rack. Be gentle with the floats, and take your time. Quote Link to comment Share on other sites More sharing options...
DerekClouser Posted July 11, 2013 Author Report Share Posted July 11, 2013 I'll start with replacing plugs and air filter, if not then I'll run it over to Brian's shop. Quote Link to comment Share on other sites More sharing options...
2fat2fly Posted July 11, 2013 Report Share Posted July 11, 2013 (edited) I'll start with replacing plugs and air filter, if not then I'll run it over to Brian's shop.I really, really doubt it's the plugs. Remove and inspect them and re-install them if you find nothing wrong. Edited July 11, 2013 by 2fat2fly Quote Link to comment Share on other sites More sharing options...
Gixxus Christ! Posted July 11, 2013 Report Share Posted July 11, 2013 Yeah, bad plug would show as a miss. Quote Link to comment Share on other sites More sharing options...
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