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Discussion Starter · #1 ·
What's up people?! Someone help an umbrella girl out? I got a 99 cbr 900 that's popping on deceleration. Usually notice it after it's been running for a while and it's nice and warm (180 degrees or higher). It's been like 80 degrees here. So, I have synced and cleaned the carbs last winter (it popped before that too). I also checked the valve clearances and they were in spec. It has a K&N and a Yoshi pipe. Not sure if it's stock carb setup. Was not thinking and didn't look when I had the carbs all apart. I can check that and repost but will probably wait till riding season is over. When I cleaned them I forgot to count the turns on the pilot screws so I put them on the initial setting according to manual and have left them there. It runs good except for the popping. I'm thinking it's lean? Should I just try to turn the pilot screws a little? If so, counter clockwise all the same amount? thanks
 

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Might be worth having a look for an exhaust leak, but if the carbs haven't been rejetted for the mods then yes its most likely its lean. for the idle screw the basic guide is if you wind it out another 1.5 turns you'll need the next size up pilot jet. The other thing you can do although it really depends on the carb is lift the needle another notch on the slide.
 

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Discussion Starter · #3 ·
Oh, forgot to mention , the boots on the carbs are deteriorating where they connect at the air cleaner housing . Don't know if they are leaking. It looks like rust (brown crap)on the plastic? I was gonna try spraying some carb cleaner while the bike is running (sound good?). I threw some high temp Honda stuff on the canister where it meets the exhaust (not at the heads). There was a leak there, but I fixed that. How would I check for leaks at the heads? Plugs look normal. I'll try and do baby steps and one thing at a time to see what works. thanks for the super fast reply Nero.
 

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Same issue here before re-jetting. K&N and Exhaust, was running lean. My guess is yours is the same.
 

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Spray some WD40 or similar at the suspect airbox rubbers with the engine idling some carb cleaners do all sorts of nasty stuff to rubber and plastics. If the idle picks up you have a leak.
 

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the joke is in your hand
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popping is actually pretty normal. without hearing yours I can't say if yours is though. mine does it, race bikes do it and they're tuned by pros.

here's an example, I made this a few weeks ago at mid ohio ama races. you can clearly hear them popping as they get off the throttle
in the beginning of the video and then skip to 4:40 when hays on the R1 comes through by himself you can really hear it popping
mid ohio - YouTube
 

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the joke is in your hand
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The popping is not the a result of the quick shifters ignition cut?
not sure if quick shifters actually work on the downshift. or they probably still need the throttle blipped. and I hope they're not down shifting at a full lean already lol you can hear that they're decelerating/coasting off throttle. I don't have one so I know that's not so on mine. but every time mine pops once or twice it's the same scenario. it used to do it a lot more when the air injection system was still hooked up.
surely you guys have heard this sort of thing before being around sportbikes.
 

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Might be worth having a look for an exhaust leak...
This.

Any carb'd bike should have a jet kit installed, regardless of exhaust. But unless you have other drivability issues, I'd bet it's the exhaust. Also, buy the carb and air box boots if you plan to keep that bike. I'd say there's a VERY high percentage that they are just about out of production, if they aren't already.
 

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What Tony said. Find those boots.

....otherwise popping was almost always caused by air getting in after the header, or from the flanges where the header meats the head. That being said you can usually hear that head flange leak, it sounds like a ticking (and will drive you nuts trying to find it).

Back when everything was carb'd most bikes popped at least a little bit. It wasn't something that I found unusual. Hell my Speed Triple pops a bit on decel, and its fuel injected.
 

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Discussion Starter · #13 ·
Is that the only way to check a leak at the head, (by listening)? I know it's very hot there.I had no leaks by the airbox boots where it's deteriorating or near the canister. I did see some lower airbox housings on ebay . I'll pick one up.Should i not bother with the pilot screws then? that's just one of the easiest things to do. I have heard of it fixing the issue too. Ill tear her apart this winter and look at whats in there and maybe jet it. I don't mind the popping. It's NOT that often and if it's normal like some say, then I won't worry about it. I just don't want to hurt the engine. Thanks again for all the replies.
 

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Is that the only way to check a leak at the head, (by listening)? I know it's very hot there.I had no leaks by the airbox boots where it's deteriorating or near the canister. I did see some lower airbox housings on ebay . I'll pick one up.Should i not bother with the pilot screws then? that's just one of the easiest things to do. I have heard of it fixing the issue too. Ill tear her apart this winter and look at whats in there and maybe jet it. I don't mind the popping. It's NOT that often and if it's normal like some say, then I won't worry about it. I just don't want to hurt the engine. Thanks again for all the replies.
Putzing with the pilots risks screwing up the pilot/main transition. In my experience when you get that off you will spend a week burning yourself trying to get that right again.

Do you have a jet kit on it?


Like I said a header leak sounds like a vacuum leak or a tick usually, that is a rather rare occurrence if you head bolts are still attached. The mid-pipe/end pipe junction is much more common, and may be as simple as replacing springs.
 

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Discussion Starter · #15 ·
I don't know if it was ever touched as far as the jetting. I bought the bike used a couple years ago. I tore the carbs apart last year and cleaned them but (like a fool) never looked at them to see if they were changed. I set all 4 screws to the initial setting and it seems to run good. The Yoshi is a bolt on. No springs. It was leaking where it attaches, but I fixed that.

Putzing with the pilots risks screwing up the pilot/main transition. In my experience when you get that off you will spend a week burning yourself trying to get that right again.

Do you have a jet kit on it?


Like I said a header leak sounds like a vacuum leak or a tick usually, that is a rather rare occurrence if you head bolts are still attached. The mid-pipe/end pipe junction is much more common, and may be as simple as replacing springs.
 

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My guess is the doughnut between the slip on and can is your issue. It's not harmful, just accelerates the wear on the exhaust packing.
 

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Check and see if your bike has the clean air valves that dump air into the exhaust ports. if so what you are hearing is the air igniting in the exhaust pipe. plug the valves on top of the valve cover.
 

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I don't know if it was ever touched as far as the jetting. I bought the bike used a couple years ago. I tore the carbs apart last year and cleaned them but (like a fool) never looked at them to see if they were changed. I set all 4 screws to the initial setting and it seems to run good. The Yoshi is a bolt on. No springs. It was leaking where it attaches, but I fixed that.
Its usually really easy to tell if its jetted or not. Just look at the top of the needles. If they have 4 slots for the E-clips its safe to say that you have a jet kit.
 
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