CBR 900RR Running like a bag of hammers. - Honda Motorcycles - FireBlades.org
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post #1 of 10 Old 05-26-2016, 11:01 PM Thread Starter
 
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CBR 900RR Running like a bag of hammers.

I have a 1995 CBR 900RR. It's got 21k on the ODO.

I bought it earlier this spring knowing it was running "a little rich". Heh.

So, here I am, about 17 sets of plugs later I'm about ready to jump it off a cliff.

The carbs had clearly been modded before, as the vacuum holes had been drilled (they are larger than the drill bit in a dynojet kit). I'm wondering if these holes being drilled too large is the issue.

I've leaned out the AF screws (I'm at 1 1/2 turns now) dynojet needles set one clip lower (leaner) and I'm running the 120 main jets. The bike has a full exhaust and a K&N.

Still, the bike seems lean higher up in the power band when the throttle is opened 3/4 to WOT. This stumble is improved with the 120 jets and DJ needles and worse with the factory needles or smaller jets. It's my understanding that the needles and main jets are responsible for how the bike runs under load or 1/2 - WOT and the A/F mix screw controls how the bike runs just off idle.

Still, the plugs foul out after a handful of rides. Black and sooty. I changed the oil and check the level regularly, it doesn't seem to have burned a drop.

Do I need to buy new carb parts? (I'm not sure what that little black bugger is called, but I don't want to try and find replacements until I know it's a good bet)

It's so frustrating to not have the proper power high in the power band under load because the bike is lean but then foul out plugs.

Suggestions?
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post #2 of 10 Old 05-27-2016, 3:29 AM
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Re: CBR 900RR Running like a bag of hammers.

I've modded many a carbed 900 and never had a plug fouling issue based soley on too much fuel. I've had 1024cc, stock carbed to 893cc jetter with pipes, K&N etc.

Generally, the slide holes are not drilled larger in any jet kit. I remember back in the 90's Dynojet kits came with a drill bit to drill out the fuel mix screw aluminum plug (tamper proof cap), and they also gave a giant sheet metal screw to screw in the hole to pull the plug out. Are you sure your slide holes are larger than OEM or are you basing it soley off the size of the Dynojet drill bit? Are you mixing Factory Pro parts with Dynojet parts? Factory Pro uses OE Keihin jets, so the 120 indicated a 1.2mm hole, whereas Dynojet uses their own stuff with their own numbers on them. So who knows the actual size of the jet.

For a stock 893cc engine 120's are fine (if actual Keihin jets) with a full aftermarket exhaust and an aftermarket air filter. You might find that the needles need to be full rich (clip in the lowest position) and that the shim for each needle is present.

The fuel crew is usually set to 2.5 turns out from lightly seated. With the CV OEM carbs whacking the throttle at 6 grand in 3rd gear should result in a nice smooth (relatively speaking) pull to redline.

That set up should not be fouling plugs. I would seem there are other issues.

Are you using NGK CR9EH9 plugs?

My 99 900RR Track Build Link:Track Build 900RRX

My Red Rocker 93 Build Link: Café 900RRP
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post #3 of 10 Old 05-27-2016, 8:37 AM
 
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Re: CBR 900RR Running like a bag of hammers.

When I buy a used bike I ask to check compression. They say no I walk.
When I acquire a strange bike, first thing is check compression before I pour a dime in it.
When I see a foul plug, poor running, can't seem to get it to sink in, it's no my bike so I let them squirm for a bit until one recommends to check compression to answer the one big clue... Do I continue to chase my tail or WOT?

Signed,
Well?
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post #4 of 10 Old 05-27-2016, 9:49 AM
 
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Re: CBR 900RR Running like a bag of hammers.

See, carbs are easy.
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post #5 of 10 Old 05-27-2016, 9:54 AM
 
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Re: CBR 900RR Running like a bag of hammers.

U funny. Carbeetootears still need some kinetic to start. You know that day you walk out to that cold bike and it does not start? That's the number you want see.

Signed,
And the whole bank reads in the cold setting is?
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post #6 of 10 Old 05-27-2016, 10:11 AM
 
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Re: CBR 900RR Running like a bag of hammers.

If he can idle, he's got at least 100 psi, and he can. It's not enough reason for running rich, but at least his carbs aren't leaking! If main jet feels right, idle screw set, maybe he can count the notches on his needle and tell us where the clip is. Maybe his choke is sticking? Maybe someone drilled his 120 jet larger?
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post #7 of 10 Old 05-27-2016, 11:30 AM
 
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Re: CBR 900RR Running like a bag of hammers.

I don't think it goes like that, 26. You need heat, heat is kinetic, kinetic helps the burn process, no compressed molecules to domino off of, more unspent is the fuel, more soot is the plug.

The beauty of this is... "IT AIN'T MY BIKE" you go getting your fingers wet looking for needle clip my jet speed needle, low hi ya do'in, fellas! Chasing your tails I see. Don't come blaming me flaming you is guess WOT?

Signed,
(Eyes can see it from here) that tail slapping your ass is don't need no glass is.
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post #8 of 10 Old 05-27-2016, 10:11 PM
 
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Re: CBR 900RR Running like a bag of hammers.

Detached finger tips
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post #9 of 10 Old 05-28-2016, 8:38 PM Thread Starter
 
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Re: CBR 900RR Running like a bag of hammers.

Thanks guys. I'm going to fix the A/F screws and go to the middle notch on the needles. I am not mixing DJ and stock parts so I'll be going to 2.5 turns on the a/f screw, middle notch on DJ needles and 120 DJ main and give it a shot.
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post #10 of 10 Old 05-28-2016, 11:29 PM
 
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Re: CBR 900RR Running like a bag of hammers.

I'm with 22 on this one. I also would start with compression, just me, also, you could be getting some spark issues as well going on there. It could be cutting out on you or be weak for that matter. If you have smaller jets why not put them in and see at least if you can get the plugs cleaner, I doubt you have to worry about a lean enough issue where you would hurt something. You need a base to start with and it sounds like you don;t have one. You could be changing jets and clips for the rest of your life. Get it running without fouling plugs if you can. Again, I doubt you could go lean enough to hurt anything. Just my 2 cents.

Paul
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