Carb gurus check in please - Wrist Twisters
 
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post #1 of 25 Old 04-06-2011, 10:19 PM Thread Starter
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Carb gurus check in please

Hey all, Im having a issue with the 900rr. It runs smooth as butter off idle and just putting around town. Say under 7kish, but over that it falls on its face pretty hard. I took the air box off and poked the jets out with a thin wire and hosed everything down with carb cleaner with no positive results.

Is it possible the petcock isnt letting enough fuel flow? I dont think this is the problem because if Im just going say 60mph in 6th and open it up it sounds like it flooding so that tells me its gettign fuel? I dont know what Im doing with carbs lol. Floats sticking? IDK?

Someone told me to run some sea foam through it?

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post #2 of 25 Old 04-06-2011, 10:34 PM
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hmm.

obviously its getting too much or too little fuel when u open her up.

coupla questions.

1. can you slowly roll on the throttle to wot and hav it run fine?
2. did it run fine before with the same jetting setup?

if 1. then your accelerator pumps are probably clogged and need cleaning.
2. if two, then the main jet is probably clogged, as well as possibly the accelerator pump(assuming it has an AP)

its possibly the floats are stuck and dumping too much fuel in her, but i doubt thats the case as you would have fuel leaking out of the carbs overflow lines

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post #3 of 25 Old 04-07-2011, 03:31 AM
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Try taking the petcock off the tank and make sure the intake screen is clean.
While it's off, take it apart and make sure it's clean inside , too.

If it were mine, I'd pull the carbs off. They'll come off all together, turn them upside down, pull the float bowls, and measure the height of the floats.
One or more of them could be set too low. If you don't have a manual, do a search for the specs online. While the carbs are off the bike , pull the tops off and check the diaphragms for any tears or pin holes. At that point, you might as well pull the main jets and inspect them too.

While the main jets are out, check the number on them and compare with known oem numbers to make sure you don't have a botched rejetting job
done by a PO. I've found Ron Ayers to be a good source for on line mircofiche
to check oem numbers.



How about the tank vent? Is that working properly? Do a WFO throttle run, the pull over asap and open the fuel cap. If it sounds like it's sucking air or is slightly stuck when you open it, it means the tank is not venting the way it should.

You really should buy an aftermarket shop manual. They're cheap on ebay or amazon. I paid $25.00 (shipped) recently for a DRZ manual, as an example.
Worth it's weight in gold when you've got your bike torn apart. Plus, it'll have a good troubleshooting section.

RB

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post #4 of 25 Old 04-07-2011, 05:19 AM Thread Starter
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Thanks for the answers Im just getting this bike together so I have no knowledge on how it ran prior. I do not have any fuel over flowing.

If I roll on it slowly it seems a to make power a tad longer but the ultimate result is the same. I didnt think these bikes had accelerator pumps? Thought that was and FI thing?

If I need to rejet it I will, Ive checked the top of the cabs those seals on the top between the carb and the "stack" I guess youd call it looked fine. Thanks for the Ron Ayers tip.

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post #5 of 25 Old 04-07-2011, 06:03 AM
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Yep.......welcome to carburetors! At least with dirt bikes you only have 1 to deal with.

Definitely sounds like it's time to pull those puppies and dig in with a service manual......float height checks, pull - clean - blow out jets, reinstall.......also wouldn't be a bad idea to re-sync the carbs to each other. Definately see what jets are installed and research to see if what's in there is normal.

If you do all this.....and it still runs like crap..... You may need to swap to different main jets or use different needle heights.

........a dyno with an exhaust gas sniffer can save you hours and hours when jetting a bike. They can do a single run and give you an idea of what to do next......instead of guessing.


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post #6 of 25 Old 04-07-2011, 09:05 AM Thread Starter
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Is there a quick breakdown on the process of re-sycronizing the carbs. Im cool with rejetting ect. because Ive done it (years ago) but Ive never attempted to re-sync anything.

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post #7 of 25 Old 04-07-2011, 09:25 AM
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its pretty straight forward...... you use a carb sync tool.... like the 'Morgan Carb Tune', or the Motion Pro Carb sync tool --- or you can even make a gauge yourself.

There's usually a vacuum nipple at the throat of each carburetor, you hook each nipple up to a hose of the Carb Tune tool ---- you then can see the difference in vacuum between the cylinders......

Then most bikes have 1 cylinder that isn't adjustable....and the rest are adjusted to that cylinder...... there's usually an adjustment screw on the linkage next to the carb you want to adjust.

You need to follow the instructions in the service manual in regards to air box on or off....what RPM to calibrate too....(usually at idle around 1,300 ro 1,500 --- as the bike runs better at sync....the idle will get higher....so you need to keep adjusting your idle screw to keep your RPM at the target calibration RPM)

What Re-sync'ing does.....is to make sure that all of your cylinders are getting an equal Air/Fuel mixture. It is quit possible that with a bike way out of wack --- that 1 cylinder could be getting more fuel than another causing rough running issues. Many people unknowingly blame a bike that is running rough and out of sync on the valve clearances.

EVERY bike that I have re-sync'd has benefitted in some way from doing so.


Now --- I do want to say.....resync'ing the carbs does make your bike run smoother --- at idle and slightly off idle to partial mid-throttle.

The issue you're having doesn't sound like a carb sync problem. But, I would highly recommend doing this to make sure your bike is running the best it can.

BTW --- FI motorcycles with throttle-bodies are also sync'd in the same way.

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post #8 of 25 Old 04-07-2011, 09:25 AM
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no clue on the carb sync.

but dont be alarmed if you have different sized jets in the middle cylinders vs the outside... i know back in the days of air cooled they had to run a larger jet in the center's to keep things a lil cooler.... watercooled im not sure if they have the same problem.

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post #9 of 25 Old 04-07-2011, 12:18 PM
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1. What year is the 900RR? Later years without the fuel pump were much easier to trouble shoot, but more susceptible to small changes in the set-up

2. Please tell me you don't have a K&N air filter installed in the airbox.

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post #10 of 25 Old 04-07-2011, 02:47 PM Thread Starter
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Thanks guys,

LDH its a 1998, and yes the previous owner installed a K&N Ive been a fan in the past but no longer. I did try running it without a air filter at all just to see if it smoothed out a little then Id throw a stocker back in there. But obvioulsly it did not, it was a last ditch diagnostic effort.

Also has a full micron. Its not a stumble per say. Its more a fall flat on its face as it starts to spin up. Runs butter smooth under "normal" commuting. You can ride it all day no prob, but if you wanna open it up it flops.

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post #11 of 25 Old 04-07-2011, 03:01 PM
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The K&N filters ruin the jetting completely on the 96+ 900RR's. They won't run worth a damn without the filter either... OEM is the best route unless you want to go all out with an Airbox Plus Kit from Factory Pro

When did the problem first start occuring? Long sit over winter? Any new mods to the bike, Fuel tank ran empty or close to it?

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post #12 of 25 Old 04-07-2011, 03:06 PM
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Also check for an aftermarket ignition advancer! I cannot count how many times I have found that someone installed one of them with TOO much advance by literally forcing the advancer plate onto the splines in a way it was not designed to fit. It causes the bike to fall on it's face like it was loosing power right before it starts to build-up.

If that little scenario only happened once I would chalk it up to a fluke, but seeing multiple incidents of it I have to conclude that somewhere in time somebody started a rumor that the advancer mod was beneficial and others started to copycat not knowing any better. Granted that may not be your problem at all, but I've spent at least 200 hours of my life jetting 900RR's and have seem some pretty odd stuff happen on a regular basis.

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post #13 of 25 Old 04-07-2011, 03:57 PM Thread Starter
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Ive only had the bike for a month or so its been this way since Ive had it. It was downed pretty good so Im assuming it sat for a bit.

Im gonna start diggin around for a OEM filter. And it does fall apart right when you'd think it would start pulling. I dug up some info on the ignition advancer and Im going to see if I have one installed, if I do Ill throw it away based what I read. Thanks for giving me some directions to work in! You guys rock.

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post #14 of 25 Old 04-07-2011, 04:01 PM
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Quote:
Originally Posted by brian View Post
I dug up some info on the ignition advancer and Im going to see if I have one installed, if I do Ill throw it away based what I read. Thanks for giving me some directions to work in! You guys rock.
Don't throw it away just make sure it is installed correctly instead of misplaced on the shaft by a couple of splines... they are actually keyed to only fit on in one way, but sometimes people were forcing them into other positions.

I probably have an OEM one sitting in a box in my garage somewhere if you end up needing for some strange reason.

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post #15 of 25 Old 04-07-2011, 04:05 PM Thread Starter
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I pulled the RH cover just in front of the clutch cover and it all looks OEM. Im not sure Im looking at the right spot though, Im learning lol.

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post #16 of 25 Old 04-07-2011, 04:40 PM
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I talked to a friend who's just getting a '93 900rr on the road. He says some guys take the fuel pump out when they go bad and let the fuel gravity feed.

He just bought a used pump off ebay for $35.00. He says new is $200.00

Not sure if your later model has the pump or not.

RB

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post #17 of 25 Old 04-07-2011, 06:07 PM Thread Starter
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If I hold it open in 6th while doing say 50mph I can make it stall. Im assuming that means its getting fuel? Ive examined the flow out of the petcock and it appears to be free flowing.

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post #18 of 25 Old 04-07-2011, 06:41 PM
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Check your coils and ignition - stator specifically. I had the same prob on my 750 and it wasnt carbs, but losing spark! Im going with that first actually. Can you rev it past 7k in neutral?

I may not have a lot to say but it doesn't mean I don't listen.
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post #19 of 25 Old 04-07-2011, 06:56 PM Thread Starter
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I dont like to rev a motor that high with no load so I havent tried. Is there a way to test the stator/coils? The carbs looked fairly clean inside so I was thinking spark as well. Thanks for all the tips Im sick as a dog so I havent dug in after starting this thread but I will soon.

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post #20 of 25 Old 04-07-2011, 07:32 PM
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Try here....

Dan's Motorcycle

I may not have a lot to say but it doesn't mean I don't listen.
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post #21 of 25 Old 04-07-2011, 10:22 PM Thread Starter
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Thanks, givin that a read over now. Im thinkin on it, I did not notice the sputter on the way home when i first purchased it, but I dont recall really winding it up either. But after I got it home I did some maintence and when I reconnected the battery I hooked it up backwards (long day I guess) I did turn the key on once. Think that might have done it?

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post #22 of 25 Old 04-08-2011, 11:17 AM Thread Starter
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Ok.... So tons of good info here Im sure Ill use it as a reference point in the future but presently I wear the Jug head hat. I mentioned I was sick, apperently not thinkin well at all either. After I cleaned out the jets, cleaned out the carbs and made sure the air box was sealed (did this all twice) I relized I forgot to hook up a vaccumm hose. BONEHEAD move but now shes running top notch!

Thanks for the help fellas.

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post #23 of 25 Old 04-08-2011, 11:27 AM
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the vacuum hose to the petcock that allows the fuel to flow to the float bowls?

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post #24 of 25 Old 04-08-2011, 03:44 PM Thread Starter
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Nope, a bigger hose that goes to the right underside of the airbox.

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post #25 of 25 Old 04-09-2011, 10:38 AM
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wow brian you should have just called me.. i would have saved you some time. but its good peace of mind to go threw all those carbs anyways

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