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Main jet air tube question

Old 06-22-2013, 07:39 AM
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Main jet air tube question

So, I have a 98 superhawk and i'm having a what i believe is a carburetor problem. The bike will start and idle, but when I go to rev it up it stumbles bad and if I try to crack the throttle fast it will kill its self. But when I hold my finger over the main jet air tube (the middle brass tube on top of the carb) for the front cylinder it will rev up just fine. The bike from what I can see is all stock except the yosh pipes. I've cleaned the carbs twice and have the fuel lines connected to a gatorade bottle with gas so I know its not the fuel petcock. Any ideas will be appreciated. Thanks
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Old 06-22-2013, 08:15 AM
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Two problems. The bike won't run for crap with the airbox off and likely you are lean anyway. You'll need to know what jets you are running, etc. to get proper help.
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Old 06-22-2013, 08:53 AM
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Im running stock jets 175 in the front 178 in the back. The bike runs a little better with airbox on but still has the same symptoms. I've tried switching the jets, put the 178 in the front and it ran the same.
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Old 06-25-2013, 08:20 AM
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Should I change the air fuel mixture screw or move up a couple jet sizes?
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Old 06-25-2013, 10:10 AM
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When you say Yoshi pipes do you meant the headers themselves or just the end cans. If just end cans then the mains I would have though would be OK and the needles would require richening up. The mixture is mainly for the control of the pilot circuit only, though it does taper off and affect the needle and mains slightly as well.

You may want to start with the following.
(:-})
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Old 06-28-2013, 11:43 AM
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Thanks for the info and the link, it was really helpful. I'll try some stuff this weekend and let you guys know the results.
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Old 06-29-2013, 07:33 AM
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So I shimmed the needle on the front carb to .08 (4 washers) from .02. It will rev up now but still has a pretty bad hesitation from 1.5 to 3.5 rpm, choking it helps a little. Should I step up my pilot jet or adjust fuel air screw currently set at 2.5. I'm also getting gas in the air box and on the front carb slide after running.
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Old 06-29-2013, 08:07 AM
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Forgot to mention that I'm already running 48 pilots in both carbs.
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Old 06-29-2013, 04:08 PM
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You can go up to 3 turns out on the fuel mixture screws before needing to step up a size on the pilot jet. You didn't say whether you have a Yoshi full system including headers. One of the guys here in the UK had a full Yoshi system and had a lot of problems low down and found that he needed to use 50 pilots. I also believe that the reason Factory pro supply 50's is to go with a full system.

I would try turning the fuel screws out another 1/4 turn and see if this helps. The rear carb should be a 1.4 turn less than whatever the front is set to.

What air filter are you using?

As for a bit of fuel on the slides this is normal as long as there's not puddles. Actually a little overspray on the slides is quite helpful as it lubricates them which helps them slide smoothly.

(:-})
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Old 06-30-2013, 08:42 AM
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Headers look stock (couldn't find a part#)... I didn't put exhaust on it but pretty sure its just the cans... I have stock air filter on it. I'll try adjusting fuel mix screw. Not sure why the front would be running so much more leaner then the back? Thanks for the help and insight
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Old 07-02-2013, 04:01 PM
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So my true newb colors are showing now. So I grabbed carbs of a running stock bike and threw them on mine and the bike runs the same. I've noticed that the bike only idles on one cylinder (the front one) and I can only get the back to fire randomly on random start ups. Even when the back does fire it only fires for a few seconds (4-8sec) then the rest on that run it wont fire. So me thinking the front was too lean was just the bike running on one cylinder and me being too stupid to realize it. So I switched the front and back coils to see if that was the problem and it wasn't, still only the front fires. Not sure why blocking the front main jet air bleed helps it rev up either. Could this be the computer? When I pull the plugs they both spark. I have the same compression in both cylinders (140) and I checked the timing on both and they are fine (according to the repair manual).
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Old 07-02-2013, 04:18 PM
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So we have gone from a suspected carb issue to electrical. I would'nt go messing with the main air jets on top of the carbs either. as for the front being leaner.... the rear carb is slightly richer to help keep the rear cylinder a bit cooler. It's not as vital with water cooled bikes but as Honda set it this way for a reason it's best to stick to that.

Just so you know, that even if a plug shows a spark it can still be faulty. I had one recently that was misfiring and both plugs showed a spark. The rear was not as good a spark and I blamed the Sunshine for not showing it as well. It turned out the rear plug was faulty and causing a misfire. So basically what I'm saying is don't rule out plugs because you see a spark.

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Old 07-02-2013, 05:20 PM
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Originally Posted by RCHAWK View Post
So, I have a 98 superhawk and i'm having a what i believe is a carburetor problem. The bike will start and idle, but when I go to rev it up it stumbles bad and if I try to crack the throttle fast it will kill its self. But when I hold my finger over the main jet air tube (the middle brass tube on top of the carb) for the front cylinder it will rev up just fine. The bike from what I can see is all stock except the yosh pipes. I've cleaned the carbs twice and have the fuel lines connected to a gatorade bottle with gas so I know its not the fuel petcock. Any ideas will be appreciated. Thanks
Do you know that it ever ran right? Cams may have jumped timing.
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Old 07-02-2013, 05:49 PM
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I switched the plugs as well same outcome...hasn't ran right since I got it, bought it thinking it was a simple carb clean/tune. I checked the timing ie checked timing sprockets, when u say the cams may have jumped do you mean the chain jumping a tooth on sprocket?
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