Air/Fuel Mixture screw head broken - Honda Motorcycles - FireBlades.org
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post #1 of 18 Old 02-28-2015, 10:59 PM Thread Starter
 
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Air/Fuel Mixture screw head broken

Hey guys. So I was doing some carb work on my 99 fireblade and came upon two locked/broken air fuel mixture screws. I have replacements but I am stuck trying to figure out how to take the old ones out. They look like these but they both only have 1 bit of the head instead of 4. How can I remove the locked ones without damaging the carb?
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post #2 of 18 Old 03-01-2015, 10:54 AM
 
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Re: Air/Fuel Mixture screw head broken

i think i know what your saying. if it were me id pull the carbs off obviously n hit them well with some penetrating oil to make sure they are good n loose and can be turned.

ive used this technique to free broken bolts that were down in the hole a bit n couldnt be grabbed with vice grips or the like. find a way to secure the carbs so you have both hands free. get a thin pointed tap or center punch and put the pointed end on the nub where you can tap it gently to unscrew it. its a time consuming process and takes some patients but as long as there is a bit the point of the punch can get traction on you should be able to tap tap tap it out slowly. you just kinda gotta get the tap oriented in such a way to give it a little turn at a time. once you get it unscrewed enough to grab it with pliers or vice grips use those to get it all the way out. like i said ive used this technique to get broken bolts out when they just had a tiny spot where it broke to get a punch to grab so if youve got 1 of 4 of the nubs shown in the picture you should be able to get them out this way. just make sure the carb is held in place well. maybe wrap it with a towel n put it in a vice or strap it down to something. its got to be secure or you wont get it going. good luck with it.

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post #3 of 18 Old 03-01-2015, 4:08 PM
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Re: Air/Fuel Mixture screw head broken

Have you ruined the slot in them? How about the type is screwdriver, is it smaller or regular size. I agree with Kevin's suggestion, but would like to add that if you pull the carbs out and get them drained and dry, you can add some heat to the screw tunnel with a small butane cooking torch or butane modeling iron. A couple heat cycles could loosen it enough to turn it. Also, I've taken larger screwdrivers and ground them down to fit inside the screw tunnel, the bigger handles give you more leverage, rather than using a thinner smaller driver. Be careful not to ruin the screw head as its only brass. Pop some pics of what your screws look like.

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post #4 of 18 Old 03-02-2015, 8:54 AM
 
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Re: Air/Fuel Mixture screw head broken

I've never had a problem with a flat screwdriver, but if they're stuck try grinding a phillips screwdriver tip down to fit flat. That way you're turning all those little brass tips at the same time, not just two.
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post #5 of 18 Old 03-02-2015, 10:33 AM
 
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Re: Air/Fuel Mixture screw head broken

im pretty sure based on the op he only has 1 outta 4 of those nibs so he cant get any screw driver to grab on them.

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post #6 of 18 Old 03-05-2015, 4:54 PM Thread Starter
 
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Re: Air/Fuel Mixture screw head broken

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Originally Posted by 954Kevin View Post
im pretty sure based on the op he only has 1 outta 4 of those nibs so he cant get any screw driver to grab on them.


Yep, spot on. I am going to take the tank and airbox off again now and take some pictures and try again. Thanks for responses everyone.
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post #7 of 18 Old 03-05-2015, 6:27 PM Thread Starter
 
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Re: Air/Fuel Mixture screw head broken

they wont budge

Last edited by fayablade; 03-05-2015 at 6:35 PM.
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post #8 of 18 Old 03-08-2015, 10:39 PM Thread Starter
 
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Re: Air/Fuel Mixture screw head broken

Is there anyway to get to the other side of the a/f screw? I am going to go round 3 with these suckers on wednesday with some PB blaster and letting it sit for a good few hours/overnight. I don't want to resort to drilling and using an easy out/torx bit as that could be disastrous.

I think this is the root of my problem with popping on decel, jerky throttle, and lumpy idle..

EDIT: also, I have these hoses that connect in an "F" shape with 3 ends that seem to connect to the nipple looking part of the carbs.. anyone know where they properly should be connected to? Are these important?
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post #9 of 18 Old 03-09-2015, 1:17 AM
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Re: Air/Fuel Mixture screw head broken

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Originally Posted by fayablade View Post
Is there anyway to get to the other side of the a/f screw? I am going to go round 3 with these suckers on wednesday with some PB blaster and letting it sit for a good few hours/overnight. I don't want to resort to drilling and using an easy out/torx bit as that could be disastrous.

I think this is the root of my problem with popping on decel, jerky throttle, and lumpy idle..

EDIT: also, I have these hoses that connect in an "F" shape with 3 ends that seem to connect to the nipple looking part of the carbs.. anyone know where they properly should be connected to? Are these important?
There is no other end of the fuel screw. There are small ports that the screw tunnel branches off to: the needle jet, a small hole in the intake bore near the bottom of the butterflies, and a port near the brass cluster of ports by the air filter side of the carbs. I would take the carbs completely apart before spraying the DB Blaster in there.

As far as the hose routing, here a link to a pic of what your looking at:

https://www.fireblades.org/forums/att...ost-cbr900.jpg

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Last edited by IanDoohan; 03-09-2015 at 1:11 PM. Reason: Typo
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post #10 of 18 Old 03-09-2015, 9:46 AM
 
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Re: Air/Fuel Mixture screw head broken

other alternative would be to cut a small groove to fit a small flathead with either a hacksaw blade (just holding the blade by hand), or a drumel with a fine cutting disc.
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post #11 of 18 Old 03-09-2015, 3:41 PM
 
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Re: Air/Fuel Mixture screw head broken

Iv had this exact issue on my CBR F3, what i did was went on ebay and bought a spare single carb from a bike breakers and swapped it out, leaving me with a functioning carb set and bike.

Then came onto removing the screw... no amount of heat or penetrating fluid was helping so out came the air drill and compressor. Starting with a 2mm drill peice (which i snapped 3) i marked on the peice the maximun depth to go down into the hole and drill to said line, and then slowly went up drill peice sizes by 2mm until i was able to see a glimpse of the o-ring at the bottom and then started to pry the rest of the screw away from the thread walls. DO NOT go any lower than the o-ring, you will destroy the carb which is soft enough as it is! This was painstakenly slow even though the brass is very soft, go slow and take many breaks and make sure you mark on your drill peice the max depth. If you dont a steady hand then a pillar drill is also a very safe option. Total time, about 2 hours.
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post #12 of 18 Old 03-09-2015, 4:33 PM
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Re: Air/Fuel Mixture screw head broken

Quote:
Originally Posted by Bluevitz_RS View Post
other alternative would be to cut a small groove to fit a small flathead with either a hacksaw blade (just holding the blade by hand), or a drumel with a fine cutting disc.
Looking at the pics close up it really looks as though the screws are just about flush with the top of the aluminum. I would give this suggestion a and just cut a straight groove, even if it takes out a little of the top of the aluminum. It's not going to matter much, and not really affect the use of the replacement screw. If the screws do come out, just clean up the tunnel and the first couple threads to make sure the new screw doesn't cross thread on the way in.

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post #13 of 18 Old 03-09-2015, 4:39 PM
 
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Re: Air/Fuel Mixture screw head broken

yeah i think that would be about your best bet. even if you get into the tunnel a bit its still going to function. take your time n get a good groove in it n hit it with some heat n a well fitting flat head in there should get it out.

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post #14 of 18 Old 03-09-2015, 5:44 PM Thread Starter
 
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Re: Air/Fuel Mixture screw head broken

Thanks for the helpful responses everyone, much appreciated.


Quote:
Originally Posted by IanDoohan View Post
There is no other end of the fuel screw. There are small ports that the screw tunnel branches off to: the needle jet, a small hole in the intake bore near the bottom of the butterflies, and a port near the brass cluster of ports by the air filter side of the carbs. I would take the carbs completely apart before spraying the DB Blaster in there.

As far as the hose routing, here a link to a pic of what your looking at:

https://www.fireblades.org/forums/att...ost-cbr900.jpg
Great link thanks! But it begs the question, what IS that top hose for?..lol

Last edited by fayablade; 03-09-2015 at 5:49 PM.
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post #15 of 18 Old 03-09-2015, 6:37 PM
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Re: Air/Fuel Mixture screw head broken

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Originally Posted by fayablade View Post
Thanks for the helpful responses everyone, much appreciated.
Great link thanks! But it begs the question, what IS that top hose for?..lol
That's the end of the vent tube that goes across the carbs and just tucks into a hole in the side of th frame. It's open and just vents into atmosphere.

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