Carb screw holes

Momaru · March 11th, 2010, 12:44 AM

A story of warning to those that replace their carb screws. Make sure you get the right size and your carb threads are properly cut.

Since the OEM carb screws suck, I ran out to my local hardware store and grabbed some 4mm 0.70pitch button-head screws. Unfortunately they don't stock our 4x18mm, so I got some 4x16mm and some 4x20mm. Installed the 4x20 next time I was working on the carbs.

I had to pull the carbs off for my current project and decided they were in need of some cleaning inside and out. I'm glad I did because little did I know, one of my screw threads wasn't completely drilled out/tapped. The diaphragm cap screw socket nearest the throttle linkage (top, right carb, right side, front) had been cracked when I put the slightly longer bolt in. Not bad enough to have the screw fall out but it could have been.

Here's some pictures of what I'm talking about. First pic I'm pointing to the cracked area with the screwdriver tip. This is behind the throttle cable mounting bracket (incidentally, this is secured with red loctite).
DSC04880.jpg
DSC04878.jpg
DSC04879.jpg

Thankfully I don't seem to have been 'screwed' too bad by this mistake, but it's probably something to at least look for if/when you have the carbs off. It'd be unfortunate to lose a few carb screws on the road due to destroyed threads. Also suppose if it really broke the wrong way it could create an air gap for the vacuum diaphragm.

Definitely feel that

. Unfortunately my roomate's out.

FWIW the 4x16 fit just fine in 13 of the 16 holes that are commonly opened on the carbs (4 per float bowl, 4 per jet needle/diaphragm cap). However 16mm is too short to be truly secure in the other three slots that require the screw to go through a metal mounting bracket (all three on left diaphragm cap).

If you can find 4x18, use them! If not, take care which size you install.

ninja250 · March 11th, 2010, 12:49 AM

Makes me want to go check what came with the kit..

Momaru · March 11th, 2010, 11:15 AM

Indeed, if you do get measurements for the supplied screws in (I assume) the factory pro kit, let us know. Might make the 'which kit' decision a little easier

HKr1 · March 11th, 2010, 02:16 PM

That sucks!!

Good heads up thou

March 11th, 2010, 12:44 AM	#1
Momaru ninjette.org certified postwhore Name: Paul Location: Roanoke, VA Join Date: Jun 2009 Motorcycle(s): 2008 Candy Plasma Blue 250R Posts: A lot.	Carb screw holes A story of warning to those that replace their carb screws. Make sure you get the right size and your carb threads are properly cut. Since the OEM carb screws suck, I ran out to my local hardware store and grabbed some 4mm 0.70pitch button-head screws. Unfortunately they don't stock our 4x18mm, so I got some 4x16mm and some 4x20mm. Installed the 4x20 next time I was working on the carbs. I had to pull the carbs off for my current project and decided they were in need of some cleaning inside and out. I'm glad I did because little did I know, one of my screw threads wasn't completely drilled out/tapped. The diaphragm cap screw socket nearest the throttle linkage (top, right carb, right side, front) had been cracked when I put the slightly longer bolt in. Not bad enough to have the screw fall out but it could have been. Here's some pictures of what I'm talking about. First pic I'm pointing to the cracked area with the screwdriver tip. This is behind the throttle cable mounting bracket (incidentally, this is secured with red loctite). DSC04880.jpg DSC04878.jpg DSC04879.jpg Thankfully I don't seem to have been 'screwed' too bad by this mistake, but it's probably something to at least look for if/when you have the carbs off. It'd be unfortunate to lose a few carb screws on the road due to destroyed threads. Also suppose if it really broke the wrong way it could create an air gap for the vacuum diaphragm. Definitely feel that . Unfortunately my roomate's out. FWIW the 4x16 fit just fine in 13 of the 16 holes that are commonly opened on the carbs (4 per float bowl, 4 per jet needle/diaphragm cap). However 16mm is too short to be truly secure in the other three slots that require the screw to go through a metal mounting bracket (all three on left diaphragm cap). If you can find 4x18, use them! If not, take care which size you install. __________________________________________________ Proud member of the Blue Army Last futzed with by Momaru; March 11th, 2010 at 11:14 AM. Reason: Spelling fail

March 11th, 2010, 12:49 AM	#2
ninja250 You are sleeping Name: Casey Location: LMFAO!!! Join Date: Nov 2009 Motorcycle(s): 2 Posts: A lot.	Makes me want to go check what came with the kit.. __________________________________________________ <Yeah, it's a 250. LMFAO! Weaksauce

March 11th, 2010, 11:15 AM	#3
Momaru ninjette.org certified postwhore Name: Paul Location: Roanoke, VA Join Date: Jun 2009 Motorcycle(s): 2008 Candy Plasma Blue 250R Posts: A lot.	Indeed, if you do get measurements for the supplied screws in (I assume) the factory pro kit, let us know. Might make the 'which kit' decision a little easier __________________________________________________ Proud member of the Blue Army

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March 11th, 2010, 02:16 PM	#4
HKr1 IC2(SW) Name: Kerry Location: Pensacola Join Date: Nov 2008 Motorcycle(s): . Posts: A lot.	That sucks!! Good heads up thou