Everyone loves a good carb question...right?

[raybear71]

Last weekend I pulled the carbs to seal up the base of the intake tubes with a little permatex black. Problem solved, no more creeping idle. The problem is I decided to drill and pull the caps on the pilot jets and when I did the right front carb the drill bit bumped the jet. Now the jet itself is fine, but when reinstalling the jet it bottoms out at about 2 full turns. I'm figuring I screwed the threads up. I set that needle at one and a half turns out just to be safe. I have the carbs I bought on ebay a few weeks ago and decided to use them for parts because they were dropped in shipment and the whole rack is crooked. So now I need some input from all of you. Will the carb thats on there run ok for now as it sits or should I change it? I'm out the door now for work, but I will check back in the morning to get your 2cents. Thanks, Ray.

[Marcarl]

From your description I don't see how you would have damaged the needle screw or the carb threads,,, maybe you got a piece of metal stuck where it shouldn't be.

[MiCarl]

That's not really a jet - more of a mixture screw.

 

I don't see any way you could drill out to where there were only two turns without drilling away most of the screw.

 

I'd pull the screw. On it are a spring, flat washer and o-ring (in that order). Use a piece of fine bent wire to fish those parts out if they don't come with the screw (rig a white rag under your area to help make sure you don't lose the tiny washer and o-ring).

 

The screw should have a long needle tip on it, almost sharp enough to prick your skin. If it's blunt you've broken it off in the carburetor and you have big troubles.

 

Look in the hole. You should see it threaded more than the threaded length of the screw. Blow some compressed air in there to clear any debris.

 

Assemble the spring, flat washer and o-ring on the screw. The o-ring will hold it all together. A bit of light oil (WD-40, PB-blaster, sewing machine oil, etc.) on the screw isn't a bad idea. Reinstall it.

 

DO NO TURN IT MORE THAN YOU EASILY CAN WITH ONE FINGER AND YOUR THUMB ON A SMALL SCREW DRIVER. YOU DON'T WANT TO WEDGE THAT NEEDLE INTO THE SEAT!

 

If the carbs are off the bike you can feel that needle poking into the carburetor throat when the screw is fully seated.

[bkuhr]

The screw should have a long needle tip on it, almost sharp enough to prick your skin. If it's blunt you've broken it off in the carburetor and you have big troubles.

 

Look in the hole. You should see it threaded more than the threaded length of the screw. Blow some compressed air in there to clear any debris.

 

This is stolen from the vmax site. Good description of ports and breakdown.

http://vmax.lvlhead.com/tips/shotgun.htm

 

Based on this I would suggest to blow compressed air from PAJ1, to remove a possible broken needle point or other debris

[KIC]

This is stolen from the vmax site. Good description of ports and breakdown.

http://vmax.lvlhead.com/tips/shotgun.htm

 

Based on this I would suggest to blow compressed air from PAJ1, to remove a possible broken needle point or other debris

 

 

THANKS ! That is a great write up. Very clear and easy to understand. :happy65:

[raybear71]

The needles were comepletely removed and inspected,also the ports were cleaned. The threads are definately gone. I'm just wondering if it will hurt it to run with the pilot jet only turned out one and a half to one and three quarter turns.

[Prairiehammer]

If you are limited to 1.75 turns out because of damaged threads, how did you get that mixture screw out to inspect it?

What size drill did you use to drill the cap? Most use a tiny drill ( 1/16" - 3/32") to drill just a big enough hole to insert a sheetmetal screw into and then using pliers, grasp the SM screw and wiggle and pull. Did you use a 1/4" drill and drill the plug at once? Like Carl says, it's very difficult to ruin the threads so much that you can't get the mix screw to be fully adjustable or to remove it. Heck, there was one guy here(?) that had a stripped out mixture screw screw slot. He cut away most of the surrounding carb body to access the mix screw enough to cut a new slot in the screw. He was able to remove the old screw and replace it with a new one and had a perfectly functioning carb.

A cursory look into the mixture screw recess or well will not reveal any threads. The threads are not visible without a good light and craning around to see DEEP down inside and are NOT VISIBLE at all with the mixture screw installed.

Re-reading your initial post you stated that the mixture screw bottomed out after just two full turns. My guess is that there is something (spring? washer? O-ring? broken needle tip?) lodged at the bottom of the hole preventing the mix screw from seating properly. The threads would have to be buggered closest to the seat. You could not have damaged the threads at that depth while the mixture screw was in place.

One thing that has happened when one drills the cap and hits the mixture screw with the spinning drill: the drill spins the screw in quickly and with force. This may damage the mixture screw by breaking the sharp tip, it may damage and deform the mixture screw seat, it may break the O-ring or even the spring. Any of these scenarios may leave damage or debris behind preventing the Mixture screw from fully seating.

Edited June 9, 2012 by Prairiehammer