Earlier this spring, I finally tried to get my (used) TM36-68 pumper installed. It turned out to be a miserable failure, because the bike just wouldn't start or idle worth a damn. Obviously a problem with the carb - plugged passage I figured - but at the time I couldn't be bothered to dig into it any more, so I put the stocker back on.

Today, I finally figured it was time to give it another go. So I gave the carb a good cleaning and inspection (so I thought), reinstalled it and had the same issues. Unsteady, surging idle, backfiring through the carb, cough and die, etc.

So, I did a little reading and came to the conclusion that my pilot fuel screw tip must have broken off in the carb due to my or the previous owner's ham-fistedness. I pulled the carb and confirmed the broken screw, but now I have a bigger problem...how to get the darn tip out of the carb?

That little tip is wedged tight into that passage, and I'm not having luck getting it out so far. The problem is that the passage is only slightly larger in diameter than a pin, and located in the throat of the carb. I can get a pin into the hole, and I can grab the pin with pliers to hold it while I tap the side of the pliers with a hammer; but so far, the end result is always just a bent pin and a still-stuck screw tip. This seems like the most hopeful method, but doesn't seem to be working. I'll give it another shot, but I'm about to give up on it.

I'm contemplating trying to drill it from the bottom side, but I don't want to ruin the carb...and since it is so small and so deep inside the body, visual access is not good. If I attempt this, I'll have to wait to use the facilities at my workplace, and even there, I don't think there's a small enough drill bit.

While I think this over, anybody else have good ideas?

 

Man, that downright sucks. I haven't studied mine that closely in awhile, so refresh my memory. Does the passage on that fuel/air screw go straight up in a line into the carb throat? If it does, I'd try a fine wire bristle pulled out of a metal brush to push from the top downward in hopes of dislodging the broken tip back out the hole for the needle. That's a shame that happened. You might research some threads on other forums where people have used some creative methods to get that tip out. Search for "removing broken fuel/air needle tip from carb".

 

Heat the carb in boiling water or (if all plastics and rubbers are removed) in a deep fryer, the needle is steel and the carb body will expend more and may free up the needle end to tap out?

 

LOL!...yeah, I saw that one when I was looking up different methods. It sounds reasonable being that the carb is some kind of aluminum pot metal and the tip is brass. I was even wondering about some kind of mild acid that's reactive with brass but not the carb body. Brass is really soft.

 

Yep. I've been able to get a sewing pin on top of the screw tip from inside the throat, but the pin ends up bending under the pressure.

Now, the situation has gotten worse...a piece of nail snapped off in the hole on the throat side of carb. It's not looking like much hope of getting it out by pushing from inside the carb throat.

I may try a boiling water bath...but there's a lot of disassembly that needs to be done to get there.

Before I do that, can anybody spin out their TM36-68 pilot fuel screw and take a good photo of the unbroken tip? Also, if you have an accurate set of calipers, could you take measurements of the tip.

While you're at it, anybody want to pull their carb and check what the seat area looks like? Conical hole, straight hole, stepped hole?

If I've got an idea what I'm up against, and what the tip is actually stuck into, I may have a better shot at drilling it out if necessary.





The base of the final taper at the tip of my screw is about 1.40mm in diameter, and it is about 1.12mm in diameter where it snapped off. I'm curious to see how long the unbroken length is, and how sharp the tip is supposed to be.

 

coming in late and sorry if i'm stating the obvious but make sure that you are only tapping on the small side of the taper. If you tap the wrong end it will only wedge in there tighter, right?
Carb bodies are made of either a zinc alloy or aluminum depending on the manufacturer.

 

Thermal Expansion Metals
I was kind of doubting that heating the carb body would loosen tip , but if i am reading this chart right, zinc expands more than brass, so it might work.
I wanted to say that small continous taps or hits may work better than heavy hits/taps. Put the pin in the hole and tap tap tap on it with something.

Good luck
Dan

 

Lutz, the tip that's broken off on your needle looks practically identical to the needle tip on the OEM CV carb. The CV carb needle does have a secondary step on the needle shaft, but the tips look basically the same.

 

Apparently it's an air screw - number 49 inside the red rectangle in this diagram. The only thing I can see in the parts diagram that looks like it'd be the screw you are having trouble with.



If that's the screw it'd be metering air incoming through either the hole circled in red or the one next to it. Which somehow seems better situation than a fuel screw buried deep inside the carb, and the front half of your carb body comes off, so in some ways the situation doesn't seem impossible?

If the threads for that screw in the carb body are still undamaged as they seem they might be from your photo, then you only need to open up that passageway. If someone can measure their tip or their passageway, then you'll know what size drill to go at it with.

I don't know how 'soft' that brass is. I just worked with my fuel mix screw and it's fairly hard stuff. Harder than the metal the carb is made out of I'd say

 

No,, that's a diagram for a different carb, TM36 non-pumper I'd guess. That diagram is from a two stroke carb, not a pumper as is used on the KLX.

What I've got is the TM36-68 pumper carb. The pilot fuel screw is located under the throat of the carb, on the cylinder head side of the slide.