Previously I’ve tried making my own adjustment tool with some brass tubing and solder, it worked for a while until the brass gave out and cracked all around. I also realised not everyone may have the right piece of tubing around, but more importantly I needed to adjust the carb on another engine and I still refused to spend a total of 30-40 US Dollars on the tool!
Now, it’s been suggested to just grab a Dremel tool with a cut-off disc and simply cut a couple grooves onto the screws, including the shroud — Well, I’m not too fond of this idea, but it got me thinking… what if I removed the screws, cut the slots, then put them back in?
That was the answer!. But how do we remove the screws, the whole point here is that we don’t have the tool to adjust the carb, let alone remove those pesky needle screws!
Well, I looked around and I noticed these old spark plugs in a box, some of them had a metal screw cap with the right diameter (almost, required some filing) this meant I could couple it to the pacman screws, but I still needed this makeshift tool to grab onto the notched screws.
The answer came by placing a thin piece of steel wire inside the original notch of the screw, once the spark-plug cap was inserted, it could grab ahold of the wire and allowed me to turn the damned screw!
The spark-plug being used as a temporary “tool” for needle screw removal. You may also notice the piece of steel wire on top of the needle, this is how the spark-plug cap binds onto the screw.
Low needle finally removed
I began by removing the L (Low) Adjustment screw/needle. After a few turns you can actually just remove it by hand. Obviously, the next logical step is to cut a slot onto it’s head. I did this by hand since the heads seem to be made out of aluminium or some mild steel (anodized alu is my best guess), so it’s rather easy to cut with most handsaws.
Close-up of the notched heads, excuse the poor quality of the picture — I improvised and I didn’t have the proper lighting, tripod, etc. at the time.
Once I got a deep enough slot, I decided to replace the needle and begin the whole process again with the H (High) Adjustment screw.
Before I put them back on though I added a bit of lithium grease onto the threads, perhaps not the best idea in the sense that this could make the needle not bind onto the brass insert and instead work itself loose with the vibrations of the 2 stroke engine, however I would rather have this happen than strip/damage the threads on the carb.
Be very careful with the needles, don’t scratch them, don’t bend them or stress them in any way.
Also I noticed the H and L needles were slightly different, the H had a tapered end whereas the L needle was straight.
Replacing them is simple, screw them all the way in, then go back 1.5 turns on each of them. This setting should be good enough to get the engine started on full-choke, you’ll have to then adjust the carb to get the right mixture on L and H.
The only other alternative to this method would be to get the needles out, go to your local repair shop and see if they’ve got matching replacements with a slot head.
Adjust your carb
A basic adjustment routine is to begin with the 1.5 turns, choke it, start it. It may not stall at this stage, adjust the L screw until it does. Now restart and try to go WOT (Wide Open Throttle), adjust the H screw until the WOT sounds right (not too lean, not too rich). After this, adjust the L screw again, this time you are looking for a quick response from the throttle toward WOT. Stop the engine, restart, try it out and adjust the H again. Once it’s cold, repeat this process if you find the engine still doesn’t sound / operate right. It’s worth noting that any movement on the needles will take a few seconds to actually reflect on the performance of the engine, this lag is common and you have to learn to “wait for it” before you keep adjusting.
If problems still persist, perhaps this is a good time to rebuild your carburetor. There could be other issues such as a broken boot (this means there isn’t a good seal between the crank-case and the carb), broken/damaged gaskets are also common in this area. If the engine starves rebuild the carb. If it randomly shuts down, you should look into the ignition system. Other issues could be varnished gasoline inside the carb, this could also present you with random behaviour when bits of varnished gas lodge into the various components of the carb inhibiting it.
Anyway, hopefully you’ll be able to find some old spark-plugs, some bits of wire and try this yourself before you butcher your engine with a Dremel tool!