Cleaning a Walbro Carb

I've been having carb problems. Pretty much anytime you have trouble with an engine, its the carb. The ignition and wires are second on the list. The rest of it is pretty tough and resilient to problems. I have been having issues with the carbs on both 10cc engines. These little buggers have such small tolerances for mixture that any debris or clog, and air leak, can cause weird stuff to happen that causes gnashing of teeth, sore backs from standing way too long to solve a problem trying the same thing over and over again because what you are doing is supposed to solve the problem. The machines are not hard, they just are complex. You've been there, don't lie.. If there was one thing I hate about gas its that the smaller engines are so unreliable day to day. The 20cc and bigger, probably the 15cc too but I don't have any, are so much more stable. So when someone tells you gas is reliable, they don't fly less than 10cc. Remember, the engine is fine, its almost always the carb.

I use this with the little red tube to blow out the passages and soak the carb.

I've take the carb apart but for the valves (throttle and choke). Both the metering and the pump side are disassembled, and the needles removed, including the metering needle. I don't peel off any gasket that doesn't want to come unless it needs replacing. The pump side gasket and valve sheet are fine, but the valve sheet might use replacing if I get one. For now its fine. I have cleaned everything thoroughly with carb cleaner spray, blowing out all the fuel pathways, soaking the carb to let any build up break away and flushing it again. I cleaned all the gaskets and the valve sheet with the carb cleaner. Carb cleaner melts gloves, by the way...

Here I reassembled the metering needle. Getting the metering spring under the round depression in the metering lever is challenging, and it must be properly seated. This will be the only frustrating part of the process, be patient. I use a flat micro driver to hold the spring compressed while keeping the lever in the head of the metering needle, and the hinge bar in its slot. Takes a few tries, and a couple of rounds of searching the floor on my hands and knees for a launched spring, but in the end it gets where its suppose to be. I don't Loctite the metering securing screw. Snug it in nicely.

Someone will happily sell you a fancy tool but any rigid piece or your Mark 1 Mod 0 Eyeball does just as well. The top of the metering lever should be exactly level with the top of the carb case. The other end on the needle head should move the metering needle noticeably when the lever is depressed, it is either open or closed. I find that the lever is only slightly bent when set properly. If this is screwed up the carb will not work well.

The metering diaphragm goes small washer thing side up. It should rest pushed out by the metering needle, Tapping it should have a nice range of motion and a quick rebound. If not the spring is likely wrong or the lever is not adjusted properly.

The metering cover is in place.

There are lock washers, but I still Loctite the screws, all of them except the metering hinge screw. I screw these down gorilla-tight.

Pump side. Gasket goes out, the valve sheet in, so that the flapper valves cover the fuel pump holes they are assigned to. Those are all the passages I blew out with carb cleaner. All of them.

Pump gasket and valve sheet in place. The valves should lay flat over the fuel holes they are assigned to. If not, the valve sheet should be replaced.

Pump side cover in place. I Loctite and gorilla-tight this screw. Make sure the gasket is properly seated, there are posts that usually assure this that pass through the gasket.

The fuel flow needles. They are different. The long skinny one is the low speed needle, the fat shorter one the high speed needle. They also have their own sized springs.

They go in their own holes. Seat the SOFTLY and completely. Walbro recommends both needles out to 1-3/4 to 2 turns as the starting point. You will need to adjust the needles. If you know what they were set at before you can try those settings.

Here the low is set to 1-1/2, the high to 2 turns.

The gasket between the crankcase and the carb is essential! It serves to prevent air leaks both ways, and to insulate the carb where the magic happens, from the heat of the crankcase/cylinder where the violence happens. Some engine use a spacer here to improve that insulation. I coat it with a thin layer of red grease.

There is a vacuum hole on one side of the carb, you can see it here. If your gasket has one small hole, it must be lined up with this passage or the carb won't work. My gasket happens to have two holes, one is vestigial.

Secure the carb to the crankcase being sure that the gasket is properly aligned. Use Loctite and again, gorilla-tight! The process is completed. Next, putting the engine on the improved test stand. I hope this cleaning solves the low needle/idle and acceleration issue. I gorilla-tightened all of the cylinder screws I could reach (two are blocked by the muffler screws, yep, Loctited and gorilla-tight).