Hi, I’ve cleaned a lot of Amal carbs. Some so bad you’d not think possible to clean.
Some so bad, you clean them & just find such bad pits they are junk. We’re not talking about that.
The problem area is the horizontal passage for idle fuel intake from float bowl to pilot jet.
The main problem is we can’t access it. If really clogged we cannot get cleaner to truly enter passage. We must be very thoughtful of placement in cleaning solution. Surface tension of cleaning solution keeps it from really getting to the clog. It looks like cleaner is in passage, but is it really?
This can be very stubborn. Don't expect instant success. At the same time we can get air to blow though & bike will run fine, then suddenly not as another bit of corrosion flakes off. It can sometimes take 3-5 cleaning cycles to get it all out. That's been my experience.
Here’s what works for me. Get a plastic container with lid large enough to fully submerge carb & have depth & side room to turn carb, yet always be submerged. Several soda straws on hand, carb cleaner spray (not parts wash), compressed air is basically a must. It takes high pressure & volume to blow out the chips.
The inside corner of the idle air passage is often corroded as well.
I start be taking 1 strand of copper wire (some use drill bit) a little smaller than .017”. Aim just right & poke it through pilot jet. Not easy, but it will go. Keep at it. Worse case use drill bit by hand! 1/64” or #78. They give a little wiggle room. Ace Hardware usually stocks both. #77 is .018” that’s too fat. Go easy we don’t want to enlarge or burr jet. gently wiggle wire or drill, but don't enlarge jet.
Also take a single strand of copper wire, bend it & stick down the floor drillings near front of slide. Wiggle it around to break up corrosion.
Clean carb & passages with carb spray. Blow dry well. Wash carb with hot water in sink. I have garage sink. If you don’t figure it out. Wife not home is best…. Blow carb dry. Residue on carb increases surface tension.
Use white vinegar from grocery store as cleaning solution. It is a mild acid. It can often clean the black from Berrimans from carb. Use full strength. I keep 1 gallon jug on hand.
Fill container deep enough. Roll carb so all surfaces are wetted. See vinegar enter all bores good as you can. Old tooth brush makes a good scrubber.
Now the nasty part. Take a straw & suck up some vinegar, but NOT into your mouth. Turn carb & blow it into idle fuel intake bottom of carb. Several times to make sure all air is pushed as possible. Do same with pilot jet bore & idle air intake bore. While you do this put fingers over the idle air intake passage at rear of carb, pilot jet bore (the mixture screw bore), the fuel intake bore. This forces vinegar into where we want it & helps displace air. Not a fast process. Remember in real life sonic cleaner can't displace trapped air if it's really trapped. So no cleaning solution really gets to the clog. Not simple stuff!
Now let carb soak 20 minutes. It's acid, don't soak it too long all at once. It will have taken 2-5 min to flush air out so total will be more like 25 minutes. It will turn zinc brighter silver. That will dull to normal grey zinc in a few weeks to a month & will look like we normally see a carb. I've done this many times.
I'll place carb upside down, sideways both ways, top side up in attempt to insure vinegar is contacting all surfaces.
After about 20 minuets remove carb & flush with hot water. I blow it dry & the passages. I then put carb very gently in vise with plastic jaws to hold it steady. An assistant is better if you have one. I sometimes don't.
Stepping back a moment, look at rear of carb at air cleaner side. You see 3 drillings. Center drilling is main low speed/idle air intake. The open hole at side is idle intake air that the mixture needle controls. The other drilling will have plug in it. This is the idle fuel passage from float bowl. Depending if carb is right or left handed the plug will be on opposite side.
This floor passages, the tiny holes at bottom of throat near front of slide are interconnected to the idle air system directly & indirectly. So we must make sure they are clean also.
We don't worry about the large center hole. We will focus on the idle intake air hole.
Point is in order to focus carb spray & air blast where we want it all the other holes MUST be blocked. So one hole we shoot cleaner & air in, we leave one hole unblocked for it to exit. If you really look & get lucky you will actually see bits of white & yellow corrosion fly out hole. Dang, how can that much junk be stuck in there?
I'll stick golf T or rubber stopper in the air intake. Then 2 fingers over floor holes. Then blow cleaner & air into pilot jet bore, exiting out the fuel intake hole that goes to float bowl. Then reverse the spray & air going into fuel intake.
Then block the fuel intake with stopper or finger & let cleaner. & air exit air intake. Reverse cleaning.
Then block pilot get bore (not with screw), blow into fuel intake, exit air intake. Reverse. Then move to floor drillings. These seem easy to clean.
Repeat this sequence 3-4 times. Pretty soon you'll start to see a pattern as carb spray exits. It will start to make sense how all is interconnected.
Finally do a visual flow test with carb spray. By covering all bores except the inter & exit for spray you'll see spray exit, including the floor drillings. Experiment & practice this until you get what you should see. If you had a clean carb to compare & use for a baseline it's quite obvious visually when things are clear.
However.... it will appear perfect, yet there still be corrosion inside that's still stuck tight. The passages are quite large so they can flow fine at the moment.
Depending on how much corrosion I see in bowl & the like, I'll repeat this entire process at least 3 times. Bad case 5 times.
I've done 5 times on my bike after 34 years of storage. 9500 miles at the time. Worked fine 2 weeks & clogged again. I could see more crust blow out onto rag I placed to catch it. Soaked & cleaned, Again good 2 weeks & needed another cleaning. A month later it clogged again. This time I pulled bowl drain & flushed on bike. Worked, got lucky! After that never another problem again. Finally several thousand miles later, slide & bore just wore out. I got new Premiere. Premiers are worth every penny. I've covered 13k on it so far. Not a trace of slide/bore wear. Needle & jet wear as they always did. Good for about 15k ish.
I fully understand this is a long & convoluted cleaning procedure, but trust me it works. I learned this the hard way. It has not failed me yet. On a '59 BMW The bowls were so corroded they seeped fuel through the bottom. Epoxy was a patch until these rare bowls could be found. E10 fuel is very hard on epoxy. Didn't last long term.
You will find if you can ride bike at least once a month or so the E10 fuel will keep insides of carbs squeaky clean. If you know bike will be layed up. Turn off fuel taps & run carbs dry.
By the way, wife & I had to refurbish mom's house for sale in a hurry. I was off bike 7 weeks. Gas in bike was from 5 gallon can filled 8 weeks ago. I did not drain or run carbs dry. I didn't expect to be off that long. Motobatt battery volts was 12.71v. Filled tank with gas from 5 gallon can. Good free tickle with gas running right down side of carb. Free clutch. Turn on key. Started first kick & ran perfectly. Did nice little 92 mile ride. I usually ride 1-2 times a week usually 50+ miles. My friend let his '73 Bonnie set 6 months. Had nearly full tank of gas from last ride. Good tickle, freed clutch. Started first kick & ran perfectly. This has been my observation on E10 fuel we use. We're in San Francisco & just east so only frost in winter. No hard freezes hardly ever below 28F.
However we only use Shell or Chevron 91 when possible. On the road in rural areas you use what you can get. Trust me... fuel brand matters! The no name stuff from the mini mart in the boondocks, tends to ping & runs poorly cold. Again you get what you can find. We were over 100 miles from a real gas station.