On the later 930 concentrics, if the pilot jet is suspected to have been reamed out too large, what is the fix, if any?
I'm not sure this is my problem, but it is the next step to solving the idle situation. Victor idles poorly, have to set the air screw almost all the way in, and set idle up higher than normal. Even then, it isn't consistent. Seems to run OK in other ranges.
Carb has been cleaned every way except ultrasonic. New needle and seat. Pilot circuit doesn't appear plugged, so I'm thinking maybe too large. Seems kinda counter-intuitive to the air screw setting... I think... but seems the only thing left?
The AMAL, and its cousin the Mikuni VM, is made up of two separate carburetors. They are housed in a common body and share the fuel in the float bowl.
They operate independently of each other.
The the main carburetor's main jet is blocked the bike will start and idle, but will not operate at high throttle openings. The opposite is true when the pilot jet (main jet for the idle carburetor) is blocked. The bike will start when well-flooded but will not idle.
With the main carburetor the slide controls the air. With the idle carburetor the pilot air screw controls the air. When the engine does not respond to the pilot air screw the typical cause when using moder fuel is a blocked pilot jet.
It is interesting to note that with the introduction of the Premier carburetor Burlen choose to use stainless steel for the pilot jet rather than the brass used in the past. Stainless jets are much less prone to react to the alcohol in modern fuel and should not be so prone to blocking up.
While I use an ultra-soic cleaner it is not the answer to a blocked pilot jet.
In 1970 the US distributors on both side of the country sent all of the dealers a jet cleaning tool made from a #78 drill and some hobby brass tubing. The blocked jet has been around as long as the pressed in jet. It is just with the alcohol the problem is more prevalent. There is a Triumph parts bulletin covering this.
While there are those who choose a guitar string of an appropriate size it just pushes the swarf upstream of the jet. Unless it is removed from the carburetor there is a very good chance it will work its way back. If you twirl the drill tool it tends to pull the swarf down stream of the jet and the "fix" is much more reliable.
I avoid promoting any of my products as a moderator, but I will make an exception. We sell these tools to many dealers in the US under part number CS-0307. Many of the dealers advertising on this site have them in stock - Try Randy Baxter.
I modified the late Concentric on my BSA by drilling an access port to the pilot jet. I used a lathe center drill with 1/4in OD to punch through the carb body opposite the idle mixture screw. As a common casting is used for left or right carbs, the body opposite the screw has a 1/4in cast in port that is not machined & is blocked from the idle fuel circuit at the bottom by a thin wall. The lathe center drill has a large shank, different sizes available, that is reduced at the ends to a small drill, about 0.12 diameter. The cast in port guides the center drill to pierce the idle circuit directly at the idle jet bush so the jet can be easily blown out or prodded. A 5/16 BSC tap easily cut threads in the soft metal for a short screw to reseal the port.
I find the press-in jet correct for the 250cc BSA but too small for the 441cc. A #78 opens the jet out to correct the mixture range for the bigger engines. Cheers, Don.
...so I have the same hesitation at idling problem in my 626 but I do not have goo in the pilot jet... or is a goo that you cannot see or detect? I used the guitar string too. Also, I used compressed air and the air flows perfectly well for every conduct... Could be too much "air" between the throttle slide and the carb body the problem?
...yes, float boat is warped; however, is have been warped for several years and I did not had this problem. I have a stay up float there, I bought one due to I had a problem with the float level and I put it with the bulletin specs; then after changed the sleeves and pistons I had this starvation problem so I tweaked again the float not using the Triumph specs to solve it. But still I have the problem described by Steve Erickson.
For the idle carburetor to work the float bowl must not be warped. If warped it can allow air to enter the fuel transfer port that leads to the pilot jet. The fuel transfer port passes through the joint between the bowl and body. When air breaks the vacuum that lifts fuel out of the bowl the idle carburetor starves for fuel. The bowl gets warped when it is overtightened. For the idle carburetor to work the float bowl gasket must seal the transfer port!
Especially at small throttle openings the lack of fuel reaching the pilot jet will cause the main carburetor to run on the lean side.
One should be careful bending the steel needle tab on the Stay-Up float. The float itself is slightly larger than the plastic float especially at the bottom back corners where it hits the bowl. This limits float movement slightly but enough to limit the ability of the metal tang from lifting the needle from the seat. This is made worse when you bend the tang to lower the fuel level. When you bend the tang it can no longer upset the needle from the seat by itself. To lift the needle from the seat you now have to rely on the head pressure and how full your gas tank is.
We have had much better results with the Stay-Up float by moving the brass seat as in the past. This allows the tang to lift/upset the needle and get fuel flowing without relying on head pressure.
Plus one on that last comment john. I have been suggesting the same thing to anyone who I have sold carbs to. After trying to bend the tang myself, it causes no end of pain and in one case I reverted to the plastic floats to save a lot of time instead correction of this.
...yes, what you say is what I did and tried to explain in the previous comment. Do not know why this hesitation is presented now (may be due to I put new pistons, rings, sleeves in the motor helping to tight it up?) Again, I have that bowl warped for long time now, due to vibration, the bowl screws wanted to fall down more than one time in the past; so tighten them a bit was mandatory if I wanted to get back home. But I have been having perfect idle (in cold) without grabbing the throttle grip etc. I guess, as I mentioned in a past thread about Aluminum AMAL, is to try to buy a new one... Would be good if they sell only the bowl.