Amal 930 head banging....

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acadian

acadian

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So I'm almost out of ideas, the timing side carb (stock twin 930 set up) seems to be dialed in nicely but the primary side carb is still giving me a headache. I've checked all the usual suspects:

- cleaned, remounted, checked for air leaks
- exhaust nut secured well, no leaks in headers
- valves set and rechecked
- new plugs and wires swapped
- running a single Dyna coil.. so it ain't a coil fault
- checked float levels

My problem is this, when I get a nice even burn between both plugs the primary side idle's like drunk hippo, while the the timing side purrs away nicely. To get the primary side to idle nicely I have to richen her to the point where she fouls the plug. Anything I'm missing here?
 
If you have not run a .016 drill #78 bit into the (pilot jet) behind the air screw then you are just spinning the wheels. Don’t poke it drill it. At least once a year at the beginning of the riding season followed by a blast of brake clean. The bit is so small and short it needs to be epoxy glued into a brake clean red plastic tube to reach the jet. I fix ten bikes a year using this method. I have never had to drill from the opposite unused side yet. Do both carbs even if new.
 
norbsa48503 said:
If you have not run a .016 drill #78 bit into the (pilot jet) behind the air screw then you are just spinning the wheels. Don’t poke it drill it. At least once a year at the beginning of the riding season followed by a blast of brake clean. The bit is so small and short it needs to be epoxy glued into a brake clean red plastic tube to reach the jet. I fix ten bikes a year using this method. I have never had to drill from the opposite unused side yet. Do both carbs even if new.
Click to expand...

I see, I've heard of the blanking plug mod from the reverse side. So you're suggesting that I use this bit through the air screw hole directly?
 
I was at Raber's the other day and mechanic had a similar problem that turned out to be a slightly warped float bowl from over tightening screws. No gas leaking, but just enough air to cause backfire. Dam Amals!
 
How did you sync the carbs? If you used vac gauges swop them over and try again.

Cash
 
This # 78 drill is tiny and usually too short to reach the jet orifice. I take a Q-tip and cut off the tip. Use the #78 drill to make a hole in the end of the q-tip by just twisting it in between your fingers so you can super glue it in there. You can now reach the jet hole and clear it.
For what it is worth, buy 2 or three of these drills. You will surely loose or break at least one. I know this first hand.
 
pvisseriii said:
This # 78 drill is tiny and usually too short to reach the jet orifice. I take a Q-tip and cut off the tip. Use the #78 drill to make a hole in the end of the q-tip by just twisting it in between your fingers so you can super glue it in there. You can now reach the jet hole and clear it.
For what it is worth, buy 2 or three of these drills. You will surely loose or break at least one. I know this first hand.
Click to expand...

Assuming gentle twisting is all that's required, is there any risk of enlarging the pilot? Does it matter?
 
No it's the drill they made them with and Yes you do not want it bigger or scratched up. No force forward just twist it in the flute of the drill will fill with crud.
 
Don't forget to check the two pilot holes in the bottom of carb bore (one under the slide, and the other on the engine side of the slide) as they can also become blocked.


I use the smallest two or three sizes of a welder's tip cleaning set like this one, to carefully clear the two pilot holes and pilot jet bush.
Amal 930 head banging....
 
When I got home I stripped the bowls off the carb to perform the above mentioned pilot jet cleaning, and decided to check the bowl surface as suggested above.... well lo and behold, the flange was warped more than 1/8". Guess I found my problem. Anyway, I performed the cleaning with an itsy-bitsy sewing needle (couldn't find a .016 bit), blew her out liberally with carb cleaner and air, and flattened the float bowl on my table saw surface with a bit of propane for coaxing. We'll see if that cures it, thanks for all the input.
 
Well, that apparently was not the problem as the issue persists. Now, unless I'm crazy, I"me pretty sure the symptoms point to something in that one carb. Here it is, when I'm setting the idle air mixture, the right carb tunes out just fine, but the left will only idle stable at too rich an air screw setting, even the smallest turn to lean it out causes it stumble and falter. Again, this is only at idle on the left carb. At any throttle opening above that she performs great. Am I nuts, or could it be something else?
 
I am getting ready to reassemble my Amals. A while back I noticed that the two banjo bolts don't match. One had a vertical bore of 1/4-inch the other was about 5/32. I found this odd and had decided to bore the smaller one out to match the larger. So tonight I set it up in the drill press to punch it out. For the first time I noticed that the larger bore had only one horizontal hole in it, and the smaller bore had two (opposite each other). I will never know (now) if this could have been causing any of the mystery problems I was having in balancing my carbs last fall as I have worked on so many things that it is impossible to know. And I don't know for sure if I have fixed it yet.

But the point of the story is...check those damn banjo bolts and see if they match! Mine do...now!
 
They won't reach in there unless you epoxy them in the end of a tooth pick or a q tip end with the cotton cut off. Use the drill in you fingers to make short hole to insert it in.
 
pvisseriii said:
They won't reach in there unless you epoxy them in the end of a tooth pick or a q tip end with the cotton cut off. Use the drill in you fingers to make short hole to insert it in.
Click to expand...

the spray tube from a can of brake cleaner or similar makes a nice handle too.

The hardest part of the #78 drill bit approach is figuring out how to store it so it doesn't end up lost or broken. That's a tiny, fragile little drill bit!

Debby
 
Yep Debby order more than one as one of mine was broken on delivery.
 
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