930 rebuild

my '72 non combat backfires on deceleration. right side is running hot [white plug deposit] , left side is rich [sooty]. i've used the number 78 drill to clean the pilots. neither airscrew seems to have much effect even after cleaning. carbs are synched and will idle down to 600 which i know is too low. bike pulls like a freight train! only problem is the backfire on the hot side and non responsive air screws. slides seem a good fit. timing is spot on.

i've reconciled myself to pulling the whole oufit, doing a deep clean, doing bushmans blanking screw mod. while i'm in there what else should i examine/replace?

Now when you use the #78 drill bit it is glued in the end of a red tube that is taped on the side of a can of brake clean. Or carefully crushed into a brass tube that has an I.D. close to the drill bit. Without the bit on a stick of some kind you are doing nothing because the drill bit can't reach the jet with just the bit and a pin vice will not fit into the screw opening. Now assuming you knew this and took one of the options for mounting the bit you should have felt the resistance when the drill bit found the jet.
My rule is that if the jet is not tight enough on the drill bit that the stick will not sag when the drill is engaged then the jet. Then the jet has been compromised and needs to be drilled out. I use a .030 or so bit and than use the older removable jets to revitalize the system. You could drill it bigger but it works fine this way.
In the forty or so years of it's life someone not as careful as you has worked on your carbs.
Yes, you should get a response from adjusting the air screws typically the engine should falter within 3/4 of a turn once out into the range of adjustment. You should be able to make it too rich and too lean.
Now normally if your bike will idle at 600 you are running on the idle circuit but if you have failed to clear the circuit you could be finding that idle via a too high slide idle setting. If you use a 3/16 drill bit shank as a feeler gauge to set the idle screws than find you have no idle this would be an indication that you are idling on the slide adjustment and not the air circuit that will make the air screws unresponsive. Be sure you know what you are idling on. I have found that the larger ultra sound units with two heaters and two sound generators are the best. I use white vinegar as medium. 50 minutes in this machine does the trick no more than that though.

Look for an air leak, once you're up and running the motor should be off the pilot circuits and they will have minimal effect.

Cash

ya i epoxied the bit to the wand. a little digression here, i used some old epoxy and after cleaning the 2nd carb pulled out the wand minus the drill bit to my horror! i ran a piece of safety wire in there and could feel the shank. what to do? i finally cut the end off the wand and mixed up some new jb weld. i stirred the epoxy w/ the wand forcing an amount into the wand. i kept packing it in there w/ the safety wire. satisfied i had enough epoxy in the bore of the wand i wiped off the excess so the exterior was clean. i then carefully fit the shank into the wand by feel and let it set up overnight. in the morning i pulled it out with the bit. got a chuckle on that one! i can feel the drill bit entering the jet and it's a close fit w/ the wand not touching the air screw hole.

i set rhe sync w/ the drill bits and adjusted for simultaneous opening. bike starts 3rd kick, points ignition. i then adjust throttle stop screws equally to get 800-900 rpm. start the air screws at 2 full turns out but adjusting has no effect.

an air leak makes sense and tommorrow i'll try that approach.

let you know what i come up with. thanks, rick

I epoxy the bit to a basketball air filler needle. I make about 5 or 6 of them at a time because it is easy to lose them. Gives you a nice grip for twisting the bit. Most of the time you don't need to do much twisting though.

Good save with the JB Weld!

Russ

The more I read about the pressed in pilot jets, the more I want to use screwed in ones.

It's just a maintenance nightmare thinking about straws and bits and oh my!

With the screwed in ones, just drop the float bowl, unscrew and clear.