by veefre Sat May 09, 2015 3:23 pmI'm sure we've all read the instructions that say to turn in an idle mixture screw by hand until it's just finger tight so as not to damage the screw or its seat. Then turn out a set number of turns (usually two or three) and then with motor on, turn in until lean stumble, then out till smooth, then about another 1/4 turn out.
And that's what I generally do. But apparently someone who worked on my 283 in the past was in the habit of turning in the idle mixture screws until they were just seated, and then turn in another 2-3 turns just to make sure.
Cause when I tried to adjust the screws, I found that one side didn't lean stumble at all when turned in, even all the way, and the other side stumbled at about 2 turns out. I wound up adjusting one side to 1-1/2 turns out and the other to about 2-1/4 turns out. And it kind of stunk on idle. Ran reasonably well, but hey, it's a small block.
So today I finally got around to pulling the idle mixture screws and discovered the screw abuse. The ends don't taper evenly to a a point. Instead, they taper and then have a sudden drop-off, with the rest of the screw looking more like the tip of a fine tip mechanical pencil than a cone. And the screw from the side that had no lean stumble actually had some threading on that fine tip, probably from forcing it in too far.
So I measured what was left of the suckers and then got online and ordered a new pair from Mike's Carbs. Then I got out the green scotchbrite and polished the tips as well as I could, trying to at least remove some of the threading on the badder of the two.
When reinstalled, I found that I could adjust both to 1-1/2 turns out (total) for a relatively good idle that stinks less than before. I'll be looking for that care pack from Mike though, hoping that the jet seat isn't also too trashed to allow for a proper idle adjustment.
And so it goes. It never seems to end, the discoveries of past mechanical abuse to a used vintage vehicle like this. But then, I 've been guilty of a few questionable mechanical practices, because I didn't now any better. I surmise someone told someone to turn in the jet "until it stops" and they just didn't know when to stop. Or they used a torque wrench.
From the threading on the mixture screw tip I'm guessing the jet seat is made of harder stuff than the brass mixture screw. Short of disasembling the carb I guess I'll find out when the new screws arrive and see how well they can be adjusted.
And that's what I generally do. But apparently someone who worked on my 283 in the past was in the habit of turning in the idle mixture screws until they were just seated, and then turn in another 2-3 turns just to make sure.
Cause when I tried to adjust the screws, I found that one side didn't lean stumble at all when turned in, even all the way, and the other side stumbled at about 2 turns out. I wound up adjusting one side to 1-1/2 turns out and the other to about 2-1/4 turns out. And it kind of stunk on idle. Ran reasonably well, but hey, it's a small block.
So today I finally got around to pulling the idle mixture screws and discovered the screw abuse. The ends don't taper evenly to a a point. Instead, they taper and then have a sudden drop-off, with the rest of the screw looking more like the tip of a fine tip mechanical pencil than a cone. And the screw from the side that had no lean stumble actually had some threading on that fine tip, probably from forcing it in too far.
So I measured what was left of the suckers and then got online and ordered a new pair from Mike's Carbs. Then I got out the green scotchbrite and polished the tips as well as I could, trying to at least remove some of the threading on the badder of the two.
When reinstalled, I found that I could adjust both to 1-1/2 turns out (total) for a relatively good idle that stinks less than before. I'll be looking for that care pack from Mike though, hoping that the jet seat isn't also too trashed to allow for a proper idle adjustment.
And so it goes. It never seems to end, the discoveries of past mechanical abuse to a used vintage vehicle like this. But then, I 've been guilty of a few questionable mechanical practices, because I didn't now any better. I surmise someone told someone to turn in the jet "until it stops" and they just didn't know when to stop. Or they used a torque wrench.
From the threading on the mixture screw tip I'm guessing the jet seat is made of harder stuff than the brass mixture screw. Short of disasembling the carb I guess I'll find out when the new screws arrive and see how well they can be adjusted.
