SU Mod: Sealing worn throttle bushings

[Oiluj]

That's exactly what I did, except I didn't have a lathe.__Chucked the shaft in a drill press and made a holder for a section of hack-saw blade to make the groove, followed by a fine file.__Wasn't nearly as pretty as CO's, but it worked fine...

[ConchZ]

I would caution everyone to use Teflon(PTFE) rings, and not plain rubber. Just imagine a ring deteriorating in gas fumes and heat to the point that it breaks and gets sucked into the intake. Where to get some PTFE rings of the appropriate size?

[hls30.com]

I would caution everyone to use Teflon(PTFE) rings, and not plain rubber. Just imagine a ring deteriorating in gas fumes and heat to the point that it breaks and gets sucked into the intake. Where to get some PTFE rings of the appropriate size?

PTFE turns really well-if you can machine the rod, it shouldn't be a stretch to turn down an easily found but oversized rings-or a rod that could be bored and wafered.

[tlorber]

Isn't this what Z Therapy is for?

[Captain Obvious]

I used Viton. I'm not worried about fuel or the heat.

[ConchZ]

Ok, I swapped over my other set of SUs. Car fired right up, idled too high...oops, forgot the return springs. Put them on, and it idles just fine. Sprayed a little carb cleaner around the throttle shafts, and got the same effect as with the other carbs. A slowing of the idle speed. Maybe this is normal? I can't imagine throttle shaft bushings being air tight. There must be some leakage.

Why am I worried about this in the first place, you may ask? The car runs fine. It all started with diagnosing hot running at highway speeds. After checking everything I could think of, I thought maybe its running lean, so I started looking for air leaks. I may have solved the highway heat problem, it was bad connections in the inline fuse holder on the electric fans. I just need a hot day to test if it's cured. Should I just stop messing with these carbs?

BTW, I also solved the vapor lock problem. First, I bent the fuel rail back as far away from the head as I could. This helped a lot, but didn't cure it. Next, my other set of carbs came with insulators that were over twice as thick as the ones with the other carbs. These cured the problem.

Matt

[Captain Obvious]

Sprayed a little carb cleaner around the throttle shafts, and got the same effect as with the other carbs. A slowing of the idle speed. Maybe this is normal? I can't imagine throttle shaft bushings being air tight. There must be some leakage.

Why am I worried about this in the first place, you may ask? The car runs fine. It all started with diagnosing hot running at highway speeds.

I thought the expectation when you sprayed carb cleaner near a vacuum leak was that the idle would go up, not down??

And I would guess that vacuum leaks around the throttle shafts wouldn't have much of an impact at highway throttle positions. I would expect that even if you were getting some air past the throttle shafts, it might have a big impact on IDLE, but once you cracked the throttle plate enough to maintain highway speeds, the impact of that leak would diminish.

I mean, you never WANT that leak, but it's impact goes down as the throttle position goes up. A little late now (as you already figured out), but I don't think leaking throttle shafts are making you run hot on the highway.

[ConchZ]

I thought the expectation when you sprayed carb cleaner near a vacuum leak was that the idle would go up, not down??

.

Starter fluid or ether would make the idle go up, but carb cleaner isn't combustible. As for throttle shaft leakage at highway speeds, you are probably right. The unmetered air getting past the throttle shaft bushings would go down as a percentage of total air flowing through the carb, as compared to its percentage at idle. Since I don't have idle problems, is it safe to say that my slight leaks around the throttle shafts is pretty normal?

[ConchZ]

I thought the expectation when you sprayed carb cleaner near a vacuum leak was that the idle would go up, not down??

.

Starter fluid or ether would make the idle go up, but carb cleaner isn't combustible. As for throttle shaft leakage at highway speeds, you are probably right. The unmetered air getting past the throttle shaft bushings would go down as a percentage of total air flowing through the carb, as compared to its percentage at idle. Since I don't have idle problems, is it safe to say that my slight leaks around the throttle shafts is pretty normal?

[Captain Obvious]

Starter fluid or ether would make the idle go up, but carb cleaner isn't combustible.

Since I don't have idle problems, is it safe to say that my slight leaks around the throttle shafts is pretty normal?

I surely won't claim to have seen them all, but every carb cleaner I've ever run across is highly flammable. I'm not talking about the engine degreasers... I'm talking carb cleaner. Mostly acetone, methanol, tolulene, etc.

And for the shaft leakage... As designed without a pliable seal there, some leakage will naturally occurr. But as long as it's not "excessive" you don't have to do anything about it. There's others on the forum with much more carb experience than myself, but my read on it would be if you can tune the carbs at idle without having to go some unusual amount of turns down on your nozzles, your plugs look good, and you're getting good power while driving, then I wouldn't worry much about the throttle shafts sealing.

[ConchZ]

I surely won't claim to have seen them all, but every carb cleaner I've ever run across is highly flammable. I'm not talking about the engine degreasers... I'm talking carb cleaner. Mostly acetone, methanol, tolulene, etc.

You are correct, carb cleaner is flamable. My bad. However, spraying it into the carb of a running car in my experience usually results in a stumble. It isn't flamability, but rather liquidity that is the problem.