The idle setting on my 340 hp varies +/- 200 rpm from where I had set it last. This occurs when fully warmed up,sometimes it will return to the set rpm with a tap of the throttle. The AFB was rebuilt by Bob Kunz and I have checked for vacuum leaks at the places I'm aware of, put some plumbers tape on some fittings ,etc. Is this typical of these older carbs or are there other areas I could check ? Thanks.
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Re: '63 SHP/idle
My 67 did that also till I replace the throttle spring with a stronger one -
Re: '63 SHP/idle
Jim Suggest you warm the engine, and check the choke and fast idle linkage.If that's ok, physically move the throttle linkage to see if the idle speed drops back. If so, perhaps you can determine if anything is binding, or whether a slightly stronger spring is needed (per Roy). LesComment
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Re: '63 SHP/idle
What's the data stamped on the vacuum can bracket?
DukeComment
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Re: '63 SHP/idle
B22..distributor just rebuilt by T. I. Specialty.Comment
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Vacuum advance - everyone please read this post
B22 is not a good match for any Chevrolet mechanical lifter cam including the Duntov. It needs 14-16" to pull to the limit, but Duntov and LT-1 cams only pull about 12" at about 900, 30-30 cam only 10". If the vacuum can is not pulled to the limit at idle it can dither, which varies idle timing, which varies idle speed.
The B22 DOES approximately match the OE 1115201, BUT CHEVROLET DIDN'T GET IT RIGHT this first year that they included vacuum advance on SHP engines. It violates the basic rule that the vacuum can should provide full advance at NO LESS THAN 2" less than typical idle vacuum so the vacuum can is "locked" at full advance at idle ('63 FI for some unknown reason has ported vacuum advance, so they won't idle worth a damn no matter what can is installed.)
I figured this out over 30 years ago, installed the 1116236 8" can in my '63 L-76, and never again had idle problems, which were chronic up to that time.
Chevrolet fixed the problem by installing the 1116236 8" can on all SHP/FI beginning in '64 (and '64 FI got full time advance) and all later L-79s, and I recommend that this can be retrofited to ALL '63 L-76.
Go to NAPA and buy a VC1810 ("B28" ID) for about ten bucks, which has the same specs as the 1116236, and install it in place of the B22. Set the initial timing at 10-14, and you should read 25-32 total idle timing at 900 with the vacuum can connected. Then go through the idle speed/mixture adjustment, and I recommend about 900 idle idle speed for mechanical lifter cams on carbureted engines. Duntov and LT-1 cams might be okay with 850 but the 30-30 needs at least 900. (add 100-200 for FI with a Duntov or LT-1 cam and 200-300 for the 30-30 cam).
The B22 (VC1802) can is my recommendation for all SB with the base engine hydraulic cam. I formerly recommended the B1 (VC680) can but it takes up to 18" to pull to the limit so I no longer recommend it. All BB and SB/Powerglide should run a 12" B20 can (VC1765). This is also optional for L-79 since most will pull 14" at 750, which makes the 2" rule.
These three (NAPA/Echlin part numbers) vacuum cans will service all Corvette engines including ported vacuum advance engines that are converted to full time advance. Just match the vacuum can to the camshaft/idle vacuum characteristics. All provide 16 +/- 1 degrees crank advance and the nominal vacuum to achieve full advance is about +/- 1" Hg.
SBs with base engine cam/manual trans - VC1802 (B22) 15" (engine idle vacuum over 17")
All SHP SBs - VC1820 (B20) 8" (engine idle vacuum less than 14")
All BBs, Powerglide SBs, opt. for L-79 and L-46 converted to full time advance - VC1765 (B28) 12" (engine idle vacuum 14-17")
These same cans with the same ID number are available in other brands including Delco, and you can cross reference the NAPA numbers at a parts store or on the other manufacturers' web sites. They are all now made by Standard Motor Products being as how Standard bought Dana Controls last year, which included the NAPA/Echlin, Borg Warner/BWD, and Niehoff brands. Delco buys their vacuum cans from Standard, but I think they have a lot of errors in their parts cross reference and specs.
Unfortunately you can't buy these vacuum cans by the ID number. You have to obtain the brand part number and then verify that the ID number is correct. The ID number is key to the vacuum cans advance/vacuum characteristics.
Install a B28 and see what happens. If you still have varying idle speed then the throttle shafts may be worn.
DukeComment
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Re: FI idle speeds
Duke, you're entitled to have your own opinions about FI idle speeds, but I sure disagree with them.
I routinely set the idle speeds at 800 rpm in FI 327's with Duntov cams. I use 850 rpm for injected 327's with 30-30 cams. Why in the world would anyone want or need 1,000 to 1,100 rpm? Surely you're kidding.Comment
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Re: FI idle speeds
It's always been my observation that for a given cam FI idle quality is poorer than the carbureted version of the engine.
Also, didn't you say that FI idle quality is poor with the tight lash I recommend for the mechanical lifter cams, especially the 30-30?
Increasing idle speed will increase manifold vacuum and usually improve idle quality. In the end it comes down to the individual engine and user. Idle should be set at the lowest speed commensurate with acceptable idle quality, but what constitutes "acceptable idle quality" varies among users, and I find that Chevrolet's recommended idle speeds are unacceptably low and will not yield acceptable quality or stability.
I don't care for severe lope, so I tend to set idle speed a bit high with SHP cams. Other opinions may vary from mine.
DukeComment
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Re: FI idle speeds
I think you've seen too many units that have been to Indiana.Comment
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CORRECTION!!!
The NAPA/Echlin VC1820 8" can is stamped "B28" not B20
The NAPA/Echlin VC1765 12" can is stamped "B20", not B28.
The VC1802 15" can is listed correctly in the post as stamped "B22".
(Wish we could edit our posts.)
DukeComment
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