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My 327/340 has a 3261S Carb which seems to have the correct components except for the two primary metering rods. They should be Part # 16-389 (.060/.069), but they are #16-98 repeat16-98 (precise size unknown but the two steps are a little under/over 1/16 (.062)). The low end acceleration (up to 1100rpm) and the hot idle are both a bit rough. What are the chances that the rod is the culprit? Any suggested suppliers? Thanks in advance Les
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Re: C2 Carb(3261S)
Check out the Chicago Corvette catalog for what might be the LARGEST one-stop selection of Carter carb components for off-the-shelf delivery at quite reasonable prices.... -
Re: C2 Carb(3461S) (correction)
I believe you are dealing with a 3461S, and you car is a '63.
The 16-389 rod is .060"/.069"
The 16-89 rod is .068"/.0555", which will run slightly ricer at cruise and considerably richer at WOT.
Not sure if this would cause your problem, but one problem is likely your vacuum advance. 1963 was the first year that vacuum advance was used on SHP/FI engines, and they did not get it right. The OE vacuum can provides 16*@16", but the engines with Duntov cams only pull about 12" at idle. Thus the vacuum can is not pulled to the limit at idle, and variation in idle vacuum will cause variation in vacuum advance, which will cause idle instability.
The problem was solved in '64 with a new vacuum can for SHP/FI engines that was pulled to the stop at idle (16*8")
This vacuum can is available from NAPA part number VC1810, and you should install this vacuum can on your distributor. Cost is about ten bucks.
DukeComment
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Re: C2 Carb(3461S)
Duke Thanks for the technical info. Doesn't look like the rod is the problem, since I usually don't engage the secondary when taking off (unless there are teenagers around). The vacuum advance WAS in fact a major part of the problem, but Ive changed it out per your suggestion a little while ago. Im in the middle of a rebuild, so I think I'll complete it w/o changing the rods and see what happens. LesComment
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Re: C2 Carb(3461S)
If you strive to avoid clutch slippage on a typical street start and accept a slight bog, the manifold vacuum can drop to a low enough level to momentarily allow the power pistons to rise exposing more jet area, so you might get a slightly overrich mixture momentarily. This might affect how the engine behaves from a start, but should not affect idle.
There are several available springs that control when the power piston rises based on manifold vacuum. I believe the standard springs allow the piston to rise beginning at about 8", and it's possible someone changed them.
If you remove the power piston covers at idle and observe the them, they should be all the way down. Years ago I noticed that mine would vibrate at idle causing a distinctive rattle. Installing the 8" vacuum can solved this problem as the higher and more steady total idle advance increased the idle vacuum to a sufficient level to keep the power pistons pulled all the way down and steady at ea my choosen idle speed of about 900.
My 3461S is also rejetted. The flow area on the primary size is the annular formed by the rod and jet. I selected a new rod and jet to maintain the same flow area at cruise, but increased WOT flow area about 5 percent. Also did the same on the secondary side - selected a jet with about 5 percent more flow area.
OE jetting is a compromise for the many different markets - altitudes, temperatures and resulting air density. Being as how I lived in Seattle at the time I felt a slightly richer WOT mixture would be better - can't say if I could feel any difference SOTP, but a richer WOT mixture provides more safety margin for detonation.
Increasing fuel flow area by five percent richens the mixture by about half and air-fuel ratio.
Duke
DukeComment
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Re: C2 Carb(3261S) - Related Question
How did you find the size of your metering rods from the part numbers?
I've got some loose AFB metering rods. With a loupe, I can read the part numbers stamped into them. How do I find out, from the part number, what their sizes are?Comment
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Re: C2 Carb(3261S) - Related Question
the best way is use a micrometerComment
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Re: C2 Carb(3261S) - Related Question
I have a sheet with all the part numbers and sizes for rods and jets that I obtained back in the seventies.
If you e-mail me the part numbers, I'll give you the dimensions. Segregate jets and rods.
One of these days I'll have to find a scanner and scan the page so I can e-mail it to anyone interested.
DukeComment
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lift the matress duke
a decent one can be bought for less than $50 the one i have cost less than $ 30 with the rebates.Comment
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Find me some space
I haven't found a place to put it - office is full, but I have a friend who can scan it.
DukeComment
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put it under the desk as
it makes a good foot rest when you are not using it.Comment
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