Dan, the metering rods could even be 3 step . If you check the vacuum at the problem point ,and then above and below you would have the range of vacuum. You could buy springs, for that vacuum range and replace them, or just give'm the stretch. I would lean towards the 3/8", sometimes 1/2". Try that first, by increasing the length , the rods pop up quicker at the same vacuum, bringing in more fuel sooner.Then polish the last 5/8-3/4"of the rods down .002" and blend the steps to smooth transitions. The position of the rod steps vary with vacuum, and engine load. The tip of the rod is always in the jet, reduce the diameter of the rod, (or up-size the jet) you increase fuel flow .Give it a try, we've done it many times. Dave.
-------------- Original message --------------
From: "Daniel Richardson" <TheRichardsonFamily@xxxxxxxxxxx>
Hi Dave (and gang):
That's the kind of old timer advice I knew was out there!
It does seem lean, and I do have the accel. pump in the max stroke hole. What am I looking for with the vacuum test with speeds at & before stumbling? What will it tell me?
I figured metering rods would be the next place to attend to - I just wasn't sure how delicate they are, or if, carefully, I can play around with them. Assuming that it's a 2 step metering rod, at about what throttle position does each step come into play? In other words, should I look to reduce diameter of a certain step? Or just reduce diameter across the board?
I will try the slight spring stretching idea first. Your guess is that because I have an original carb, it's just running lean on today's gas? I've covered the other places to look already?
Thanks again for the info,
Dan Richardson
300L Family Heirloom
----- Original Message -----
Sent: Wednesday, October 17, 2007 5:13 PM
Subject: Re: IML: '67 Carter carb flat spot
Dan, you can probably solve your flat spot, or fumble by some metering rod, and mostly spring modifications. A vacuum test at the speed prior to, and when the stumble occurs, may be helpful. Two easy cures: stretch the metering rod power en-richment springs, a 1/4-3/8" this will help to en-rich the mixture sooner (higher vacuum). The other thing is chuck-up the metering rod in your drill, and polish the steps to a more gradual transition. You can also reduce the diameter of the rod, thus en-richening without a jet change. Make sure the accelerator pump linkage is in the max stroke hole too. You can't hurt much, and if the carb is original, it's lean by todays gas quality. Ya'll have a nice day, Dave.
-------------- Original message --------------
From: therichardsonfamily@xxxxxxxxxxx
> Here's a question for the carb tinkerers (hi Dave):
>
> '67 Imperial 440, w/ Carter AFB - the model that went on HP engines w/ bigger
> secondaries. Idles smoothly, idle screws adjusted. At WOT she goes like a
> r__ed ape - rubber in 2nd gear with a 3:55 suregrip.
>
> 18 inches of vacuum at idle - gauge moves just like it should when I rev the
> engine - as per the IML website (which is really neat, BTW - everyone should
> look at that page!).
>
> Timed at 12 degr. BTC - new chain & gears - Mallory dual point distributor -
> mechanical advance appears to work - if I suck on the vacuum advance, it also
> moves timing forward. Have not found a shop with a distributor machine yet.
> Plugs are new - wires
& cap are not (I'll get them on soon) but seem to be OK.
> Again, she's a rocket with my foot in it.
>
> I have a flat spot from about 1/3 to 2/3 throttle. I see no black smoke during
> this flat spot. Carb has been rebuilt (by an amatuer - me), and seems ok.
> Choke is open when warm - linkage adjusted correctly - accelerator pump seems to
> work right - bowl vent closes just beyond idle - VERY low exhaust restriction
> (i.e. 2 glass packs + small resonaters out the sides)
>
> So... the question is - how do I fix the flat spot? Smaller metering rods
> becuse of the open exhaust? Or is there something else I may be missing? Throw
> some old school thoughts at me to try and tweak it.
>
> Thanks, as always, for the help,
>
> Dan Richardson
> 300L Family Heirloom
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