Hi Folks,

I need Your help once more:

I can't get a satisfying idle on my '69 L68 (auto)
I've replaced the metering-block with an correct "5257" and installed a new power-valve and acceleration-seal (menbrane) on the center-carb (#4056). Anyway I don't know, what is the correct type of power-valve I need for my engine (can anyone tell me?). I took the one what was in e Holley-Rebulit-Kit for my carb (it has 3 round holes).

While running the engine in my garage, I get an idle of ~ 900 rpm and ~700 in gear (messured with the car gauge) - what I regard as "o.k.".
When driving a few miles, the idle reduces to ~800/~600, what gives a "shaky" feeling and is definately too low. I'm always in fear, that engine will stall.

I've adjusted the idle-mixture-screws as good as I could (in, until engine starts to stall, than out again, until highest rev, than another 1/2 turn out.

Now I'm at the end of my knowledge and hope, that You have an idea, where I could look for a fault.

Regards from Germany

Gerrit

 

 

the correct power valve is 6.5

 

Make sure that on the end carbs that the throttle blade are SHUT. This is very important........the end carbs should act like they are not even there. If they are cracked open even the slightest bit....it can cause idle issues.
Also.....take the time to research putting a correct timing curve in the distributor. My 427/400 that I had responded HUGE to having the distributor curved and proper timing set. This will affect idle as well. The vacuum advance should be hooked to direct intake vacuum on these. Make sure ALL of your vacuum hoses are in good shape as well.
Hope you find the issue.....I loved my 427/400......wish I still had it.

Good luck,

Jebby

 

The secondarys are linked in the correct way. They are full shut down on idling (I asured that first). All vacuum hoses are new and in very good condition.
So what about timing? How should that be set? I guess, I have a mechanic do that for me, because I don't have a "timing-gun" and I dont know, how to to the correct justage.

Meanwhile I've changed the whole carb-setup for the (completely restored by Jerry Luck) spare setup, that I had in a show-case on my desk for years . I thougt, it would be even better to have those fine carbs in my Vette, than on my desk .... It seems, that idle is better now. Anyway I want to look for the timing, to make that perfect as well.

By the way: When I installed the new carb-setup, the front carb spills lot of fuel out of the vent in the fuel bowl, so I've canged the bowl for the old one, what was fine. I think, probably the needle for the fuel level was worn? The skimmer worked perfekt anyway. Or could that have another reason?

Thanks and regards from over the pond

Gerrit

 

 

It looked, as if there was no limitations in the fuel bowl at all, because the fuel came out of the upper vent like a spring. As far, as I remember, fuel-level is rised by turning the nut counter-clockwise and lowered by turning it clockwise. Is that correct?

Gerrit

P.S. The link for the time-setting would be great!

 

you are correct about the direction of turning the nut to raise and lower the float. Send an email to Lars at V8fastcars@msn.com for the timing paper

 

 

I always use a vacuum gauge when checking my carburator idle setting. If your Vette has K66 transistorized ignition it will take care of the dwell. If points set them to 28-32 degrees(30degrees works), next disconnect the manifold vacuum line that goes to the brake booster and air tank for the lights and wiper door and block the vacuum to the engine. remove the vacuum line to the distributer and plug the vacuum gauge into it making sure that the hose is coming out of the tube on the carburator that has full manifold vacuum( usually on the throttle plate below the butterflies. If you don't have a timing light that has advanced settings on it, you have reached a roadblock. Normal setting with distributer was probably 4 degrees. you could probably go to 8-10 without any problem. 12-14 begins pushing the advance curve. The vacuum gauge will show manifold vacuum 18-22 hg. That is probably a good place to be. Some cams may be lower ,check specs. Any higher would show up as early ignition timing. while doing these adjustments you will have to lower the idle speed screw to keep within normal range. (800 for manual/air off). After setting the timing tighten up the distributer hold down bolt and adjust the carburator idle setting again using the vacuum gauge. Once everything is set take it out for a ride and see if it pings. If it does retard it a notch or get higher octane gas. Make sure the front and rear carbs come in at the correct rpm. If they don't check for leaks and /or change the springs in the vacuum canisters to correct that situation. If everything is satisfactory re attach the brake booster first to see if anything changes(Vacuum gauge and tach). If all is ok reattach the headlight wiper door vacuum and check engine manifold vacuum and idle speed. If anything changes when reattaching these lines check that system. Any vacuum leak will affect the engine and performance. It's one of the reasons that tri power systems are temperamental and need constant attention.