-
I am having a problem getting this thing to idle. The bottom line is when I check for vacuum at idle there is none. If I am correct without vacuum at idle the fuel will not be pulled thru the idle circuits. My setup is as follows- 2 holley 660cfm carbs atop a ram manifold. The carbs have been modified where I have replaced the secondary metering block with a primary block. This was done about 3 yrs ago. When it was done it worked ok sometimes and was very sensitive to any adjustments. I now have a new engine and when I ran it on the trailer I was able to get the idle to work but at around 1000 rpms. I took it to the lake last week for the first time and it wouldn't idle at all. As soon as I let off the throttle it died. I hooked a vacuum guage to it and had no vacuum at low rpm only when I started to open the butterflys did the vacuum guage start to register. Since this was the first time out with the new engine when I got home I checked the plugs and noticed them to be very white(lean). The main jets that I was running were 68 all around. I put 72 in and will try it this weekend. I know by changing the main jets won't affect the idle. I took the carbs off and disassembled them and blew out all the passages again making sure there were no obstructions in the idle passages. One question, on the metering block there is a small jet called the idle restrictor is this the same as the idle jet?
I went back to square one and set both carbs exactly the same, idle mixture screws turned out 1 1/2 turns, the idle adj screw set so the butterfly is not exposing the idle slot in the carb bore. So my main concern is why I don't have vacuum at idle. I have checked for vacuum leaks and don't see any. Any suggestions would be appreciated.
Barry
Barry
-
dumb question, are you sure you had a manifold vacumn source and not a ported vacumnsource? Ported will show no vacumn at idle, comes up as you tip throttle in, and drops again under increasing or full throttle. Will show highest vacumn at state stgeady throttle and load conditions.
This was used to provide vacumn to the distrubutor (rather than manifold vacumn) so more intital timing could be added to improve fuel milage and drive-away performance on some vehicles.
Best bet is a port from below the throttle blades (look at the carb from the bottom and find one that you can verify), or go straight to a manifold fitting. I always make sure I have at least one manifold fitting just for this reason.
If you have no manifold vacumn at idle you either have a BIG leak, or WAY too much cam. Lowest i've ever seen idle manifold vacumn that would run (sort of) was 4-6" @ 700 on my old circle track motor. Is it possible one of the secondary throttles is hanging open??
Hope this helps, and good luck. :idea: :clover:
-
.Best bet is a port from below the throttle blades (look at the carb from the bottom and find one that you can verify), or go straight to a manifold fitting. I always make sure I have at least one manifold fitting just for this reason.
Now you got me thinking I know the fitting I am using to check with is on the base plate but I never bothered to check if it was above or below the butterflys. Is this manifold fitting you mention something you installed or is it something I could install on one of the spacers beneath the carb?
Barry
-
Are the choke towers still on? If they have been machined off this could be your problem, especially if you don't have adjustable air bleed screws.
-
Are the choke towers still on? If they have been machined off this could be your problem, especially if you don't have adjustable air bleed screws.
yes the choke towers have been removed. Are you talking about the air/fuel mixture screws on the sides of the metering block if so yes I have those on the primary side only
