Carb Idle
 

After completing the cam breakin procedures of my two rebuilt engines, I cannot get the quadrajet to Idle while in gear. The carbs were rebuilt and set up to my engine specs. They were done by SMI (Shawn Murphy Induction).
I can get a decent 800 RPM in neutral but when I put it in gear idle starts dropping off and then dies in about a minute. If I set the idle while it is in gear(under load in the water) to an acceptable level, when I put it in neutral RPMs go up to about 1100 RPM. Both carbs are doing the same thing. The idle mix screws at the front are backed out 1 1/2 to 2 turns. Just started backing them out until engine started running rough and turned them back in 1/4 or so.
These are 1989 quads with heat stove type choke. Disconnected while I tried to adjust carbs. Engines are 89 454 with rect. heads, stock merc. alum. high rise intake. Engines have a total of 2 hrs run time. Could use some help or insight.
thanx
'30 BAJA "FARFROMPUKEN"

Re: Carb Idle
 

Try cracking the secondaries open, Just a whisker.

Re: Carb Idle
 

Don't know much about quadrajets, so how do I open the secondaries alittle?

Re: Carb Idle
 

First, In order to see if this helps correct the problem....... try putting a little piece of shim stock under the throttle stop for the secondaries(maybe .010 or .020 ). I can't recall if you can adjust the secondary throttle stop without removing the carb. I know the Holley has to be removed in order the turn the adjustment screw because it is accessed from the bottom side of the base plate. If you just crack the secondary throttle plate you should see the idle increase slightly. then try backing down the primary throttle stop to achieve correct RPM. This should now stabilize the idle. Hey-- it has worked for me.

Re: Carb Idle
 

Last year I had exactly the same problem. I rebuild my 454 magnum 1989 with a little lager cam (crane cam from the 420HP) and upgrade exhaust etc.
My idle was the same as yours. I have experience a lot with Q-jets and they are very fine carb up to 450 hp.
I had to take off the carb and drill a little hole (2 mm) in each primary throttle blade. Never drill lager than 2.5 mm or you cannot adjust the idle down. (If you drill too large you can seal the hole with a little epoxy but try to avoid it.) Remember to drill equal and on the front-side of the blade. Drilling has the same effect as open the secondaries but are a lot essayer to adjust perfectly.
I don't know what cam you are using but if you are larger than stock your initial timing may need a Little more than 8-10 to raise the vacuum at idle. I found that my engine need 14 degrees in initial timing. If you are using your thunderbolt IV ignition be careful not to use the 24 degree ignition module if you advance your timing that makes 38 total.I WOULD STAY UNDER 34 DEGREE TOTAL. That means you have to find another ignition module.
(I use the HP 20 degree module) They are no longer available from mercury but with a little research you may find a good used one on ebay.
After that I idle 800 rpm with a little or no rpm drop when putting in gear.

Re: Carb Idle
 

Thanks for the info. Purchased an edelbrock to see if all my problem was with the quad. Ran fine with new carb. Will try the mods you are talking about.
thanks