I need some advice...........please. My '77 L-48 with Q-jet and automatic will not idle below 1200 RPM and stay running. The idle surges about 300 - 400 RPM. It also dies when put into gear. I have replaced cap, rotor, plugs, wires, vac advance unit, vac lines, and the carb has just been rebuilt. Set timing to 8 deg with vac advance disconnected and plugged. Sprayed starter fluid all around intake to search for vac leaks but found none. It was doing the same thing before carb was rebuilt. Idle mixture screws have been set anywhere form 1/2 turn open to just about falling out. I have read everything I can get my hands on from Lars and the carb is set up per his suggestions. When running, you can look down the main venturi and see gas dripping. Have checked bowl plugs and found no leaks and gaskets align with all holes in float body. What am I missing? Someone.............anyone, please give suggestions on what to try next!

 

has it run right at all since carb was rebuilt??? only time mine did this, carb was "real" dirty. if it did this on first start after carb rebuild, i'd suspect either an improper rebuild or....... did you check to be sure fuel filter is not in backwards. wouldn't be the first time someone, even a "pro" did this. a "pro" at a local ford dealership just did this on my wifes diesel truck. ever seen what diesel "sprayed" all over an engine bay does when the fuel filter is "blown" out? ain't pretty.

check proper fuel filter installation.

 

Push it off a hill and collect insurance. Hmmm, maybe you could get in trouble for that?

 

Checked the filter, its in correctly. It was had the same symptoms before the carb rebuild, that's what made me think the carb needed to be rebuilt. Is it possible that the meetering rods or jets could be worn and need replacement? Or, could the engine just be shot and cause these symptoms?

 

get rid of the q-junk and get a Holley mech. secondaries carb

 

can you (have you) checked to see if you're getting enough fuel pressure (possible fuel pump problem)????

 

i once had a chev v8 do just that and it was the coil..
tho gas "dripping" dont seem rite,should be being "sprayed" in there.
excess gas may do it,check return line from fuel pump??
maybe vise grips on fuel line to cut down gas flow to test??
check plugs to see if running rich ??
dangerouse to do but unhooking fuel line and dumping it into a container and using a spray bottle to squirt gas into carb to start and keep running could help tell you if it was fuel prob or ignition.
people get hurt all the time messing with fuel,bad idea to look into a carb at any time motor is running,use a mirror.
in the past have hooked up a gravity feed fuel source ,a vented container above the level of the carb.to find fuel pump probs.the float in the carb controls the fuel level in it.
hope somebody comes up with better sugestions..

 

dude, youve really gotta know what your doing to get those quad carbs running. thats why everyone hates them. even if you rebuild. and shouldnt those meter rods been in the rebuild kit? also the body of the carb itself could be worn, even new rods wouldnt fix it. also check for more vac leaks. check the manifold seals, front and back. these are notorious for this problem. the quad carbs are good if your a carb guru who loves the old stuff. redo the manfold, and buy a demon, or the edelbrock carb. the edelbrock is very close to you quad carb, and will run like a top.

 

The Q-jets were good carbs for their time.. but are WAY TOO COMPLICATED.. Holley's on the other hand are built very simle and are much easier to rebuild and/or tune... There's no doubt that a well tuned Q-jet can perform just fine... but once it won't perform fine - it'll take an expert to make it perform good again.. Very few people are able to rebuild/fine tune Q-jets..

Here's a possible direct replacement for Q-jet Vetters:

http://store.summitracing.com/defaul...tt=spread+bore

Keep the Q-jet in a box for originality and use a Holley to drive around..

 

it could be the accellerator pump in the top of the carb, you can always get a bad new one.
did you do a compression test on the engine? this would eliminate a few possibilities.

 

Engine idle is not affected by metering rods. Vacuum and fuel is it for idle. Try spraying some starting fluid (ether) around your manifold intake ports. (old trick from a drag mechanic) Your idle should jump up if you are getting leaks at the intake. Try disconecting all vacuum lines to the subsystems and just hook up 1 line from the carb to your distributor and one to your pcv valve and make sure the valve is seated properly. Put a vacuum gauge on the intake and adjust your mixture screws for the highest amount of vacuum. Do this 1/4 turn at a time and 1 side at a time. As for your fuel line... disconnect your line from the carb, take a large coffee can and have someone turn of your engine. Be careful. High volume pumps can push alot of fuel quickly. Check your voltage to your HEI. I have had some small blocks with too small of gauge wire to the coil. It registers 12 volts but resistance is too much and it causes a draw on the ignition system causing erratic idling. Other than that all the post had good ideas. Your thoughts on a shelled motor.....If it was running real rough before the carb rebuild it can be alot of things. A bad valve, slipped timing chain, cracked compression ring, a crack in your cylinder sleeve or head, on and on.
I had a guy with a hole in a piston once that pulled his hair out trying to find the "carb" problem. Erratic idling is the sh**ts sometimes. Don't overlook the simple things. Good luck. I've built alot of these motors in the past. It's hard to kill a bow tie. They usually just fall asleep.

 

Thanks to all who have given suggestions. Now I have a few things I didn't think of to try next. I will keep everyone posted on what the outcome is. Got to go back to work tomorrow, will probably be a few days before I can get all suggestions tried. If I don't find something fairly quickly to solve the problem........the Holley is looking better and better. That stock cast iron intake is kinda ugly as well, may be time to start the mods!

 

I'm thinking stuck float, or float set too high. Double check that first.

 

hey fast idle, did you steal my vette color?

 

Set the initial advance up to 16 and reconect the vacuum advance. The high idle speed is most likely causing the nozzle drip (or the carburator is flooding due to a float problem). The main metering system is trying to come on line. Once you have the advance set try to back the idle down.

You need to look at fuel pump pressure, the condition of the needle and seat (dirt in it) and the float level.

You need to check system by system. Sooner or later you'll come up with something that doesn't fit right.

BigBlockk

Later.....

 

Do you mean to have the vacuume advance conected when timing is set to 16? Forgive my ignorance, but the timing mark indicator on my engine only goes to 12 before and 8 or 10 after TDC. Please explain.

Will have to purchase a fuel pressue gage to check the pump with, probably Saturday. The float is not binding, moves freely. It is set to .405" from top of bowl casting (half way between what Lars suggested). At first it was set to 15/32 per Chilton's specs and then I even tried setting it 1/4" lower but no change. Air horn gasket is wet on the edges. Do you think that a bad fuel pump could create too much fuel pressure and over ride the needle valve. Also about float, last night I read that the needle clip should be over the back edge of the float arm. I have it over the front (open part pointing to front of carb), per Chilton's and rebuild kit instructions. Which is correct, over the front edge or the rear?

 

With the vacuum advance disconnected and the engine running, advance the timing slowly. The idle speed should rise. Don't use a timing light for this, go by the sound of the engine. Now, back off on the idle speed screw on the carburator. Keep increasing the advance and lowering the idle speed until it will idle smoothly at 700 or 800 rpm. Now look into the carburator to see if you still have nozzle drip.

I'm thinking the ring on the ballencer has slipped and is giving you a false timing reading. You may have had the idle speed cranked up on the carburator because the timing was way retarded.

This will give you enough to think about for now (translation: I worked all night and need to go to bed). Try this and report your findings.

Good luck.

BigBlockk

Later.....

 

Did you use any compound such as silicone on the fuel line inlet threads?

 

big block, if he sets idle at 800 with vacuum disconnected won't that make his idle with vacuum awfully high????? mine drops about 400 rpm when i pull the vacuum line.

 

Whatever idle number you choose the object is to get the idle down to something under where the main system starts to deliver fuel. IF the ignition advance smoothes the idle and allowes the throttle to be closed this is not a carburator problem it is an ignition problem.

If the ignition is way retarded the idle speed on the carburator will have to be opened to keep the engine running. The primaries in the Q-jet are very sensitive. This engine chugging along like it is could be swallowing enough air to start the mains. If you advance the ignition AND the idle speed goes up to a point to where you need to adjust it down on the carburator, I think you have found the problem. Or at least A problem.

BigBlockk

Later.....