Carb issue with Holley 4160 on 1957 intake.

I have a '56 with 312 automatic. Yrs ago someone switched car to 1957 intake and dizzy . Car has always run strong but uses a lot of fuel. Like teenage boys at a keg party!. Exhaust tips are full of black, very dry soot. In heavy slow traffic and long lights car stumbles and revs drop off due to what I suspect is excess fuel in exhaust system. Last week when this happened car back fired and quit at a stop. Huge cloud of blk soot came out of rear of right exh. manifold. What a mess.!! Engine compartment had been detailed well, till that. So...Checked float levels, rear a bit high and I reset it. Front ok. Jets were .059". I changed to smallest they make @ .049". Car runs ok...but hesitates badly till 1650 RPM +-. Installed new accelerator pump. Tried various linkage settings with no real effect. Holley book says this carb should have .053" jets out of the box... Power jet is ok. Fuel seems to dribble into carb from accelerator pump at low rpm but squirts well when throttle opens up 1/4 or more. Should I just go back to the .059" jets and live with running rich ? Timing is right on and good vacume as well. For last 2 yrs car has started immediately and has lots of power.....just a gas hog. And raw gas exhaust smell... Ideas anyone ?
 

biddle

Forum Moderator
Staff member
Please use the 4 digit model to help with site searches and Google indexing. I have updated your subject
 

jack-in-sac

Well-Known Member
Yes that does sound like a rich condition. One thing; what is your miles per gallon, what do you consider gas hoggish?? Aside from that; Is the vacuum advance working properly? How many miles on engine? What are you using for degrees of timing? How are you timing, is your timing seeming correct with about 17 inches of vacuum? It does sound like high float levels are part of the problem. As an aside; do you have a road draft tube or a retro fitted pcv valve? A "sludgy" pcv valve can cause stalls.
 
Hi, I run the same carb on our 57 and had a similar a problem. #59 jets are to big #49 are way to small. I have tried different jets and #57 seems to be ok. The rear float is supposed to be lower than the front. The front level should just have a slight dribble out of the bung but I find it better just below the hole. The accelerator pump SHOULD not dribble fuel at idle. There is a check valve (tapered rod) under the discharge nozzles. Check the power valve for burrs if it’s a cast type they sometimes have a piece of cast left on the mating surface. Also the gasket needs to be thick enough to allow it to seal, to thin and the threads will not allow it to tighten on to the seat surface. My engine likes around 12 to 14 degrees of static advance. I mounted a PCV kit from Thunderbird HQ including the spacer under the carburettor to accept the hose, originally it was fitted to the rear of the inlet I fitted a small plug. I have also fitted a MSD drop in distributor, coil and MSDs best plug leads a huge improvement over the original. Spend some time with a vacuum gauge to get the mixture righ. On the Holley website there’s a section on adjusting the mixtur. Good luck.
 
Getting about 9 mpg city highway. Vac running 15 to 19 ". Car has 32000+ verified miles on first time around. Floats are set to Holley specs and may be a bit low if anything. Car did have a home made pcv set up that I removed last yr. Had a fitting screwd into the intake at rear behind carb. They had a fitting with a check valve and line went to the air cleaner from the hole where steel road draft was. . Now I plugged hole with steel pipe plug and let the hose hang down side of tranny this is direct from valley pan.. Also has a line from oil cap breather to air clnr. Maybe .50" ID. Vac advance is NOS and I checked it ,... its pulling spark advance in dizzy just fine. When cold at start up the condensed water coming out exhaust tips leaves black puddles on the floor. Then shoots they out about 4 ft till warmed up. Believe timing is about 6 deg btdc. By buddies around the corner have a big fleet trk garage and do a lot of fleet work and do a bit of race engine stuff. They checked what I did and are stumped.
 

jack-in-sac

Well-Known Member
Getting about 9 mpg city highway. Vac running 15 to 19 ". Car has 32000+ verified miles on first time around. Floats are set to Holley specs and may be a bit low if anything. Car did have a home made pcv set up that I removed last yr. Had a fitting screwd into the intake at rear behind carb. They had a fitting with a check valve and line went to the air cleaner from the hole where steel road draft was. . Now I plugged hole with steel pipe plug and let the hose hang down side of tranny this is direct from valley pan.. Also has a line from oil cap breather to air clnr. Maybe .50" ID. Vac advance is NOS and I checked it ,... its pulling spark advance in dizzy just fine. When cold at start up the condensed water coming out exhaust tips leaves black puddles on the floor. Then shoots they out about 4 ft till warmed up. Believe timing is about 6 deg btdc. By buddies around the corner have a big fleet trk garage and do a lot of fleet work and do a bit of race engine stuff. They checked what I did and are stumped.
It sounds like you are doing the right things. Mileage should be about up to 5mpg more on highway. Perhaps play with the advance to see vacuum responds.. Another look at the accelerator pump? Dribble isn't quite right. Check floats again. Also what do the spark plugs look like? That can help in determing what is going on. Good luck J.
 

Ward 57

Well-Known Member
I'm no expert But.... You are running rich and checked all the mechanicals. I'm going to bet you have a vacuum leak. An intake vacuum leak makes the carb thinking it has to dump more fuel thinking the throttle is more open than it is. Also with all the water in the exhaust, all clues point to an intake manifold fitting or gasket. When it cools the coolant is sucked into the manifold. You won't see it on a vacuum check but all the signs point to the head/intake manifold junction.
 
You haven't talked about the color of the plugs. The plugs tell you what the engine is doing. Pvc, timming ect. Is all irrelevant at this point. If holley says .053 why did you go smaller? With the. 049 and the hesitation what color are the plugs ? Sounds lean but the plugs will tell you. Get your plugs right , then deal with your timing and advance. Forget pvc it has nothing to do with it. Just some thoughts.
Tom
 

jack-in-sac

Well-Known Member
You haven't talked about the color of the plugs. The plugs tell you what the engine is doing. Pvc, timming ect. Is all irrelevant at this point. If holley says .053 why did you go smaller? With the. 049 and the hesitation what color are the plugs ? Sounds lean but the plugs will tell you. Get your plugs right , then deal with your timing and advance. Forget pvc it has nothing to do with it. Just some thoughts.
Tom
My mention of a pcv valve was as an aside: As an aside; do you have a road draft tube or a retro fitted pcv valve? A "sludgy" pcv valve can cause stalls.
My reference is to stalling only I did not state it had anything to do with the other problems.
 
I have a '56 with 312 automatic. Yrs ago someone switched car to 1957 intake and dizzy . Car has always run strong but uses a lot of fuel. Like teenage boys at a keg party!. Exhaust tips are full of black, very dry soot. In heavy slow traffic and long lights car stumbles and revs drop off due to what I suspect is excess fuel in exhaust system. Last week when this happened car back fired and quit at a stop. Huge cloud of blk soot came out of rear of right exh. manifold. What a mess.!! Engine compartment had been detailed well, till that. So...Checked float levels, rear a bit high and I reset it. Front ok. Jets were .059". I changed to smallest they make @ .049". Car runs ok...but hesitates badly till 1650 RPM +-. Installed new accelerator pump. Tried various linkage settings with no real effect. Holley book says this carb should have .053" jets out of the box... Power jet is ok. Fuel seems to dribble into carb from accelerator pump at low rpm but squirts well when throttle opens up 1/4 or more. Should I just go back to the .059" jets and live with running rich ? Timing is right on and good vacume as well. For last 2 yrs car has started immediately and has lots of power.....just a gas hog. And raw gas exhaust smell... Ideas anyone ?
Are you absolutely sure your power valve is good? The diaphragms can fail after a backfire and causes nearly all of the conditions you describe. If you can remove the carb without tipping it and then remove the 4 power valve cover screws you should find no gasoline in the cover. If you do the diaphragm is bad or the gasket between the valve and the carb body is leaking. Some later Holleys have a check ball to prevent backfire damage to the power valve.
 
Are you absolutely sure your power valve is good? The diaphragms can fail after a backfire and causes nearly all of the conditions you describe. If you can remove the carb without tipping it and then remove the 4 power valve cover screws you should find no gasoline in the cover. If you do the diaphragm is bad or the gasket between the valve and the carb body is leaking. Some later Holleys have a check ball to prevent backfire damage to the power valve.
Also is the check ball and pin weight installed under the accelerator pump discharge screw ? If they are missing it can cause this.
 
Top