Greetings all,

I just spent the weekend trail riding with my 78 F150 460 4x4 and found some minor problems.

On very rough terrain, the engine (stock '71 460) sputters and sometimes dies. My guess is it's the floats in the carb. Aside from going to an off road carb or LP, is there any adjustment I can make to fix this? I do have a motorcraft 4bbl that I could swap in. Is that a better carb than the holley for this type of application?

Next, the inside of the pipes are thick with black soot. Does that mean it's running too rich? Any tips on adjusting the air/fuel mixture to correct this?

Last, is timing by vacuum really the best way to set the timing? I'm at 8 BTDC and haven't tried the vacuum method, but was told it's the best way.

Thanks in advance for any help.

Kevin K.

 

kevin i just got my 750 holley tuned perfect on my 460. yes you might be running to rich. heres how to adjust it. on the side of each bowl you will see a flat screw (passenger side) use a flat blade screw driver and take it out with the motor idling. gas will problably come out so put a rag under each screw. next you will need a 5/8 wrench. at the top of each bowl you have a needle and seat, you need to loosen the srew at the top of each bowl with your screw driver and then turn the whole piece with your wrench. clockwise lowers your float level, C.clockwise raises it. adjust the front and the back till the gas barely dribbles from the side screw hole. this is one of many adjustments on your holley. they are the BEST carb, people just dont give them a chance because they are tempermental. you may have other problems though. jets, accelerator pump, power valve, check to see if you choke is func. properly too. as far as timing, plug vac to you vac advance set base at 8-10, reconect vac advance to manifold vac. and test it. let me know if you have more holley questions.........

 

First off the Motorcraft is only a cheap copy of the Holley. The soot in the exhaust means to much fuel. That's what's killing the engine. It's being spilled into the engine through the bowl vents. For your off roading, Holley makes some real long vent baffles for this. They used to be white in color. This will stop the too rich condition on the inclines, either up or down. I used them on a drag car that carried the frontend real high and would stumble because of it. The baffles solved it. Lowering the float level will help too, but only drop it a 16th to an 8th of an inch. You might have to readjust the idle mixture. All I've ever done with mixture adjusting is just listen to the engine, when rpm's peak adjust the other screw and I back and forth 3 times. All the locals that are not carb savy come to me. I set timing by total advance and ignore initial except to see if it ends up were it did last time. Disconnect the vacuum, plug if you want to, I don't though. Rev motor to about 4000 rpm(keep it short and don't hold it there for more than 5 to 10 seconds) and look for 30 to 32 degrees total timing and lock the dist. down. Check a second time to make sure it's still where you set it. Reconnect vacuum and you are good to go. Max timing is what's important, cause that will fry your motor quicker than anything with to much total timing. I like recurving the advance curve to a 10 to 13 degree curve in the dist, 20 to 26 degrees at the crank. The stock curve is usually 18 degrees or more. The vacuum method is not reliable.

 

In my experience, this is the pro[per way to set your holley:
1)pull both the site plugs l9ocated on the passenger side of each float bowl.
2)start the engine.
3)if fuel starts pouring out of the bowls, shut the motor down until you lower the floats a little.
4)get a 5/8 wrench and a large flat head screwdriver.
5)loosen the center screw on the top of the float bowl.(one side at a time)
6)the nut under the screw will either raise(counter clockwise) or lower(clockwise) the float level.
You want the fuel to just BARELY dribble out of the site plugs.(front and rear respectivly)
7)once you have reached the optimum float level, tighten the screw.

Now that you have the float levels set correctly, adjust the idle mixture as follows:
1)On each side of the meetering block(right between the float bowl and the air horn. 1 meetering block on vacume secondary carbs, and 2 on double pumpers.)
2)starting on the passenger side, turn the screw in all the way. Be careful on bottoming the screws out. Dont tighten them tight.
3)turn the screws out 1 and 1/2 turns counterclockwise.
4)start the engine
5)start on the passenger side and turn the mixture screw in until the engine almost dies, then back it out 1 and 1/2 turns.
6)go to the drivers side and perform the same proceedure on that side.

Hope this helps. I did this on my 67 mustang and took it through emissions and passed meeting todays standards. Make sure your timing is set correctly though.
As for timing, I always just set it where it runs best at the race track. That tells me a lot there. However, on a rock crawling 4X4, it may be set differently to get more torque and less top end.

 

One and a half turns is an intitial setting for fuel bleed idle screws and about 7 turns on the air bleed, emission carbs. I've worked on some HP carbs that had mixture screws in both the front and rear metering blocks, usually race carbs. However with the intitial setting done now turn either side in until motor slows down or stumbles, then turn out, counting turns until motor slows and loads up. Turn back in half the turns you came out. Do other side and recheck both sides. It doesn't matter a damn which side is done first. Don't make it hard. Holley carbs are KISS(Keep It Simple Stupid) carbs and too many people try to make it hard, it isn't. You main problem is spilling fuel through you vents, fix it first, it might even solve you rich problems. Fooling the emission tester is fairly simple if you understand the system and want to cheat it. Hell, I even made a 1969 428 SCJ with a 3X2 carb setup pass once, to win a bet.

 

LOL Bear. I know that. Your right, it doesnt make any difference what side you do first, I simply said to do the passenger side first because you have to start on one side or the other. That was just the side I chose.
I stand by my statement about how many mixture screws the carb will have. You state as follows:

I've worked on some HP carbs that had mixture screws in both the front and rear metering blocks, usually race carbs.

My statement was as follows:

1)On each side of the meetering block(right between the float bowl and the air horn. 1 meetering block on vacume secondary carbs, and 2 on double pumpers.)

I think Double pumpers would qualify as race carbs also in most cases. Either way, you most likely will not have more than two mixture screws on a vacume secondary. (there is always a person who will disagree and have some sort of proof. There's always an exception to any rule, and carbs are no different.)

 

Thanks for the great info guys!

I'll be printing this out and taking it home tonight to give it a shot. I'll let you know how it goes,

Thanks again!

Kevin K.

 

OK, I made the adjustments last night and here's what I found.

Both float bowls were low. I gave each of the 5/8" nuts almost a full turn to get the fuel level up to the hole on the side.

Then I went to the two small screws between the float bowls and the air horn. The were both set at about 1/2 turn out. I screwed them all the way in and then out 1 1/2 turns. I also turned them in to make it die, but nothing happened. When I turned the passenger side one all the way in, the idle actually went up.

I took it for a test drive and it's noticably better. No sputtering when I stomp on the gas from a stop.

So, do I leave the little adjustment screws at 1 1/2 turns out or do I mess with it more? How do I know if I'm still running rich?

Thanks a lot guys!

Kevin K.

 

Kevin, To find out if your still running rich, pull all your plugs and either clean them, or replace them. Either way, they need to be clean and white when you put em back in. Take the truck out for a trip. Try to stay out of the throttle. When you get back, pull the plugs again. If their black and sooty, then your running rich still. If their a nice tan color, your fine.

For the Idle adjustment screws, turn them both in all the way, then back them both out 1 full turn and see if you can make an adjustment that way. When your finished, both sides should be turned out the same amount of turns.

 

I'll do that tonight.

Are those adjusting screws both for air/fuel or is one for air and one for fuel?

Kevin K.

 

Each screw meters fuel only to the carb barrel on that side. Air is metered by a fixed air bleed(jet). Try tweeking them a little. Like a quarter turn in on each. If it runs faster try a quater turn more. If in doesn't work try out(I doubt if they are to lean). You want the highest RPM you can get then richen it up(turn out) and 1/8th of a turn. By the way, I've seen them be as much as a 1/2 turn difference side to side to get the best idle. If you can get them the same is best.

 

Gotcha! Thanks!

K.

 

kevin, the correct way ive learned, to adjust the mixture screws is with a vacuum gauge. hook it to manifold vacuum and see where your at. should have around 17-18 HG on a stock motor. you turn the screw a little at a time till your vacuum is highest and you idle is smoothest. as far as being rich, just have someone rev it in park and watch the exhaust. if its smoking black your to rich, if not your problably fine. this isnt the most accurate way but its quick and remember ALWAYS BETTER RICH THAN LEAN !

 

Yeah, and depending on you cam and a number of other factors you may not ever see that much vacuum. If you must use a gauge, just try for the highest vacuum and don't worry about which number the needle is pointing at. A gauge just makes it harder, I would perfer a tach over a vacuum gauge and go for the highest RPM(same result and you aren't pulling vacuum lines). Then again I just listen to the engine and tune for the best(fastest and smoothest) running as I can get it. This is simple and you need only have a screw driver to adjust these things. KISS is the way to keep it and let the guys trying to make it hard do it the hard way. I have a room full of trophies from racing and all were won with a Holley(s) carb on board and I never used a tach or a vacuum gauge except to trouble shoot a problem that won't go away with the ear tuning process.

 

As Bear said, it is best to keep the idel mixture screws as close together as possible. When you hook up the vacume gauge, it will tell you a whole plethora of things. It can tell you if you have leaking valves and such. I also agree that with Holley carbs, the KISS rule is best. Now, I always tune my carbs by ear. BUT, it takes some practice to do that. I've tuned many carbs(probably not as many as Bear though) and Holleys are the simplest ones I have found to tune.