Can anyone help me out on this one? I have a 1985 F-250 4x4 with a 460 that seems to be running rich. I looked in my manual and it says that this carb(Holley 4180) can only be adjusted by factory trained techs so it will not tell me where the air/fuel mixture screw is located. Can anyone tell me where it is and how to go about leaning out the mixture a little. My fuel mileage is the *#%@!

 

i don't have a holley but look for at and when you find it turn it in clockwise to lean it out.

 

There are four idle bleed screws on that carb. They are under the fuel bowls and may have anti-tamper plugs over the screws. They are difficult to see and even after removing my carb I could not figure out what type of tool was needed to turn the screws. Maybe a very small allen wrench, but I could not get anything to fit the screws.

I’m not sure how you have determined that it is running rich, but if it is if fact doing so, then it could be a blown power valve. It is a two stage valve and can be accessed by removing the front fuel bowl. If it is blown then you may want to install the anit-blow out kit so that it would get blown again.

Good luck,

Mark

 

Thanks for the info Mark,

As for how I determined it was running rich, a self proclaimed mechanic pulled up next to me while at a stoplight and informed that he could" smell " that I was running too rich. I checked out the choke and it seems to be opening all the way when warm. It does load up some when idling for 15-20 minutes and belches black smoke when I accelerate.

Is this power valve easy, inexpensive to replace? Do I need to remove the carb. to replace it or can I do it in place? And lastly, is there a method of determining if the power valve is in fact bad? Thanks for the help!!!

 

The black smoke would be the strongest indication to me – guys on the side of the road I wouldn’t pay any attention to.

Removing the front fuel bowl will access the power valve. To do that you need to remove the fuel line and the four screws that hold the bowl in place. The carb does not have to be removed. The valve is screwed into the metering block which is sandwiched between the bowl and the main body of the carb. After it is clean of gas you can simply suck or blow through it and if the diaphragm is blown then you will pull air through it. There are two gaskets - between the bowl and the metering block and then between the block and the body – that will need to be replaced. Don’t be tempted to reuse them.

If the vavle needs replacing carefully look for the number stamped on it and get the same valve. Don’t get a single stage valve as trucks really need the two stage type. I'm not sure what they cost but the two stage is more expensive than the single stage. There are kits that will allow for the retro fitting of blow out protection so that it won’t get blown again. Also, you should check the fuel level in the bowls and make sure it isn’t too high. That is the one easy thing to do on a Holley.

If you decide that is too much work and money for a two decade out carb I can strongly recommend a remanufactured Edelbrock. No power valve to blow out and it is easy to tune.

Mark

 

Thanks again Mark!!

I am planning on putting on an aftermarket intake and carb (edelbrock performer and 750cfm electric choke) see post EGR intake question. I am just trying to get a little better fuel economy out of the beast until it warms up. I will look into this power valve as it seems easier to check than attempting to adjust the air/fuel on this antique.

Thanks again

 

excellent choice! At least get the carb. I have a smaller 600cfm and i like it a lot.

 

if your power valve is shot the truck will not run it will only start and it will fill your motor with gas as fast as the fuel pump can pump.the power valve is what sets the flow of gas to the carb.

 

If your worried about your gas mileage, the 600cfm carb would be better than the 750cfm, or at least that's what I've determined from research and what other people are saying on this forum. I too have a 1480 holley and am planning on dumping it for the edelbrock 1406 (600 cfm).

 

As far as gas mileage, I am not really worried about it (it is a 460 afterall) , I am more concerned about getting the best efficiency for the power. I tow a 24 foot trailer often in the summers as my family loves camping in the wilds of Montana. Can anyone tell me if there is much noticeable difference in power (compared to the loss in fuel milaege) in going from a 600 cfm to a 750cfm.

 

Daily driving you will probably not find a whole lot of difference between the two. It is when the motor reaches high RPM’s that the 600 will run out of ability to supply sufficient flow before the 750. But, these low revving motors have a hard time getting to that point.

The Edelbrock is a non-square design in that the primary butterflies are smaller than the secondaries. While it has a square bore mounting design it is a bit of spread bore. The benefit of the spread bore design is that the smaller primaries allow for better off idle throttle response and better fuel economy. When you really need additional power the larger secondarys are there to provide the flow.

Now let say – just for reasoning purposes - that the primary side flows 40% of the total CFM. On the 600 that would be 240 total CFM and on the 750 it would be 300 CFM. Now let’s further assume that you typically drive opening the primaries about a quarter of the way. That means that that the 600 would be flowing up to about 60 CFM (600*.40*.25) and the 750 up to about 75 CFM. Not a real big difference and if the 600 needed to flow 75 CFM it would only have to be opened about 30% not the assumed 25%.

As you are probably aware the Ford engineers spec’ed a 600CFM unit. If you use the various CFM calculators the 600 will provide plenty of flow using the RPM limits and efficiency that these motors realistically have. But, if you think your motor will run out of carb before it runs out of ability to keep revving, then the 750 will provide all that it would need.

I have an Edelbrock 600 and it does all that I need for it to do. That even includes occasionally smoking the dual rear wheels. The most important thing is to get the idle, cruising, and power air/fuel mixtures set correctly.

Mark

 

Be aware that the power valve is subject to smaller leaks too. Not all of them completely "blow out". I have 4180 equipped Mustang in the garage now that had a smallish leak in the power valve. This made the car run like it was flooding out. Amazing amounts of black smoke at a idle and just revving it. But it was quite driveable at higher RPM's. Just as long as you didn't want to go far as driving through town at 80 mph to make it home before all the sparkplugs foul out tends to draw attention.