I just got this truck about a month ago, and I've been searching for the past week, trying to find the solution to my 79 Bronco carb issues. It's a 351M with a factory Holley 2bbl, recently rebuilt, new float, needle & seat, and hoses leading to the bowl. I've tried every adjustment mentioned in this forum, and here's what I get. No matter where I set the float, the carb is overflowing in gas. I have set it with the bowl off, and through the sight hole. If I adjust it to where there is just a very very slight trickle from the sight hole, it will idle great, but run out of fuel while driving. If I bump the level up very little, it will begin overflowing while idling, but supply just enough to drive, but not long on WOT. The float and needle setup in this seems backwards to me, as the float has to push the needle up against the flow of fuel to turn the flow off, and that leads me to think that too much pressure would hold that valve open. It does appear to me that the pump was replaced at some point previous. Is there a way for me to regulate this pressure, or is there something wrong with the carb. I'm not interested in rebuilding this carb again, so if it is the carb, I will likely buy a new one from Edelbrock as I haven't heard the best about Holley's. Thanks for the help!
Scott M.

**I forgot to mention that I do not currently have the equipment to gauge the fuel pressure.**

 

If your using a high performance fuel pump,then you need to regulate it,if not,then go with a new carb. or head for your local performance shop.

 

I don't know that it's a high performance pump, but I'm going to try to find some numbers on it tonight to see if that's what happened. The original owners had some carb work done on it before I got it, and were not satisfied from what I was told, so it sat for a while. The guy I got it from did minor work to it, but mostly tuneup work, plugs, wires, cap & rotor to try to get it to run correctly. When I got it, you couldn't even touch the gas, since it was bubbling over inside and flooding the whole thing out. Hence, where I am today. I want to drive this thing so bad, but this &#*@ carb won't let me. I love the truck, and if I change the carb out, and I definitely going to drag this old one down a dirty gravel road for a few miles while I laugh deviously.

 

too much pressure buy a stock fuel pomp

 

There are inline regulators that you can buy that have a dial to adjust the pressue.
I would just try a new stock replacement pump first. They are cheap.

 

Ok, I'll give that a shot once this stupid winter storm passes!

 

good luck buddy

 

I'm asking a lot of questions, but I have a slightly new one. I had to drive the Bronco today, since this ice and junk kept my T-bird buried, and it did very well for the most part. Here's the issue, and I would hope that a fuel pump would take care of this too. Upon acceleration, if I give slight pedal, RPM's rise, a little more, and it hesitates and backfires, and if I push a little more, it accelerates harder. I can floor it while driving, and it will go, if I feather the pedal past the hesitation point. I've always associated backfiring with timing, but if it's still this fuel related issue, I will wait. I want to knock out as many things as possible tonight, as I have a heated enclosure to work in, cause outside, it's about 4* Not ideal working conditions. Thanks again for all wisdom!

 

Ok, the fuel pump did not fix the problem, actually, it increased the fuel spilling over. I did readjust the float, but it is now bottomed out and still giving too much fuel. I'm done with this carb. Unless someone has a sure fire fix, I'm ordering my new Edlebrock carb. This Holley POS sucks.

 

The hesitation when you accelerate is the accelerator pump. Why not just rebuild the carb completely? That's what I'd do.

 

I'm at a point, that I don't want to keep messing with an old carb, it was rebuilt recently, as I was told about 1 year ago, and things have been replaced and adjusted, and at the moment, since I've seen the rebuild kit, and I don't see what is going to fix this overflow problem. I don't mean to sound stubborn, but I'm just looking at what I see in the kit, and the things that will be replaced, and I don't see anything that would regulate the fuel flow. I know I'm not a carb builder, so I say this as an opinion, but it doesn't make any sense to me, to have a weak float try to fight a brass needle, against the flow of fuel, to turn it off. Wouldn't it make more sense to reverse that action and let gravity do the work? Because I still think that an overabundance of fuel pressure is pushing this needle open, and nullifiing the effect or usefulness of a float. I have double checked to make sure that the correct fuel filter is on, which it is, and I don't see anything else that would restrict this flow. So, is there something inside, besides the needle, that regulates the pressure of fuel entering this carb? If there is, it will save be $250 on the new carb. Thanks again for all the info!

 

Gravity doesn't do the work; the fuel does the work. The fuel rises up and the float literally floats up to a level and the leverage action pushes the needle into the seat. As fuel leaves the main jets, the float moves back down and opens the needle slightly. It's a back-and forth mechanism that keeps a constant amount of fuel in the bowl.

If you watch the engine running with the air horn off, you're not supposed to see the needle valve shut the fuel off completely. If it did, the fuel level would drop. If that happened long enough the engine would stall. It's moreso a regulatory mechanism than a simple open\closed switch. Like I said, you won't ever see the needle shut the fuel off completely because it's not supposed to.

If the carb isn't running right then the fact that it was rebuilt\adjusted doesn't matter because a tuneup only does any good when the adjustments are done correctly. Obviously yours wasn't adjusted correctly. I only say all this in the interest of saving you some money. You've already got the kit it sounds like. Now all you need is cleaner and a free weekend. A new carb is expensive, and it'd be a shame to spend money on a new carb when there is a chance your old one might be usable.

 

Ok, that makes sense. I have been under the impression that the needle was to be able to shut the fuel off. I understand now. So since this thing is overflowing, while I'm in for the rebuild, is there a particular section that I should pay any extra attention to? I do plan to take my time and examine this thing, so I can learn how it functions and be able to troubleshoot later on. Thank you again!

 

The section that will interest you most is setting the float height\drop. The kit should have a sheet with instructions and what to set it to.

Also, some tips for your first carb rebuild. You need the gallon can of Chem-Dip to soak the metal parts. Disassemble the carb completely and never soak any rubber\neoprene\plastic parts. They give you a dipping basket to drop parts into the can. I usually can't fit the throttle body and air horn into the can with the basket so I dump the cleaner into an old bucket, and then work from there. Don't touch or smell the cleaner...it's nasty stuff. The basket can be used for the little parts. I usually soak the throttle body, then the air horn, then the basket of parts. Soak each run for an hour and then set it out. Then spray it down good with a fresh can of carb cleaner, to get all the cleaner off. Again, don't touch the parts until all the cleaner is off and the parts are dry, and don't touch\smell the spray stuff either. Use compressed air to blow out the small passages in the carb once it's dry, and wear goggles during all this so nothing gets you in the face.

The carb kit includes replacements for all the soft parts that wear out over time. You'll reuse the old float. My advice would be not to throw any of the old parts away until you're sure the kit has a suitable replacement that fits. Finally, when you bolt the carb to the intake, make sure you use the thick type gaskets. Some rebuild kits include paper thin carb base gaskets and they are junk.

Other than that, just study the diagram carefully. Good luck!

 

Thank you very much for all the information. I may still rebuild this carb, and hold on to it as a backup, but since tax season is upon us, I am now considering a mild upgrade, to the 4 bbl tune. I have some possible parts coming to me a good prices, so it may be a good time to take advantage of it. Even though I don't plan on needing this carb for a while, I do want to rebuild it for that emergency need. Is there a preferred method of storage, ie sealed container, vacuum seal, or other. I do want to keep it ready to go if the need should arise. Again, thank you for all of your help!!