sauerf100s(No Email Addresses In Posts!)
I thought I knew a little about being a mechanic, but this one has me stumped. I just rebuilt a Ford 302 engine, to replace a 300 6-cyl. in a 65 F100. The engine is bored .040," fitted with Keith Black hypereutectic pistons and Total Seal rings, `decked, align honed,balanced and blueprinted. Rebuilt 69 302 heads with oversize valves, three angle valve job, ported and polished, screw in studs with guide plates, springs to match the cam (installed at correct height), and roller rockers. Cam is Blue Racer .472/.496 lift and 280/290 degrees duration. Pete Jackson geardrive timing set, set up at 0. Carter performance fuel pump, Holley 600 double pumper with 68/78 jets, 6.5 power valve, on a Weiand Stealth manifold, everything port matched. Ford Duraspark distributor fired off by a MSD 6-A box (Instead of Duraspark control module). Accel super coil with new Accel wires, cap, and plugs. Hooker headers, Flow Tech mufflers, 2 1/4" mandrel bent full-length exhaust. Behind the engine is a 94 Cobra T-5 tranny with a Hays clutch set, going to a 9" rear with 3:50 gears.
I set the timing at 10 degrees BTDC, and adjusted the valves at 3/4 of a turn preload. The oil pump was primed before installing the distributor of course. I'm trying to give you all the details, so maybe you can figure this out. The engine started and ran right off, and it was broke in at about 2500 RPM's for a half hour. Then I checked the carb float level and other carb adjustments, and optimized the timing by ear. After making final adjustments on the clutch cable, I took the truck for a drive. I just drove around town for the first 50 miles or so, and the engine ran great, but I never got on to it. I went back home, changed the oil and filter, and went out on to the interstate.
While going through the gears, the engine would run great to a certain RPM, and then just fall flat. Almost like it wasn't getting gas. Starting from a dead stop, it would have great power at first, and just fry the tires, and then all of a sudden it would lose power and barely run. If I let off on the gas when this happens, it will continue to run well, until flooring it again. The same thing happens if I step on the gas gradually. Runs great to a certain point, and then @#$%'s the bed. I have a glass fuel filter, and it stays full of fuel. I don't have any way of checking the fuel pressure. I have all 3/8" fuel line coming from the stock 5/16 steel fuel lines. At first I thought the fuel line was collapsing, so I rotated the fuel pump, and shortened up the fuel line and made it straight. Didn't do any good, same problem. I've tried adjusting the timing, checking the plugs to make sure the air/fuel ratio was close, and checking all the wire connections and clamps on the fuel lines. I'm going to swap out the carb tomorrow, but I really don't think that's the problem. At this point, I'm not sure if it's electrical, fuel delivery, or the Chevy valves in my heads (just kidding). I have no idea what the problem is.
If you can come up with some suggestions of what the problem is, you would really help me out a bunch. I've put a lot of time and money into this truck, and it really bums me out the way it turned out. I've had many projects in the past, but have always been able to make things right. Hopefully you can get back to me before I start banging my head against the wall.
Many Thanks,
Steve

 

Have you checked to make sure your throttle is opening all the way? It may be hitting the intake or it may be binding. Where are you taking vacuum from for the distributor advance. What is your distributor out of? You may need to recurve the distributor to math the new engine. Just a couple thoughts. Don

 

I was taking vacuum from the port on the left side of the metering block. I discovered there was barely any vacuum there, so I changed it over to the left base port on the carb. The butterflies are opening all the way. The distributor is from an 80 T-bird, with new pickup, rotor and cap. I used the carb, distributor, and MSD ignition on the same engine before rebuilding and it ran great. It was in a different truck though. I even kept the wiring harness from the other truck, so I ruled out wiring mistakes. That's why I was looking for fuel delivery problems. Before swaping the carb today for a Carter I have, I'll check the fuel line under the cab, and the pickup tube in the tank. I doubt there is a problem there though, because I drove that truck every day to work with the 300 in it, and never had a problem. Thanks for geting back so quickly.

 

As you described I would think ignition. Do you have a rev limiter? Sticky mechanical or vacuum advance? I would go back through the electrical syatem beforw swapping out the carb. Look for corrosion on connectors, bad ground. Let us know how this turns out. By the way that small block sounds like a real "HOSS".
William in Atlanta

 

The secondaries may be too lean. Any out of the box Holley I ever tried was by quite a bit.

 

Have you pulled the plugs to see if it's running rich or lean. I would look harder at a fuel problem, it sounds like its to lean or not getting enough gas at higher rpms. Most electrical problems are more of a miss rather than a leveling off. Hope this helps Eric

 

[updated:LAST EDITED ON 04-Mar-02 AT 05:10 PM (EST)]OK Before ripping things apart, Do you have black exhaust when thromping on the gas when it is park? If so your jetting is too rich. Remember the secondaries don't open until there is a load on the engine ie... driving down the road and too much fuel will choke the engine. You may end up having to get smaller jets. I have 62 primaries and 66 secondaries on my 351W. But first lets start with the basics again. Setting things right the first time will cut down on second guessing later.

Buy a gauge they are only $16.00 at most stores including Sears. If this is not an option then use your finger to feel for vacum. You should have "0" vacum with the engine at idle for your vacum advance on the distributor. It's suppose to pull vacum as the throttle plates open. Hence why it is ported above the plates. Second, you might be bogging down because your starting with an initial spark setting which is probablly ATC for it to run with the vacum advance hooked up. I learned the hard way, this is why I am typing this now. Did you set the timing with the vacum line off of your distributor? If so you were correct to do so. If not then reset your idle timing with the vacum advance port plugged. Once set, hook up your vacum line to your distibutor. Does it run rough all of a sudden? If it does disconnect the vacum line again and install the vacum gauge. You should have no vacum on the distibutor port. Search your carb vacum ports until you find one that in not pulling vacum until the throttle is opened. If everything is fine go to step 2.

On the side of your carb fuel bowls you will find two brass flat head screws (one on each). These are the float sight holes. You should only have fuel up to the bottom of the holes. NOT fuel dumping out the hole when the screw is removed. If you do, you have to adjust the needle and seat valves. They are located on top of the fuel bowls with a flat head screw and 5/8 jamnut. Loosen the screw just enough the move the 5/8 jamnut. Turning the jamnut will change the float settings allowing more/less fuel to enter the fuel bowl.

There are a million little things that could be causing all of this. I am just tring to give you a place to start. If you do all of this and nothing hit us back with what you do or don't find. I can type mre later. I am having a bad case of get homeitis right now.

If you go to www.holley.com there is a much better explination of what I am talking about AND they have pictures which I don't. Also I have an issue of carcraft that has a great article on setting your carb. The creator of Demon carbs made it. It still applies because Demon's are loosely based on Holley's. I hope this helps some.

 

You did not say what kind of oil pump you used..stay away from the "high Vol." pumps. We put a 302 in a 72 Maverick, that came from PAW. Was set up for the B&M blower. When you ran it hard, it would die, While you tryed to start it, is sounded like a jumped timing chain. Backed off the vales to "0", and the dieing went away...the lifters were pumping up and holding the vales open..Just my two cents..

 

im wondering if your advance curve is wrong for your rebuilt engine. if your engine was stock the factory dizzy and msd may have worked perfectly. but you may getting too much advance too early or not enough at higher rpm. what is your base timing at idle? what is your idle speed? what is your timing at idle with the vacuum advance connected? what is your timing at 2000 rpm? check those things and i may be able to help. Don

 

Since we are all throwing out ideas, try removing the gas cap. If you have replaced it with a none vented cap, you may not be able to MAINTAIN fuel flow to the larger carb. My $.02

 

[updated:LAST EDITED ON 05-Mar-02 AT 09:14 PM (EST)]First of all, I want to thank everyone for the suggestions. I tried swapping out the carb for the Carter AFB I have on a truck with a 352. It ran exactly the same. Then I replaced the short hose under the rear of the cab. It had cracks in it, and started to leak as soon as I touched it. I thought I found the problem. NOT! I went for a drive, and it was a LITTLE better, but still cut out at high RPM's. I tried loosening the gas cap too, but that didn't do anything. I went back and checked all distrib wire connections. All were tight and clean. To to hit on some of the comments and suggewstions I got so far: My MSD has no rev limiter. It's the 6-A type. The vacuum advance seemed a little stiff before I installed the distrib, so I cleaned it and lubricated it first. Is it possible to be too loose? At idle, my exhaust smells a little rich, but that's the way a double pumper always has been on any of the engines I've had. Maybe that's a sign of being jetted too rich. I've played with the idle mixture using a tach/dwell to get best RPM at idle. Still smells rich. Funny thing is, no black smoke when I hit the gas hard. And the plugs appear to be burning real clean. Since the original carb is a double pumper, the secondaries open as I push down on the gas more. It has progressive linkage. I'm kind of confused by Mark Covill. First you say to set the timing with vacuum advance plugged (which I always do) Then you say that there should be no vacuum at idle. HUH? The port where I had the advance hooked to at first has nothing at idle. Another truck I have was this way too, and I could never get it to run good at low RPM's. Once I connected the advance to the bottom of the carb (low vacuum at idle), it ran a lot better at idle. So I applied this theory to the built 302. It too ran better at idle. It got rid of the slight misfire I had at idle also. I've played with the timing a lot. I advanced it until it wouldn't hardly turn over while trying to start. Then I retarded it until it wouldn't barely idle. I went back to a happy medium, and it seemed to like that the best.I know all about setting the float level on Holley carbs. I've been around them for over 20 years, and that was one of the first things I learned. I always have a tuff time getting the jetting just right though.
I AM using a Melling high volume oil pump. I always have in the past though, and never had a problem. Maybe it's a problem now, since I installed a windage tray. This may keep more oil down in the pan where it belongs. I don't know about that theory though. It sounds great while cranking to start. It doesn't even go a full turn before it fires. And once it's warm, you don't have to hit the gas. it starts just fine, so I don't think the valves are being held open. I think the only thing bad the high volume pump would do is heat the oil up a little bit.
Base timing was set at 10 deg BTDC. Idle speed is 800 RPM's. My timing light is an antique, so I have no way of knowing the timing at any speed bu idle. At least I ruled out the carb. A mechanic friend said there is a screen on the end of the fuel pickup in the tank. It may be gummed up. He's seen that before. The 3oo with the single barrel carb wasn't pulling enough gas for it to be a problem. I'll let you know if that was the problem tomorrow.
It looks like I'm writing a book. Thanks Y'all. Steve

 

OK, Maybe I'm not explaining the problem good enough. When I nail the throttle, the tires will just shred and the engine will scream for the first few seconds. If I short shift, it'll fry the tires in the first two gears before it begins to die. If I still keep the pedal to the metal, it will keep running. Just not very good. Then if I let off the gas just a little bit, it begins to run fine again. I have a T5 five speed with 3:70 gears, and at 70 MPH in third gear it still runs good.(I have no tach yet) so I really still don't know what the malfunction is. When I say let off the gas a little, I mean only a quarter of an inch or so. Maybe a half inch at the most.

 

Hej Steve!

Just 2 little ideas. One: your mechanic friend is correct, there is a screen on the pickup in the tank. Because you are flowing so much fuel, a partially plugged screen that never was a problem before, may now be. Two: I used to own a Jag with a three carb 3.8 liter inline six. It had a high speed problem too. Anything over about 250 Km/hr and it would bog down. The problem was the fuel pump could not keep up with those big carbs at speed. Found out that was a common problem for the hi-performance Jags because Jaguar used standard fuel pumps even in their hi-output engines. Your stock fuel pump may not be able to handle the volume of fuel needed. (or it may be a combination of 1 and 2) Good luck, Herman

 

I know this sounds kind of dumb but did you check the motor to frame ground. I have seen this same problem two times in my years of working on cars and trucks . One was on a 69 GTO with a 455.Exactly the same problem as you. Just a thought.

 

I wish there was some way you could open the float inspection plug on your carb to see what happened to the gas level when you got the problem.
But, I guess you only feel the problem on the road when driving. And then it is hard to take a look.... <<<smile>>>
Unless you have a friend sitting there to watch...

Nah, to dangerous if you get a fire.

But, seriously... if you could come up with a way to check the level during high load of the engine, you would know if you had a fuel delivery problem, or not.


Bill