77 F150 w/ 460 not revving above 3400 rpm's
 

Okay, first of all, the truck runs pretty well, considering it still has the Motorcraft 4350 spread bore carb. Fires up on the first try and gets me everywhere I want to go. Acceleration is steady, no hiccups or stutters. Idle is the only things that is not perfect, but I'm scare to touch it anymore since it gets me up the road and back.

However, I installed a tachometer this weekend and verified what I had thought for a while now: It's not revving as high as I'd expect. I drove it quite a bit yesterday for the first time still installing the tach and I couldn't get it past 3400 rpms and that was the only time it got that close. Most of the time 3000 was it. If I floor it from a slow roll, it accelerates smooth and steady, but it doesn't get very high before shifting. I believe the rear has a 3.53 or so (or whatever Ford provides in that ball park). I'm turning about 2000 rpm at 55 mph with 30 inch tires.

First thing I know to check is whether the throttle linkage is traveling the whole distance when depressing the gas peddle. With the entire setup (carb, intake, linkage) being stock, I don't know why it wouldn't. I was also told that there's a modulator that has a vacuum line going to it on the transmission that I can adjust to get deeper shift points.

Someone asked me if I had enough fuel pressure but it never feels like I'm running out of fuel. Back when I was adjusting the floats, I did have them set too low and would run out of fuel at higher speeds, but I got them adjusted properly, I feel.

I just ordered a Holley Avenger 770. This 460 has an RV cam but that's about it right now. Headers and aluminum intake down the road. We'll see if that makes a difference but if anyone has any idea what what limit rpms, while at the same time running pretty well, I'm all ears. Someone also asked me about timing, but the man that built this motor was a very good mechanic and I don't think the timing is an issue.

Thanks

it wasn't clear from your post if you tried revving while parked or if you were only checking max Rpm while drving...
It would only take you 30 seconds to confirm if the primary butterfly is opening all the way by looking down the throat of the carb...
Have you checked with the "man that built this motor"?

I have only checked the max RPM's while driving. I believe I did rev it a couple of times in the driveway, but I can't remember for sure. If it wasn't for the weather, I would have checked what you mentioned today and looked down to see if the primaries are opening all the way. I'm assuming at wide open throttle, the secondaries would as well.

As far as the man that built it, I can ask him at some point. He has been a great friend of the family for my entire life. He is now in his late 70's, so I don't like to burden him with a lot of this. My dad bought this truck from him around 2002 and my dad decided to pass it along to me last December. He has helped a lot with this truck over the years and you never want to become burdensome with things like this. It's why I don't like to sell friends and family cars myself. ;)

Running smooth at low rpm but won't tach up makes me think valve train problems. Have you pulled the valve covers to see if your rockers are loose? If its not running rough at 3400 rpm (valve float), and you have no vacuum leaks, or blow by, I'd be thinking the camshaft lobes are wiped out and it just won't flow enough air to rpm past 3400.

Are you saying it's shifting to soon or the engine won't rev over 3400 ? they're totally different conversations

What happens if you hold it in 1st or 2nd at WOT ?

What I'm saying for sure is that it won't get past 3400 rpm's, at least in drive (D). I haven't tried it by manually putting it in 1st yet. I'll give it a try tomorrow afternoon when the road conditions are safe enough. I guess whether it's shifting too soon is subjective. I never really thought about it shifting too soon before putting the tach on. But any other vehicle, whether it's my work truck (2015 F150 with the standard V6 - no EcoBoost), my 2005 Nissan Altima 3.5 or my 2002 Escalade with the 6.0, when I mash the gas to the floor, they all rev to red line. I know the 460 is a low end torque monster that's not supposed to rev to 7000, but I've had many guys tell me it should get close to 5000. Hopefully I can see what this carb is doing and determine if the secondaries are opening or if it's just the kickdown on the transmission I'm feeling. When my dad gave me this truck, I was expecting a lot more "umph" from it. It's got about 40k on the rebuild, which including a mild RV cam. Other than that, she's completely stock.

It should rev until it floats the valves even if you had no secondaries it would just take longer to get there.

In order to determine if you have an engine problem or a transmission problem you need to hold it a lower gear and see what happens.

lots of 460's are low compression and if it is then it's going to be a dog , this might be your power problem. but it still should rev normally.

Okay, took her for a run this morning. I appears the linkage on the carburetor is not binding anywhere and has full travel. So, after she warmed up for a few minutes, I took her for a drive. Dropped her in first, turned onto a main road, leaned into the gas and laid a nice tire. In 1st, I was able to get to 4000 with no problem. With that said, I didn't want to push it higher than that. I'm not sure if it's because it's a 460 with semi-loud exhaust, but it did feel like it was hitting near that peak power band, so I decided to stop there. I need to see if I can find some information on the 77 460's and where they hit their peak horsepower. I didn't hear anything that scared me, though, just don't think this motor has been pushed that hard in many, many years. The good friend of ours that owned this, I believe, has this truck setup the exact way he wanted it. The shift point at 3400 rpm is probably exactly where he wanted it for daily driving, along with the rear end that he has in it. I think that possibly, in the summer, when he towed a camper trailer, he probably swapped in a 3.73 for towing.

One thing that I did was address the poor idle that I was having, after it warmed up. Adjusted the air/fuel mixture, with the use of a vacuum gauge and got it from barely 14/15 to a nice, steady 18. Now, the more I get comfortable with this carburetor, I'm wondering if I should have purchased the Holley Avenger 770 that I just ordered. All the information I've found said that the Motorcraft 4350 is a 715 cfm carburetor. So 770 shouldn't be out of the question, right?

What kind of kick down linkage, etc.

I mean, does it have a rod that comes up from behind intake and runs down to transmission? If so, you want that rod to reach full travel at WOT. To check it, requires popping rod off ball at carb or unbolting it, push it down and open throttle and compare, adjust rod to make match. When adjusted correctly, governor in transmission will determine shift point in passing gear.

My '77 will kick down and pull to near 5k or when I relax throttle to let it up shift from either 1st or 2nd as the case may be … which I will usually do. I just don't like reving it way up there.
I put a shift kit in trans in late '80s which included some mod to trans governor wgts or springs, I think it shifted at a slightly lower rpm stock before that.

Mine is oem 3.50 gears, C-6, and just driving along, about 2,400 give or take at 60 mph, 31/10.50-15s.

770 cfm is OK, but that oem mtrcraft was / is enough.

Yes, the kickdown linkage is hooked up. I haven't disconnected it to see if it's traveling the entire distance it should, but I believe it is kicking down like it should. Sounds like we have similar gearing and RPM's, my tires are 30's but we're close. I did, however, download an app on my phone that does mph and on the way home just now it appears that my speedometer is 4 mph too fast (Dash will say 35 but the app says 31). I will verify this app with my car later today to see if it's accurate, since the car has the factory tires on it. I'm debating on whether to send the 770 back. I did some tweaking all morning with the carb I have after reading a great tutorial and I have it running and idling the best it has since I got it. The only thing I found, which may be part of the rpm issue is the secondaries. On the 4350, there is a plate on the secondaries (pardon my lack of terminology, I'm no carb expert) that is similar to the choke on the primaries. I would assume that they would open under wide open throttle. When I checked this earlier today, I tried to push it open, but it wasn't moving freely. For a moment, I thought that maybe it wasn't supposed to open, but I pushed a little harder and it suddenly pushed open. I worked it open and closed several times. I also made a slight tweak to the accelerator pump and air valve and then took a ride. It drove better than it has ever driven....idle, low-speed cruising. When I got to the main road, I punched it. Still only goes to 3400 but it felt like the secondaries did kick in, not for very long, but it's a start. I tell ya, if I can get this carb to run consistent, I may just stick with it.

It's not that I want to race the truck or that I will be constantly flooring, I just think that it's odd that it won't get up to 5000 like a lot of folks (including you) say it will. A guy on Facebook did share a video with me of a vacuum module on the front of the transmission that you can tweak and that will prolong the shifts. I may tinker with that at some point to see if will be allow the rpm's to clime higher.

I believe this 460 is the one that came with the truck.....is there a reason to believe it didn't? I can ask the man that my dad got it from if that is the case.

There is likely a link on the carb to stall / prevent the rear air valve over secondaries from opening while choke is cold or closed.

I thought you had a 4wd, my bad.

I have had guys swear they had a 460 and argue when the parts they bought din't fit …. go look and sure enough, they had a 351M or 400.

Valve Cover Bolt Numbers
2 bolts: "Y" Blocks
239/256/272/292/312 (produced from 1954 to 1964)
5 bolts: FE Series
332/352/360/361/390/391/406/410/427/428
6 bolts: SBF group
221/260/289/302/351W

7 bolts: 385 Series
429/460

8 bolts: 335 Series
351C/351M/400


That vacuum modulator will cause part throttle shifts to be delayed a little when engine is under load, but is not intended nor functions as a kick down or passing gear. I'll include pictures of extension.

I'd have to disagree with 4 barrels not coming on these trucks. I'm certain this one did and I'm certain it is the original. Here's a section of an article that I'll post the link to as well:

"Ford trucks, Lincoln cars, Jeep and AMC continued to use Autolite four-barrels with a third generation carburetor referred to as the model 4350. Lincolns and trucks with the 460-cu.in. engine continued to use the 4350 until 1978. American Motors eight-cylinder engines also made use of the Autolite four-barrel carburetors in 1975 and 1976, and Jeep continued the use of the 4350 until 1978."

• 1975-'78 Lincoln with 460-cu.in. engines
• 1973-'78 pickups with 460-cu.in. engines
• 1975-'78 AMC and Jeep with 360, 390 and 401-cu.in. engines

Here's the link to the entire article: https://www.hemmings.com/magazine/hm...s/1539523.html

I checked the kick down this afternoon. I disconnected it from the carburetor and moved it fully, then reconnected it and moved the throttle fully. It goes the distance like it should.

I've got it purring like a cat right now. Beginning to wonder if I will send the Holley 770 back. I've got a leaky radiator and an exhaust leak that needs to be fixed.

I see ….so your's is a 2wd?