No go when cruising
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Tuned
Joined: Sep 2018
Posts: 364
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From: Eagar, az
No go when cruising
Howdy all. So I got this problem That I can't find an answer for for the life of me. 1973 f100 with 360/c6. Just rebuilt engine, and runs decent-only about 15 miles on it so far. Seating my rings, and when accelerating to 60 it takes forever. Off from a stop is great. I can blip the throttle, and it will shoot out from under me with fantastic response, but say I am cruising at anything over 20 mph, and give it more throttle.. won't do much. Just kinda loads up the more I step on it. Not really much difference from 1/4 throttle to 3/4 throttle other than the engine sounding like it's laboring a little more. This isn't new either. It's happened since I owned it 10 years ago. I am at 8000 feet elevation and pulling 15.5 vacuum. I just got done reading about vac advance, and was wondering if mabey weak vacuum isn't bringing advance in right? It works, but I really have to use most of the lung power I have to pull it in . Any other pointers on what to check?
Lead Driver
Joined: Oct 2018
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it's probably your timing. but it won't be your vacuum advance, the more throttle you give it the more it drops out, at WOT you have no vacuum so no advance. What you need to do is use a dial back and check your curve. your mechanical all in should be in the low 30's. you should be connected to ported vacuum.
If you don't have a light you can peak it. at an idle advance the distributor to the highest idle speed you can get. then back it down a bit but leave it loose enough you can move it with a little effort. go out on the road and put the hammer down hard, if it knocks or pings back it off until it stops, then a touch more. if it doesn't ping advance it until it does, then back it off until it doesn't. do not leave it where it pings, that's detonation and it's an engine killer.
now set your idle mix and speed. and see how it starts, if it's kicking the starter then you're going to have to back it off until it doesn't and go to work on your curve.
A 360 is a dog, so be realistic about what you expect. but if it's still a pig it's time to check your carb.
If you don't have a light you can peak it. at an idle advance the distributor to the highest idle speed you can get. then back it down a bit but leave it loose enough you can move it with a little effort. go out on the road and put the hammer down hard, if it knocks or pings back it off until it stops, then a touch more. if it doesn't ping advance it until it does, then back it off until it doesn't. do not leave it where it pings, that's detonation and it's an engine killer.
now set your idle mix and speed. and see how it starts, if it's kicking the starter then you're going to have to back it off until it doesn't and go to work on your curve.
A 360 is a dog, so be realistic about what you expect. but if it's still a pig it's time to check your carb.
Thread Starter
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Tuned
Joined: Sep 2018
Posts: 364
Likes: 22
From: Eagar, az
You are correct in that i don't have a light. Timing is set to highest vac, and tapped back just to where it starts to drop. Advance is on ported on a holley 2300(4412) 500cfm. I do realize this motor is a workhorse dog, but i am thinking it should be better than 0-60 in like 30 seconds quarter mile. After timing, i adjust carb to highest vac- usually 3 turns out total. Is this the wrong way? Engine starts with a bump of the keyL Everytime. If i bump back timing any more at all it starts getting Shakey, and quickly drops vac around .5, if i bump it up a tiny bit, it kicks back on starts. also if related, has a stutter, misfire on idle, and throttle for the first couple minutes it's running, then suddenly runs smooth after 2 blocks of driving, and stays that way till cooled back down
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Tuned
Joined: Sep 2018
Posts: 364
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From: Eagar, az
I've thought about the trans many times over the years. Due to feeling like i am accelerating with the brake pressed, and the motor really trying to go. Also the sound of the engine when stepping on it after already going 30mph sounds just like power braking at a stop. It shifts totally normal though. I know i still need to do some fine tuning in timing, and carb. Mabey rejet? I am running 72 jets bumped down from 76 that came with the holley. Didn't want to spend too much time right off the bat tuning with truck idling before it was broke in.
Lead Driver
Joined: Jun 2006
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From: Near Yosemite CA
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Tuned
Joined: Sep 2018
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From: Eagar, az
I do. Hooked to manifold vac. It's a different one than stock. When I bought truck 10 years ago it wouldn't shift. Well it would, but it would wind up to like 3 grand and you would have to back off throttle a little, then it would shift into second gear. I replaced that, and it was fine, other than every now and then reving past second or third gears shift point. While other times shifting too soon. These don't happen too often though, mabey every few days of daily driving it will happen at some random shift. Also seems common, but putting it in reverse really slams it into gear with a big thunk, and jerk
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Lead Driver
Joined: Oct 2018
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Manually shift it. if it's still bogging down you ruled out a stack shifting or early shifting possibility. if it does it in 3rd gear at cruise speed that also rules it out also.
look at timing and carburation.
look at timing and carburation.
Thread Starter
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Tuned
Joined: Sep 2018
Posts: 364
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From: Eagar, az
Did some manual shifting at lunch, and first gear has me bumping my head on the back window every time I blip throttle-throughout the gears range. Second gear is a little bit less, never bumping the window, but 3rd gear is almost nothing. Cruising at 35-40 mph, and giving it a good amount more throttle (removed kick down arm) it will go from 40-55/60 in about a quarter mile. The engine just thump deeper like under severe load. With the kickdown in place it jumps to like 5 grand after shifting down, and forces me to let off. Don't want to do that until I get some miles on this rebuild
Cargo Master
Joined: Oct 2020
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What does it have for an exhaust system? Have you tested to make sure that it isn't stopped up in some way? This can happen when a car or truck sits around for a long time and animals decide to build a home inside of the muffler.
Thread Starter
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Tuned
Joined: Sep 2018
Posts: 364
Likes: 22
From: Eagar, az
So stuck an inspection camera at work up into the exhaust to the chambers, and it's clear. Was able to articulate the lens to see around the corner into the first chamber, and saw nothing. So on to the transmission. I know almost zero about transmissions, and never had the need to learn. it shifts good, and sometimes it shifts so smooth I hardly notice. The reverse lunge/clunk is probably the lash in the 9" rear, coupled with high pressure in trans from what I am reading? Been like that for the 10 years I had it, and never got worse from daily driving/weekend 2 track exploring. After going around the issues with this problem, it seems 3rd and mabey 2nd gear are where the issues are. Should I just lower my expectations on what a 360 can pull in 3rd gear?
Lead Driver
Joined: Jun 2006
Posts: 5,692
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From: Near Yosemite CA
No, I would drop the C6 and see wth is going on with it, your tc could be going causing the slippage or, since you've had it 10 yrs it's probably due for a rebuild and a new TC, have you serviced it in 10 yrs...?
The 360 will do a decent job if tuned to altitude and should not perform like you are saying, just to be clear, YOU HAVE SOMETHING WRONG in your transmission. Bite the bullet and drop it out, tear it apart, rplc worn, broken parts, source new TC, seal it up and see what you get
The 360 will do a decent job if tuned to altitude and should not perform like you are saying, just to be clear, YOU HAVE SOMETHING WRONG in your transmission. Bite the bullet and drop it out, tear it apart, rplc worn, broken parts, source new TC, seal it up and see what you get