so I have returned once again regarding my '71 F-100 360/C6, last time i wrote here the truck was a mess, i have gotten a lot of progress and i feel as though its almost done. i got the timing on the marks, checked with a timing light and doing so clarified that my mechanical advance was working and it was, truck idles pretty good now, still somewhat finicky on cold starts but good after a minute or two. it goes into gear, it holds the idle in gear, it creeps, brakes work good etc.

now onto what i'm here for, when the truck is in gear (under load) and i initially give it some throttle from a stop it almost immediately hesitates and wants to die (and if i don't force it it will catch itself and i can work the pedal and make get it going) so once its going its fine mostly but obviously i won't be able to drive it like that.

so what could this be? mechanical advance not right? vacuum advance not doing its job/anything at all? carb too rich or lean or accelerator pump shot (again....) or float sticking???? seriously don't understand since it runs so well most of the time. i wanna say carb issues or vacuum advance? i've been waiting to drive this truck for over 2 years and i feel im so close....

if it helps any, it doesn't like anything past say 1/2 throttle or a little less even when under load. by that i mean it cuts out and hesitates and catches itself and goes on, usually...

 

The 2100/2150 series of carbs on this era of trucks had an accelerator pump rod with holes on either end for tailoring the "pump shot". Maybe you know this already? Some people maybe don't...The uppermost hole is for temperature below 40° F, second from top 40° F thru 80° F, etc., basically the angle of the dangle changes and gives a bit more fuel in cold weather.

Too much fuel "pump shot" will cause a bog or hesitation too, similar to a lean condition. So make sure it's in the right slot.If you have a manual choke, you can determine if a particular carb circuit is running lean or rich pretty handily. It could be ignition timing is a little slow ... it could be the idle mixture screws are set too rich.. it could be the float height is way off .. No way for us to tell from here, so you'll have to do the legwork.

If you really want to dial in your engine/carburetor better, you really want a mechanic's vacuum gauge. Can get them for maybe $15 to $20, they take a little study to learn everything they can diagnose. Maybe 20 to 25 different engine faults or conditions? They even test fuel pump pressure. This is important too. If you want to do a good tune-up, you have to check everything. There aren't any shortcuts. Start with a cylinder compression test. Measure, don't guess, and set whatever it is you're adjusting or replacing so it's right at the factory spec. If the ignition timing is advancing that's good, but it needs checked to see how much and how fast, separate from the vacuum advance. If that's defective, it will cause a vacuum leak. Etc.

Post a clear close up picture of a spark plug or two. That shows pretty much everything.

 

ill see what i can get tomorrow. When i checked the mechanical advance i did have the vacuum advance disconnected as well as when i set the timing. I knew the carb was too rich but i kept backing the screws out and it didn't seem to make a difference. i'm also just running it off temporary small lawn mower gas tank since my pump is shot again after sitting for about a year or so (there is still gas in the tank and no fuel comes out, been disconnected and put into a bottle but nothing ever has come out). but i wouldn't think that would affect it? plugs are new as of a couple months ago but ill see what i get from that. i revved and held the engine at around 2500-3000rpm and it advanced it about 15 or so degrees id say? maybe 20? ill take a pic of that too, if i can lol. it advanced maybe 10 degrees at around 1500-2000 rpm, maybe ill try to get a video. how fast should it advance? i rebuilt the carb not long ago, maybe a couple months ago, it didn't look to bad but i replaced everything i could figure out to swap out. new accel pump diaphragm and such, cleaned it really good, but honestly don't know the science behind accel pumps especially regarding the 2100/2150 like you stated. it does have a manual choke and most of the time works on cold starts, but since i play with it each time i see the truck its hard to tell what the cause would be for that.

IIRC turning the dizzy clockwise is advancing and CC is retarding correct? i feel like i had it a bit retarded too much (just from eyeballing the position of the dizzy then compared to now) when it drove without major hiccups. i do need to do a compression check i won't try to avoid that even though it seems to have good compression with how easily it starts majority of the time. the carb and all ignition components (except the coil possibly judging its cosmetic appearance) were replaced around 7-8 years ago and has sat most of that time until i started working on it again in 2017. cap and rotor last i checked didn't look corroded.

 

Agreed. Accelerator pump adjustment is where I'd start. Had this exact issue on my '67 F100 and '73 Bronco. Play with the rod. My issue always went away went motor was at proper temp.. but when cold it would almost die.. made for turns on to busy streets very sketchy. Works perfect now. Still will die if not warmed up at ALL and you try to take off but its a 50 year old vehicle so I let it warm up for 3-4min.

 

that was mostly how it was, but now it won't hardly even cooperate from a stop/after turning etc even when its warmed up, better but still not right. like i said tho i have no idea how to adjust anything on a carb except idle speed, mixture, and that's about it lol.

 

Like I said, there aren't really any shortcuts. Even if you already knew everything there is to know about carburetors, you'd still have to check everything out one thing at a time. Because it's likely all bjggered up after 50 years. Everything you need to know is in free manuals in .pdf for download if you dig, websites, YT videos. Take it one step at a time.

One thing to check for in older carbs that saw a lot of miles is sideplay or wobble of the throttle butterfly rod where either end is secured in the carb body. The holes gets wallered out. If wear gets excessive, it will have a bad vacuum leak causing some of the symptoms. Vacuum leaks are probably one of the biggest problems that cause carburetor troubles.

As far as the ignition timing goes, another problem that we didn't have when these trucks were new, something to watch out for, is a defective balancer, where the timing marks are. The outer steel weight will slip when they get old and with it the timing marks have moved too. So a fella who doesn't know this sets the timing to factory spec with a light at say 6° or 8° BTDC or whatever it may be, except in reality it's really at 3° ATDC and now, it runs like crap. Not gonna say this is for sure the problem here, but if you can eliminate it as a possibility that's a good thing. Slow or late ignition timing prevents the carburetor from working correctly, it depends on a strong manifold vacuum signal through it. Ignition timing changes the manifold vacuum in a big way, just a couple degrees either way.

 

yeah in the back of my head i wondered if something like that could happen with the damper. never have tested the theory but i wouldn't be surprised given how long its sat and it would explain why the engine seems to run a little better and behave somewhat better when i retard the timing before the marks on the balancer.

ill play with the carb some more and do some searching on how to tune it a little more properly. the carb isn't that old, its less than a decade old and hasn't had hardly any miles put on it since its been on the truck. i know the throttle shaft and all that is good and tight, no play in it etc. im pretty sure there aren't any vacuum leaks or at least any obvious ones because i don't hear/feel it anywhere but i've been meaning to put a vacuum gauge on it like i have been a compression test.

i was hoping this would be more of an easier fix. i feel every time i post something in forums im always told to just look up stuff in manuals, i get it there's good info there, but i came here for other suggestions or maybe a common fix or people who have experienced it and know how to fix it so i maybe don't have to do a bunch of searching... also the truck does only have 78k miles and they are original miles. its been in our family since the late 80's/early 90's. at some point i wanna make my own timing marks, someone made some marks on there, either just to see it better or because the originals became inaccurate.

 

I get that, everybody wants to post the symptoms of a particular problem they run into, and then hope it jogs the memory of someone else and they will post "The Answer". Sometimes it actually works that way, though not very often.

And not everybody wants to make a career out of tuning a carburetor or setting the valves, they just want to get gramps old truck to start and run. I get that too.

The thing with a tune-up though, the thing with these engines, even pre-computer controlled engines, every adjustment or setting is affected by something else upstream, and in turn affects something else farther downstream. There is an underlying assumption that there aren't any other defects at any point along the way. There's just that "one" single problem - a screw that needs tightening - after 50 years - and that will fix The Problem. Everything else, is OK, that for example the engine temperature is correct, the voltage from the alternator is correct, the carburetor needs the ignition timing to be right on the money from idle to 4000 RPM, the exhaust isn't restricted, the gasoline hasn't turned to goo inside the tank, and mice havet setup shop in the oil pan. Nobody is there to look over your shoulder and check this stuff out.

To be honest I do kind of wonder about people who don't utilize the manuals. When I was growing up, there was pretty much the Public Library for a generic Chilton's and some other stuff, and that was basically it for a semi-broke teenager. I just took stuff apart and hoped it worked when I got it back together. Usually did pretty good, but... Today I can get the Ford, Autolite carburetor manuals, shop manuals, everything, and there are webpages with all kinds of stuff, it is amazing. Even videos where carb guys walk the user through, and point out common mistakes and errors. It doesn't make sense to "ask the internet" or random stranger really about something when the manual is literally at your fingertips.

So yeah, a step by step disgnosis is the only way to achieve a decent tune-up that will last. It really is quicker, it just doesn't seem like it. If the damper/vibration absorber is toast, it needs to be replaced or rebuilt. A compression test is always the first step on pg.1 para. 1 in every Tune-up and Shop manual, because if there is something wrong internally there is no point in trying to tune it up or spend money on parts. A mechanic's vacuum gauge will really help you if you take the time to study it. Trust Me.

 

Yeah you’re right, I guess I’m just somewhat annoyed by the fact I’ve been working on this thing for the last almost 3 years now and I feel like I’ve been chasing the same thing and I can’t seem to figure much out even with research. Plus I was in a weird mood last night lol

anyways here’s plug #1, looks lean surprisingly if I’m reading it correctly. Not wet at all either (also a pleasant surprise to me)

 

Wow... cylinder #1 has a whopping 110psi.... and yes that was WOT... ouch.

only went up to 117 with oil in it.

 

Hey Tedster, your post #8 about researching not withstanding, how would you check for this? I would think that I can put a rod in cylinder 1 and rotate it to TDC and compare the marks. Is it that simple?
Thanks for the good advice. I subscribed as a good tune up is next on my list for the 67 352 engine.

 

That would get you close enough to see if it is off. Just have someone slowly rotate the engine while someone holds the rod so you can be very accurate when you feel it stop.

The most accurate way is install some kind of piston stop in the spark plug hole(Either purchase or make one from a broken spark plug). Something that would stop the piston from reaching TDC(just enough). Then MANUALLY rotate the engine one way and put a mark on the balancer where it stops at the pointer. Then rotate it back the other way til it stops and mark the balancer. The spot in between is the true TDC.

 

Ok I think I figured it out, unfortunately low compression is low compression and I expected that from something that’s sat for 10+ years before I got my hands on it. It’s just a huge bummer as it’s got such low mileage.

Anyways, I advanced the timing to try and counteract the said issue with the balancer and I believe that was the issue as now it doesn’t have any hesitation much at all, and I did a little victory/“test” burnout and it seemed very willing to do so lol didn’t die, didn’t try to or act like it wanted to die, and I even gave it a good bit of throttle and it was fine. I let off the gas and left it in gear to come back to idle and it did so just fine without dying.

Now is is there any way I can increase that compression a few numbers or is it worth doing anything with? Does it matter if I try to drive it with such low compression? Makes sense why it’s got no beans but has plenty of torque still haha.

 

Maybe some Marvel Mystery oil diet might help with stuck rings(if that is the issue)? No guarantee at all. If the rings are just worn out, no real easy fix for it.

 

110 isn't great, but it's not cause for calling the Depression Hotline just yet. Especially, if it hasn't been run for a while.

Did you remove all the other spark plugs before the test? Was the engine warmed up? How did the other seven (7) cylinders turn out? What is concerning is when a cylinder or two is real low relative to the rest, like 75, something like that.