I am curious what you are all running for your setup? and if mine sounds pretty good or needs to be changed/adjusted. I have 13 Degrees of timing and my mix screws on the high end of 2 1/4 turns out on a 2 barrel 2150.

 

What others give you is nothing more then their baseline. You need to tune using a vacuum gauge for best results. With 13 degrees of base timing what is your total advance and at what rpm? Your idle mixture screws only matter at idle anything above that is controlled by the jets and those need to be sized properly.

 

I have tuned it in with a vacuum gauge. Getting around 15-18 inches at idle. I need to order a tac and find what rpm my total advance is. I think my jets say 75 on them, not sure if that is the size or just a number.

 

Alright I really could use some help here, I changed my timing today because my 351m will not idle with 13 deg advance and the mix screws 2 1/4 turns out. I left it at 13 deg and changed it to 3 turns out on the mix screws and it will barely idle in a gear. Auto trans btw not sure What rpm but all in I think the timing is around 43-47.

 

Ok you are 3 different things. none of it in order..

First set your base timing 12° with vac advance disconnected
then set your base idle 600-650 rpm

Then ignore the turn on the mix screws the 2.5 turns is just a base setting so the engine will run/idle.

Adust the idle mix for max manifold vacuum (if you do not have a vacuum gauge adjust for max engine rpm) once you have adjusted the idle mix screws you likely will need to re-adjust the engle idle. Re-adjust engine idle then readjust the idle mix screws again for max manifold vacuum or engine rpm, you may have to do that dance a couple 3 times till the idle mix is dialed right in. Ideally, you want to set the idle mix with the air cleaner installed.

 

I do not have a tachometer right now sadly.
The engine basically will not idle with 12 degrees even with the mix screws way out. I cant find engine rpm right now but by ear. I have been told over and over never to mess with the throttle blades and the leave the transfer slots set at a square and they are. I have no vac advance at idle from the ported port on the carb because the blade covers the port in the venturi.
I know at 13 degrees of timing with the mix screws dialed into 3 it kind of runs ok. The vac from manifold is around 14 inches but It dies at stops. I hear people saying they have the mix screws at like 1.5 turns or something way under mine.

 

The engine will idle at 12° if you adjust the idle speed. And whoever told you to not to mess where the throttle blades have zero effing clue. So do yourself a favour and quit listening to them right now.

The idle adjust screw will adjust the engine RPM (see below) by changing the position of the throttle blades. (The 2150 idle adjust screw (2100 pictured) is a different style screw but it is in the same location)
That is what you will use to adjust the engine rpm. To do by ear with no experience, set the idle so the truck does not stall or stumble when put in gear and is not revving so much that it is straining against the trans either, you should do around 10MPH when idling in gear with no throttle on level ground with an auto.

You will be able to ballpark engine idle speed to the 650 rpm range with the above.

 

Ok well now I am concerned, Been messing with the truck all day. I was able to increase the throttle blades a decent bit without seeing ANY vacuum to the distributor. Adjusted the screws in to Like 2 or 2.50 with 13 degrees and the truck was finally running great (the best its ever ran). Then I go in and look at the oil pressure gauge and at idle its on low. I shut the truck off immediately because the truck used to have middle to high oil pressure at idle. Check oil and it smells a bit gassy and is somewhat low so I add oil and listen for any bad noises and nothing. When revving the gauge says the oil pres gets barley to the middle. Start the truck again and it runs bad like bad bad. So I take the carb apart again clean it lose the float spring find the float spring put it all together and it really is not happy. I am at a loss, I am not a noob at all when it comes to cars just the carb parts but even that I understand, This motor has fought me for like two months to idle, I'm getting tired, maybe these 351m really do suck this bad:/

 

351M/400s are detuned emission bast*** children, but they are far from suck. You have a carb with an issue you haven’t gotten fixed yet, but you can fix it. Check your plugs, wires, rotor, cap, make sure they are good, and set timing at 12-14 degrees with the vacuum plugged. And leave it all alone until you get the carb sorted out.

It sounds like you have a vacuum leak somewhere. First check all emissions vacuum lines or get rid of them if you live in a state without emissions. I had the same issue with a 2150 that was sucking air around the throttle shaft. Had to have the idle mixtures way out, and the idle set high for it to run. Drove me crazy until I figured it out. Get it running and spray carb cleaner/starting fluid at the base of the carb and see if engine RPM changes. The EGR plates also like to rot out and suck air. The throttle shaft is an easy fix, but a little tedious. I fixed mine, got the choke system setup properly, and it barely even turns over before starting, even after sitting for a week.

Be methodical and change/adjust one thing at a time. Making a bunch of changes and then it runs better or worse, you don’t know what caused it. Keep plugging, you will get it.

 

How’s the condition of the carb? I wouldn’t be surprised if you are sucking a lot of air at the throttle shaft. Not the end of the world but you will have the air screws way out of what you expect.
This is pretty good rebuild/base tune write up
https://www.therangerstation.com/tec..._2150_carb.pdf
If you’re not knocking you have enough oil pressure. I’ve always felt the engine will let you know before you notice any gauge, and always too late.

 

bingo, thanks for posting that link. That’s the one I used, just couldn’t remember/find it. Great resource.

 

So I took the carb apart and cleaned it today and it was pretty nasty, got a new fuel filter and installed it and the truck runs somewhat decent now. So if i spray starting fluid on the throttle shaft and the idle raises at all that is a vacuum leak? It seemed really like a really tight fit like in my opinion not leakable but spraying starting fluid at both sides indeed made the idle rise. The throttle shaft has zero wear somehow, no raised spots or worn areas so my guess is it is the carb housing that needs to be bushinged? I mean I'm talking like I could slide a hair in between maybe a little over that.

 

That’s a good start. The throttle shaft is made of steel, riding in an aluminum housing. The constant turning motion eggs out the aluminum housing, allowing air to be bypassed into the Venturi around the shaft. My carb I think was 3-4 turns out on each side trying to make up for all the unmetered air. Spraying the throttle shaft would cause the motor to idle up, and sometimes stumble. If it’s not leaking, it shouldn’t do anything. If you have this problem, I have the reamer and some bushings I bought for mine, I can send you to do the job. A wiser man that me instructed me of a procedure that makes it really simple with only hand tools.